Effect of ZrB2 addition on microstructure evolution and mechanical properties of 93 wt.% tungsten heavy alloys

Highlights: • Fine-grained 93W alloys was successfully fabricated by powder metallurgy. • Ultrafine W-Ni-Fe composite powder with a high purity was adopted. • ZrB₂ was added into tungsten heavy alloys to improve the performances. • Strengthening and fracture mechanism of tungsten heavy alloys were analyzed. In this study, 93 wt.% tungsten heavy alloys reinforced with highly uniform and dispersed ZrO₂ particles were successfully manufactured by powder metallurgy method. In order to fabricate fine-grained tungsten heavy alloys with outstanding performances, ultrafine 93W-4.9Ni-2.1Fe composite powder fabricated using a two-step reduction approach was selected as raw material. Microstructure and mechanical properties were experimentally examined to investigate the influence of ZrB₂ addition. Meanwhile, transmission electron microscope and energy spectral analysis identified that ZrO₂ particles were generated through the reaction between ZrB₂ and oxygen from the grain boundaries. The ultimate tensile strength, elongation, and hardness of 93W-0.75ZrB₂ alloys could reach to 963 ± 16 MPa, 18.4 ± 1.3% and 387.6 ± 4.4 HV, respectively, benefitted from the combination of fine-grained strengthening and oxide dispersion strengthening mechanisms. The W grains without observable texture were homogeneously distributed in the γ matrix phase based on electron back-scattered diffraction analysis. Moreover, it was determined that the main fracture types of 93W-ZrB₂ alloys were W grain cleavage failure and ductile matrix rupture, closely related to the ZrB₂ content in alloys. The current work provided a possible method for purifying the boundaries and enhancing the strength and elongation of W-Ni-Fe alloys simultaneously.