Characterization of microstructures and age hardening of Fe_1-2xAl_xV_x alloys

The Fe-rich corner of the Fe–Al–V system has shown phase separation into disordered A2 and ordered L2₁ phases. In a former work we model this ordering reaction by using ab-initio thermodynamics. The approach is now employed to suggest the Fe_1−2xAl_xV_x alloys in order to reduce the Al content by increasing the addition of vanadium looking for a better ductility of the solid solution which can be afterwards strengthened by coherent L2₁ precipitates. Four alloys with compositions in the range 0.08 < X < 0.15 were studied. The phase transition temperatures and microstructures of the alloys were characterized by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), respectively. The region (A2 + L2₁) occurs for 0.10 < X < 0.15 up to maximum temperature of 720 °C, higher temperatures causes the appearance of (A2 + B2), B2 and (B2 + L2₁) regions. The microstructure in the (A2 + L2₁) region consists of nanosized precipitates of L2₁ phase in A2 matrix which morphology evolutes with temperature and ageing time. The hardness values, measured at room temperature, for the alloys with X < 0.125 and ageing temperature between 650 and 700 °C are comparable to those obtained with other Fe–Al based alloys.