Z. Dong, U. E. Klotz, A. Bergamini, EMPA, Dübendorf, Switzerland
Since S. Kajiwara and coworkers found that the addition of a small amount of Nb and C improves the shape recovery properties of conventional Fe-Mn-Si based alloys, the new generation Fe-based SMAs without training has drawn a lot of attention. In this work, three Fe-Mn-Si alloys alloys with small amounts of C, N and V were designed based on thermodynamic calculations using the ThermoCalc® software package in order to modify the transformation temperature. The work showed that the optimum heat treatment, depending on the alloy composition, was 1100-1150°C/5-10h for the solution treatment followed by the aging treatment at 750-850°C/2h. With such a suitable combination of solution and aging treatment the new alloys showed excellent shape recovery of up to 90% after 4% elongation. In particular, the effect of aging treatment on shape recovery and γ↔ε transformation behavior were studied systemically for the VC precipitated alloy in this paper. It was suggested that the shape recovery effect in Fe-Mn-Si based alloys was strongly influenced by the fine second phase precipitation.
Summary: three Fe-Mn-Si alloys alloys with small amounts of C, N and V were designed based on thermodynamic calculations using the ThermoCalc® software package in order to modify the transformation temperature. The work showed that with a suitable combination of solution and aging treatment the new alloys showed excellent shape recovery of up to 90% after 4% elongation. It was suggested that the shape recovery effect in Fe-Mn-Si based alloys was strongly influenced by the fine second phase precipitation.
