Effect of Ti content on abnormal grain growth of Fe-Mn-Al-Ni-Ti shape memory alloy

Abstract In this paper, the effects of Ti content on the solvus temperature of γ -phase and abnormal grain growth (AGG) in Fe 43.5− x Mn 34 Al 15 Ni 7.5 Ti x ( x = 0, 0.5, 1 and 1.5) shape memory alloys (SMAs) were investigated. It is found that, the increase of Ti content leads to a significant reduction of the solvus temperature of γ -phase, a significant refinement of γ -phase, and a decrease of subgrain size. After 3 times cyclic heat treatments, the average grain size of Fe 42 Mn 34 Al 15 Ni 7.5 Ti 1.5 SMA reaches about 9.0 mm, which is about twice of that for Fe 42.5 Mn 34 Al 15 Ni 7.5 Ti 1 SMA. This is attributed to the small subgrains can provide a higher subgrain boundary energy (Δ G s ) and grain boundary (GB) migration rate. The subgrain size of Fe 42 Mn 34 Al 15 Ni 7.5 Ti 1.5 SMA (9.7 μ m) is significantly smaller than that of Fe 42.5 Mn 34 Al 15 Ni 7.5 Ti 1 SMA (21.3 μ m). Thereby, the Δ G s (15.3 × 10 −2 J mol −1 ) and GB migration rate (11.3 × 10 −6 m s −1 ) of Fe 42 Mn 34 Al 15 Ni 7.5 Ti 1.5 SMA are significantly higher than those of Fe 42.5 Mn 34 Al 15 Ni 7.5 Ti 1 SMA (7.1 × 10 −2 J mol −1 , 6.3 × 10 −6 m s −1 ). In addition, when the applied strain was up to 10%, the maximum superelastic strain of Fe 42 Mn 34 Al 15 Ni 7.5 Ti 1.5 and Fe 42.5 Mn 34 Al 15 Ni 7.5 Ti 1 were 5.5% and 5.1%, respectively. In summary, the addition of 1.5 at.% Ti in Fe–Mn–Al–Ni–Ti SMA can promote the AGG with relatively small loss in superelasticity.