Martensitic transformation behaviors with various Ni contents in Ti_50-xNi_40+xCu_10.0 alloys

In the present study, Ni content dependence of martensitic transformation (MT) temperatures in Ti_50-xNi_{40+ x}Cu_10.0 alloys (X= 0.0-3.0) was investigated in order to reveal the MT behavior at low temperatures. The Ti-Ni-Cu alloys are in B2 single- phase up to 42.4 at% Ni at 1363 K. B2/B19 or B19/B19' MT temperatures decrease with increasing Ni and a lowest temperature of 124 K was detected. In the alloys with Ni compositions over 41.2 at%, pre-martensitic "intermediate" phase was detected by specific heat measurement. While the middle eigenvalue λ2 are close to 1.0, which were found independent of the Ni content, the thermal hysteresis, Δ T _hys, increases with increasing Ni content, which is explained by drastic decrease in transformation entropy change.