Hot isostatic pressing of WB4 and WB4-TaB2 based ultrahard materials

Ultrahard WB4-B and WB4-TaB2 based materials have been obtained by applying glass encapsulated HIPing to mixtures comprised of WB4 and free boron with and without metallic tantalum additions. Porosity removal is more efficient in the alloy containing metallic tantalum, achieving near full density at temperatures 300 °C lower than those reported so far for these materials. The WB4 phase is better stabilished by HIPing at 1350 °C than at 1100 °C. This is due to the formation of TaB2, which, at 1100 °C, likely occurs by direct reaction between metallic Ta and the surrounding WB4 particles. At 1350 °C, diffusion is enhanced and the reaction between free B and Ta particles becomes more probable. The hardness of hipped specimens ranges from 43 GPa to 24 GPa depending on the applied load. K1c values calculated from indentation cracks reach 5.6 MPa.m1/2, assuming Palmqvist type crack shape. •Ultrahard WB4 and WB4-TaB2 based materials have been obtained by glass encapsulated HIPing.•Densification is enhanced by adding metallic Ta powders reaching near full density after HIPing at 1350 °C.•Metallic Ta powders react preferentially with WB4 or free boron particles depending on the HIP temperature.•Hardness values reach 43 GPa with an applied load of 0.49 N. K1c values reach 5 MPa.m1/2.