SYNTHESIS AND PROPERTIES OF COMPOSITES BASED ON ZIRCONIUM AND CHROMIUM BORIDES

Abstract

This paper provides experimental data on ZrB2–CrB composite production by SHS compaction. Thermodynamic data were used to calculate adiabatic flame temperatures of the Zr–Cr–B system and compositions of equilibrium synthesis products and to determine optimum conditions for SHS composite production. It was shown that equilibrium products of combustion synthesis are ZrB2 and CrB refractory compounds that ensure high thermodynamic stability of SHS composites. They are used as a dispersed phase (ZrB2) and a ceramic binder (CrB). As the binder content increases from 25 to 64 wt.%, the adiabatic combustion temperature decreases from 3320 to 2350 K. A solid dispersed phase (ZrB2) and a molten binder (CrB) are formed at these conditions. It was identified that SHS composites with a residual porosity less than 1% can be produced due to molten binder formation. The effect of reaction mixture composition on the phase composition, microstructure, physical and mechanical properties of SHS composites was studied. It was found that the residual porosity of SHS composites is ~1 % at the 30–50 wt.% CrB content. Vickers hardness is 31,3 to 42,6 GPa, and flexural strength is 480 to 610 MPa. It was shown that physical and mechanical properties depend on the residual porosity of SHS composites. The obtained ZrB2– 30CrB SHS composite was used to make cutting inserts and conduct tests for high-strength hardened steel machining. The test results proved that ZrB2–30CrB ceramic inserts feature high wear resistance when machining ShKh15 chromium bearing steel with a hardness of 61–65 HRC.