Tsuyoshi Irisawa

Thermal cycling life of plasma-sprayed alumina coating on cast irons has been performed in comparison with the alumina coating on steel. The samples were prepared by plasma-spraying alumina on flaky graphite cast iron and spheroidal graphite cast iron without an undercoat and with an undercoat of nickel based self-fluxing alloy or nickel-chromium alloy. Thermal cycling test revealed that the coating on flaky graphite cast iron shows a good thermal shock resistance and undercoating improves the property appreciably by preventing oxide formation on the substrate.

高速フレーム溶射法を用いて作製した皮膜は溶融及び未溶融粒子が混在した組織となる。出発粉末の粒径の大きい皮膜ほど未溶融粒子の割合は大きくなる。未溶融粒子の割合の大きい皮膜ほど硬さが高くなることがわかった。

冷却条件を変化させた炭素鋼基材上に減圧プラズマ溶射法で高炭素クロム鉄合金皮膜作製した。得られた皮膜は微細な炭化物を有する緻密な皮膜となり、微細な炭化物を有する皮膜ほど高硬度である。この皮膜にHIP処理を施したが硬さの向上は得られなかった。

Powder of a nickel-chromium alloy (about 20 wt.% chromium) was low pressure plasma sprayed onto substrates which were cooled to various extents. As the maximum temperature of the sprayed deposit was increased up to approximately 1148-1235 K during spraying, the strength of the deposit, measured on tensile test pieces machined from the deposit, increased owing to the combined effects of precipitation strengthening and enhancement of adhesion between the flattened particles composing the deposit. It is proposed that an adequate rise in temperature of the deposit during spraying improves its strength more effectively than annealing a deposit held at low temperatures during spraying, as long as the heating temperature and the heating time of these two deposits are similar to each other.