| The present study aims at investgating a spray condition and heat treatment effects on the microstructure and mechanical properties of NiCr coating layer by Diamond-Jet spray system. NiCr self fluxing powders were sprayed on the Cu-Ag substrate under various spray conditions such as distance and grit blasting of substrate, and then heat-treated at temperature range of 500∼1,000℃. Optimum spray condition was evaluated in relation with the mechanical properties and microstructure of the coating layer. In 150㎜ spray distance, the mechanical properties such as adhesive strength, microhardness and wear resistance approved to be excellent, comparing with 250 and 300 ㎜ spray distance is less than that of coating layer in 250㎜ and 300㎜. In grit blasting of the substrate, it was observed that the adhesive strength of coating layer blasted steel grit is superior to that of blasted Al₂O₃ #30 grit. After heat treatment of the NiCr coatings, it was found that the microhardness and wear resistance of the coatings increases with an increase of heat treatment temperature. In particular, the microhardness showed the highest value at 1,000℃. The porosity of the coatings was remarkably decreased with an increase of heat-treatment temperature. Also, diffusion layer(about 20㎛) was observed to be formed at the interface between the coating layer and Cu-Ag substrate at the temperature range of 900∼1,000℃. |
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