Laser produced functionally graded tungsten carbide coatings on M2 high-speed tool steel

The objective of the investigation was to produce functionally graded, carbide alloyed multilayer coatings on M2 high-speed steel by laser alloying with direct injection of WC powder into the melt pool. Single layer coatings with a wide alloying range corresponding to 12-58 wt.% W and 1.3-4.3 wt.% C, respectively, were produced by varying laser beam power and beam traverse velocity. Depending on the alloying degree, four different types of structures were observed in laser alloyed coatings; they were characterized by scanning electron microscopy and X-ray microanalysis. Multiple laser alloying with beam power decreasing at each successive stage was used for producing a triple-layer coating with tungsten content increasing from layer to layer and reaching 75 wt.% in the upper layer. The observed hardness was in the 1100-1200 HV range for single layer coatings with 40-50% W and as high as 1600 HV in the upper layer of a triple coating with 75% W. The coating with 58 wt.% W showed wear resistance five times as high as compared with the unalloyed laser-melted M2 steel.