セラミックコーチングの接着性に関連する高温加熱による素地金属 (18-8不銹鋼) の酸化について

Owing to the large thermal expansivity of 18-8 stainless steel, it is known that some preparatory procedure is necessary in order to obtain good adherence in ceramic coating. And the author has confirmed that good adherence could be obtained by preoxidizing the base-metal at high temperature for very short time to produce a very thin film of oxides on the surface.A series of experiments was, therefore, carried on to study the behavior of base-metal in high temperature oxidation and its effect on the adherence of ceramic coating. Moreover, the author discussed the reason why the addition of small amounts of copper oxide and vanadium oxide to mill batch improved the adherence.Following conclusions were drawn from the results obtained in present investigations:(1) The pretreatment under the condition of forming an uniformly distributed so called cloudy layer on metal surface gave better adherence of ceramic coating.(2) Such improvement of adherence may be due to the uniformly distributed amorphous substance at the metal-coating interface produced by the reaction between the coating and the oxide layers on metal.(3) Without the cloudy layer the interface looks like as being composed by transpartent glass covered in direct contact the metal surface, although X-ray confirmed the existence of unknown crystalline substance. This crystal did much harm to the adherence of the coating.(4) Copper oxide used as mill addition was found to be reduced to metallic copper at the interface during the firing. The small amount of oxygen liberated from copper oxide impeded the growth of above mentioned crystals.(5) In the area of the base metal comming in direct contact with the base metal it was observed that, without exception, the transformation from γ- to α-iron was occured during the firing.