Ceramic and Ceramic Composite Materials with Improved Friction and Wear Properties

Abstract

Dry friction and wear tests were performed with self-mated couples of SiC with 50 wt%TiC, SiC-TiB₂, Si₃N₄ with 30 wt%TiN, Si₃N₄ with 5, 10 and 20 wt%BN and a binary carbo-nitride composite (Ti,Mo)(C,N) at room temperature and 40°C or 80°C. The results are compared with currently available SiC and Si₃N₄ materials. In a normal environment the examined ceramic composites used during these studies are able to form a lubricious oxide reaction layer or a film of an intrinsic solid lubricant on a hard substrate. The binary carbo-nitride composite had a wear coefficient smaller than 10⁻⁶ mm³ · N⁻¹ ·m⁻¹, sometimes smaller than 10⁻⁷ mm³ · N⁻¹ · m⁻¹, that was independent of temperature from ambient up to 800°C. At 22°C the addition of hexagonal BN reduced the friction of Si₃N₄. Simultaneously, the wear coefficient was independent of sliding velocity and below 10⁻⁶ mm₃ · N⁻¹ · m⁻¹. Friction and wear increased with increasing temperature. The addition of TiC to SiC reduced friction and wear. At room temperature, Si₃N₄−TiN exhibited a lower wear than Si₃N₄. At 800°C, the wear coefficient of Si₃N₄ was reduced by two orders of magnitude by the addition of TiN as TiO_2-x forming substrate. The addition of TiB₂ to SiC was only beneficial at 400°C and above 0.5 m·s⁻¹ compared to SiC by decreasing the wear coefficient.