Effects of sintering method and Al2O3 content on microstructure and mechanical properties of WC-10Co cemented carbide

Ultra-high toughness and ultra-high hardness WC-10Co- x Al 2 O 3 cemented carbides were successfully prepared by vacuum liquid phase sintering (VS) and spark plasma sintering (SPS) using ultrafine WC and commercial Co powders as raw materials, respectively. The effects of nano-Al 2 O 3 content and sintering process on the relative density, average grain size, microstructure and mechanical properties of WC-10Co alloys were investigated. The results showed that the densification degree of the samples decreased with the increase of Al 2 O 3 content. In addition, the relative densities of the samples prepared by SPS were lower than those of the samples prepared by VS. For the samples prepared by VS, the average grain size increased first and then decreased as the Al 2 O 3 content increased from 3 wt% to 9 wt%, and the percentage of coarse grain showed the same trend. When the addition of Al 2 O 3 was 6 wt%, the average grain size reached the maximum value of 1.39 ± 1.03 μm. Meanwhile, the sample with 6 wt% Al 2 O 3 had a typical inhomogeneous dual-grain structure, and the percentages of fine grain (< 1 μm) and coarse grain (> 1 μm) were about 50%, which displayed the highest fracture toughness of 18.59 MPa·m 1/2 . The dual-grain structure not only improved the toughness, but also compensated the loss of hardness. However, for the samples prepared by SPS, with the increase of Al 2 O 3 content, the average grain size of WC decreased, while both hardness and toughness were continuously improved. When the Al 2 O 3 content increased to 9 wt%, the grain size reached the minimum value of 0.25 ± 0.08 μm, and meanwhile, the hardness and toughness reached the maximum value of 19.69 GPa and 12.29 MPa·m 1/2 , respectively. Moreover, as the Al 2 O 3 content increased, the transverse rupture strength (TRS) of the samples prepared by VS increased first and then decreased, and the TRS of sample with 3 wt% Al 2 O 3 reached the maximum value of 1410 MPa. However, the TRS of the sample prepared by SPS showed a decreasing trend.