Abstract

In order to improve the wear property of high Cr - high Ni overlay alloy coatings with dispersed NbC particles formed by PTA (Plasma Transferred Arc) welding process, the isothermal ageing at 773 ~ 1023K was carried out. The precipitation behavior and the wear property of the NbC-dispersed alloy were examined, compared with the NbC-free alloy, by using vickers hardness tester, SEM, TEM, EDX, XRD and Ohgoshi wear tester. It has been found that the hardness of the NbC-dispersed alloy increased by the isothermal ageing without a solution heat-treatmnet after PTA welding, its age-hardenability is higher than the NbC-free alloy and consequently the wear property is remarkbly improved. This is probably due to a continuous precipitaion of α '- phase. Namely, although, in the NbC-free alloy, both a nodular precipitation of α '-phase and a continuous precipitaion of α '-phase occurred, in the NbC dispersed alloy, any precipitation can't be observed except for the continuous precipitation of α '- phase. It is considered that such different precipitation behaviors have been caused by niobium atoms dissolved in the matrix of the NbC-dipersed alloy.

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