Stainless steel powders with different molybdenum (Mo) contents were deposited on the substrate surface of 45 steel using a 6 kW fiber laser. The microstructure, phase, microhardness, wear properties, and corrosion resistance of coatings with different Mo contents were studied by scanning electron microscopy (SEM), electron probe microanalyzer (EPMA), X-ray diffraction (XRD), microhardness tester, wear tester, and electrochemical techniques. The results show that good metallurgical bonding was achieved between the stainless steel coating and the substrate. The amount of M₇(C, B)₃ type borocarbide decreases and that of M₂B and M₂₃(C, B)₆ type borocarbides increases with the increase of Mo content in the coatings. The amount of martensite decreases, while the amount of ferrite gradually increases with the increase of Mo content. When the Mo content is 4.0 wt. %, Mo₂C phase appears in the coating. The microstructure of the coating containing Mo is finer than that of the Mo-free coating. The microhardness decreases and the wear resistance of the coating gradually improves with the increase of Mo content. The wear resistance of the 6.0 wt. % Mo coating is about 3.7 times that of the Mo-free coating. With the increase of Mo content, the corrosion resistance of the coating firstly increases and then decreases. When the Mo content is 2.0 wt. %, the coating has the best corrosion resistance.

Ni-based alloy powders with different contents of cobalt (Co) have been deposited on a 42CrMo steel substrate surface using a fiber laser. The effects of Co content on the microstructure, composition, hardness, and wear properties of the claddings were studied by scanning electron microscopy (SEM), an electron probe microanalyzer (EPMA), X-ray diffraction (XRD), a hardness tester, and a wear tester. The results show that the phases in the cladding layers are mainly γ, M₇(C, B)₃, M₂₃(C, B)₆, and M₂B. With the increase in Co content, the amounts of M₇(C, B)₃, M₂₃(C, B)₆, and M₂B gradually decrease, and the width of the eutectic structure in the cladding layer also gradually decreases. The microhardness decreases but the wear resistance of the cladding layer gradually improves with the increase of Co content. The wear resistance of the NiCo30 cladding layer is 3.6 times that of the NiCo00 cladding layer. With the increase of Co content, the wear mechanism of the cladding layer is changed from abrasive wear to adhesive wear.

High-hardness iron-based alloy coatings are extensively utilized in aerospace, automotive, and industrial equipment due to their exceptional wear resistance and long service life. Laser cladding has emerged as one of the primary techniques for fabricating these coatings, owing to its rapid cooling and dense microstructure characteristics. However, the production of high-hardness iron-based alloy coatings via laser cladding continues to face numerous challenges, particularly when controlling the morphology, quantity, and distribution of the reinforcing phases, which can lead to cracking during processing and service, thus compromising their usability. The cracks of the cladding layer will be suppressed through good microstructure design and control, resulting in a wide range of performance for high-hardness Fe-based alloy coatings. This paper reviews recent advancements in the design and control of the organization and structure of high-hardness iron-based alloy coatings from the perspectives of material composition, processing parameters, and external assistance techniques. It summarizes the properties and applications of various materials, including different alloying elements, ceramic particles, and rare earth oxides, while systematically discussing how processing parameters influence microstructure and performance. Additionally, the mechanisms by which external auxiliary energy fields affect the melt pool and solidified microstructure during laser cladding are elucidated. Finally, the future development directions of laser cladding technology for high-hardness iron-based coatings are anticipated, emphasizing the need for further quantification of the optimal coupling relationships among the gain effects of composite energy fields.

The technology of the TiB₂/TiB cladding layer addresses the issue of the insufficient wear resistance of cup-shaped parts composed of titanium alloy materials. In order to eliminate the cracking problem of laser cladding TiB₂/Ti-based alloy, 30%TiB₂/Ti-based alloy gradient coating was prepared on the surface of titanium alloy by laser cladding in this study. The results revealed that the microstructure of the matrix and the cladding layer is metallurgically bonded. The microstructures of the cladding layer appear as rod-like and coarse-grained features on the surface, and fine needle-like and small-grained morphologies inside. The fine needle-like TiB precipitated in situ from the melt has a flat interface with Ti and exhibits a low degree of interfacial mismatch, while the interface between small particle-like TiB and Ti is wavy and has a high degree of interfacial mismatch. The gradual increase in the amount of TiB is present from the surface to the bottom of the cladding layer, while the amount of unmelted TiB₂ particles decreases. The chemical structure of the cladding layer is mainly presented as TiB₂, TiB and α-Ti phases. The maximum hardness of the cladding layer is 725 HV_0.2, where it is more than twice the hardness of the substrate. The fretting wear resistance of the cladding layer is better than that of the titanium alloy substrate under low loads (50 N–100 N), while a high load (more than 150 N) triggers a reverse outcome.