Microstructure and properties of high-entropy diboride composites prepared by pressureless sintering

Three kinds of high-entropy metal diboride composites were successfully prepared by pressureless sintering. The as-synthesized (Hf0.2V0.2Ta0.2Ti0.2Nb0.2)B2 (HEB-Hf), (Zr0.2V0.2Ta0.2Ti0.2Nb0.2)B2 (HEB-Zr) and (Cr0.2V0.2Ta0.2Ti0.2Nb0.2)B2 (HEB-Cr) powders were used as the matrix, and Ni metal was used as the binder phase. The results demonstrated that three kinds of single-phase high-entropy metal diboride powders (HEB-Hf, HEB-Zr, and HEB-Cr) were successfully synthesized by a facile high-energy ball milling-assisted boro/carbothermal reduction method, at 1600 °C for 2 h. Each HEB powder had a hexagonal structure, and the five main elements were evenly distributed. Further, Ni as the binders effectively improved the density and fracture toughness of the sintered HEB composites. In the case of maintaining high hardness, the fracture toughness of the HEB composites was greatly improved. Meanwhile, The composites exhibited excellent properties when the heat-treating temperature was increased to 1600 °C. The hardness of the HEB-Hf, HEB-Zr, and HEB-Cr composites were 24.2 ± 0.6, 23.8 ± 1.2 and 21.8 ± 0.8 GPa, and their fracture toughness were 9.2 ± 0.3, 7.1 ± 0.7 and 7.3 ± 0.5 MPa∙m1/2, respectively. This manuscript reports a novel method for future commercial production of high-entropy diboride. Further, there will be more applications for high-entropy diborides because of their increased toughness when prepared by this method.