Synthesis and Properties of Composites Based on Zirconium and Chromium Borides

Resumo

Experimental data on the fabrication of composites based on the ZrB₂–CrB system by SHS compaction are presented. Adiabatic combustion temperatures of the Zr–Cr–B system and compositions of equilibrium synthesis products are calculated using the thermodynamic data, and optimal fabrication conditions for SHS composite production are determined. It is shown that the equilibrium synthesis products are ZrB₂ and CrB refractory compounds. They provide the high thermodynamic stability of SHS composites, which are applied as a dispersed phase (ZrB₂) and ceramic binder (CrB). The adiabatic combustion temperature decreases from 3320 to 2350 K with an increase in the binder content from 25 to 64 wt %. A hard dispersed phase (ZrB₂) and molten binder (CrB) are formed under these conditions. It is revealed that the formation of a molten binder provides the formation of SHS composites with residual porosity lower than 1%. The influence of the composition of the reaction mixture on the phase composition, microstructure, and physicomechanical characteristics of SHS composites are investigated. It is established that the residual porosity at the CrB content in the limits of 30–50 wt % is <1%. Herewith, the Vickers hardness varies in a range of 31.3–42.6 GPa, while the ultimate bending strength varies in a range of 480–610 MPa. It is shown that physicomechanical characteristics depend on the residual porosity of SHS composites. Cutting plates are fabricated from the ZrB₂–30CrB SHS composite and testing is performed with the treatment of high-hardness chilled steels. The results evidence that ceramic cutters made of the ZrB₂–30CrB composite possess high wear resistance when treating ShKh15 bearing steel with hardness of 61–65 HRC.