Effect of small gamma precipitates on the two-way shape memory effect in aCu-Zn-Al alloy

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