Effect of vacuum annealing on performances of in-situ Al2O3 reinforced Fe-Cr-Ni composites

Fe-Cr-Ni alloys were widely applied to produce aero-engine, industrial gas turbine and other equipments because of their high temperature strength and toughness and creep resistance. In-situ Al2O3/Fe-Cr-Ni composites were prepared by hot pressing sintering process and in-situ synthesis method. In order to reduce the effect of brittle phase on the properties of composites, the prepared samples were kept in vacuum for 2 h at 1000 ℃. Effect of heat treatment on microstructures and mechanical properties of Al2O3/Fe-Cr-Ni composites at room temperature was investigated by XRD and SEM. The results show that Al2O3/Fe-Cr-Ni composites are mainly composed of Fe-Cr-Ni alloy phase, Fe-Cr phase and Al2O3 ceramic reinforcement phase. The Vickers hardness, bending strength and fracture toughness of the hot pressed sintered samples are 4.16 GPa, 298.31 MPa and 8.04 MPa·m1/2, respectively. Austenitic transformation of Fe-Cr phase in composites results in the reduction of hardness to 2.98 GPa through high-heat treatment at 1000 ℃. The values of bending strength and fracture toughness increase obviously with the increasing of the ductile phase contents in the alloy matrix, which are 459.33 MPa and 12.81 MPa·m1/2, respectively.