The pseudoelastic behavior of Fe-Mn-Si-based shape memory alloys containing Nb and C

The pseudoelastic behavior of an Fe-28Mn-6Si-5Cr-0.53Nb-0.06C (mass%) alloy with respect to the thermomechanical treatment of pre-warm-rolling and subsequent ageing is investigated. A partial pseudoelasticity appears between A(s) and M-d, where A, is the reverse martensitic transformation start temperature and Md is the temperature above which the martensitic transformation cannot be induced by stress. It can be reasonably interpreted as transformation pseudoelasticity, like for thermoelastic shape memory alloys such as Ti-Ni-based alloys and Cu-based alloys. The thermomechanical treatment is effective in enhancing the pseudoelasticity by increasing the M-d temperature. It is also found that the alloy exhibits a partial pseudoelasticity below A(s) when the sample is deformed into a two-phase state: fcc and hcp. A conceivable reason for the driving force of the reverse transformation (from hcp to fcc) on unloading is the back-stress experienced by Shockley partial dislocations residing at the tip of the martensite plates, which originates from NbC precipitates. Perfect pseudoelasticity is also obtained when the specimen is subjected to cyclic loading.