Thermo-mechanical processing, microstructure and tensile properties of a tungsten heavy alloy

The effect of heat treatment and swaging on microstructure and mechanical properties of a tungsten heavy alloy (WHA) of composition 90.5W-7.1Ni-1.65Fe-0.5Co-0.25Mo (wt%) has been examined in this study. The volume fraction and the contiguity of W-grains in the sintered microstructure decrease from 80% to 75% and 0.7 to 0.3, respectively, following an intermediate heat treatment comprising annealing at 1373 K followed by oil quenching. The average aspect ratio of W-grain increases with the increase in swaging deformation. While the bulk hardness of the alloy increases with increase in swaging deformation, a minor drop in hardness is observed following intermediate heat treatment. Peak broadening is observed in the X-ray diffractograms following thermo-mechanical processing with full width at half maxima (FWHM) of W110 peak exhibiting a similar trend as that of hardness. The as-sintered alloy exhibits low yield strength, tensile strength and very low elongation to failure. Subsequent thermo-mechanical treatment results in substantial improvement of both strength and elongation. A strength value of 1427 MPa with elongation of 5-6% has been achieved following 40% swaging. Work hardening behavior of the alloy in heat treated condition has been studied and the results are correlated with slip lines and dislocation behavior of the alloy.