The present authors previously reported that the high-strength WC-Co cemented carbide could be obtained by milling (WC+Co+Zn) powders and subsequently sintering the WC-Co-Zn mixture. In this report the effects of the amount of Zn mingled, sintering conditions and mean grain size of WC on the strength of Zn-added WC-10% Co medium-carbon alloys were first investigated. Secondly Second by the strengthening mechanism in the alloy was in detail studied in relation to the defects (such as pores, coarse WC grains and Co pools), which were observed on the ruptured surface as the origin of fracture.
Results obtained were as follows: (1) The strength was not sensitive to sintering conditions. (2) The effect of Zn addition decreased with increasing mean grain size of WC. (3) In Zn-added alloy with usual grain size of WC (1.5-1.8μ), the fracture rate starting from coarse WC grains (<-15 μ) increased, leading to the fact that the high strength of the alloy was caused by the decrease in density of large pores which are in general more responsible for the fracture than coarse WC grains.