L. Jian et Cm. Wayman, SHAPE-MEMORY EFFECT AND RELATED PHENOMENA IN A MICROALLOYED FE-MN-SI ALLOY, Materials characterization, 32(3), 1994, pp. 215-227
An Fe-32Mn-6Si-0.05Nb-0.04C alloy aged at different temperatures was e
mployed to study the epsilon (hcp) martensite transformation, the mech
anism of the shape memory effect (SME) associated with the epsilon mar
tensite transformation, the effect of precipitation strengthening, and
the effect of thermomechanical treatment and deformation temperature
on the SME. The results of transformation temperature studies show tha
t the M(s) temperature for various heat-treated specimens is in the ra
nge of 75-100-degrees-C, the A(s) temperature is 112-125-degrees-C, an
d the Neel temperature of this material, T(N), is 8-degrees-C. The SME
decreases with increasing plastic deformation and increases with decr
easing deformation temperature and increasing thermomechanical trainin
g. The critical strength of aged specimens is higher than that of quen
ched ones due to the precipitation strengthening of NbC, which improve
s the SME for plastic deformation amounts less than 2% at room tempera
ture. The microstructure observation by transmission electron microsco
py shows that stacking faults play an important role in the formation
of the epsilon martensite. Surface relief examination at different tem
peratures and the electrical resistance versus temperature relationshi
p reveal that the epsilon martensite transformation takes place contin
uously at temperatures below the T(N) temperature. An SME mechanism fo
r Fe-Mn-Si based alloys is proposed.