Relationships between martensite transformation temperatures and compositions in Fe-Mn-Si-based shape memory alloys

The correlation between gamma <----> epsilon martensite transformation temp eratures (M-s, A(s)), the thermal hysteresis (A(s) - M-s) and the alloy com positions has been determined by using the multiple linear regression metho d based on existing experimental data for Fe-Mn-Si-based shape memory alloy s. The empirical quantitative equations are: M-s (K) = 282 - 6.3Mn + 37.2Si - 8.1Cr - 6.3Ni; A(s) (K)= 502 - 5.1Mn + 7.8Si - 4.3Cr - 9.2Ni; A(s) - M-s (K) = 220 + 1.2Mn - 29.4Si + 3.8Cr - 2.9Ni (the alloy compositions are in weight per cent.) It has been demonstrated that the addition of Mn, Cr and Ni tends to lower the martensite transformation temperatures, but Si tends to increase them markedly. This agrees quite well with previous results whi ch indicate that Mn, Cr and Ni increase the stacking fault energy of these alloys while Si decreases it. Moreover, the transformation thermal hysteres is decreases with increasing Si and Ni concentration but increases with inc reasing Cr and Mn content. The above-mentioned results are very useful for the composition design of this type of alloy.