Influence of WC Content on Microstructure and Properties of Laser-Cladded FeCoNiCr High-Entropy Alloy Coatings

Objective High-entropy alloys (HEAs) exhibit excellent properties owing to their four unique effects and have great application potential in marine, nuclear power, new energy, and other fields. However, multielement HEAs fabricated using laser cladding (LC) tend to form a single solid-solution phase. The matching of strength and ductility is a key problem that must be urgently solved to promote the application of LC HEA coatings. In this study, FeCoNiCr HEA coating was reinforced by adding different contents of hard WC particles, which contributed significantly to the matching of the high ductility of the FCC-structured HEAs and the high hardness of the WC particles. The addition of hard particles to FCC-structured HEAs provides a new method to eliminate the mismatch between strength and ductility. Methods Two types of powders were mixed at a certain mass percentage, and the mixing process was conducted using a planetary ball mill. The LC process parameters were optimized by varying the laser power and scanning speed. The LC coatings were cut into cubic samples for microstructure characterization. The forming quality was observed using optical microscopy (OM). An X-ray diffractometer was used for the phase composition analysis. The scanning electron microscopy (SEM) was used to characterize the sample microstructures, and the wear tests were performed using a wear-testing machine. The corrosion resistance of the coatings was measured using an electrochemical workstation. Based on the experimental results, the effect of WC content on changes in the microstructure, microhardness, wear resistance, and corrosion resistance of the FeCoNiCr high-entropy alloy was systematically investigated. Results and Discussions In order to fully combine the high ductility of FCC-structured HEAs with the high hardness of WC particles, 10%-60% (mass fraction) WC/FeCoNiCr HEA composite coatings were fabricated. As shown in (Fig.3), the crack-free 60% WC-reinforced FeCoNiCr HEA composite coating was successfully manufactured. Furthermore, it was demonstrated that with an increase in the WC content, the content of the FCC phase in the FeCoNiCr HEA composite coatings decreased, whereas the carbide precipitation content increased, as shown in Fig.4. Figure 8 confirms that the wear resistance of the composite coatings with 60% WC was approximately 233% higher than that of the coatings without WC addition. Conclusions In this study, the influence of different WC contents on the microstructures and properties of LC FeCoNiCr HEA coatings was investigated. According to the results of the flaw detection experiments, the composite coatings were well formed with no macrocracks. With an increase in the WC content, the phase composition of the coating gradually changed from a single FCC phase to the multi-phase of FCC phase, WC, W2C, and Co4W2C phases. Moreover, the grains of the coatings were refined with the addition of WC, and block- and fishbone-like structures appeared in the 60% WC composite coatings. With 60% WC addition, the average microhardness of the coating cross-section reached 501 HV0.2, which was about 186% higher than that of pure FeCoNiCr HEAs coating. Although the addition of WC continuously improved the wear resistance of the composite coatings, the corrosion resistance of the composite coatings gradually decreased, mainly due to the decrease in FCC phase with good corrosion resistance in the FeCoNiCr HEAs.