Martensitic transformation behavior of Ti–Ni–Sn alloys

Microstructural features and martensitic transformation behavior of Ti–Ni–Sn alloys were investigated by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). In a Ti–49.5Ni–0.5Sn alloy, Ti2Ni phase embedded in Ti–Ni matrix containing 0.7 at%Sn was observed. In a Ti–49.0Ni–1.0Sn alloy, Ti2Ni, unknown phase and Ti–Ni matrix containing 1.1 at%Sn were observed, while Ti2Ni and two different Ti–Ni matrices with 2.1 at%Sn and without Sn were observed in a Ti–50.0Ni–1.0Sn alloy. In a Ti–48.5Ni–1.5Sn alloy, Ti2Ni, Ti3Sn and Ti–Ni matrix containing Sn about 1.2 at% were observed. The B2–R–B19′ transformation occurred in Ti–49.5Ni–0.5Sn, Ti–49.0Ni–1.0Sn and Ti–48.5Ni–1.5Sn alloys, while the B2–B19′ transformation occurred in a Ti–50.0Ni–1.0Sn alloy. Substitution of Sn for Ni of an equiatomic TiNi alloy was effective to induce the R phase transformation.

► We fabricated Ti–Ni–Sn alloys with Sn content less than 1.5 at% for investigating an effect of Sn on transformation behavior of an equiatomic TiNi alloy.
► We found that substitution of Sn for Ni of an equiatomic TiNi alloy induced the R phase transformation and thus the B2–R–B19′ transformation occurred in Ti–Ni–Sn alloys.
► We also found that Ti2Ni phase, unknown phase, Ti3Sn and Ti–Ni matrix coexisted in Ti–Ni–Sn alloys depending on alloy composition.