Mitsuo Ueki

Micro-grained cemented carbide with high strength

Abstract The present work is concerned with further improvement of the strength of ultra-fine grained cemented carbide. It has been reported already that the strength of the alloy is strongly affected by its structural defects, e.g. pores, Co pools, extraordinary coarse carbide grains or impurity compounds. In this work, the effects of carbide grain growth inhibitors. Co contents and impurities of starting powders on the strength of the alloy have been investigated in relation to the structural defects appearing on the fracture surface of transverse-ruptured specimens. The results obtained showed that the amount of impurities of starting powders most closely affected the strength of the alloy, and an extremely high-strength cemented carbide having transverse-rupture strength of over 500 kgf/mm2 was obtained by using highly purified WC powder.

Structure Change Appearing around Vickers Hardness Indentation on TiC-based Cermets at High Temperature

It was found that the binder phase frequently appeared around Vickers hardness indentation (V.H.I.) to form dotted structure of binder in TiC-based cermets at high temperature, and this phenomenon was never found in WC-based cemented carbides. Then the present study as to the phenomenon was carried out using TiC-(0, 20) vol%TiN-20 vol%Mo2C-(5-20) vol%%Ni cermets in relation to the alloy composition, structure and hardness testing conditions. It was made clear that the appearance of the binder phase was influenced by the factors mentioned above, and also caused by the fact that the plastic flow of the binder phase under compressive stress due to V. H. I. occurred more easily than that of the alloy, depending on the alloy structures, testing temperatures, etc.

Structural Defects in P30 Cemented Carbide

The microstructural defects acting as fracture source in P30 alloy, prepared by the use of recycled starting powder, were studied. Special defects, that is, pores accompanied by the βt layer (A1 defect) and binder pools to which βt layer attached (A2 defect) were often observed in sintered alloy and HIP-treated alloy, respectively. The strength of HIP-treated alloy was sharply affected by the appearance of the A2 defect. It was confirmed that the formation of A1 defect was caused by the segregation of extremely fine particles of impurity oxides, etc., where the segregation took place inevitably in the mixed powder. The result of model experiments showed that impurity atoms dissolved in the binder phase at the periphery of pores and then decreased the solid-solubility of W. It was suggested that the concentration gradient of W, Ti and Ta solutes in the liquid binder was produced near the pore, leading to the formation of the βt layer as above mentioned.