Compositional Dependence of Hydrogenation Properties in Ti_1+y(Fe_1−xMn_x)_1−y (0.2≦x≦0.5, 0≦y≦0.08)

Abstract

  Compositional dependence of hydrogenation properties in Ti_1+y(Fe_1−xMn_x)_1−y were investigated. The annealed alloys mainly showed B2 structure (CsCl) and some of them contained a small amount of secondary phase. The lattice constant of B2 phase increased and their equilibrium pressures decreased with increasing Mn or Ti content. Ti₅₀Fe₄₀Mn₁₀ and Ti₅₀Fe₃₅Mn₁₅ showed two distinct flat plateaus on pressure-composition isotherms. Ti₅₂Fe₂₈Mn₂₀ and Ti₅₃Fe₂₅Mn₂₂ also showed two distinct flat plateaus below certain temperatures. Above those temperatures, however, only their first plateau became slant without hysteresis keeping the second plateau flat. In addition, the first plateau was slanted without hysteresis even at room temperature in Ti₅₄Fe₂₃Mn₂₃. These results suggest that Ti_1+y(Fe_1−xMn_x)_1−y have critical temperatures for the first phase transformation from the α-solid solution phase to the β-Ti_1+y(Fe_1−xMn_x)_1−yH_~1 and they decreased with increasing Mn or Ti content.