超硬合金の耐食性と主として結合相中ε相との関係

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Effects of e phase, carbon and Fe contents on the corrosion resistance of WC-Co cemented carbide in acidic solutions were investigated. The WC-10% Co alloys with various carbon and Fe contents were sintered at 1375°C for 1 to 1.5 hrs. The ε phase was formed by grinding the surface of specimens.<BR>Results were as follows: (1) The corrosion resistance of the alloy was decreased with increasing carbon and Fe contents, as has been reported previously. In addition, it was found that the a phase is harmful for the corrosion resistance in every case, in particular in the case of high carbon alloys. (2) The corrosion front was almost flat in two phase alloy, even in the alloy with a small amount (<-0.2%) of Fe. On the contrary, that of three phase specimen with free carbon showed ruggedness. This phenomenon was more marked with increasing Fe contents. These rugged fronts seemed to be due to precipitation of the iron compound in addition to the free carbon. (3) Residual stresses in the surface layer due to grinding did not affect the corrosion resistance, which was confirmed using specimens containing Fe more than about 0.6%, where in this case the transformation, γ→ε, does not occur.
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