Effect of swaging on microstructure and mechanical properties of W-Ni-Co alloys

The effect of deformation during warm swaging on mechanical properties of W-Ni-Co alloys was investigated. The alloys, based on 92%W with Ni/Co ratio of 7/3 and 8/2, were processed through liquid phase sintering followed by heat treatment and swaging. Multistep swaging deformation at 400 degrees C leads to increase in strength at the expense of ductility. For a given deformation, the alloy with 7/3 Ni-Co shows higher strength and lower ductility as compared to the alloy with 8/2 Ni-Co ratio. This is attributed to the presence of fine W precipitates (0.2-0.3%) in the matrix phase, which is relatively more in 7/3. Higher ductility of the 8/2 alloy is characterized by shear lip failure of the matrix in contrast to shallow dimple failure of the matrix in 7/3 and this appears to be consistent with the presence of fine, undeformable W precipitates in the matrix phase. The analysis of work hardening shows a three slope behaviour in the heat treated condition where as the swaged specimens show a single slope behaviour. This has been explained in terms of deformation of softer matrix in the initial stage (Stage I and II) and that of the two phase aggregate later (Stage III). The results are discussed in relation to the studies carried out on similar alloys.