Improvement of the ductility of a bimodal microstructured PM Ni3Al by thermal treatment

The effect of a thermal treatment at 1523 K on the microstructure and mechanical properties of powder metallurgy (PM) Ni3Al with bimodal microstructure synthesised by a route involving rapid solidification, milling of powders and consolidation by hot isostatic pressing has been studied. The microstructural evolution of the material after 4, 24 and 120 h at 1523 K compared with the material after consolidation has been characterised by grain size measurements and microhardness tests. The intermetallic annealed for 4 h showed a bimodal microstructure that was very similar to that exhibited by the material after consolidation, although a slight grain growth took place. A more homogeneous microstructure was observed after annealing for 24 and 120 h. The tensile behaviour of the material annealed for 24 h was better than that of the hipped material. The material tensile tested at room temperature broke above 1100 MPa with 18% of elongation to failure. An increase of these values was observed at a testing temperature of 473 K. Above this temperature, the material became brittle, breaking in the elastic regime at 673 K. It has been demonstrated that this microstructure can improve the ductility and therefore the formability of PM Ni3Al, while keeping the strength values high.