Effect of WC addition on microstructure and tribological properties of bimodal aluminum composite coatings fabricated by laser surface alloying

Successful deposition of aluminum composite coatings has been achieved by scanning the laser beam over the 304 stainless steel substrate using a mixed powder of A1SiTiNi and WC. The effects of different WC contents on the microstructure and properties of the bimodal composite coatings were investigated. The friction and wear behaviors of the laser-deposited composite coatings were evaluated using a pin-on-disc testing machine by sliding against tungsten carbide balls at room temperature with a load of 100 N, linear sliding speed of 0.031 m/s, sliding radius of 3 mm and a total sliding distance of 56.5 m. Prior to the wear test, the surface of the coating was ground and polished. For the coating with 20% WC content (wt.%), it possesses high microhardness and wear resistance as well as low coefficient of friction owing to its bimodal microstructure. The coatings are mainly composed of equiaxed crystal in the fully melted region and net structure in the partially melted region, while the partially melted particles are embedded in the fully melted region. In addition, the partially melted region is expanded to further enhance the properties of the coatings with the addition of WC. The phases of FeAl, FeNi, Al5Cr and WC are found in the coatings. The microhardness of the coating with 20% WC is 4.4 dines that of the substrate. With the increase of WC content, the maximum coefficient of friction of the coatings is increased. The coating with 20% WC possesses the lowest wear rate, which mainly involves abrasive wear when sliding against the tungsten carbide ceramic counterpart.