Structure and Phase State of Ti(49.4)Ni(50.6) (at%) Hydrogenated in Normal Saline

The paper analyzes the surface structure and phase state of Ti(49.4)Ni(50.6) (at%) hydrogenated at 295 K in normal saline (0.9% NaCl aqueous solution with pH = 5.7) at 20 A/m(2) for 0.5–6 h. The analysis shows that the average hydrogen concentration in the alloy increases with the hydrogenation time t(H) as follows: slowly to 50 ppm at t(H) = 0.5–1.5 h, steeply to 150 ppm at t(H) = 1.2–2 h, and linearly to 300 ppm at t(H) = 2–6 h. According to Bragg–Brentano X-ray diffraction data (θ–2 θ, 2 θ ≤ 50°, CoKα radiation), the alloy in its scanned surface layer of thickness ~5.6 µm reveals a TiNiH(x) phase with x = 0.64 and x = 0.54 after hydrogenation for 4 and 6 h, respectively. The structure of this phase is identifiable as an orthorhombic hydride similar to β(1)–TiFeH(0.94) (space group Pmcm), rather than as a tetragonal TiNiH(x) hydride with x = 0.30–1.0 (space group I4/mmm). Time curves are presented to trace the lattice parameters and volume change during the formation of such an orthorhombic phase from the initial cubic B2 phase in Ti(49.4)Ni(50.6) (at%).