The effect of heat treatment on the transformation temperature in Au52.5-x-Cd47.5-Agx shape memory alloys

Yuki Matsuoka 1Natsuko Kudo 

1. Nara Women's University, Kita-Uoya Nishimachi, Nara 630-8506, Japan

Abstract

Au52.5-x-Cd47.5-Agx is one of noble metal based β -phase alloy, which undergoes a martensitic transformation on cooling. The Ag substitution for Au affects martensitic transformation temperature, crystal structure, and the orthorhombic distortion although it is expected that the substitution has no changes in atomic size, electron concentration.

The Au52.5-x-Cd47.5-Agx alloy have been studied and reported in which the Ag composition is below 41 at.%. The alloys have ¥beta-phase structure at room temperature and transform to martensite phase when they are cooled. But the alloy which have x > 41 at.% has not been studied because the transformation temperature go down to below 100 K.

In this work, Au9.5-Cd47.5-Ag43.0 alloy was prepared by melting the component elements. The electrical resistivity was measured from room temperature to 100 K to determine the transformation temperature. The X-ray powder diffraction measurements and Rietveld analysis both at room temperature and at 77 K were performed on this alloy.

At this chemical composition, both of β-phase and α - phase exist at room temperature. Almost β - phase transformed to martensite phase, but α-phase doesn't transform to other phase on cooling. To avoid the coexistence of α - phase, the sample was annealed at 873 K and subsequently quenched into ice-water. The single phase sample of β-phase was obtained by this process. The electrical resistivity measurement and the X-ray powder diffraction measurements were performed again on the quenched sample. The martensitic transformation temperatures were different more than 50 K between these experiments. The difference of transformation temperatures is thought to be caused by the size effect of sample.

 

Presentation: poster at E-MRS Fall Meeting 2005, Symposium C, by Yuki Matsuoka
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-04-15 08:12
Revised:   2009-06-07 00:44