Improvement of wear property of NbC high Cr high Ni overlay alloy coating formed by plasma transferred arc welding process

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 similar to 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 continous precipitaion of alpha '- phase. Namely, although, in the NbC-free alloy, both a nodular precipitation of ct. phase and a continous precipitaion of alpha '-phase occurred, in the NbC dispersed alloy, any precipitation can't be observed except for the continuous precipitation of a: phase. It is considered that such different precipitation behaviors have been caused by niobium atoms dissolved in the matrix of the NbC-dipersed alloy.