Lattice Softening and Martensitic Transformation in Cu–Ni–Zn β Phase Alloys

Abstract

Cu 50- x Ni x Zn 50 β phase alloys undergo a martensitic transformation from the CsCl-type ordered cubic (B2 structure) to the AuCuI-type tetragonal (Li 0 structure). The martensite L1 0 phase appears at room temperature when Ni composition x becomes larger than 32.5 at.%, i.e. when electron atom ratio ( e / a ) becomes smaller than 1.175. In order to clarify the origin of B2–Li 0 transition, composition and temperature dependence of the elastic constants in Cu 50- x Ni x Zn 50 alloys were measured. The elastic constant C '=( C 11 - C 12 )/2 decreases with increase in x and d C '/d T is positive (i.e. lattice softening) in the cubic phase, which are suggested to have an important role on the martensitic transformation in these alloys.