Correlation between fcc–fct transformation behavior and spinodal decomposition in γ-MnCu alloys

The effect of γ phase aging was investigated on fcc–fct martensitic transformation behavior for Mn–14∼30 at.% Cu alloys. The martensitic transformation in these alloys is ‘quasi martensitic’ as characterized by a small hysteresis and a continuous change in lattice parameters below the transformation temperature. It was shown that by aging at temperatures ranging from 630 to 690 K, the transformation temperature increased markedly and the residual resistivity decreased in parallel. Differential scanning calorimetry (DSC) peak profiles were also modified significantly by aging and the heat of transformation increased. A good linear correlation has been found between the changes in the transformation temperature and those in the resistivity. It is also shown that the observed increase in transformation temperature, decrease in resistivity and their linear correlation can be well explained by the rule of mixture assuming a heterogeneous microstructure, which formed as a result of the spinodal decomposition.