Effect of trace Y₂O₃ on microstructure and properties of WC−6Co cemented carbides with inhomogeneous structure

Inhomogeneous structure WC−6Co cemented carbides with the different Y₂O₃ additions (mass fraction) were prepared by low pressure sintering. The microstructure and properties of the cemented carbides were investigated by scanning electron microscope (SEM), X-ray diffraction analyzer (XRD), energy dispersive spectrometer (EDS), metallographic microscope, electronic universal mechanical test machine, hardness meter, and coercivity magnetometer. The results show that, the relative density and phase composition of the cemented carbides are not affected by Y₂O₃ addition. Y₂O₃ forms a stable solid solution with the impurity elements such as sulfur and oxygen, which disperses in the WC grain boundary, hinders the fusion and growth of WC grains, reduces the size of WC grains, and inhibits the homogenization of WC grains in inhomogeneous structure. With the increase of Y₂O₃ mass fraction, the hardness of the cemented carbides increases gradually, and the bending strength shows a trend of rapid rise and then decline. The optimum properties of the cemented carbides are obtained when the Y₂O₃ mass fraction is 0.048%, the hardness and bending strength are 1530 kgf·mm⁻² and 2902 MPa, respectively.