Control of microstructural characteristics and martensitic transformation behavior of Ti–Ni–Cu alloys by Pt doping

The effect of the substitution of Pt for Cu on the microstructure and martensitic transformation behaviors of Ti–Ni–Cu alloys was investigated systematically. The solution-treated Ti–Ni–Cu–Pt alloys were found to consist of the B19 martensite and Ti₂(Ni,Cu,Pt) phases at room temperature. The (011) compound twin was more frequently observed than the (111) type I twin in the Ti–Ni–Cu–Pt alloys owing to the lower shear strain and shear angle of the (011) compound twin during the transformation process. During heating, the lower temperature single B19 martensite transformed in one stage into high-temperature B2 austenite. Conversely, the B2 austenite was transformed directly into B19 martensite during cooling. As the Pt content increased from 1.0 at.% to 3.0 at.%, the transformation temperatures first decreased and then increased. In addition, a narrower thermal hysteresis and perfect thermal cycling stability can be obtained by tailoring the Pt content. The excellent thermodynamic characteristics can be attributed to the lower frictional work and good geometric compatibility.