Application of Response Surface Method to Optimize Thickness and Hardness of Chromium Carbide Coatings Created by Thermo-Reactive Diffusion (TRD)

by Thermo-Reactive Diffusion is one of the methods to modify the surface properties or change the chemical composition of the surface in which, through the penetration of chromium element through the coating atmosphere and the carbon atom of the substrate by the diffusion process react with each other and due to low The energy of carbide formation creates a hard and dense coating of chromium carbide on the steel surface. To make chromium carbide, the sample is placed in a mixture of ferrochrome, borax and boric acid. To obtain the optimal state of three variables of temperature (in three levels of 980, 1000 and 1020 ° C), time (in three levels of 2, 6 and 10 hours) and distance of the sample from the molten surface (in three levels of 1/4 h, 1/2 h and 3/4 h) were used. The results show that the hardness of coating is about 1300-2800 Vickers and the thickness is about 40 microns. The results for the optimal state show that the highest probability of the optimal state was obtained at 9.26 h, 1020 ° C and 0.75 h distance from the molten surface. The optimal output results obtained from the mentioned conditions are a thickness of about 37 microns and a hardness of about 2650 Vickers, the achievement of these results was reported to be about 99%. The obtained results were validated with real value which is consistent with experimental values ​​at 95% level. Height from the molten surface has the greatest effect on thickness and hardness.