WC-20%Co系超硬合金の耐酸化，耐熱衝撃性に及ぼすWC粒度の影響

Abstract

The relations among oxidation resistance, thermal shock resistance and metallurgical structure parameters of WC-20% Co sintered alloys with different WC-grain sizes (3.8–14 micron-m) were investigated by means of oxidation tests in air at temperatures of 750 to 850°C, and using a newly developed thermal shock test apparatus. To evaluate the thermal shock resistance of these alloys, tests were carried out using an electro-spark discharge apparatus and measuring the total length of thermal crack produced 0.05 mm below the sparking surface. Structure parameters of WC-20% Co alloys were measured with the photomicrographs quantitatively.The results obtained are as follows:(1) Oxidation process of WC-20% Co alloy is controlled by the OXIDE/METAL interfacial reaction. It obeys a linear law which has an apparent activation energy of 42.1 kcal/mol.(2) Oxidation resistance of these alloys depends mainly upon the cobalt content, which exists on the oxidation front surface, and upon the WC-grain size in the sintered structure.(3) Thermal shock resistance increases with increase in WC-grain size.