Mechanical and Tribological Properties of a Nano‐Si ₃ N ₄ /Nano‐BN Composite

The mechanical and tribological properties of a nano‐Si ₃ N ₄ /nano‐BN composite were studied. The composite was prepared via high‐energy mechanical milling and subsequent spark plasma sintering. Y ₂ O ₃ and Al ₂ O ₃ were used as sintering additives. After sintering, the average crystalline size of Si ₃ N ₄ 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‐Si ₃ N ₄ /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‐S ₃ N ₄ /nano‐BN composite under a normal load of 20–22 N, whereas, a friction coefficient of 0.37 was obtained for the micro‐Si ₃ N ₄ /micro‐BN composite. Specific wear coefficients of 0.418 × 10 ⁻⁴ and 0.625 × 10 ⁻⁴ mm ³ /N/m were obtained for nano‐sized and micro‐sized Si ₃ N ₄ /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.