| 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 ㎫. Stress dependence of the martensitic transformation start temperature(Ms) in this alloy was very small(0.199 K/㎫) as compared to Ti-rich Ti-Ni alloys(0.313 K/㎫). 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 Ti₃Ni₄. Stress dependence of Ms in an aged Ti-50Ni-2Si alloy(0.285 K/㎫) was smaller than that(0.360 K/㎫) in Ni-rich Ti-Ni alloys. |
|
