Influence of the martensitic transformation on the hydrogenation properties of Ti50−xZrxNi50 alloys

Abstract

Abstract Ti50−xZrxNi50 alloys with 0≤x≤24 develop either austenitic or martensitic crystal structures when prepared by melt-spinning or induction melting, respectively. This outcome is a consequence of the particular alloy microstructure resulting from each preparation method, which induces a difference of 100°C on the martensitic transformation temperatures for alloys with the same composition. Austenitic alloys absorb hydrogen up to 1.5 hydrogen atoms per AB unit (H/AB) at 130°C and 20 bar, without displaying any plateau pressure for hydrogen pressures between 0.1 and 10 bar. In contrast, martensitic alloys exhibit a plateau pressure with hydrogen concentrations between 1 and 2.1 H/AB, and reach a maximum hydrogen concentration of 2.6 H/AB under the same thermodynamic conditions. Consequently, martensitic alloys form a dihydride compound that, for the representative case of Ti32Zr18Ni50 alloy, has a formation enthalpy of −12.3±0.2 kcal mol H2−1.