WEAR-RESISTANT TiN–20 wt.% Si₃N₄ AND TiN–20 wt.% TiB₂ COMPOSITES PRODUCED BY MICROWAVE SINTERING

Abstract

Comprehensive research on microwave sintering of TiN–20 wt.% TiB2 and TiN–20 wt.% Si3N4 composites was conducted. At a constant microwave power of 900 W, the TiN–20 wt.% TiB2 composite could be effectively consolidated to a residual porosity of 9% at 1370 °С and the TiN–20 wt.% Si3N4 composite to a residual porosity of 6% at 1407 °С. According to a comparative analysis of these composites consolidated by conventional sintering to 1550 °С at a rate of 50 °С/min in a resistance furnace, the composites had a residual porosity of more than 25%. The microwave-sintered samples showed dense areas of predominantly spherical shape (D ~ 5 µm) formed by titanium nitride and titanium diboride phases. This zonal segregation of dense areas to form TiN and TiB2 spherical agglomerates was due to heterogeneous distribution of the electromagnetic field throughout the multimode microwave oven, leading to locally overheated areas within the materials being processed. The structural features of the TiN–20 wt.% TiB2 and TiN–20 wt.% Si3N4 composites were found to influence their mechanical and tribological properties. The measured hardness of the TiN–20 wt.% TiB2 composite was 19.5 ± 1.1 GPa and that of the TiN–20 wt.% Si3N4 composite was 19.8 ± 0.8 GPa. Wear resistance tests of the composites in friction against the VK6 hardmetal showed quite high tribological properties: linear wear of 12.5 µm/km (TiN–20 wt.% Si3N4) and 11.3 µm/km (TiN–20 wt.% TiB2) and friction coefficient of 0.43 and 0.26, respectively. A comparative analysis of the TiN–20 wt.% TiB2 and TiN–20 wt.% Si3N4 composites consolidated by microwave and conventional sintering allowed the conclusion that a uniform fine-grained structure, which would enhance the mechanical and tribological properties, could be produced by increasing the microwave sintering temperature in the 600–1500 °С range to 50 °С/min and above and using hybrid microwave heating.