Effect of Liquid Phase Sintering and Post-Treatments on the Microstructure and Mechanical Properties of a W–Ni–Co Alloy

Overview & Synopsis

A multiscale characterization of a tungsten heavy alloy (W-Ni-Co) prototype was conducted after key processing steps, including liquid-phase sintering, heat treatment, and final thermomechanical processing under industrial conditions. The as-sintered dual-phase microstructure featured small W nodules with remarkably low contiguity (16%-17%) embedded in a Ni-rich matrix with grain sizes ranging from the micrometer to millimeter scale. Heat treatment induced the precipitation of fine W particles within a refined Ni solid solution. Crystallographic orientation relationships between precipitates and the surrounding Ni phase were identified, supporting a precipitation mechanism consistent with thermodynamic analysis. Subsequent swaging and annealing resulted in a remarked high combination of strength (1700 MPa) and ductility (7.7%). Electron backscatter diffraction mapping highlighted heterogeneous local strains, revealing that the W nodules retained significant residual deformation, whereas the Ni matrix underwent recovery. Among the various mechanisms of microstructural evolution, including precipitation, phase transformation, and grain-size evolution, deformation during the swaging step predominantly affected the final hardening of the alloy.