domasb

• Birenis, Domas; Ogawa, Yuhei; Matsunaga, Hisao; Takakuwa, Osamu; Yamabe, Junichiro & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2019). Hydrogen-assisted crack propagation in α-iron during elasto-plastic fracture toughness tests. Materials Science & Engineering: A. ISSN 0921-5093. 756, s. 396–404. doi: 10.1016/j.msea.2019.04.084. Fulltekst i vitenarkiv Vis sammendrag

  Elasto-plastic fracture toughness tests of a commercially pure iron were performed in air and in hydrogen gas at two different pressures. Some unique characteristics of hydrogen-enhanced cracking were exhibited at both the macroscopic and microscopic length scales, based on the observation of fracture surface, fracture plane, plasticity distribution and dislocation structure. The possible mechanisms responsible for the hydrogen-induced degradation of fracture toughness are discussed.

• Ogawa, Yuhei; Birenis, Domas; Matsunaga, Hisao; Takakuwa, Osamu; Yamabe, Junichiro & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2018). The role of intergranular fracture on hydrogen-assisted fatigue crack propagation in pure iron at a low stress intensity range. Materials Science & Engineering: A. ISSN 0921-5093. 733, s. 316–328. doi: 10.1016/j.msea.2018.07.014. Fulltekst i vitenarkiv
• Ogawa, Yuhei; Birenis, Domas; Matsunaga, Hisao; Takakuwa, Osamu; Yamabe, Junichiro & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2018). Hydrogen-assisted fatigue crack propagation in a pure BCC iron. Part I: Intergranular crack propagation at relatively low stress intensities. MATEC Web of Conferences. 165. doi: 10.1051/matecconf/201816503011. Fulltekst i vitenarkiv Vis sammendrag

  The role of hydrogen on intergranular (IG) fracture in hydrogen-assisted fatigue crack growth (HAFCG) of a pure iron at low stress intensity was discussed in terms of the microscopic deformation structures near crack propagation paths. The main cause of IG fracture was assumed to be the hydrogen-enhanced dislocation structure evolution and subsequent microvoids formation along the grain boundaries. Additionally, the impact of such IG cracking on the macroscopic FCG rate was evaluated according to the dependency of IG fracture propensity on the hydrogen gas pressure. It was first demonstrated that the increased hydrogen pressure results in the larger area fraction of IG and corresponding faster FCG rate. Moreover, gaseous hydrogen environment also had a positive influence on the FCG rate due to the absence of oxygen and water vapor. The macroscopic crack propagation rate was controlled by the competition process of said positive and negative effects.

• Birenis, Domas; Ogawa, Yuhei; Matsunaga, Hisao; Takakuwa, Osamu; Yamabe, Junichiro & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2018). Interpretation of hydrogen-assisted fatigue crack propagation in BCC iron based on dislocation structure evolution around the crack wake. Acta Materialia. ISSN 1359-6454. 156, s. 245–253. doi: 10.1016/j.actamat.2018.06.041. Fulltekst i vitenarkiv Vis sammendrag

  A new model for hydrogen-assisted fatigue crack growth (HAFCG) in BCC iron under a gaseous hydrogen environment has been established based on various methods of observation, i.e., electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM), to elucidate the precise mechanism of HAFCG. The FCG in gaseous hydrogen showed two distinguishing regimes corresponding to the unaccelerated regime at a relatively low stress intensity factor range, ΔK, and the accelerated regime at a relatively high ΔK. The fracture surface in the unaccelerated regime was covered by ductile transgranular and intergranular features, while mainly quasi-cleavage features were observed in the accelerated regime. The EBSD and ECCI results demonstrated considerably lower amounts of plastic deformation, i.e., less plasticity, around the crack path in the accelerated regime. The TEM results confirmed that the dislocation structure immediately beneath the crack in the accelerated regime showed significantly lower development and that the fracture surface in the quasi-cleavage regions was parallel to the {100} plane. These observations suggest that the HAFCG in pure iron may be attributed to “less plasticity” rather than “localized plasticity” around the crack tip.

• Birenis, Domas; Ogawa, Yuhei; Matsunaga, Hisao; Takakuwa, Osamu; Prytz, Øystein & Yamabe, Junichiro [Vis alle 7 forfattere av denne artikkelen] (2018). Hydrogen-assisted fatigue crack propagation in a commercially pure BCC iron. PVP - American Society of Mechanical Engineers. Pressure Vessels and Piping Division. ISSN 0277-027X. 6B-2018. doi: 10.1115/PVP2018-84783. Fulltekst i vitenarkiv Vis sammendrag

  Hydrogen effect on fatigue performance of commercially pure BCC iron has been studied with a combination of various electron microscopy techniques. The fatigue crack growth (FCG) in gaseous hydrogen was found to consist of two regimes corresponding to a slightly accelerated regime at relatively low stress intensity factor range, ΔK, (Stage I) and the highly accelerated regime at relatively high ΔK (Stage II). These regimes were manifested by the intergranular and quasicleavage types of fractures respectively. Scanning electron microscopy (SEM) observations demonstrated an increase in plastic deformation around the crack wake in the Stage I, but considerably lower amount of plasticity around the crack path in the Stage II. Transmission electron microscopy (TEM) results identified dislocation cell structure immediately beneath the fracture surface of the Stage I sample, and dislocation tangles in the Stage II sample corresponding to fracture at high and low plastic strain amplitudes respectively.

• Birenis, Domas; Ogawa, Yuhei; Matsunaga, Hisao; Takakuwa, Osamu; Yamabe, Junichiro & Prytz, Øystein [Vis alle 7 forfattere av denne artikkelen] (2018). Hydrogen-assisted fatigue crack propagation in a pure BCC iron. Part II: Accelerated regime manifested by quasi-cleavage fracture at relatively high stress intensity range values. MATEC Web of Conferences. 165. doi: 10.1051/matecconf/201816503010. Fulltekst i vitenarkiv Vis sammendrag

  Hydrogen effect on fatigue performance at relatively high values of stress intensity factor range, ΔK, of pure BCC iron has been studied with a combination of various electron microscopy techniques. Hydrogen-assisted fatigue crack growth rate is manifested by a change of fracture features at the fracture surface from ductile transgranular in air to quasi-cleavage in hydrogen gas. Grain reference orientation deviation (GROD) analysis has shown a dramatic suppression of plastic deformation around the crack wake in samples fatigued in hydrogen. These results were verified by preparing site-specific specimens from different fracture features by using Focused Ion Beam (FIB) technique and observing them with Transmission Electron Microscope (TEM). The FIB lamella taken from the sample fatigued in air was decorated with dislocation cell structure indicating high amount of plasticity, while the lamella taken from the quasi-cleavage surface of the sample fatigued in hydrogen revealed a distribution of dislocation tangles which corresponds to smaller plastic strain amplitude involved at the point of fracture. These results show that a combination of critical hydrogen concentration and critical stress during fatigue crack growth at high ΔK values triggers cleavage-like fracture due to reduction of cohesive force between matrix atoms.

• Ogawa, Yuhei; Birenis, Domas; Matsunaga, Hisao; Thøgersen, Annett; Prytz, Øystein & Takakuwa, Osamu [Vis alle 7 forfattere av denne artikkelen] (2017). Multi-scale observation of hydrogen-induced, localized plastic deformation in fatigue-crack propagation in a pure iron. Scripta Materialia. ISSN 1359-6462. 140, s. 13–17. doi: 10.1016/j.scriptamat.2017.06.037. Fulltekst i vitenarkiv Vis sammendrag

  In order to study the influence of hydrogen on plastic deformation behavior in the vicinity of the fatigue crack-tip in a pure iron, a multi-scale observation technique was employed, comprising electron channeling contrast imaging (ECCI), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The analyses successfully demonstrated that hydrogen greatly reduces the dislocation structure evolution around the fracture path and localizes the plastic flow in the crack-tip region. Such clear evidence can reinforce the existing model in which this type of localized plasticity contributes to crack-growth acceleration in metals in hydrogen atmosphere, which has not yet been experimentally elucidated.

Se alle arbeider i NVA

• Birenis, Domas; Jemblie, Lise; Olden, Vigdis & Thøgersen, Annett (2018). Phase transformation induced hydrogen embrittlement in clad pipes. Fulltekst i vitenarkiv
• Birenis, Domas (2017). Multi-scale observation of hydrogen induced successive crack growth (HISCG) in fatigue of commercially pure iron. Fulltekst i vitenarkiv
• Birenis, Domas (2017). Phase transformation induced hydrogen embrittlement in clad pipes. Fulltekst i vitenarkiv
• Birenis, Domas (2016). Atomic level study of hydrogen-induced degradation on BCC-Fe using electron microscopy. Fulltekst i vitenarkiv
• Birenis, Domas (2015). Atomic level study of hydrogen-induced degradation on offshore steels using electron microscopy. Fulltekst i vitenarkiv
• Birenis, Domas (2020). Fundamental investigations of hydrogen embrittlement by using electron microscopy. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The scope of this thesis was to explore the applications of electron microscopy in the field of hydrogen embrittlement (HE). The fundamental understanding of HE is still lacking and requires some advanced approaches to improve it. Electron energy-loss spectroscopy (EELS) was tested as a potentially viable technique for indirect hydrogen detection at nano-scale with transmission electron microscope (TEM). Hydrogen trapped at the grain boundaries or dislocations changes electronic structure of local iron atoms in pure Fe specimens as predicted by density functional theory (DFT). Such alterations could in principle be observed by EELS experiments, however they were not successful presumably due to knock out damage by the high dose electron beam, and high background signal because of low concentration of hydrogen. In addition, dislocation structures were studied in post-mortem specimens fractured in hydrogen, air and nitrogen gases. Scanning electron microscopy and scanning TEM have shown plasticity and dislocation organization variations in different atmospheres, which implied that hydrogen alters dislocation motion.

Se alle arbeider i NVA