Solid state cooling with elastocaloric materials (Coolem) (completed)

• Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhard; Kušnír, Jakub; Grabec, Tomáš & Seiner, Hanuš [Show all 11 contributors for this article] (2026). Screening for new elastocaloric materials in a compositionally graded NiCuTiZr thin film. Materialia. 50, p. 1–16. doi: 10.1016/j.mtla.2026.102896. Full text in Research Archive Show summary

  NiTi-based shape memory alloys can be used as the active material in elastocaloric cooling devices. For optimal performance, they should simultaneously exhibit high reversibility and low temperature hysteresis, which can be achieved by ensuring that the middle eigenvalue of the primary stretch matrix λ2=1. Also, an adequate transformation temperature and a high enthalpy of transformation are required. In this study, a systematic screening for highly reversible shape memory alloys was performed, using compositionally graded Ni-Cu-Ti-Zr thin films generated by magnetron sputtering. Based on experimental data from the literature, a model predicting λ2 from the quaternary film compositions indicated a range of targeted compositions with λ2=1. The properties of the thin-film compositions were experimentally investigated to corroborate the theoretical possibilities. Martensitic phase transformations were observed with differential scanning calorimetry, demonstrating a systematic change in transformation temperatures with composition. X-ray diffraction confirmed a transition between B2 austenite and B19’ martensite structures, similar to binary NiTi compounds. The targeted compositions did not exhibit the expected temperature-driven phase transformations with low hysteresis. Tensile testing revealed superelastic behaviour, but the samples were intrinsically brittle with large hysteresis and mechanical instability. This was explained by phase separation and the formation of Ti2Ni- and Ni4Ti3-like minority phases. Despite the failure to demonstrate new shape memory alloys with high reversibility, the study suggests a path to efficient searches for new alloys with novel functional properties.

• Larsen, Aleksander Amble; Gorantla, Sandeep; Nguyen, Phuong Dan; Rosnes, Andreas; Xu, Yijiang & Iordanidou, Konstantina [Show all 10 contributors for this article] (2026). Atomic-Resolution EDS Characterization of Ordering in a β–Cu–Zn–Al Alloy. Metallurgical and Materials Transactions A. ISSN 1073-5623. doi: 10.1007/s11661-025-08093-9. Full text in Research Archive Show summary

  Abstract Atomic ordering in single-crystal β –Cu–Zn–Al, relevant to the martensitic transformation and functional properties, is investigated using analytical STEM. Atomic-resolution EDS along the [110] zone axis, where all Wyckoff positions are spatially resolved, reveals three chemically distinct site occupancies. Correlation with HAADF-STEM contrast provides real-space evidence consistent with L2 1 ordering. In agreement with experiments, first-principles calculations show a slight energetic preference for L2 1 over D0 3 , with finite-temperature free-energy calculations indicating that this preference persists at elevated temperatures.

• Karami, Mostafa; Carvalho, Patricia Almeida; Gunnæs, Anette Eleonora; Løvvik, Ole Martin & Chen, Xian (2025). Grain boundary compatibility and its impact on the reversibility of superelastic micropillars. Journal of the Mechanics and Physics of Solids. ISSN 0022-5096. 205, p. 1–12. doi: 10.1016/j.jmps.2025.106309. Full text in Research Archive Show summary

  The mechanical reversibility of stress-induced martensitic transformations is critical for the functional durability of superelastic materials, particularly at small scale. This study investigates the impact of grain boundary (GB) compatibility on the mechanical reversibility of martensitic transformations in bicrystal Cu67Al24Mn9 micropillars. By combining the geometrically nonlinear theory with high-resolution transmission electron microscopy (TEM) and nanomechanical compression experiments, we demonstrate that the crystallographic orientation and geometric coherence of GBs play a decisive role in transformation reversibility. Micropillars with GBs satisfying a necessary condition for rank-one connections between twin laminates exhibit diffuse GB morphology and recoverable transformation strains over 10,000 cycles. The findings validate recent theoretical predictions on kinematic compatibility in polycrystalline systems with non-transforming defects. The rank-one criterion underlies a design strategy for polycrystalline superelastic alloys to achieve high fatigue-resistant without altering chemical composition. The theoretical framework opens new directions for advancing microstructural design in shape memory alloys.

• Amundsen, Monika; Pike, Nicholas; Løvvik, Ole Martin; Carvalho, Patricia Almeida & Gunnæs, Anette Eleonora (2022). New structure and insight on the phase transition within the Cu-Pd-Sn system with 25 at. % Sn. Materialia. 24, p. 1–6. doi: 10.1016/j.mtla.2022.101461. Full text in Research Archive Show summary

  The Cu-Pd-Sn material system has a (Cu, Pd) 3 Sn phase region that shows an interesting and unexplored marten- sitic phase transformation. Literature on this system is limited and the description of the phases present is incom- plete and partly contradictory. With focus on a specific Cu-rich composition in this phase region (Cu 33 Pd 42 Sn 25 ) and having employed a combination of differential scanning calorimetry, X-ray diffraction, optical microscopy and density functional theory (DFT) methods we analyze the phases involved and the phase transformation tem- peratures. The martensitic transformation was found to occur at approximately 378 K upon heating and at 328 K under cooling conditions. The crystal structure of the high temperature (HT) austenite phase was identified as face centered cubic with lattice constant 𝑎 = 6 . 2261(1) Åat 473 K. DFT simulations of plausible atomic arrange- ments indicated that the HT phase was an L2 1 ( 𝐹 𝑚 ̄3 𝑚 ) type structure. The martensitic LT phase was found to be orthorhombic with a D0 11 ( 𝑃 𝑛𝑚𝑎 ) type structure with lattice parameters a = 8.9860(3) Å, 𝑏 = 5 . 9347(2) Åand 𝑐 = 4 . 5328(2) Åat 298 K.

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• Løvvik, Ole Martin; Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhard; Kušnír, Jakub & Grabek, Tomas [Show all 11 contributors for this article] (2025). Phase change materials for elastocaloric cooling. Full text in Research Archive
• Løvvik, Ole Martin; Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhardt; Kusnir, Jakub & Grabek, Tomas [Show all 10 contributors for this article] (2025). Martensitic phase transformations in a compositionally graded thin film. doi: https:/www.icomat2025.org/wp-content/uploads/2025/09/Full_program_ICOMAT2025_10092025.pdf. Full text in Research Archive
• Larsen, Aleksander Amble; Huang, Xinyue; Carvalho, Patricia A.; Gunnæs, Anette Eleonora; Løvvik, Ole Martin & Chen, Xian (2025). Size and Orientation Effects in Cu-Zn-Al Shape Memory Micropillars. Full text in Research Archive Show summary

  Introduction and objective Martensitic phase transformations in Cu-Zn-Al alloys give rise to functional behaviors such as superelasticity, the shape memory effect, and elastocaloric responses, making them attractive for various applications, including solid-state cooling. While the bulk behavior of these alloys is well-characterized, their response under small-scale mechanical loading is complex and remains an area of ongoing research. This study explores the effects of pillar size and crystallographic orientation on stress-induced martensitic transformation in Cu-Zn-Al single crystals using nanomechanical compression testing. Methods Two compositions of β-phase Cu-Zn-Al single crystals were selected for nanomechanical studies. Samples were cut and prepared with surface orientations corresponding to the (001), (011), and (111) planes of the austenitic phase, as confirmed by electron backscatter diffraction (EBSD). Micropillars with diameters ranging from 0.2 to 3 µm were fabricated using focused ion beam (FIB) milling. Mechanical uniaxial compression tests were performed at room temperature using a nanoindenter to induce martensitic transformation in the pillars. Results Micropillar compression experiments revealed a clear size effect on the martensitic phase transformation. Smaller pillars showed diminished or incomplete transformation compared to larger ones. In addition, crystal orientation significantly influenced the nature and extent of the transformation, with certain orientations exhibiting more substantial transformation strains during compression. For some orientations, no transformation was observed, indicating a strong dependence on crystallographic alignment. These observations highlight how geometric confinement and crystal orientation affect martensitic phase transformation behavior in Cu-Zn-Al.

• Løvvik, Ole Martin (2024). Sykling, radongass og oversikt over hva vi vet. [Radio]. Intervju i Abels tårn, NRK P2. Full text in Research Archive
• Løvvik, Ole Martin (2023). Hvor dramatisk er det å la kjøleskapdøra stå åpen flere minutter? [TV]. Intervju i Praktisk Info med Jon Almaas, TV Norge. Full text in Research Archive
• Løvvik, Ole Martin (2023). Storsatsing på utvikling av materialer med automatisering og kunstig intelligens. [Radio]. Intervju i Abels tårn. Full text in Research Archive
• Løvvik, Ole Martin (2023). Om varmepumper, magnetisme og tyngdekraft. [Radio]. Intervju i Abels tårn. Full text in Research Archive
• Løvvik, Ole Martin (2023). Norwegian efforts towards a materials acceleration platform: combining high-throughput experiments, modelling, and machine learning/artificial intelligence. Full text in Research Archive
• Løvvik, Ole Martin (2022). Thermoelectrics of alloys and intermetallic materials: potential benefits and challenges of using SPS. Full text in Research Archive
• Løvvik, Ole Martin; Carvalho, Patricia A.; Stange, Marit Synnøve Sæverud; Sunding, Martin Fleissner; Rajput, Kalpna & Larsen, Aleksander Amble [Show all 9 contributors for this article] (2022). Elastocaloric cooling with TiNiCuZr alloys? Full text in Research Archive

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