The production and synthesis mechanism of submicron Ti(C,N)-based cermets by reactive hot-pressing technology from a Co–Ti–C–BN system

Abstract

The phase formation mechanism of Ti(C,N)–TiB₂–Co composite cermets during the reactive hot-pressing process was investigated by delicate microstructure and phase analysis of Co–Ti–C–BN powder compacts sintered at different temperatures. The results showed that Ti–BN and Co–Ti solid diffusion reactions occurred. As the sintering temperature was increased 1020°C, Co–Ti liquid was formed by the eutectic reaction between Ti and the preformed CoTi₂. Subsequently, TiB combined with B to yield TiB₂ through the mass transfer of liquid, whereas Ti_0.3N and Ti₂N gradually transformed into TiN. With increasing sintering temperature, Ti(C,N) was fabricated by the diffusion of C into TiN unit cell, and B reacted with Ti affording TiB₂. High-density submicron Ti(C,N)-based cermets could be synthesized at low temperatures due to the formation of Co–Ti liquid at 1020°C and an applied pressure of 34 MPa. The Ti(C,N)–TiB₂–Co composite cermets prepared at 1150°C possessed the optimum relative density, average particle size, hardness, and fracture toughness of 99.8%, 0.571 µm, 1947 HV₁₀, and 6.6 MPa·m^1/2, respectively. Moreover, the dry friction and wear resistance of Ti(C,N)–TiB₂–Co composite cermets is 2.5 times higher than that of YT15 cemented carbide.