WC-Co超硬合金のクラック伝播に及ぼす有効残留圧縮応力の見積り

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The WC-(6-30)%Co high carbon alloys with mean grain size of about 1.7μ were in vacuum sintered, and subsequently four side surfaces of specimens were ground by diamond wheel to prepare the bending test pieces, or further polished to remove the surface layer associated with the residual compressive stress due to grinding. Two sorts of test pieces in each alloy were Vickers-indentated under various loads at the span center, and used for the transverse-rupture test. The difference in strength between two sorts of test piece was examined in each alloy and the residual compressive stress, which may effectively suppress the crack propagation in WC-Co alloys, was estimated.<BR>The results obtained were as follows: 1) A linear relationship between the difference in strength and the depth of Vickers indentation was observed within the accuracy of this experiment, and the value obtained by extrapolating the straight line to zero depth of indentation was considered to he an effective compressive stress (σre) on the surface of ground specimen. The σre of 6, 10 and 30%Co alloys, for example, was about 160, 100 and 10 kg/mm2, respectively; showing that the value decreased sharply with increasing Co content of the alloy. 2) The difference in strength was not almost affected in each alloy by the depth of Vickers indentation. Namely, the strength of ground specimens having indentation was usually higher by about are than that of polished specimens. Under the same depth of indentation, the strength of ground specimens did not almost change with the Cc content, although that of polished specimens decreased by a large amount with decreasing Co contents. Discussions on those results as well as on are were made.

WC-Co超硬合金のクラック伝播に及ぼす有効残留圧縮応力の見積り

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