WC-Co基超微粒超硬合金の基礎研究と製品開発

抄録

Inhibition mechanism of grain growth by metal carbide addition for WC-Co based ultrafine-grained cemented carbide was studied to develop 100 nm-grained cemented carbide. Two hypotheses of inhibition mechanism, a) inhibition by adsorption atoms at steps/kinks on WC crystal surface and b) inhibition by segregation layers on WC basal plane, were proposed. To judge which hypothesis is based on the inhibition mechanism, observation of TEM microstructure and analysis of segregation amount on WC/Co and WC/WC interfaces in WC-Co based cemented carbides including metal carbide additives were performed.

Determining the presence or absence of segregation layer on WC crystal surface during liquid phase sintering was the judgement point of inhibition mechanism. The judgement was considered comparison between predictive phenomena on each hypothesis and experiment results. The experimental results supported that grain growth inhibited by adsorption atoms at steps/kinks on WC crystal surface during liquid phase sintering and segregation layer formed by precipitation during cooling after liquid phase sintering. Segregation mechanism of grain growth inhibitor was proposed based on the composition, solubility limit in liquid Co and that in solid Co of the inhibitor.

Developments of 100 nm-grained WC-Co based cemented carbides with cobalt content of 4 and 10% were succeeded based on the resolution of inhibition mechanism. The hardness and transvers rupture strength of developed cemented carbides were 2300 HV and 4.7 GPa for 10%Co, 2600 HV and 3.0 GPa for 4%Co, respectively. Using the technique, 0.2 µm-grained cemented carbides were commercialized.