Spinodal decomposition in ternary Mn-Cu-Cr alloy and its influence on martensitic transition temperatures

Abstract

The effect of partial substitution of Cu by Cr on the spinodal decomposition of face-centered cubic (f.c.c.) austenite in the as-quenched Mn-10Cu-4Cr alloy is studied after different ageing treatments by small-angle neutron scattering (SANS) and in situ neutron diffraction. Under the same quenching conditions, additional α-Mn phase with A12 structure in the Mn-10Cu-4Cr alloy is observed as compared with Mn-13Cu alloy at room temperature (RT). The replacement of Cu atoms by Cr atoms retards the spinodal decomposition of austenite during ageing compared to the binary Mn-13Cu alloy according to SANS and Differential scanning calorimetry (DSC) results. The reason is that Cr enriches in the α-Mn phase, and thus its addition leads to the formation of the α-Mn phase. Compared to the Mn-13Cu alloy, there is an increase in the tetragonality of the face-centered tetragonal (f.c.t.) martensite, which may be attributed to changes in magnetic interaction owing to partial substitution of Cu by Cr. The higher tetragonality value leads to a higher volume effect during martensitic transition (MT) of Mn-10Cu-4Cr alloy than that of Mn-13Cu alloy (around 1.5 times). The lattice parameters of the f.c.t.-martensite do not converge exactly to the parameter of the f.c.c.-austenite at the MT temperature due to replacement of Cu by Cr. Instead, there is a jump of the lattice parameters during phase transition.