Mechanical high-energy treatment of TiNi powder and phase changes after electrochemical hydrogenation

Abstract

The paper presents the results obtained for the effect of ball milling of Ti–Ni powder, which is close in composition to the equiatomic one, on electrochemical hydrogenation. It is shown that the average size of the powder particles measured by BET and laser diffraction methods is found to reduce during milling, while the average size of the powder particles measured by SEM changes to attain its minimum within 30-s milling due to destruction and subsequent aggregation of particles. The powder in its initial state consists of a mixture of TiNi (austenite, martensite), Ti2Ni, and TiNi3 phases, and after ball milling, an X-ray amorphous phase is formed. The CDD size of the TiNi phase (austenite) reduces from 25 to 4 nm. It is found that the lattice parameters of the TiNi (austenite) and Ni3Ti phases do not change during electrochemical hydrogenation, whereas the crystal lattice parameter of the Ti2Ni phase increases, which indicates the predominant interaction of hydrogen with the Ti2Ni phase. The lattice parameter of the Ti2Ni based phase corresponds to Ti2NiH0.5 and Ti2NiH0.8 hydrides depending on the milling time and hydrogenation time. It is found that there is an “incubation period” of hydrogenation of the Ti2Ni phase, which attains 90 min.