The transverse-rupture strength ( sigma m) of P30 cemented carbide (WC-36% beta //t-8%Co; beta //t, solid solution of WC/TiC/TaC equals 45/22/33) was studied in relation to structural defects acting as the fracture source. It was found that sigma m of as-sintered alloy was always affected by the defect of pores, being often accompanied by beta //t layer or beta //t segregation. In case of HIP-treated alloy, such defects as cobalt pools surrounded by the beta //t layer or attached to by the segregated beta //t appeared, caused by the pores above mentioned. However, in the alloy (s-alloy) prepared by using commercially available spray-dried-powder, pores accompanied by beta //t layer or cobalt pools having beta //t layer were not observed. The higher strength of s-alloy was due to this fact. It was found that sigma m of P30 alloy, whether it was as-sintered alloy or HIP-treated alloy, was closely related to the structural defects peculiarly formed in this alloy.
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