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• Gulbrandsen, Egil; Tucho, Wakshum Mekonnen & Hansen, Vidar Folke (2026). Searching for Evidence of Hydride Formation on Corroding Magnesium. Corrosion. ISSN 0010-9312. 82(6), p. 508–526. doi: 10.5006/4919. Full text in Research Archive
• Rai, Ayushi & Hansen, Vidar Folke (2026). Microstructural evolution and nanograin coherence in VO2 thin films grown by pulsed laser deposition. Scientific Reports. doi: 10.1038/s41598-026-52338-5. Full text in Research Archive Show summary

  Vanadium dioxide (VO2) thin films exhibit a reversible semiconductor–metal transition near room temperature, and their performance is strongly governed by microstructural and interfacial factors. In this study, VO2 thin films were deposited on Z-cut quartz substrates by pulsed laser deposition under varying oxygen partial pressures and substrate temperatures. Plan-view transmission electron microscopy (TEM) techniques such as selected-area electron diffraction (SAD) and nanobeam diffraction (NBD) as well as confocal Raman spectroscopy were employed to examine the microstructure and crystallographic features of the films. The VO2 films display a dense, polygonal morphology, composed of faceted grains with characteristic sizes of 50–200 nm. These polygonal grains are formed during deposition in the high-temperature metallic R phase and transform upon cooling into semi-coherent VO2 M1 nanograins with minimal lattice mismatch. The observed morphology is attributed to surface and interface energy anisotropy acting across the amorphous SiO2 interlayer, which promotes random in-plain orientation. Confocal Raman mapping further supports phase uniformity and orientation variation across the grains. Overall, this work provides new insight into the mechanisms governing polygonal grain formation and coherence within VO2 thin films on quartz, highlighting how interface-energy-driven growth can stabilize ordered microstructures even in the absence of epitaxial constraint.

• Rai, Ayushi; Locovei, Claudiu; Pelin, Gianina Popescu; Socol, Gabriel; Ivan, Ioan Alexandru & Kuncser, Victor [Show all 8 contributors for this article] (2026). Impact of nanostructural features of thermochromic VO2/TiO2 bilayers on their electrical and optical properties. Applied Surface Science. ISSN 0169-4332. 720. doi: 10.1016/j.apsusc.2025.165367. Full text in Research Archive Show summary

  VO2-based thermochromic thin films are promising for energy-efficient smart window applications due to their reversible metal–insulator transition near 68 °C. However, practical limitations such as high transition temperature, limited visible transmittance and substrate compatibility remain challenges. In this study, VO2/TiO2 bilayer thin films were deposited by PLD on glass, fused silica, and quartz substrates to investigate the effect of buffer layer, film thickness, and strain on their structural, optical, and electrical properties. Comprehensive characterization using in situ grazing incidence X-ray diffraction, synchrotron GIXRD, and high-resolution Transmission Electron Microscopy revealed that TiO2 buffer layers, in the anatase or brookite phase, significantly influences the growth orientation and strain distribution in VO2 films. Residual strain mapping indicated up to 5 % compressive strain in VO2 and >10 % tensile strain in the TiO2, promoting partial stabilization of the intermediate M2 phase. Thickness-dependent studies showed a strong trade-off between optical transmittance and electrical switching amplitude: thinner films exhibited higher luminous transmittance (up to 30 %) and sharper IR switching, while thicker films yielded larger resistivity switching contrast. These results demonstrate that interfacial strain, film thickness, and substrate choice are critical parameters for tailoring VO2-based coatings and optimizing thermochromic performance for scalable smart window technologies.

• Sayyar, Navid; Tucho, Wakshum Mekonnen; Undheim, Espen & Hansen, Vidar Folke (2025). Adaptive Control of Additive Manufacturing Parameters in Pulsed Laser-Based Directed Energy Deposition of Super Duplex Stainless Steel: Hybrid Taguchi-Grey Relational Approach. Metals and Materials International. ISSN 1598-9623. 32, p. 195–229. doi: 10.1007/s12540-025-02003-9. Full text in Research Archive Show summary

  Process parameters determine the quality characteristics of additively manufactured (AMed) parts. During Laser-based Directed Energy Deposition (DED-LB), an elaborated parametric analysis is required to control the materials’ behaviour precisely. This work deals with the effect of process parameters on process stability in terms of consistent melt pool geometrical features, such as aspect ratio of the bead and dilution, formation of pores, and ductility of super duplex stainless steel (SDSS) during pulsed laser and powder DED-LB. Independent variables including laser power, deposition speed, pulse frequency, and flow rate of the shielding gas were selected as controlling factors to deposit single tracks and plates of SDSS. Experiments have been designed and conducted according to L16 orthogonal array of Taguchi methodology. Relative density was estimated using Archimedes method. Ductility was estimated by tensile testing of the builds. For geometrical evaluation, phase characterization, and microstructural assessment, specimens were subjected to optical and Scanning Electron Microscopies, and Electron Backscattered Diffraction. Overall results were interpreted and explained using the Taguchi approach and analysis of signal-to-noise ratio. Single objective parameter-property relationships were achieved and discussed. Conclusive parametric remarks under the multi-attribute optimization were derived using weighted Grey Relational Analysis. A desirable parametric combination was extracted, and the associated quality responses were verified by the satisfying confirmatory deposition. The key role of parameters on the process stability, microstructure, and mechanical behaviour was further discussed. This work offers a practical solution to the multi-response optimization problems that can be used in AM and surface treatment of SDSS.

• Rai, Ayushi; Bienz, Siiri; Hansen, Vidar Folke; Zenobi, Renato & Kumar, Naresh (2025). Nanoscale Structural Insights into Thermochromic VO2 Thin Films Using Tip-Enhanced Raman Spectroscopy. ACS Applied Materials & Interfaces. ISSN 1944-8244. 17, p. 32625–32634. doi: 10.1021/acsami.5c04827. Full text in Research Archive
• Belsvik, Marius Aga & Hansen, Vidar Folke (2025). Process parameter optimization for directed laser deposition of hot work tool steel Dievar. The International Journal of Advanced Manufacturing Technology. ISSN 0268-3768. 138, p. 1129–1142. doi: 10.1007/s00170-025-15426-w. Full text in Research Archive Show summary

  Tool steel utilized in hot work applications are prone to costly and time-consuming maintenance repair due to wear generated on the tool surface from static and dynamic high temperature loading during the production processes. Traditionally, the repair is mainly done by subtractive machining of the tool profile. Implementation of an additive manufacturing technology such as directed laser deposition can greatly reduce maintenance time by targeting specifically the worn areas of the tool surface. In the presented work, a commercially available hybrid additive manufacturing and computer numerical control system is used to deposit a powdered hot work tool steel called Dievar. The central composite design is used in the experimental setup to optimize the most influential input parameters; powder feed rate, traverse speed, and laser power by analyzing single track geometry. The presented process window produced defect free parts without the need for preheating, Applying a powder feed rate of 6.5 g/min, traverse speed of 550 mm/min, and laser power of 1500 W, yielding an average as-built hardness of 610 HV0.5 while retaining the required pre-hardened properties in the heat-affected zone in the substrate, with a minor hardness reduction of 4–5% post-deposition. Additionally, the research revealed that the established boundary conditions for aspect ratio and dilution is not an absolute requirement to achieve a fully dense part without lack of fusion or cracks. Engineers working in the field of additive manufacturing may use the presented method to find optimal process parameters and qualify the implementation of directed laser deposition in their industry, avoiding a unnecessarily large selection of samples for testing and thus saving time and resources.

• Sayyar, Navid; Hansen, Vidar Folke; Tucho, Wakshum Mekonnen & Minde, Mona Wetrhus (2024). Microstructural Investigations on Super Duplex Stainless Steel UNS S32750 Fabricated by Blown-Powder Directed Laser Deposition. In Pavlou, Dimitrios; Correia, José A.F.O.; Fazeres-Ferradosa, Tiago; Gudmestad, Ove Tobias; Siriwardane, Sudath C.; Lemu, Hirpa G.; Ersdal, Gerhard; Liyanage, Jayantha Prasanna; Hansen, Vidar Folke; Minde, Mona Wetrhus; MUDIYANSELAGE, Chandima RATNAYAKE; Delimitis, Andreas; El-Thalji, Idriss; Adasooriya, Mudiyan Nirosha Damayanthi; Samarakoon, Samarakoon Mudiyansele Samindi & Hemmingsen, Tor (Ed.), Analytical and experimental methods in mechanical and civil engineering : Contributions of the 1st olympiad in engineering science (OES 2023). Springer Nature. ISSN 9783031497223. p. 13–26. doi: 10.1007/978-3-031-49723-0_2. Full text in Research Archive
• Tucho, Wakshum Mekonnen; Sletsjøe, Anders Thon; Sayyar, Navid & Hansen, Vidar Folke (2024). Optimizing Tensile Properties and Hardness of Inconel 718 by Cold Rolling. Metals. 14(4). doi: 10.3390/met14040455. Full text in Research Archive Show summary

  The as-received commercial Inconel 718 material was solid solution heat treated (ST), cold-rolled (CR), and precipitation-hardened (PH) to investigate the effects of deformation on the tensile properties, hardness, and texture. Three sets of specimens (0%, 20%, and 50% CR) were ST at 1100 °C/1 h, CR, and aged (720 °C/8 h + 650 °C/8 h) for the analysis. The ultimate tensile strength (UTS), 0.2% yield strength (YS), and elongation of 50% deformed condition were 1645 MPa, 1512 MPa, and 3.8%, respectively. The 20% deformation resulted in a balanced UTS (1348 MPa), YS (1202 MPa), and elongation (11%). The contribution of precipitation hardening to the strength decreased, while the contribution of CR increased with an increasing percentage of deformation. As the level of deformation increased, the size and quantity of γ″ decreased proportionally. The CR specimens produced a high density of nano/micro twins with twin planes oriented perpendicular to the RD-ND surface. The gradient of crystal orientation and internal features of large austenitic grains were generated by their preferred rotation. The cross-slip of screw dislocations induced a complete β-fiber consisting of {110}<112>, {112}<111>, and {123}<634>, with doubled intensity at the higher deformation. Additionally, the specimens were highly susceptible to the twinning-induced orientation emerged by a predominant <110>//ND. In the as-deformed condition, an incomplete but intense α-fiber, clustered between {110}<001> and {110}<112>, was characterized. Apart from achieving the highest strength, the current work demonstrates the effects of CR on the material strength without the complex influences of δ precipitates.

• Tucho, Wakshum Mekonnen; Bjørge, Ole Kristian; Bista, Shusil; Nedreberg, Mette Lokna & Hansen, Vidar Folke (2024). Comparative Studies of Mechanical Properties and Microstructure of LPBF-Fabricated Virgin and Reused 316L Stainless Steel. In Pavlou, Dimitrios; Correia, José A.F.O.; Fazeres-Ferradosa, Tiago; Gudmestad, Ove Tobias; Siriwardane, Sudath C.; Lemu, Hirpa G.; Ersdal, Gerhard; Liyanage, Jayantha Prasanna; Hansen, Vidar Folke; Minde, Mona Wetrhus; MUDIYANSELAGE, Chandima RATNAYAKE; Delimitis, Andreas; El-Thalji, Idriss; Adasooriya, Mudiyan Nirosha Damayanthi; Samarakoon, Samarakoon Mudiyansele Samindi & Hemmingsen, Tor (Ed.), Analytical and experimental methods in mechanical and civil engineering : Contributions of the 1st olympiad in engineering science (OES 2023). Springer Nature. ISSN 9783031497223. p. 27–56. doi: 10.1007/978-3-031-49723-0_3. Full text in Research Archive
• Tucho, Wakshum Mekonnen; Ohm, Bjørn Andre; Canizalez, Sebastian Andres Pedraza; Egeland, Andreas; Mildt, Martin Bernard & Nedreberg, Mette Lokna [Show all 7 contributors for this article] (2024). Effects of δ Phase and Annealing Twins on Mechanical Properties and Impact Toughness of L-PBF Inconel 718. Journal of Manufacturing and Materials Processing (JMMP). 8(4). doi: 10.3390/jmmp8040135. Full text in Research Archive Show summary

  In this study, the effects of the δ phase and annealing twins on the hardness, tensile properties, and Charpy impact toughness of Inconel 718 fabricated using L-PBF were investigated. The as-printed components underwent two stages of heat treatment to modify their microstructure and phases. The δ phase was induced through solid-solution heat treatment at 980 °C for 1 h, while annealing twins were formed at 1100 °C for 3 h. Following precipitation hardening, specimens containing δ precipitates exhibited a higher ultimate tensile strength (13%), yield strength (27%), and hardness (12%) compared to those rich in annealing twins. The enhanced mechanical strength was attributed to the presence of δ precipitates and differences in the extent of recrystallization, leading to variations in the density of retained lattice defects, including subgrain boundaries and primary phases. Conversely, specimens with annealing twins demonstrated a significantly higher impact toughness (four times) and ductility (twice) than those with δ precipitates. Annealing twins were found to enhance plasticity by impeding dislocation movement, while δ precipitates reduced plasticity by acting as sites for void formation and crack propagation. Microstructural, compositional, phase, crystallographic, and fractographic analyses were conducted using OM, SEM, TEM, and XRD techniques to identify the factors influencing the observed differences. The results indicate that the heat treatment approach involving annealing twins can effectively enhance the ductility of Inconel 718 while maintaining the necessary mechanical strength.

• Rai, Ayushi; Istrate, Cosmin; Socol, Gabriel; Iacob, Nicusor; Hansen, Vidar Folke & Mihailescu, Cristian N. [Show all 8 contributors for this article] (2024). Correlation of nanostructural features with phase transition in thermochromic VO2 thin films for smart windows Applications. In Pavlou, Dimitrios; Correia, José A.F.O.; Fazeres-Ferradosa, Tiago; Gudmestad, Ove Tobias; Siriwardane, Sudath C.; Lemu, Hirpa G.; Ersdal, Gerhard; Liyanage, Jayantha Prasanna; Hansen, Vidar Folke; Minde, Mona Wetrhus; MUDIYANSELAGE, Chandima RATNAYAKE; Delimitis, Andreas; El-Thalji, Idriss; Adasooriya, Mudiyan Nirosha Damayanthi; Samarakoon, Samarakoon Mudiyansele Samindi & Hemmingsen, Tor (Ed.), Analytical and experimental methods in mechanical and civil engineering : Contributions of the 1st olympiad in engineering science (OES 2023). Springer Nature. ISSN 9783031497223. p. 3–12. doi: 10.1007/978-3-031-49723-0_1. Full text in Research Archive
• Sayyar, Navid; Tucho, Wakshum Mekonnen & Hansen, Vidar Folke (2024). Pulsed laser directed energy deposition of super duplex stainless steel: engineering microstructure and improving mechanical properties. The International Journal of Advanced Manufacturing Technology. ISSN 0268-3768. 136, p. 983–1008. doi: 10.1007/s00170-024-14899-5. Full text in Research Archive Show summary

  Alloys developed by fusion-based additive manufacturing often suffer from the coarse columnar grain structure and their effect on properties. This work involves the practical application of pulsed laser in laser-based directed energy deposition (DED-LB) of super duplex stainless steel which led to engineering the microstructure, improving the mechanical properties, and changing the dominant texture. Pulsed laser DED-LB (here P-DED) with laser spot sizes of 1 and 2 mm and different frequencies were used. Refine-grained ferritic steels containing porosity were produced when using a small laser spot size. Ferrite-to-austenite (α → γ) transformation was constrained to the grain boundaries under the effect of small excitation overlaps. Using broader laser, higher energy input, and ultra-short pulse intervals encouraged γ nucleation, promoted the density, and decreased the content of undesirable oxides that are typically formed during the conventional DED-LB (here C-DED). The local ferritization under the fusion lines of C-DED was avoided by P-DED. Directionally solidified α, extending into several layers, was inhibited by P-DED with optimum overlap. Enhanced supercooling resulted in an in situ grain refinement and columnar-to-equiaxed morphological transition. Defect-free microstructure and effective distribution of interphase boundary surface by P-DED, with a laser spot size of 2 mm and ⁓99% excitation overlap, largely improved the toughness and elongation (with acceptable strength). Pulse-induced convection and isotropic heat flow during P-DED with smaller laser spot size subsided the trend of preferred orientation. However, an alignment of < 001 > α with deposition direction during P-DED with the broader laser preserved the typical {001} < 100 > solidification texture and, consequently, the transformation texture.

• Sayyar, Navid; Hansen, Vidar Folke; Tucho, Wakshum Mekonnen & Minde, Mona Wetrhus (2023). Directed laser deposition of super duplex stainless steel: Microstructure, texture evolution, and mechanical properties. Heliyon. 9(4). doi: 10.1016/j.heliyon.2023.e15144. Full text in Research Archive Show summary

  Microstructure and texture evolution of directed-laser deposited super-duplex stainless-steel, in the as-received block, were characterized using light and electron microscopies and electron backscattered diffraction. Mechanical properties in different directions were studied. Local FCC-depleted and FCC-rich zones and extensive precipitation of oxides were detected at the matrix wherein the different types of reformed austenite were surrounded by the elongated coarse ferrite. A vertical gradient of austenite content, caused by overall change in cooling rate, generated a waning hardness distribution along the building direction. The texture of austenite across the different deposition layers was not as intense as that of the ferrite. A dominant <001> ⫽ND fibre, embedding strong Cube {001} <100>, was calculated for ferrite on the layer away from the bottom while the Goss {011} <100> appeared in the layer near the building substrate due to the considerable epitaxially developed grains. The less intensified multi-component texture of austenite at the layer near the substrate changed to <011> ⫽ND fibre adorned by Rotated-Goss and Goss components at the upper layers where an incomplete fibre {001} <uvw> with a major Rotated-Cube was also partially inherited from the parent phase. The inter-phase boundaries obeying Kurdjumov-Sachs orientation relationship were predominantly formed at all layers. A slight increase of Σ3 coincidence site lattice interfaces was observed in austenite across the build direction. The possible mechanical anisotropy was depressed due to complex and multi-component transformation texture of the austenite. The material showed brittleness corresponding to significantly high tensile strength and low impact toughness.

• Delimitis, Andreas; Kyratsi, Theodora & Hansen, Vidar Folke (2022). Electron channeling studies of atom site preference and distribution in doped Mg2Si1-xSnx thermoelectrics. Materialia. 24. doi: 10.1016/j.mtla.2022.101486. Full text in Research Archive Show summary

  The electron channeling effect, i.e., the dependence of the characteristic x-ray emission on the crystallographic direction of the incoming beam in an analytical transmission electron microscope was employed to elucidate the crystal site location and distribution of the dopant and host ions in Mg2Si1-xSnx thermoelectric (TE) materials, doped with low amounts of Bi. Experiments performed both in pure Bi-doped Mg2Si and mixed Mg2Si1-xSnx (x = 0.4, 0.6), firmly confirmed that Mg occupies the two tetrahedral T sites, 8c (¼, ¼, ¼) and (¼, ¼, ¾), with some vacancies present, too, whereas Si and Sn the 4a (0, 0, 0) and 4b (½, ½, ½) octahedral C and N sites, respectively. Bi ions follow the trend of Si and Sn, occupying 4a sites, but also there is a partial distribution of them in 4b sites. We moreover observe a certain degree of asymmetry along the {111} directions in Mg2Si1-xSnx, predominately for the variable distribution of Bi and Sn in the lattice, which indicates Bi substitution for Sn in an uneven fashion. The channeling results are in line with TE property measurements, especially in relation to lower thermal conductivity and negative Seebeck coefficient due to Bi incorporation in the lattice. These findings demonstrate once more the effectiveness of the channeling technique to provide direct crystallographic information and refine atom positions in materials, particularly for nanoscale crystal grains.

• Tucho, Wakshum Mekonnen & Hansen, Vidar Folke (2021). Studies of Post-Fabrication Heat Treatment of L-PBF-Inconel 718: Effects of Hold Time on Microstructure, Annealing Twins, and Hardness. Metals. 11(2), p. 1–20. doi: 10.3390/met11020266. Full text in Research Archive Show summary

  The widely adopted temperature for solid solution heat treatment (ST) for the conventionally fabricated Inconel 718 is 1100 °C for a hold time of 1 h or less. This ST scheme is, however, not enough to dissolve Laves and annihilate dislocations completely in samples fabricated with Laser metal powder bed fusion (L-PBF) additive manufacturing (AM)-Inconel 718. Despite this, the highest hardness obtained after aging for ST temperatures (970–1250 °C) is at 1100 °C/1 as we have ascertained in our previous studies. The unreleased residual stresses in the retained lattice defects potentially affect other properties of the material. Hence, this work aims to investigate if a longer hold time of ST at 1100 °C will lead to complete recrystallization while maintaining the hardness after aging or not. For this study, L-PBF-Inconel 718 samples were ST at 1100 °C at various hold times (1, 3, 6, 9, 16, or 24 h) and aged to study the effects on microstructure and hardness. In addition, a sample was directly aged to study the effects of bypassing ST. The samples (ST and aged) gain hardness by 43–49%. The high density of annealing twins evolved during 3 h of ST and only slightly varies for longer ST.

• Hansen, Vidar; Kosinskiy, Andrey & Taftø, Johan (2020). Distinguishing space groups by electron channelling: centrosymmetric full-Heusler or non-centrosymmetric half-Heusler? Acta Crystallographica Section A: Foundations and Advances. A76(2), p. 211–213. doi: 10.1107/S2053273319016942. Full text in Research Archive Show summary

  X-ray emission under electron-channelling conditions is used to distinguish between a non-centrosymmetric half-Heusler and a centrosymmetric full-Heusler crystal. For TiCo1.5+xSn the space-group determination based on a Rietveld refinement procedure became challenging for increasing Co content (x > 0.2), while electron channelling proved successful for higher Co content (x = 0.35). This technique can be used on crystals as small as (10 nm)3.

• Belsvik, Marius Aga; Tucho, Wakshum Mekonnen & Hansen, Vidar (2020). Microstructural studies of direct‑laser‑deposited stainless steel 316L‑Si on 316L base material. SN Applied Sciences. ISSN 2523-3963. 2. doi: 10.1007/s42452-020-03530-3. Full text in Research Archive
• Adasooriya, Mudiyan Nirosha Damayanthi; Tucho, Wakshum Mekonnen; Holm, Erlend; Årthun, Terje; Hansen, Vidar & Solheim, Karl Gunnar [Show all 7 contributors for this article] (2020). Effect of hydrogen on mechanical properties and fracture of martensitic carbon steel under quenched and tempered conditions. Materials Science & Engineering: A. ISSN 0921-5093. 803. doi: 10.1016/j.msea.2020.140495. Full text in Research Archive Show summary

  The change in the mechanical properties of tempered high strength carbon steel (AISI 4130) due to hydrogen embrittlement (HE) has been investigated using slow strain rate tensile tests (SSRT). The heat treatment processes consisted of austenitization at 873 °C for about 45 min before quenching in salt bath and tempering at temperatures between 350 °C to 550 °C for about 1 h. The SSRT tests were performed on both hydrogen pre-charged and uncharged samples. Vickers hardness test was carried out to study the variation in hardness with the tempering temperature. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were performed for Microstructural characterizations and fracture surface analysis. The fracture surface analysis shows a transition of failure mechanism from brittle intergranular cracking at the lowest tempering temperature to ductile micro void coalescence at the highest temperature. TEM analysis reveals formation of carbide precipitates of the samples which were tempered. The AISI 4130 was subjected to HE for hydrogen charging when the tempering temperatures were 430 °C and lower, corresponding to a hardness value of 450 HV and greater.

• Delimitis, Andreas; Hansen, Vidar & Gjønnes, Jon (2019). Geometry determination and refinement in the rotation electron diffraction technique. Ultramicroscopy. ISSN 0304-3991. 201, p. 68–76. doi: 10.1016/j.ultramic.2019.02.011. Full text in Research Archive Show summary

  The necessary parameters (rotation axis, incident electron beam direction and beam tilt path) in order to describe the diffraction geometry in the Rotation Electron Diffraction (RED) method during data collection are determined and refined. These parameters are prerequisites for the subsequent calculations of excitation errors, sg, for zero (ZOLZ) or higher order Laue zones (HOLZ) reflections. Comparison with simulated results, for a CoP3 thermoelectric crystal, shows excellent agreement between the two approaches -calculated and simulated. In addition to their determination, a thorough refinement methodology for the incident electron beam direction and beam tilt path has been applied, too, based on Kikuchi lines of HOLZ reflections. Incorporation of the refined excitation error values can be considered both in theoretical calculations for diffracted beam intensities, based on the Bloch wave method, as well as in deducing integrated intensities from experimental rocking curves. The methodology described in this study is quite indispensable, as it forms an essential step for performing dynamical calculations in RED, enabling thus enhanced accuracy in structural parameter clarification. The latter is especially important in the case of thermal factors refinement for e.g. thermoelectrics, which are imperative for material properties’ evaluation.

• Hansen, Vidar; Echevarria-Bonet, Cristina; Minde, Mona Wetrhus & Taftø, Johan (2018). Determination of atomic positions and polar direction in half-Heusler material Sb1- xSnxTi1-y-zHfyZrzCo using electron channeling. AIP Advances. 8(12), p. 1–9. doi: 10.1063/1.5042816. Full text in Research Archive Show summary

  Variation of electron-induced x-ray emission with the crystal direction of an incoming electron beam (channeling) is used to study the crystal site preference of different elements in a promising thermoelectric half-Heusler material. This material has Sb, Co and Ti as the main constituting elements, with lower contents of Hf, Zr and Sn. It is confirmed experimentally, in accordance with previous assumptions, that Sb and Sn occupy one of the octahedral sites, 4a (0, 0, 0), Ti, Zr and Hf the other octahedral site,4b(½, ½, ½),andCoatomsoccupythetetrahedralsite,4c(¼, ¼, ¼)inthecubic spacegroup F¯43m with lattice constant a = 0.598±0.001 nm. Furthermore, a strong asymmetry along the polar directions is observed, which is as it should be in a halfHeusler material, when the Co atoms have a strong preference for one of the two sets of tetrahedral sites. Such asymmetries can not be observed by kinematical diffraction according to Friedel’s law, thus demonstrating that the observation of element characteristic signals under channeling conditions is a unique technique for determining the sense of polar directions and distinguishing crystal symmetry alternatives in small crystal grains and nanocrystals.

• Tucho, Wakshum Mekonnen; Lysne, Vidar Hellandsjø; Austbø, Jon Håkon; Sjølyst-Kverneland, Atle & Hansen, Vidar (2018). Investigation of effects of process parameters on microstructure and hardness of SLM manufactured SS316L. Journal of Alloys and Compounds. ISSN 0925-8388. 740, p. 910–925. doi: 10.1016/j.jallcom.2018.01.098. Full text in Research Archive
• Tucho, Wakshum Mekonnen & Hansen, Vidar (2018). Characterization of SLM-fabricated Inconel 718 after solid solution and precipitation hardening heat treatments. Journal of Materials Science. ISSN 0022-2461. 54(1), p. 823–839. doi: 10.1007/s10853-018-2851-x. Full text in Research Archive
• Hjuler, M.Leth; Hansen, Vidar & Fabricius, Ida Lykke (2018). Interpretational challenges related to studies of chalk particle surfaces in scanning and transmission electron microscopy. Bulletin of the Geological Society of Denmark. ISSN 0011-6297. 66, p. 151–165. Full text in Research Archive
• Guo, Kun; Hansen, Vidar; Li, Hailong & Yu, Zhixin (2018). Monodispersed nickel and cobalt nanoparticles in desulfurization of thiophene for in-situ upgrading of heavy crude oil. Fuel. ISSN 0016-2361. 211, p. 697–703. doi: 10.1016/j.fuel.2017.09.097. Full text in Research Archive Show summary

  Monodispersed nickel (Ni) and cobalt (Co) nanoparticles (NPs) with different sizes are synthesized via the thermal decomposition of organometallic precursors by controlling the reaction temperature and surfactant amount. X-ray diffraction analysis of the as-prepared NP samples shows the formation of cubic Ni metal phases with good crystallinity, while the cubic Co metal samples are semi-amorphous. Transmission electron microscopy characterization further confirms that two Ni NP samples with average sizes of 9 and 27 nm, and Co NPs with an average size of 6 nm are successfully prepared with a narrow size distribution. Furthermore, catalytic performance of these monodispersed NPs towards the hydrodesulfurization (HDS) reaction, which plays a pivotal role in the upgrading of heavy crude oil, is evaluated under reservoir-relevant conditions using thiophene as a sulfur-containing model compound. Different parameters including particle size, catalyst dosage, hydrogen donor ratio, temperature, and reaction duration are systematically studied to optimize the catalytic HDS performance. The morphology and size of the spent NP catalysts after the reaction are also analyzed. The results show that the 9 nm Ni NPs exhibit the best HDS activity and stability compared with other catalysts, which suggests that such well-dispersed Ni NPs are promising candidates for the in-situ upgrading and recovery of heavy crude oil from underground reservoirs.

• Tucho, Wakshum Mekonnen; Cuvillier, Priscille; Sjølyst-Kverneland, Atle & Hansen, Vidar (2017). Microstructure and hardness studies of Inconel 718 manufactured by selective laser melting before and after solution heat treatment. Materials Science & Engineering: A. ISSN 0921-5093. 689, p. 220–232. doi: 10.1016/j.msea.2017.02.062. Full text in Research Archive
• Buxhuku, Mika; Hansen, Vidar & Gjønnes, Jon (2017). The measurement of intensities in the Rotation Electron Diffraction Technique. Micron. ISSN 0968-4328. 101, p. 103–107. doi: 10.1016/j.micron.2017.06.006. Full text in Research Archive
• Buxhuku, Mika; Hansen, Vidar; Oleynikov, Peter & Gjønnes, Jon (2013). The determination of rotation axis in the Rotation Electron Diffraction Technique. Microscopy and Microanalysis. ISSN 1431-9276. 19(5), p. 1276–1280. doi: 10.1017/S1431927613012749. Full text in Research Archive
• Sjølyst-Kverneland, Atle; Hansen, Vidar; Thorkildsen, Gunnar; Larsen, Helge Bøvik; Pattison, P & Li, X.Z. [Show all 7 contributors for this article] (2011). Transformations and structures in the Al-Zn-Mg alloy system: A diffraction study using synchrotron radiation and electron precession. Materials Science & Engineering: A. ISSN 0921-5093. 528(3), p. 880–887. doi: 10.1016/j.msea.2010.10.001. Full text in Research Archive
• Sjølyst-Kverneland, Atle; Hansen, Vidar; Thorkildsen, Gunnar; Larsen, Helge Bøvik; Pattison, Philip & Li, XZ [Show all 7 contributors for this article] (2010). Transformations and structures in the Al?Zn?Mg alloy system: A diffraction study using synchrotron radiation and electron precession. Materials Science & Engineering: A. ISSN 0921-5093. doi: 10.1016/j.msea.2010.10.001. Full text in Research Archive Show summary

  The structure of the hardening ??-phase precipitates in Al?Zn?Mg alloys has been investigated by using precession electron diffraction and X-ray synchrotron radiation diffraction. The latter was recorded as a three-dimensional, continuous intensity distribution from a single alloy grain, from which patterns of remarkable sharpness from the precipitate particles could be extracted. High resolution electron microscopy revealed extensive structural variations with prolific faults in the ?? precipitates. The ??-structures are described in terms of two structure models based on two icosahedral elements that are inherent in the equilibrium ?-MgZn2 structure. The role of these icosahedra in the transformations of the alloy system is discussed.

• Haakenaasen, Randi; Selvig, Espen; Hadzialic, S; Skauli, Torbjørn; Hansen, Vidar & Tibballs, J.E. [Show all 12 contributors for this article] (2008). Nanowires in the CdHgTe material system. Journal of Electronic Materials. ISSN 0361-5235. 37(9), p. 1311–1317. Full text in Research Archive Show summary

  HgTe nanowires have been grown by molecular beam epitaxy (MBE). They are nucleated at Au particles on Si or GaAs substrates and subsequently self-organize and grow laterally on the surface into 20-50 nm wide, 0.5-1 mu m long twisted, but single-crystal, wires. Further growth gives longer, wider, and straighter polycrystalline wires. When unimpeded by Au particles on the surface, the wires become straight and consist of segments of cubic < 111 > HgTe and hexagonal < 001 > Te parallel to the wire. Te nanowires and Au nanowires have also occasionally been formed. All attempts to grow CdHgTe on Si substrates with or without Au particles have resulted in polycrystalline layers. The phase diagrams and diffusion coefficients imply that CdHgTe or HgTe nanowires will not grow by the vapor-liquid-solid technique at the low MBE growth temperatures. SiO2 functions as a mask for selective growth of HgTe, but not for CdHgTe.

• Selvig, Espen; Hadzialic, S; Skauli, Torbjørn; Steen, Harald; Hansen, Vidar & Trosdahl-Iversen, L [Show all 9 contributors for this article] (2006). Growth of HgTe nanowires. Physica scripta. Topical Issues. ISSN 0281-1847. 126, p. 115–120. Full text in Research Archive
• Hansen, Vidar; Vevecka-Priftaj, A; Fjerdingen, J; Langsrud, Y & Gjønnes, Jon (2006). The influence of silicon on age hardening kinetics and phase precipitations in Al-Mg-Zn alloys. Materials Science Forum. ISSN 0255-5476. 519-521, p. 579–584. Full text in Research Archive
• Kverneland, A.; Hansen, Vidar; Vincent, R.; Gjønnes, Kjersti & Gjønnes, Jon (2006). Structure analysis of embedded nano-sized particles by precession electron diffraction. eta '-precipitate in an Al-Zn-Mg alloy as example. Ultramicroscopy. ISSN 0304-3991. 106(106), p. 492–502. Full text in Research Archive
• Gjonnes, J.; Hansen, Vidar & Kverneland, Atle (2004). The precession technique in electron diffraction and its application to structure determination of nano-size precipitates in alloys. Microscopy and Microanalysis. ISSN 1431-9276. 10, p. 16–20. Full text in Research Archive
• Hansen, Vidar; Karlsen, Ole Bjørn; Langsrud, Yngve & Gjønnes, Jon (2004). Precipitates, zones and transitions during aging of Al-Zn-Mg-Zr7000series alloy. Materials Science and Technology. ISSN 0267-0836. 20, p. 185–193. Full text in Research Archive
• Gjønnes, Jon; Hansen, Vidar & Kverneland, Atle (2004). The precession technique in electron diffraction and its application to structure determination of nano-size precipitates in alloys. Microscopy and Microanalysis. ISSN 1431-9276. 10, p. 16–20. Full text in Research Archive
• Hansen, Vidar; Karlsen, Ole Bjørn; Langsrud, Yngve & Gjønnes, Jon (2004). Precipitates, zones and transitions during ageing of Al-Zn-Mg-Zr 7000 series alloy. Materials Science and Technology. ISSN 0267-0836. p. 185–193. Full text in Research Archive
• Gjønnes, Jon; Hansen, Vidar; Andersen, S.J.; Marioara, C.D. & Li, XZ (2003). Electron crystallography of aluminium alloy phases. ?. 218, p. 293–307. Full text in Research Archive

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• Pavlou, Dimitrios; Correia, José A.F.O.; Fazeres-Ferradosa, Tiago; Gudmestad, Ove Tobias; Siriwardane, Sudath C. & Lemu, Hirpa G. [Show all 16 contributors for this article] (2024). Analytical and experimental methods in mechanical and civil engineering : Contributions of the 1st olympiad in engineering science (OES 2023). Springer Nature. ISBN 9783031497223. 586 p. Full text in Research Archive

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• Holmestad, Randi; Gunnæs, Anette Eleonora; Nord, Magnus; Hage, Fredrik Sydow; Hansen, Vidar Folke & Prytz, Øystein [Show all 7 contributors for this article] (2024). Electron diffraction in physical science in Norway – past, present, and future. Full text in Research Archive
• Rai, Ayushi; Delimitis, Andreas & Hansen, Vidar Folke (2023). TEM investigations of thermochromic VO2 thin films for smart windows applications. Full text in Research Archive
• Khazeni, Dena & Hansen, Vidar Folke (2023). Comparative analysis of Co-Cr-Fe-Mo alloy fabricated by Laser Powder Bed Fusion and casting for dental and maxilla facial application. Full text in Research Archive
• Hansen, Vidar Folke & Minde, Mona Wetrhus (2023). Introduction to University of Stavanger & High resolution microscopy analysis of additively man- ufactured implant materials. Full text in Research Archive
• Delimitis, Andreas; Rai, Ayushi; Mesaritis, G.; Ioannou, Ioanna; Hansen, Vidar Folke & Kyratsi, Theodora (2022). Atomic site distributions in medium / high temperature range application thermoelectrics: an HRTEM and electron channeling study. Full text in Research Archive
• Rai, Ayushi; Mihailescu, Cristian N.; Hansen, Vidar Folke & Delimitis, Andreas (2022). Structural investigations of nanocrystalline VO2/Si and VO2/LSAT epilayers for thermochromic windows applications grown by pulsed laser deposition. Full text in Research Archive
• Rai, Ayushi; Hansen, Vidar Folke; Mihailescu, Cristian N. & Delimitis, Andreas (2022). Characterisation studies of thermochromic VO2 thin films for smart windows applications. Full text in Research Archive
• Delimitis, Andreas; Hansen, Vidar Folke; Symeou, Elli; Kyratsi, Theodora; Minde, Mona Wetrhus & Taftø, Johan (2019). DETERMINATION OF HOST AND DOPANT ION DISTRIBUTION IN MG2SI1-XSNX THERMOELECTRIC MATERIALS BY ELECTRON CHANNELING. Acta Crystallographica Section A: Foundations and Advances. 75, p. e321–e321. doi: 10.1107/S2053273319092350. Full text in Research Archive Show summary

  Detailed structure studies by electron microscopy methods have been widely exploited due to the unique capabilities electrons provide. Precise identification of atomic positions is feasible by employing spectroscopy techniques in an analytical transmission electron microscope. In this aspect, methods such as energy dispersive Xray spectroscopy (EDS) are utilised, under strong channelling conditions, where the yield of element characteristic X-ray emission can be modified and manipulated, dependent upon crystallographic directions of the incident beam. These channelling effects are powerful in determining atomic site locations in crystals and techniques such as ALCHMI (Atom Location by Channeling Enhanced MIcroanalysis) have been developed and evaluated. Structural analyses employing electron channelling have a recent focus in systems for renewable technologies and energy harvesting, such as thermoelectric (TE) materials. TEs based on Mg2Si1-xSnx have gained increased interest, due to inexpensive production costs, abundancy and a toxic nature of raw materials, especially for power generation applications within the intermediate temperature range (500–900 K). Synthesis of Mg2Si1-xSnx in nanocrystal morphologies, often coupled by incorporation of dopants in their host matrix is exploited, with a scope to efficiently reduce thermal conductivity, particularly for Sn-rich or Bi doped Si-rich compounds. Previous studies confirmed the multiplicity of phases in this system, however, the precise distribution of host and dopant ions location is still controversial. Application of the electron channelling technique is therefore more than essential in order to accurately determine and refine their structural characteristics. Experimental outcomes will be demonstrated and discussed.

• Delimitis, Andreas; Hansen, Vidar Folke; Symeou, Elli; Kyratsi, Theodora; Minde, Mona Wetrhus & Taftø, Johan (2019). Determination of host and dopant ion distribution in Mg2Si1-xSnx thermoelectric materials by electron channeling. Full text in Research Archive Show summary

  Detailed structure studies by electron microscopy methods have been widely exploited due to the unique capabilities electrons provide. Precise identification of atomic positions is feasible by employing spectroscopy techniques in an analytical transmission electron microscope. In this aspect, methods such as energy dispersive X-ray spectroscopy (EDS) are utilised, under strong channeling conditions, where the yield of element characteristic X-ray emission can be modified and manipulated, dependent upon crystallographic directions of the incident beam. These channeling effects are powerful in determining atomic site locations in crystals and techniques such as ALCHEMI (Atom Location by CHanneling Enhanced MIcroanalysis) have been developed and evaluated. Structural analyses employing electron channeling have a recent focus in systems for renewable technologies and energy harvesting, such as thermoelectric (TE) materials. TEs based on Mg2Si1-xSnx have gained increased interest, due to inexpensive production costs, abundancy and atoxic nature of raw materials, especially for power generation applications within the intermediate temperature range (500–900 K). Synthesis of Mg2Si1-xSnx in nanocrystal morphologies, often coupled by incorporation of dopants in their host matrix is exploited, with a scope to efficiently reduce thermal conductivity, particularly for Sn-rich or Bi doped Si-rich compounds. Previous studies confirmed the multiplicity of phases in this system, however, the precise distribution of host and dopant ions location is still controversial. Application of the electron channeling technique is therefore more than essential in order to accurately determine and refine their structural characteristics. Experimental outcomes will be demonstrated and discussed.

• Delimitis, Andreas; Gjønnes, Jon & Hansen, Vidar Folke (2019). Refinement Approaches in the Diffraction Geometry of the Rotation Electron Diffraction Method. Full text in Research Archive Show summary

  Rotation Electron Diffraction (RED) has been established as a quite powerful method for structure analysis and refinement. Although its capability is based, among others, on eliminating dynamical diffraction effects, some residual ones may still exist, which limit method accuracy. A way of improving RED correctness is to account for these dynamical interactions, by employing Bloch wave calculations to theoretically deduce diffracted beam intensities and estimate structural data. As a first step, the diffraction geometry in RED experiments needs to be precisely determined and refined. In this study, we aim on determining the rotation axis and deriving analytical calculations and refinement of the incident electron beam direction and beam tilt path. This is accomplished by a combination of Kikuchi line pattern analysis and simulation, from zero order and higher order Laue zones (ZOLZ and HOLZ) reflections. Employing Kikuchi lines, especially of HOLZ reflections, is highly suitable as they are extremely sensitive to tilting experiments in RED, thus enabling calculations with increased precision. Subsequent expressions of excitation errors, sg, for ZOLZ and HOLZ reflections will be also deduced. The importance of this methodology for subsequent dynamical calculations of diffracted electron beam intensities by the Bloch wave formalism will be demonstrated. Results of the refinement strategy from RED experiments on thermoelectric materials will be analysed and evaluated.

• Delimitis, Andreas; Gjønnes, Jon & Hansen, Vidar Folke (2019). Rotation Electron Diffraction for Structure Determination and Refinement: Applications in Nanocrystalline Thermoelectrics. Full text in Research Archive Show summary

  Their unparalleled spatial resolution and strong interaction with matter render high energy electrons ideal for structure determination by diffraction methods, some of which date back since the 1950’s. However, it was soon realised that the complex dynamical interactions between electron beams impose a significant drawback towards enhancing data accuracy. A major breakthrough in overcoming this was accomplished initially by Precession Electron Diffraction (PED) and, more recently, by Rotation Electron Diffraction (RED), where the beam intensities can be treated, to a certain extent, kinematically. In addition, RED further enabled the acquisition of complete three dimensional (3D) electron diffraction data, without the need for additional hardware attachments in the transmission electron microscope. Nonetheless, RED experimental outcomes must account for remaining dynamical effects that limit accuracy and precise determination of fine structural parameters, such as thermal ones, i.e. Debye-Waller factors. Incorporating such dynamical effects is accomplished by Bloch wave calculations of diffracted beam intensities, which require a priori determination of excitation errors sg and refinement of diffraction geometry in RED. In this contribution, the methodology to incorporate these dynamical interactions in RED will be presented, focusing on refinement of diffraction geometry and subsequent sg calculations. RED investigations have been predominately applied in materials for renewable technologies and energy harvesting, such as thermoelectrics. Synthesis of thermoelectrics in nanocrystal morphologies is widely exploited with a scope to improve their properties and performance; consequently structure determination by RED, down to refinement of thermal parameters is highly essential.

• Tofan, Raluca; Echevarria-Bonet, Cristina; Berland, Kristian; Schrade, Matthias; Sørby, Magnus Helgerud & Hauback, Bjørn Christian [Show all 10 contributors for this article] (2016). The effect of spark plasma sintering on structure and phase stability in half-Heusler thermoelectric alloys. Full text in Research Archive
• Tofan, Raluca; Echevarria-Bonet, Cristina; Berland, Kristian; Schrade, Matthias; Sørby, Magnus Helgerud & Hauback, Bjørn Christian [Show all 10 contributors for this article] (2016). Microstructural characterization of spark plasma sintered (X,X’)NiSn half‐Heusler alloys. Full text in Research Archive
• Song, Xin; Persson, Clas; Norby, Truls; Flage-Larsen, Espen; Karlsen, Ole Bjørn & Hansen, Vidar [Show all 16 contributors for this article] (2014). Conversion of Heat and Energy: Thermoelectrics. Full text in Research Archive
• Valset, Kjetil; Prytz, Øystein; Hansen, Vidar & Taftø, Johan (2012). Quantitative study of structure factors at large reciprocal vectors using convergent beam electron diffraction: Application to anharmonicity of the thermal motion in Mg2Si. Full text in Research Archive
• Løvvik, Ole Martin; Valset, Kjetil; Rauwel, Protima; Prytz, Øystein; Flage-Larsen, Espen & Song, Xin [Show all 12 contributors for this article] (2012). Thermoelectricity in Oslo. Full text in Research Archive
• Buxhuku, Mika; Hansen, Vidar; Oleynikov, P. & Gjønnes, Jon (2012). Determination of crystallographic tilt axis in Rotation Electron Diffraction. Full text in Research Archive
• Buxhuku, Mika; Hansen, Vidar & Gjønnes, Jon (2012). The geometry and measurement of integrated intensities in Rotation Electron Diffraction method. Full text in Research Archive
• Qureishy, Thomas; Hansen, Vidar; Karlsen, Ole Bjørn; Gunnæs, Anette Eleonora & Taftø, Johan (2012). Superstructures in Mg2Si1-xSnx. Full text in Research Archive
• Buxhuku, Mika; Hansen, Vidar & Magnus, Sørby (2012). Electron and powder diffraction techniques for accurate structure factors. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). This heat pump can last 10 000 years. [Internet]. Scientific Computing. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). Researchers claim that new heat pump can last almost forever? [Internet]. Engineers Edge. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). Researchers from University of Stavanger Work on a Heat Pump that Lasts Forever. [Internet]. Azocleantech. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). Forskere fra Universitetet i Stavanger Arbeidet med en varmepumpe som varer evig. [Internet]. Azocleantech. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). A Totally New Take On Heat Pumps. [Internet]. Efie.net. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). New heat pump could last 10,000 years, experts say. [Internet]. Environment news blog. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). This heat pump can last 10 000 years. [Internet]. Abovetopsecret. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). This heat pump can last 10000 years... [Internet]. Fluid World. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). Wärmepumpen: Kältemittel bald überflüssig. [Internet]. Innovations Report. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2011). Researchers Develop a Heat Pump That Can Last 10,000 Years. [Internet]. Zeitnews. Full text in Research Archive Show summary

  Researchers now are testing an entirely new heat pump. While those we use today last ten to twenty years, the new one will last almost forever.

• Buxhuku, Mika; Karlsen, Ole Bjorn; Gjønnes, Jon; Gjønnes, Kjesti & Hansen, Vidar (2011). Accurate structure factors of skutterudites:Electron Diffraction Techniques. Acta Crystallographica Section A: Foundations of Crystallography. ISSN 0108-7673. 67, p. 696–697. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2010). Denne varmepumpa kan vare i 10000 år. [Journal]. UniverS : magasin for Universitetet i Stavanger. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2010). Denne varmepumpa kan vare i 10 000 år. [Internet]. forskning.no. Full text in Research Archive Show summary

  Forskarar prøver no ut ei heilt ny varmepumpe. Medan dei vi brukar i dag ryk etter ti til tjue år, vil den nye vare nesten evig.

• Bording, Jan Kåre & Hansen, Vidar (2010). Varmepumpe for evigheten. [Journal]. Aftenposten (morgenutg. : trykt utg.). Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2010). Varmepumpe for evigheten Form og størrelse kan tilpasses etter behov. Full text in Research Archive Show summary

  Forskere ved Universitetet i Stavanger er i ferd med å utvikle en ny termoelektrisk varmepumpe som vil kunne vare nesten evig.

• Bording, Jan Kåre & Hansen, Vidar (2010). Termoelektrisitet - en "ny type" varmepumpe. Full text in Research Archive Show summary

  Hvordan virker en konvensjonell varmepumpe og hvor effektiv er den. Hva er termoelektrisitet, hvordan kan dette brukes til å varme hus og hva er dets gode og mindre gode egenskaper.

• Bording, Jan Kåre & Hansen, Vidar (2010). Denne varmepumpa kan vare i 10000 år. Full text in Research Archive Show summary

  Forskarar prøver no ut ei heilt ny varmepumpe. Medan dei vi brukar i dag ryk etter ti til tjue år, vil den nye vare nesten evig.

• Bording, Jan Kåre; Prytz, Øystein; Hansen, Vidar & Taftø, Johan (2009). Improved thermoelectric materials through nanostructuring: implications for energy savings. Full text in Research Archive
• Böttger, Paul Heinrich Michael; Valset, Kjetil; Flage-Larsen, Espen; Prytz, Øystein; Bording, Jan Kåre & Karlsen, Ole Bjørn [Show all 10 contributors for this article] (2009). An overview of our basic and applied thermoelectric research activity. Full text in Research Archive
• Bording, Jan Kåre & Hansen, Vidar (2009). Improved thermoelectric materials through nanostructuring: implications for energy savings. Full text in Research Archive Show summary

  In a small scale test of thermoelectric heat-pumps we have achieved an energy efficiency of 2.65 at a temperature difference of 10 degrees. In the test we used commercial Peltier elements with Bi2Te3 based thermoelectric materials. Thermoelectric materials have a dimensionless figure of merit, ZT, given by where is the absolute temperature, the thermal conductivity, the electrical conductivity and the Seebeck coefficient of the thermoelectric material. is defined by which means that a voltage difference of is set up across the material at a temperature difference . An energy efficient Peltier element needs both a p-type and an n-type thermoelectric material with high ZT, and the efficiency of the Peltier element is somewhat reduced due to parasitic effects. According to general predictions based on thermodynamics the upper limit for the energy efficiency of a heat-pump with Peltier elements having ZT = 1 is 3 at a difference of 20 degrees between indoor and outdoor temperature [1]. A strategy for improving the dimensionless figure of merit is to modify the material at the nanoscale, thereby reducing the phonon contribution to the thermal conductivity. Recently, a dimensionless figure of merit above 1.5 has been achieved in bulk p-type Bi2Te3 based materials fabricated by melt spinning [2,3]. With a dimensionless figure of merit of 1.5 for the Peltier element, the upper limit for the energy efficiency of the heat-pump would rise from 3 to 4. This improvement would reduce the electricity consumption to 25 % compared with the use conventional electrical heating. Advantages of thermoelectric heat-pumps compared to traditional ones would be the elimination of compressors and unwanted climate gases. In a recently started project we will perform large scale tests of thermoelectric heat pumps to assess their feasibility for large scale heating. Thermoelectric heat pumps require a design different from conventional heat pumps, so effort will be put on optimizing this design.

• Hansen, Vidar; Oddsen, Ingunn Cecilie; Kverneland, Atle; Larsen, Helge Bøvik; Pattison, Philip & Thorkildsen, Gunnar [Show all 7 contributors for this article] (2009). Diffuse scattering from zones and particles in the Al-Zn-Mg alloy system. Full text in Research Archive
• Oddsen, Ingunn Cecilie; Hansen, Vidar; Kverneland, Atle & Gjønnes, Jon (2008). Phase transition in age-hardening Al-Zn-Mg alloys. Full text in Research Archive Show summary

  HREM images of precipitates embedded in Al matrix has been analysed and compared to the known lattice parameters of the metastable _h¿- phas and the equilibrium _h ¿ phase. The local variation in the stacking o the icosahedrons suggests that the particles may consist of both phases, with a gradually continuous transition starting near the edges of the particle.

• Hansen, Vidar; Kverneland, Atle; Li, X.Z.; Thorkildsen, Gunnar; Larsen, Helge Bøvik & Gjønnes, Jon (2008). Elektronmikroskopi og synkrotronrøntgen diffraksjonsstudier av transformasjoner og strukturer i 7xxx-legeringer. Full text in Research Archive
• Hansen, Vidar; Kverneland, Atle; Thorkildsen, Gunnar; Larsen, Helge Bøvik; Vincent, Roger & Gjønnes, Jon (2007). Structure analysis of the n'-precipitate in Al-Zn-Mg alloys by the precession technique in electron diffraction and synchrotron radiation. Full text in Research Archive
• Hansen, Vidar; Kverneland, Atle; Thorkildsen, Gunnar; Larsen, Helge Bøvik; Pattison, Philip & Gilmore, Cristopher [Show all 8 contributors for this article] (2006). Structure determination of nanosized semi-coherent Al-Mg-Zn precipitates by precession electron diffraction and synchrotron X-ray diffraction. Full text in Research Archive
• Hansen, Vidar; Kverneland, Atle; Larsen, Helge Bøvik; Pattison, Philip; Vincent, Roger & Gjønnes, Jon (2005). Structure Determination of Embedded Precipitates by Precession Electron Diffraction and Synchrotron Radiation: A Comparison. Full text in Research Archive
• Hansen, Vidar (2004). Elektronmikroskopi ved HIS; Utrustning og aktiviteter. Full text in Research Archive
• Hansen, Vidar; Kverneland, Atle; Vincent, Roger; Li, X.Z.; Stiller, Krystyna & Gjønnes, Jon (2004). Precession electron diffraction, high-resolution microscopy and atom probe analysis of nano-sized precipitates in Al-Zn-Mg industrial alloys. Full text in Research Archive
• Kverneland, Atle; Hansen, Vidar; Vincent, Roger & Gjønnes, Jon (2004). Strukturmodeller for herdefasen etta merket-MgZn i 7xxx legeringer. Full text in Research Archive
• Knutsen, Turid; Hansen, Vidar; Håkansson, B; Gunnæs, Anette; Jørgensen, Sissel & Våland, Torstein [Show all 7 contributors for this article] (2003). A Study of Amorphous and Crystalline Ni78Si8B14. Full text in Research Archive
• Kverneland, Atle; Hansen, Vidar; Gjønnes, Jon & Vincent, Roger (2003). Structure solution of the hardening etta prime precipitate in Al-Zn-Mg alloys by the precession technique in electron diffraction. Full text in Research Archive
• Kverneland, Atle; Gjønnes, Jon; Hansen, Vidar & Vincent, Roger (2003). Structure solution of the hardening n'-precipitate in Al-Mg-Zn alloys by the precession technique in electron diffraction. Full text in Research Archive
• Hansen, Vidar; Kverneland, Atle; Li, X.Z; Stiller, Krystyna; Vincent, Roger & Gjønnes, Kjersti [Show all 7 contributors for this article] (2003). Crystal structures along the transformation path during age hardening in Al-Zn-Mg alloys by high resolution electron microscopy, precession electron diffraction and atom probe analysis. Full text in Research Archive
• Hansen, Vidar (2003). Fast stoff reaksjoner i aluminium, en norsk gullgruve. Full text in Research Archive
• Hansen, Vidar (2002). Tid-temperatur transformasjoner i 7xxx-aluminiumslegeringer. Full text in Research Archive
• Sørbrøden, Erik; Hansen, Vidar; Olsen, Arne; Holme, Børge & Taftø, Johan (2002). Imaging of hardening particles in an Al-Mg-Zn alloy using plasmon electron energy losses. Full text in Research Archive
• Gjønnes, Jon; Hansen, Vidar & Li, X.Z (2002). The collection of electron intensity data and its use in structure determination. Full text in Research Archive
• Gao, Robert Qiang; Stiller, Krystyna; Hansen, Vidar; Oskarsson, Anders & Danoix, Frederic (2002). Influence of Aging Conditions on the Microstructure and Tensile Strenght of Aluminium Alloy 6063. Full text in Research Archive
• Sayyar, Navid; Hansen, Vidar Folke; Tucho, Wakshum Mekonnen & Minde, Mona Wetrhus (2026). Super duplex stainless steel manufactured by laser beam directed energy deposition and powder – Microstructure, properties, and parameter optimization. Universitetet i Stavanger. ISSN 9788284394923. Full text in Research Archive Show summary

  Over the past decades, additive manufacturing (AM) has emerged as a promising technique for fabricating metallic components. It offers design flexibility, enables near-net-shape production, and minimizes material waste and post-processing requirements. These are benefits that are particularly valuable for high-strength alloys with limited formability such as duplex stainless steel (DSS). DSS is a unique category of alloys distinguished by a microstructure consisting of roughly equal proportions of ferrite and austenite. Its dual-phase content can effectively merge beneficial properties of both phases and maintains the alloy’s desirable balance of mechanical and corrosion performances. As a result, DSSs are widely used in applications such as offshore structures, chemical processing, and power generation where mechanical reliability and corrosion resistance are critical. AM offers the potential to tailor microstructures and properties in ways that are challenging to realize with subtractive techniques. However, understanding microstructural behaviour and phase evolution during layer-by-layer deposition, as well as controlling key process parameters are essential. This study investigates Directed Energy Deposition - Laser Beam / Powder (DED-LB/p) processing of super duplex stainless steel (SDSS), with a focus on understanding the relationships between processing conditions, microstructure, and materials behaviour. The work is structured into three stages: Stage Ⅰ: Through preliminary investigations, evolution of the phases and microstructure, formation of crystallographic texture and its underlying causes, and mechanical behaviour were discussed in detail. Investigations into DED-LB/p processing of SDSS confirmed the feasibility of producing dense parts with a fully developed duplex microstructure. However, pronounced global and local phase imbalances, strong epitaxial ferritic growth, and columnar grain structures were observed as a consequence of layer-by-layer fabrication and spatially varying thermal histories. The ferritic solidification texture was partially inherited by the austenitic phase through orientation relationships, resulting in limited mechanical anisotropy. Localized microstructural inhomogeneities and coarse ferritic grains contributed to reduced toughness. These findings underscored the need for targeted microstructural engineering, through process optimization strategies, to refine grain morphology, homogenize phase distribution, and ultimately enhance the mechanical performance. Foundational knowledge necessary for reliable AM of SDSS components via DED-LB/p was established in this stage. Stage Ⅱ: In-situ control of thermal conditions was addressed to study the potential for engineering the microstructure during pulsed laser DED-LB/p, achieving a favourable grain structure, changing the dominant preferred orientation, and enhancing the mechanical and corrosion performances of SDSS, both in as-built and solution-annealed states. This stage involved the practical application of pulsed laser in DED-LB/p of SDSS. Compared with continuous-wave laser processing, pulsed DED-LB/p modified solidification dynamics through localized melt agitation, leading to significant grain refinement and a transition from strongly columnar to predominantly equiaxed ferritic grain structures. It promoted a more homogeneous grain morphology and resulted in a more uniform spatial dispersion of the phases. In addition, the use of pulsed laser mode facilitated gas escape and reduced the formation of Mn- and Si-rich oxide inclusions, thereby enhancing overall microstructural and mechanical integrity, particularly toughness and ductility. Texture development was strongly dependent on energy input and pulsed laser spot size, with smaller beam conditions promoting near-random textures. Stage Ⅲ: A hybrid statistical approach, combined Taguchi-grey relational methodology, was used to optimize the DED-LB/p process parameters. The focus was on the effects of process parameters on the formation of pores, ductility, and process stability in terms of consistent melt pool geometrical features. Independent variables including laser power, deposition speed, pulsed laser frequency, and shielding gas flow rate were selected as controlling factors. Single objective parameter-property relationships were achieved and discussed. Conclusive parametric remarks under multi-attribute optimization were derived and the associated quality responses were verified. The key role of parameters in the process stability, microstructure, and mechanical behaviour was discussed. This stage offers a practical solution to multi-response optimization problems in AM and surface treatment of SDSS, using DED-LB/p.

• Rai, Ayushi; Hansen, Vidar Folke & Delimitis, Andreas (2026). Multimodal Characterization of VO2-Based Thin Films for Smart Windows Technologies. Universitetet i Stavanger. ISSN 9788284394633. Full text in Research Archive Show summary

  Thermochromic vanadium dioxide (VO2) thin films are promising materials for energy-efficient smart window applications due to their reversible metal-insulator transition near 68 °C. However, the structural complexity of VO2, including the coexistence of multiple polymorphs, strain effects, and nanoscale heterogeneity, presents significant challenges for understanding and optimizing their functional performance. This thesis investigates the structural and nanoscale characteristics of VO2 and VO2/TiO2 thin films grown by pulsed laser deposition, with a particular focus on how growth conditions and microstructure influence thermochromic behaviour. A multimodal characterization approach was employed, combining grazing-incidence X-ray diffraction, transmission electron microscopy, selected area and nanobeam electron diffraction, confocal Raman spectroscopy, and tip-enhanced Raman spectroscopy. X-ray diffraction provided an overall assessment of phase composition and crystallinity, while electron microscopy revealed columnar grain growth, interface structure, and local strain accommodation. Diffraction techniques at the nanoscale enabled reliable phase identification and revealed semi-coherent grain growth associated with microstructural evolution during phase stabilization. The influence of nucleation on grain size, crystallographic orientation, and surface roughness was also clarified. Tip-enhanced Raman spectroscopy offered nanoscale chemical and structural insight beyond the limits of conventional techniques, revealing local variations in phase and strain that affect thermochromic performance. The results demonstrate that no single technique is sufficient to describe VO2 thin films and that a multimodal approach is essential to link growth, structure, and functional properties.

• Hansen, Vidar Folke & jan, Koles (2021). 3D printed Aluminium Bronze. Microstructure and mechanical properties of an aluminium-bronze alloy. Universitetet i Stavanger. Full text in Research Archive Show summary

  Design and production of the blades is a sophisticated process that needs to be optimized for given permanence of the rotor. Shape of the rotor requires complicated casting. For small series of production it is wise to use 3D printing technology. Aluminium - Bronze as a production material offers good combination of strength, exibility, corrosion resistance and ease of printing. Micro-structural properties were studied on a specimen printed by robotized direct-energy-deposition machine using 2200W laser. Analysis was carried out on optical microscope, scanning electron microscope and transmission electron microscope. Also X-ray spectroscopy was performed. It was found that the Al bronze contains α Cu and Fe3Al phase.

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