Effect of small γ precipitates on the two-way shape memory effect in a Cu-Zn-Al alloy

After the treatment for the Stabilization of Stress-Induced Martensite (SSIM) in Cu-Zn-Al alloys, it was found that the small gamma precipitates in the beta austenite are ellipsoidal with a large strain field oriented in the same direction, while in the martensite, the gamma precipitates changed their shape from ellipsoidal to spheroidal, which relaxed the strain field. To check whether the strain field of the gamma precipitates is available to produce thermoelastic martensitic transformation, in situ observations with a heating sample holder in TME were performed. It was found that after heating above the A(s) temperature, the spherical gamma precipitates in the martensite recovered their strain field and elliptical shape. During cooling, the strain field of the gamma precipitates disappeared again. This means that the strain fields of the gamma precipitates trained by the SSIM method play an important part in the thermoelastic martensitic transformation that presents the two-way shape memory effect. (C) Elsevier Science Inc., 2000. All rights reserved.