WC-Co超硬合金の抗折力と引張強度との関係

Abstract

The relation between transverse-rupture strength (σm) and tensile-rupture strength (σt) in cemented carbides was studied paying attention to the microstructural defect as a fracture source. The conventional WC-10 and 20%Co alloys with a mean carbide grain size of 1.3 μm were used as specimens. Hot-isostatically pressed WC-10%Co alloy was also used. The transverse-rupture test was done according to the JIS, and the dimensions of the tensile test specimen were 4.0 mmφ in gage section and 30 mm in length.The results obtained were as follows: (1) The ratios of \barσm⁄\barσt in this study were about 1.7 and 1.4 in conventional WC-10 and 20%Co alloys, respectively. These ratios were quantitatively explained, when the difference in dimensions of fracture sources between the two tests, the location of defects in the transverse-rupture test specimens and the overestimated value of σm (from usual beam formula) in particular in high cobalt alloys were taken into account. The ratio was confirmed to approach the value of 1.0, as the distribution of defect size within specimens became narrower. (2) For further confirmation of the above explanation, the exponent of Weibull’s equation was examined in both tests. It was found that the exponent did not generally coincide in each test, as expected from the above results. Thus, the strength of the alloy including the ratio of \barσm⁄\barσt was by no means considered to be explicable by Weibull’s theory.