Shape Memory Characteristics of Thermo-Mechanically Treated and Aged Ti-Ni-Si Alloys

摘要

Transformation behaviors, microstructures and shape memory characteristics of thermo-mechanically treated and aged Ti-Ni-Si alloys were investigated by means of differential scanning calorimetry, electrical resistivity measurements, X-ray diffraction, transmission electron microscopy, constant load thermal cycling tests and tensile tests. In a thermo-mechanically treated Ti-48Ni-2Si alloy, two stage transformation behavior, i.e., the B2->R->B19' was observed on cooling and the critical stress for slip deformation increased to 696 MPa. Stress dependence of the martensitic transformation start temperature(Ms) in this alloy was very small(0.199 K/MPa) as compared to Ti-rich Ti-Ni alloys(0.313 K/MPa). Two stage transformation, i.e., the B2->R->B19' occurred in an aged Ti-50Ni-2Si alloy while the solution treated alloy did not show martensitic transformation behavior. The difference in transformation behavior was attributed to the precipitation of Ti_3Ni_4. Stress dependence of Ms in an aged Ti-50Ni-2Si alloy (0.285 K/MPa) was smaller than that (0.360 K/MPa) in Ni-rich Ti-Ni alloys.