Effect of alloying addition and microstructural parameters on mechanical properties of 93% tungsten heavy alloys

Liquid phase sintering, heat treatment and swaging studies on three tungsten heavy alloys, 93W-4.9Ni-2.1Fe (wt%), 93W-4.2Ni-1.2Fe-1.6Co (wt%) and 93W-4.9Ni-1.9Fe-0.2Re (wt%) were carried out in detail with respect to microstructure, tensile and impact properties. All the alloys were sintered and swaged to 40% deformation. The results indicate that Re addition reduces the grain size of the alloy compared to W-Ni-Fe and W-Ni-Fe-Co alloys. W-Ni-Fe-Re alloy shows superior tensile properties in heat treated condition as compared to W-Ni-Fe and W-Ni-Fe-Co alloys. SEM study of fractured specimens clearly indicates that the failure in case of W-Ni-Fe-Re was due to transgranular cleavage of tungsten grains and W-W de-cohesion. W-Ni-Fe and W-Ni-Fe-Co alloys also failed by mixed mode failure. However, in these cases, ductile dimples corresponding the failure of the matrix phase was rarely seen. Thermo-mechanical processing resulted in significant changes in mechanical properties. While W-Ni-Fe-Re alloy showed the highest tensile strength (1380 MPa), W-Ni-Fe-Co exhibited the highest elongation (12%) to failure. A detailed analysis involving microstructure, mechanical properties and failure behavior was undertaken in order to understand the property trends.