Microstructures and shape memory characteristics of dual-phase Co–Ni–Ga high-temperature shape memory alloys

✍ Scribed by Yan Li; Yan Xin; Liang Chai; Yunqing Ma; Huibin Xu

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 870 KB
• Volume: 58
• Category: Article
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2010.03.001

✦ Synopsis

The influence of microstructure on mechanical properties and shape memory characteristics of Co-Ni-Ga high-temperature shape memory alloys were investigated in this study. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were employed to detect the microstructures. We found that these alloys were composed of dual phases, a non-modulated tetragonal L1 0 martensite and a face-centered cubic (fcc) c phase. The martensite was twinned and well self-accommodated. The c phase was a Co-based solid solution with 30% lower hardness than martensite. Although the fracture mode was intergranular, the strength and plasticity of the alloys increased markedly with the increasing volume fraction of the c phase. The presence of the c phase in grain boundaries rather than in the martensite is favorable to shape memory recovery. This was revealed by the maximum shape recovery strain over 5.0% that was obtained in the Co 46 Ni 25 Ga 29 alloy, with the c phase formed mainly in grain boundaries.