Interfacial Characterization and Surface Wear Mechanism of Ti(C, B)/Ni60A Composite Coating Prepared by In Situ Extra High-Speed Laser Cladding

H13 die steel easily fails under friction and wear due to its low purity, poor homogeneity, and unreasonable matching between strength and toughness. The preparation of wear-reducing and wear-resistant coatings through extra high-speed laser cladding (EHLA) is important for the restoration and remanufacturing of metallurgical spare parts. This method provides an solution for the in-service life extension of H13 die steel. However, cracking at the EHLA interfaces induced by residual stresses due to low substrate dilution rates, remarkable cooling rates, and differences in thermal expansion between dissimilar metals acts as a limitation to the application of EHLA. This work aimed to alleviate stress muta-tion at the fusion interface of EHLA coatings, improve the fusibility of EHLA coatings on H13 die steel, and obtain wear-reducing and abrasion-resistant features on the surfaces of EHLA coatings. In this study, a Ti(C, B)/Ni60A composite coating was prepared with almost defect-free microstructures on an H13 die steel substrate by coupling EHLA with direct reaction synthesis to introduce an in situ exothermic reaction into EHLA cladding to achieve the above aims. The obtained material was compared with the pure Ni60A coating prepared through EHLA alone. Residual stress distribution at the fusion interface of the Ti(C, B)/Ni60A composite and Ni60A coatings was determined using the Giannakopoulos & Suresh (G&S) energy method based on nanoindentation. SEM, EDS, and EBSD were performed to investigate the microstructures, phase compositions, and characteristics of the two coatings and cladding interfaces. A focused ion beam setup was used to obtain information on the superficial wear of the two samples, and double spherical aberration TEM was conducted to analyze the superficial wear characteristics of the two coatings. The superficial wear mechanism of the Ti(C, B)/Ni60A composite coating was deter-mined along with the changes in the surface microhardness of the two coatings. Results revealed that the Ti(C, B)/Ni60A composite coating interface was affected by the emission of approximately 670 kJ Joule heat by the in situ reaction of Ti and B4C. The interfacial width of the coatings reached 22 mu m, which was 11 times that of the Ni60A coating prepared through EHLA (2 mu m). This increase effectively re-duced the stress gradient in the interfacial region and alleviated the stress mismatch on both sides of the interface. However, the surface hardness of the Ti(C, B)/Ni60A composite coating was only 360-400 HV0.2, which was less than half of that of the Ni60A coating. The wear losses of the two materials were in the same order of magnitude owing to the support provided to the Ti(C, B)/Ni60A composite coating matrix by the in situ authigenic TiCB, Ti3B4, and other phases. Such support reduced abrasion and conferred wear resistance. The above observation was also a result of the formation of equiaxed ultrafine grains at a depth of 180 nm below the wear surface area through the coupling of the plastic rheology-heat-force fields. This phenomenon dynamically strengthened the worn surface