Effect of carbon addition on microstructures and mechanical properties of laser cladding AlCoCrFeNi2.1 alloy coatings

In order to further improve the hardness, wear resistance and high temperature oxidation resistance of the surface of steel, the AlCoCrFeNi2.1 high entropy alloy (HEA) and its carbon reinforced alloy coatings on H13 steel were prepared by using the laser cladding method. The microstructures, mechanical, friction, and wear properties and oxidation resistance were studied, and the effect of carbon on the coating during the laser cladding process was discussed. The results show that the coatings are always composed as the dual eutectic morphologies with columnar and equiaxed structures and the grain size decreases obviously with the increase of laser power. By addition of carbon, the grain boundary of the coating becomes larger, and there is the formation of Cr7C3 phase. The texture characteristics of the and direction are formed in the composite coating. The hardness of the HEA coating is significantly higher than that of the substrate, and when the laser power is 1200 W, the hardness of the carbon-containing coating is increased by 27.8 % and 79.1 % compared with that of the HEA coating and substrate, respectively. The addition of carbon significantly reduces the friction coefficient of HEA coating, and the wear mechanism primarily exhibits abrasive and adhesive characteristics. In addition, higher laser power leads to lower oxidation rates for the coatings, and the surface oxides are mainly composed of Al2O3 and Cr2O3. The addition of C reduces the oxidation weight gain per unit area and oxidation rate of AlCoCrFeNi2.1 coating by 28.4 % and 47.2 %, respectively, which significantly improves the oxidation resistance of the composite coating. The results provide theoretical guidance for the application of high entropy alloys in strengthening coatings. [Display omitted] •Laser power has little influence on the phase composition, showing a two-phase structure of FCC and BCC.•Additon of Cf and increased laser power enhance the oxidation efficiency of HEA coatings.•Strengthening mechanisms include two-phase, solid solution, and fine grain strengthening.