Ti-Ni Powder Structure after Mechanical Activation and Interaction with Hydrogen

The paper studies the interaction between hydrogen and the multiphase Ti–Ni alloy of near-equiatomic composition after its high-energy mechanical activation in a planetary ball mill generating a centrifugal acceleration of 60 g. It is described that mechanical activation results in a non-monotonous change in the average size of particles due to their destruction followed by agglomeration. After mechanical activation for 10 seconds, the width of X-ray lines changes in all phases. It is found that during the hydrogenation process, the crystal lattice parameters of the TiNi (austenite) and TiNi₃ phases do not change, in contrast to the Ti₂Ni phase, whose lattice parameter increases by 2.5%. This fact suggests that the main hydrogen interaction in multiphase Ti–Ni alloys of near-equiatomic composition occurs with the Ti₂Ni phase. Hydrogenation of the multiphase Ti–Ni alloy powder changes the lattice parameter of the Ti₂Ni phase, such that it matches the lattice parameter of the Ti₂NiH_0.5 and Ti₂NiH_0.8 hydride phases after mechanical activation for 30 and 300 seconds, respectively. The paper identifies the critical time of the defect accumulation during high-energy mechanical activation. With increasing time of hydrogenation, oxide layers destroy, thereby facilitating the hydrogen penetration into powders.