Mechanical and Tribological Properties of a Nano-Si3N4/Nano-BN Composite

The mechanical and tribological properties of a nano-Si3N4/nano-BN composite were studied. The composite was prepared via high-energy mechanical milling and subsequent spark plasma sintering. Y2O3 and Al2O3 were used as sintering additives. After sintering, the average crystalline size of Si3N4 and BN was 50 nm. Hardness (Vicker and Knoop) was evaluated under a high load of 0.05-2.0 kg for the nano/nano- and the micro/micro-Si3N4/BN composite with the same composition. The indentation fracture toughness values of both composites were also evaluated. Tribological studies were conducted to study the friction and wear behavior of both composites. A friction coefficient of 0.4-0.7 was obtained for the nano-S3N4/nano-BN composite under a normal load of 20-22 N, whereas, a friction coefficient of 0.37 was obtained for the micro-Si3N4/micro-BN composite. Specific wear coefficients of 0.418 x 10-4 and 0.625 x 10-4 mm3/N/m were obtained for nano-sized and micro-sized Si3N4/BN composites, respectively. Higher hardness, higher fracture toughness, and lower wear were observed in the nano-sized composite, as compared with the micro-sized composite.