Abstract

Densification of plasma sprayed NiCrAlY coatings was studied from the view point of hybrid spraying combined with YAG laser irradiation. Configuration of a laser irradiation beam was varied in three different ways while performing low pressure plasma hybrid spraying and the microstructure of each coating was investigated in comparison with a conventional plasma sprayed coating. Of the three types of hybrid spraying, namely, (D pre-laser-irradiation for preheating of a steel substrate, ©simultaneous laser irradiation, and (3) post-laser-irradiation for remelting of the plasma sprayed coating, simultaneous irradiation formed the optimum microstructure showing both the least amount of porosities and high hardness. Some metallurgical bonding was also observed at the interface with this type of spraying. The two other types of hybrid spraying resulted in either a significantly porous microstructure with pre-irradiation, or a low hardness coating with post-irradiation. The characteristics of these microstructures in each coating are explained with reference to thermal hysterisis behaviors.

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