Extreme high-speed laser cladding (EHLA) technology was used to prepare Al₂O₃-316L coatings on Ti6Al4V rods. The effects of scanning speed, powder feeding rate on single-track coating quality, and 316L powder content on multi-track coating quality and corrosion resistance were explored. Results show that with the following optimum process parameters, including scanning speed of 250 mm/s and powder feeding rate of 8 g/min, the coating can present superior quality with the 316L powder in a mass fraction of 20%. It is shown that all Al₂O₃-316L coatings exhibit superior corrosion resistance compared to the substrate. As 316L content increases, the corrosion resistance of coatings increases followed by decline. With 316L powder in a mass faction of 20%, the electrochemical impedance of the coating is 2.27 times that of the substrate.

In order to improve the surface hardness and wear resistance of Ti-6Al-4V alloy, a cladded coating of TiO₂ and TiN was prepared on the surface of Ti-6Al-4V alloy by laser cladding, and the microhardness, wear resistance, microstructure and element distribution of the coating were explored. Compared to the substrate, the surface hardness and wear resistance of the coating are significantly improved. It is shown that with TiO₂ and TiN powder in a mass ratio of 1∶9, the hardness and specific wear rate of the coating can reach 1936.1HV_0.1 and 2.06×10^-14 mm³/(N·m), respectively, which are 5.4 times and 3.26 times those of the substrate. The main components of the coating include α-Ti, TiN, and TiN_0.6O_0.4, which is the reason for the significant increase in hardness and wear resistance of the TiO2-TiN cladded coating. The research results provide a theoretical and experimental basis for improving the hardness and wear resistance of Ti-6Al-4V alloy by laser cladding technology.

A FeCoCrNiMn high-entropy alloy (HEA) coating was prepared on the 201 stainless steel surface by adopting high-speed laser cladding technology, and then the microstructure, phase distribution, microhardness of FeCoCrNiMn coating, as well as its wear properties in dry sliding condition were all investigated. It is found that such laser cladded FeCoCrNiMn HEA coating consists of a single FCC structure, with no obvious cracks observed. It also forms a good metallurgical bond with the substrate. The microhardness of the coating is around (439±2.1)HV, nearly two times that of 201 stainless steel substrate, and the strengthening mechanisms mainly include strengthening by grain refinement and solid solution strengthening. Also, the FeCoCrNiMn coating presents an obviously better wear resistance than 201 stainless steel, with an average  friction factor of 0.246 and a specific wear rate of about 2.59×10^-6 mm³/(N·m).The wear mechanisms for it include adhesive and abrasive wear. It is concluded that such FeCoCrNiMn HEA coating prepared by high-speed laser cladding technology can significantly improve the surface hardness, wear resistance and service life of machine components.

In order to improve surface hardness and corrosion resistance of 304 stainless steel, a medium-entropy alloy (CoCrNi) coating was prepared on the surface of 304 stainless steel by laser cladding, and phase composition, element distribution and corrosion resistance of the cladded coating were studied. The results show that the treatment has achieved good metallurgical bonding between the cladded CoCrNi coating and the substrate, with no cracks, pores and other defects. The cladded coating is composed of single FCC phase, and exhibits dendrite and inter-dendrite structure. The elements are uniformly distributed on the cladded coating without obvious segregation. The uniform distribution of Cr element plays a positive role in improving corrosion resistance of the coating. The CoCrNi coating has its polarization resistance (101.65 kΩ) higher than that of 304 substrate (90.56 kΩ), and also significantly higher corrosion resistance.

316L stainless steel coatings were prepared on the surface of 304 stainless steel by using laser cladding at different scanning speed, and then metallographic microscopy, X-ray diffractometer, scanning electron microscopy and microhardness tester were adopted respectively to investigate the macroscopic morphology, phase composition, microscopic structure and microhardness for the coatings. The results showed that the 316L coating had a single-phase austenitic structure, and as the scanning speed increased, the grain size of the coating became smaller due to the reduction in the laser power density and heat input, and an increase in the cooling speed. It is found that the microhardness of the coatings is positively correlated with scanning speed, and the 316L coatings prepared by laser cladding at a scanning speed of 1 400 mm/min presents the highest microhardness of about 275HV_0.3. The improvement of the microhardness of the coating is ascribed to the effect of solid solution strengthening caused by lattice distortion combined with the effect of fine crystal strengthening. The wear test showed that the average friction coefficient of 316L coatings was significantly lower than that of 304 stainless steel substrate. And the 316L coating prepared by laser cladding at 1 400 mm/min has a friction coefficient of 0.424 and wear rate of 2.29 × 10^-6 mm³/(N·m), and is prone to abrasive wear.

Fe-Cr-B based wear-resistant coating was prepared on the surface of 45 steel by ultra-high-speed laser cladding. The effects of laser power, scanning speed and powder feeding speed on the aspect ratio and crack of single pass cladding layer were studied by orthogonal experimental method, and the effects of overlap rates on the surface quality of cladded layer was also studied. The optimal process parameters were determined as follows: laser power of 2 300 W, scanning speed of 250 mm/s, powder feeding speed of 24 g/min, and overlap rate of 70%. The results show that the hardness of the coating is between 754HV_0.2 and 831HV_0.2, which is 2.36 times to 2.60 times of the matrix hardness. Under the same conditions, the volume wear of the coating is only 3.64% of electroplated hard chromium coating.

A coating of 316L+x%NbC (x=0,5,10,15) was prepared on the surface of 304 stainless steel by laser cladding, and the effect of NbC content on the phase composition, microstructure, micro-hardness and wear behavior of the prepared coating was then investigated. The results show that with NbC content at 5%-15%, the phase composition of coating consists of NbC, Cr₇C₃ and γ-Fe; while the prepared 316L coating by adding NbC has its matric structure significantly refined, and traces of Nb element are dissolved in the phase of γ-Fe, forming a gap solid solution. By adding NbC, the micro-hardness and wear resistance of coating are substantially improved, but the friction coefficient and wear rate are remarkably decreased. It is shown that the coating of 316L+15%NbC has micro-hardness as high as 381HV_0.3, friction coefficient of 0.437 by average (41% lower than the coating 316L), and wear rate of 2.95×10⁶ μm³/(N·m), (around 50% compared to 316L coating).

With micro-nano TiC as reinforcing phase and nickel powder as matrix powder, a TiC reinforced Ni-based coating was fabricated by laser cladding technology, and the effect of TiC on microstructure and wear resistance of the coating was investigated. The results show that Ni-based coating has its microstructure predominately composed of γ-Ni and TiC, and a high content of TiC is prone to cause TiC segregation at the top of coating. With the increase of TiC content, coating will have its hardness increase gradually, especially have an obvious improvement in the surface hardness. A three-body wear test shows that the wear resistance of this composite coating decreases as TiC content increases, indicating that the brittle reinforcement phase is not conducive to improving wear resistance of the coating under impact load.

A Fe-based cladding layer was prepared on the surface of 27SiMn steel by using laser cladding technique, and effect of preheating on the microstructure and mechanical properties of the heat affected zone (HAZ) of 27SiMn steel was investigated. The results show that a large amount of martensite appears in the HAZ of 27SiMn steel after laser cladding process. The tensile fracture is composed of river-pattern cleavage plane, tear edge and dimple, representing a quasi-cleavage fracture; preheating treatment effectively reduces the amount of martensite and brings pearlite structure. When the preheating temperature is 100 ℃, the quenched layer has its hardness decreased by 25.4%, elongation increased by 11.5%, and tensile strength decreased by 14.3%. When the preheating temperature rises to 300 ℃, ductile fracture occurs in the material under tensile force. Appropriate preheating can effectively reduce the martensite in the HAZ of 27SiMn steel and alleviate the decline in the toughness of 27SiMn steel caused by quenching, thus improving the safety during the service of hydraulic cylinder made of laser cladded 27SiMn steel.

By using laser cladding technology, a high-speed steel coating was prepared on the surface of 316L stainless steel, and the influence of powder feeding rate and scanning distance (lap ratio) on the performance of the cladding layer was investigated. It is found that the cladding layer can present a better performance with the powder feeding rate of 0.4 r/min and the scanning distance of 0.9 mm. The surface of the cladding layer is smooth without spheroidizing defect, and there is a low dilution zone between the cladding layer and the matrix, showing good metallurgical bonding. The cladding layer has a compact internal structure without defects of pores and scum, in which there are planar grains, columnar grains and equiaxed grains in turn from the bottom to the top. The cladding layer is composed of α-Fe and carbides, and the carbides are uniformly distributed without obvious segregation. The average hardness of the cladding layer is 3.68 times that of the substrate. The distribution curve of the dynamic friction coefficient of the cladding layer shows little fluctuation, which is obviously less than that of the matrix.

With three kinds of iron-based powders (X₁~X₃) as raw materials, three kinds of cladding layers were coated on 45 steel by laser cladding technology. The microstructure, friction and wear properties of the cladding layers were investigated, with which electroplated hard chromium layer was selected to compare. The results show that three kinds of cladding layers all have a compact microstructure and are mainly composed of α'-martensite, austenite and δ-ferrite phases. X₁ powder cladding layer has more developed dendrites and finer grains. The hardness of X₁ cladding layer is significantly higher than X₂ and X₃ cladding layers, but lower than electroplated hard chrome layer. In addition, three kinds of cladding layers have the dry friction coefficient closer to electroplated hard chromium plating, but have a better wear resistance, which has a positive correlation with the hardness. The mechanisms of wear are mainly abrasive wear and fatigue wear.

Laser cladding technology was applied to form a Ni-based WC-Co coating with high wear resistance on TBM cutting teeth to solve the wear out failure. With Ni60B as the binding phase, WC-Co ceramic nanoparticle reinforced Ni-based composite coatings were claded on 42CrMo steel substrates. Wear-resisting performances of the coatings were tested with a MM200 ring-block wear testing machine in dry friction and water friction environment, surface hardness for the original coatings and worn ones were measured by microhardness tester, and their transforms in microstructure and composition were analyzed by SEM and EDS. It shows that the wear resistance of cutting teeth can be improved by laser-claded coatings, while the tiny precipitated phase in the worn claded layers displays a dispersion strengthening effect, and the surface microhardness of layers can be increased by 10%. Under the same wearing parameters, hardness of coatings after dry wear is higher than those after wet wear.