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Crystallographic analysis of hydride phase transformation and its effect on mechanical property of commercial pure titanium

Abstract : Nucleation and formation of hydride precipitates are important factors on limiting the lifetime of Ti alloys. In this work, the hydride phase transformation in commercial pure titanium is thoroughly investigated by experimental and theoretically crystallographic method. The two dominant orientation relationships (ORs) of hydride transformation by the method of electrolytic hydrogen charging are {0001} //{001} <12̅10>//<110> with interface plane of {101̅0}//{11̅0} (OR1) and {0001}//{11̅1} <12̅10>//<110> with interface plane of {101̅3}//{11̅0} (OR2). The grain orientations of {101̅0} or {101̅3} interface planes parallel to the diffusion surface are most favorable for OR1 and OR2 hydride transition, respectively. The hydride variants with interface plane parallel to the diffusion surface is preferentially selected because of the highest capacity for strain accommodation. The c-axis or a-axis parallel to the diffusion direction are unfavorable orientations, due to the complicated interactions between different hydride variants. The multi-dimensional microstructures of hydride layer were characterized to investigate the accommodation mechanisms for hydride transformation. Plastic accommodation behaviors are necessary inside hydride layer. Both {101̅2} extension and {112̅2} contraction twins are induced at the interface of OR2 hydride platelets. The selected twin variant has the highest accommodation capacity for local distortion of hydride nucleation. The {101̅2} twins are transformed into {101̅1} twins in order to the further growth of hydride platelet. Hydride microstructure on the cross section of hydride layer were observed for the first time, the interactions of different hydride variants relax the anisotropic misfit strain inside hydride layer. The intergranular hydride pair is another accommodation behavior during hydrogenation, which prefer to be formed at the grain boundary with both low angle (< 30o) and high angle (75o< θc < 85o) boundaries. The mechanical property of titanium surface changed by hydrogen charging was investigated by nanoindentation tests and tensile deformation tests. After hydrogenation, the nanohardness increases while elastic modulus decreases due to the formation of hydride precipitation. The orientation dependent hardness of δ-hydride formed after 168 h charging is less sensitive than that of α-Ti. The average HIT value of δ-hydride is 3.8 ± 0.3 GPa, which is higher than titanium matrix (2.8 ± 0.3 GPa) showing the hard nature of hydride phase. During tensile deformation, hydride layer shows a poor deformability, but the interactions between dislocations and twins occur for OR2 hydride platelets: the transmissions of prismatic slips into hydride precipitations and the hindering of hydrides on the growth and thickening of {101̅2} tension twins.
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https://hal.univ-lorraine.fr/tel-03335527
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Submitted on : Monday, September 6, 2021 - 12:00:34 PM
Last modification on : Tuesday, September 7, 2021 - 3:21:27 AM

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  • HAL Id : tel-03335527, version 1

Citation

Qian Wang. Crystallographic analysis of hydride phase transformation and its effect on mechanical property of commercial pure titanium. Materials Science [cond-mat.mtrl-sci]. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0034⟩. ⟨tel-03335527⟩

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