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The non-stoichiometric Zr 0.9 Ti x V 2 ( x = 0, 0.2, 0.3, 0.4) alloys are designed to explore the effect of non-stoichiometry on phase constituent, microstructure and hydrogenation properties of Zr-based AB 2 Laves alloys. The alloys are prepared by non-consumable arc melting and annealed at 1273 K for 168 h in argon atmosphere to ensure the homogeneity. Phase structure investigation shows the α-Zr/β-Zr phase and V-BCC phase originating from the non-equilibrium solidification can be reduced after annealing, C15-type ZrV 2 becomes the dominant phase. Meanwhile, a small amount of Zr 3 V 3 O phase generates when x ≤ 0.2 and the β-Zr transforms to α-Zr when x > 0.2. High density annealing twins are observed in ZrV 2 matrix by TEM. Activation behavior, hydrogenation kinetics and PCT characteristics of annealed Zr 0.9 Ti x V 2 are investigated in the temperature range 673–823 K. With the decrease in B/A ratio or increase in Ti content, the initial hydrogen absorption speed decreases obviously, the plateaus of PCT curves become wide and flat, meanwhile the hydrogen absorption capacity and the stability of metal hydrides increases. Twin defects observed in these alloys play an important role in accelerating the hydrogenation kinetics. In addition, phase constituent after hydrogenation is analyzed. [ABSTRACT FROM AUTHOR]

Medium manganese (Mn) steel has excellent strength and ductility and is widely used in the automobile industry and elsewhere; however, hydrogen embrittlement (HE) is considered as one of the most serious issues of its application. In this paper, in situ transmission electron microscopy was used to study the microstructural evolution and fracture micromechanisms of medium Mn steel under the influence of hydrogen and annealing. The results indicated that two specimens with different annealing processes showed transformation-induced plasticity and twinning-induced plasticity, albeit to a varying degree due to different microstructures with distinct mechanical properties. It was shown that hydrogen affected the fracture micromechanisms, which promoted the initiation of microcracks at the boundaries of martensite transformed from austenite. Moreover, the main cracks propagate in a zigzag fashion, following hydrogen charging, due to the hardness of the martensite. These findings provide directions for improving HE resistance through microstructural regulation of medium Mn steel. • In situ TEM tensile tests verify fracture mechanism of medium Mn steel. • Hydrogen promotes crack initiation at specific interface, e.g. martensite boundary. • Annealing greatly alters deformation mode, work hardening rate and the L u ¨ ders band. • The detailed fracture process of pre-hydrogen charged steel is in situ tracked. [ABSTRACT FROM AUTHOR]