T. Ohba, S. Morito, Shimane University, Matsue, Japan; S. Nakamura, Teikyo University, Utsunomiya, Japan
AuCd alloy has two martensite structures depending on compositions; one appears around Au52.5Cd47.5 and another around Au50Cd50. They are orthorhombic g2’ phase and trigonal z2’ phase, respectively, both have CsCl type structure as parent phase. Electrical resistance on these AuCd alloys, Au52.5Cd47.5 and Au50.5Cd49.5, were measured at various aging times. The electrical resistance decreases suddenly at the martensitic transformation in Au52.5Cd47.5 and increases at the transformation in Au50.5Cd49.5 in lowering temperature. Those sudden temperature changes correspond to martensitic transformation temperature, Ms. The martensitic transformation temperature, Ms, decreased after aging at parent phase for Au52.5Cd47.5., but not for Au50.5Cd49.5 On the contrary, the increase of reverse transformation temperature, As, was observed for Au50.5Cd49.5, but not for Au52.5Cd47.5. Those changes in electrical resistance indicated that microstructure changed through the aging at parent phase. Further long time aging at room temperature, that is, aging in martensitic state, were made and recovered the original electrical resistance. That means the diffusion occurred in martensitic state, recovering stable original microstructure.
Summary: Electrical resistance measurements were made for Au-47.5Cd and Au-49.5Cd alloys with various aging time at parent phase. The martensitic transformation temperature, Ms, decreased for Au-47.5Cd, but not for Au-49.5Cd. On the contrary, the increase of reverse transformation temperature, As, was observed for Au-49.5Cd, but not for Au-47.5Cd. Further long time aging at martensite state recovered the original electrical resistance, indicating that the diffusin occurred in martensitic state.
