STUDY ON THE ELECTRO-SPARK DEPOSITION PROPERTIES OF SKH51 TRANSITION COATING IN COMPOSITE GRADIENT COATING

Abstract

Because of the limitation of deposition thickness in electro-spark deposition (ESD) technology, composite coatings are increasingly used in electro-spark deposition. The deposition quality of transition coating is the key to improve composite coating. The deposition quality of transition coating is the key to improve composite coating. SKH51 material belongs to tungsten and molybdenum based materials and a high-speed tool steel with small and homogenous carbide particles. It has high hardness and excellent thermal hardness. It has good impact toughness and wear resistance, and can be used as the intermediate layer of carbon steel material and super-hard cermet coating. Consequently, a gradient structure is established. In this article, SKH51 material was deposited on the surface of 45 steel by the electro-spark deposition. With orthogonal experimental design, 16 sets of deposition experiments were conducted by selecting 4 factors and 4 levels. The coating thickness, coating surface roughness and maximum wear width of 16 samples were measured and counted. SKH51 coating wear surface is mainly abrasive wear and oxidation corrosion which is due to dry friction resulting in high temperatures on the surface. Because the surface of SKH51 coating was rough, the wear mass was used, the error will be larger. So the wear mark width is used to compare the wear resistance of the samples. The normalization method was used to unify the different unit coating evaluation objectives into a single metric. Three groups of weighting factors were determined using the requirements of transition coatings for coating performance indicators. Then, it was substituted into the objective function, and each experimental group normalizes the parameters for calculation. As a result, three distinct sets of maximal goal functions were obtained. The optimal value of the objective function corresponded to the 12th sample group. Finally, the deposition process parameters of the 12th sample were regarded as the optimal process for the SKH51 transition coating.