Microstructure and Properties of Fe-Based/WC-10Co-4Cr Coatings by Plasma Cladding

The work aims to prepare wear-resistant coatings with high strength and hardness for the worn surface of mechanical parts, to prolong their service life and avoid various faults caused by wear. WC-10Co-4Cr/Fe300 alloy composite coatings were prepared on the surface of 40CrMnMo by the plasma cladding technology. The effects of WC-10Co-4Cr content in different mass fractions on the microstructure and properties of the coatings were studied. The microstructure and phase of the cladding layer were characterized by metallographic microscope, ultra depth of field optical microscope, SEM, EDS and XRD. The hardness and wear resistance of the cladding layer were tested by a digital display hardness tester and a pin disc friction and wear tester. The results showed that the coating surface had good continuity without obvious cracks and holes. There was a clear interface between the cladding layer and the matrix of each sample, a thin and narrow white bright band could be clearly seen, no obvious holes and cracks appeared in the bonding area, and the coating and the matrix showed good metallurgical bonding. From the microstructure of the cross section of the cladding layer, with the increase of WC-10Co-4Cr content, the solidification rate of the cladding layer decreased, the temperature gradient and the undercooling degree were large, so the cellular crystals at the bottom of the cladding layer gradually increased. The dendrite content in the middle of the cladding layer increased. The EDS results showed that when the mass fraction of WC-10Co-4Cr was 30%, more WC melts and diffuses into the Fe based alloy, and the W content decreased with the distance from WC particles. With the increase of WC-10Co-4Cr alloy powder, hard phases such as Fe2W2C, Fe3W3C, Fe6W6C, (Cr, Fe) 23C6, WC and W2C were formed in the cladding layer, and the surface grains were refined. Therefore, the average hardness of the cladding layer had been significantly improved. When the mass fraction of WC-10Co-4Cr reached 20%, the hardness of the cladding layer was 518.5HV0.2, about 1.7 times that of the substrate. The main friction mechanism of the cladding layer was abrasive wear. The average friction coefficients of matrix and Fe-based cladding layer were about 0.90 and 0.77 respectively, and there was little difference between them. The average friction coefficients of WC-10Co-4Cr coating with 10%, 20% and 30% WC-10Co-4Cr content were about 0.70, 0.61 and 0.54 respectively. In terms of friction coefficient, WC-10Co-4Cr/Fe cladding layer was significantly lower than that of matrix and Fe matrix. With the gradual increase of WC-10Co-4Cr content, the wear loss weight on the surface of the cladding layer gradually decreased, indicating that the wear resistance of the cladding layer gradually became better. The wear resistance of the cladding layer with 30% WC-10Co-4Cr was the best, and its wear amount was only 0.007 9 g, which was 0.018 6 g less than the total wear amount of the substrate. From the wear morphology of the surface of the cladding layer, it could be seen that with the increase of WC-10Co-4Cr content, the surface of the cladding layer tended to be smooth, and there was no large number of deep furrows. The wear degree was significantly reduced, which could greatly improve the wear resistance of the substrate surface. In conclusion, the addition of Fe6W6C, (Cr, Fe)23C6 strengthening phase formed by the reaction of WC-10Co-4Cr powder and Fe300 alloy powder significantly improves the hardness and wear resistance of the cladding layer. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.