The influences of carbonitriding treatment on the microstructure, residual stress and mechanical properties of Ti-containing cemented carbides are investigated. Three powder compacts of WC-7.0Co-2.0Ni-3.0Mo-0.5TiC cemented carbides were liquid phase sintered in vacuum at 1,300 oC for 1h. Three specimens with cobalt-enriched surface layers were obtained. They were subsequently carbonized by a post-sintering heat treatment process in nitrogen. The carbonitriding treatment results in the formation of fine-grained TiN phases and N-diamond C phases in situ on their surfaces. X-ray diffraction spectrums reveal their differences in the grain size and forming phases of the Ti-containing phases for cemented carbides before and after carbonitriding treatment. This method can reduce the grain size of Ti-containing hard phase and increase microstrains in it. To analyze the residual stress, the specimen before and after carbonitriding was measured by recording the peak positions for each 2θ at five different tilt angles (ψ = 0 o,20.7 o, 30 o, 37.8 o and 45 o) by a X-ray diffractometer. The microstructure and defects of cemented carbides were investigated by SEM before and after the carbonitriding treatment. It is concluded that: (1) high bond strength between the Ti-containing skin and the WC-Co substrate, (2) high wear resistance of the Ti-containing skin after carbonitriding, (3) compression stress state existing in Ti-containing skin, (4) the technology of carbonitriding treatment contributes to form an aesthetic Ti-containing skin in the surface of cemented carbides and improve its wear resistance.

Keywords: FG WC-Co, Ti-containing skin, Carbonitriding treatment, Residual stress, Wear resistance.