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Laser cladding uses a high-energy laser beam as a heat source to rapidly melt and solidify the cladding material onto the substrate to form a high-performance coating. This technology provides an efficient and economical method to repair and remanufacture precision equipment such as engines and spacecraft. However, the inherent non-equilibrium solidification properties of laser cladding often lead to problems such as coating anisotropy, high porosity, and elemental segregation. Optimizing process parameters and heat treatment do not always eliminate these defects. Therefore, it is necessary to seek a more appropriate solution. Introducing laser remelting on the surface or between the layers of the coating to cause it to remelt and redistribute can refine the grain size, reduce defects, and improve the uniformity of the composition, thus enhancing the performance of the coating. This paper reviews and summarizes the application and development status of laser remelting technology in laser cladding and discusses it in terms of surface quality, hardness, wear resistance, and corrosion resistance of the coating. It also identifies the potential of external field-assisted laser remelting technology in further optimizing coating performance. Finally, based on the review, suggestions are provided for selecting remelting parameters. [ABSTRACT FROM AUTHOR]

In this work, Fe-based alloy coatings were prepared on the surface of ductile iron by laser cladding. To improve its wear resistance and consider the economic and time cost of other post-treatment processes, laser remelting was chosen to strengthen the coatings. The effect of laser remelting energy density (0−11.45 J/mm2) on the phase composition, microstructure evolution, hardness, and wear resistance of the coatings were investigated. The results show that the coating consists of γ-(Fe, Cr) and carbides and that remelting energy density has little effect on its phase composition. After remelting, the hardness uniformity of the coating was significantly improved, but increasing the remelting energy density had little effect on it. The hardness and wear resistance of the coatings were inversely related to remelting energy density. At a low remelting energy density of 5.66 J/mm2, the hardness and wear mass loss of the coating were 111.49% and 54.36% of the original coating, respectively. The mechanism for the improved hardness and wear resistance is the microstructure refinement induced by laser remelting. Increased remelting energy density reduces the microstructure refinement of the coating, but the coatings still showed good hardness and wear resistance due to the diffuse distribution of carbides at higher remelting energy density conditions of 9.43-11.45 J/mm2. [ABSTRACT FROM AUTHOR]

Post-casting austenite often possesses better corrosion resistance than martensite. In order to compare the difference of corrosion resistance between austenitic stainless steel coating (ASSC) and martensitic stainless steel coating (MSSC) in the powder metallurgical state, two stainless steel Fe-based alloy coatings of the same process parameter were prepared on the surface of 40Cr steel by using laser cladding technology. Through SEM, EBSD, XRD and electrochemical tests, the microstructure, phase and cross-section metallurgical bonding condition of the coating were studied, and the difference in corrosion resistance between the two was comprehensively analyzed. The results showed that the main phase structure of ASSC was the FCC phase, and the main phase structure of MSSC was the BCC phase. The average self-corrosion current (9.92 × 10−8 A/cm2) and average self-corrosion rate (1.04 × 10−3 g/m2·h) of MSSC were 4.77 % and 5.62 % of ASSC, respectively. In addition, the polarization resistance, impedance value, and passivation film density of MSSC are higher than ASSC, MSSC has less damage from corrosion. The combination of factors, such as fabric refinement and passivation film density, makes the corrosion resistance of MSSC better than ASSC. • Two stainless steel Fe-based alloy coated on the 40Cr steel by laser cladding. • Comparison of corrosion resistance of coatings with different crystal structures. • Microstructure, physical phase and grain of two samples were studied. • Corrosion morphology and corrosion mechanism of each coating was analyzed. [ABSTRACT FROM AUTHOR]

Laser cladding is less used in the repair of cast iron parts. In this paper, multiple layers of austenitic stainless steel powders with different overlap rates were laser clad by the process of adding a transition layer to explore the feasibility of multilayer cladding of grey cast iron. The study results show that the higher cladding layers tends to cause cracking and warping of substrate, and the increased overlap rate of the Ni transition layer can effectively inhibit these failures. The wear mass of Fe-based coatings with 33.3%∼66.7% overlap was 1.00–2.68 mg. After wear, the Fe2p and Ni2p potentials were shifted, the intensity of the O1s characteristic peaks increased, and the wear oxidation increased wear quality loss. [ABSTRACT FROM AUTHOR]

• Fe-based coating was fabricated on the ductile iron by high-speed laser cladding. • Coatings were post-treated with different durations of chromic acid anodization. • Microstructure of samples before and after chromic acid anodization were studied. • The electrochemical corrosion resistance of each sample was analyzed. Fe-based alloy coatings were coated on surface of ductile cast iron by high-speed laser cladding, and the effects of chromic acid anodization on corrosion resistance of coatings were analyzed. The results show that as chromic acid anodization time increases, corrosion rate falls and then rises. After 20 min, the coating had Cr and Fe oxide passivation film, maximum impedance value (5.40 × 105 Ω·cm2) and polarization resistance (50.6 kΩ·cm2), and minimum self-corrosion current (0.77 μA/cm2). Its corrosion resistance had improved significantly. [ABSTRACT FROM AUTHOR]

The effects of overlap rate and defects on the corrosion resistance of laser fusion clad austenitic stainless steel coatings were studied. In this paper, the Ni transition layer and Fe-based coating were sequentially prepared on grey cast iron, and the corrosion morphology and corrosion mechanism of the coating were comprehensively analyzed through physical phase, microstructure and electrochemical tests. The coating phase was mainly γ-Fe, which formed strong selective orientation and texture strength at the (100) crystal plane; overlap ratio and defects affected the recrystallization changes, and the stresses near the defects were high. Increased overlap rate (Fe-based alloy 50 % → 66.7 %) could result in microstructure refinement, reduced corrosion rate v (A8 6.22×10−4 g/m2·h→A9 3.12×10−5 g/m2·h), and improved corrosion resistance. Corrosion cracking extended the crack and embrittled the alloy at the tips of the cracks, so that its (|Z| max 0.67 ∼ 1.31×104 Ω cm2) influence on the corrosion resistance was much higher than that of the pore (|Z| max 5.85 ∼ 10.2×104 Ω cm2). The best corrosion resistance of the process was achieved with an overlap ratio of 66.7 % for both the Ni transition layer and the Fe-based coating. • Different laser overlap cladding manufactured transition layer – Fe-based coating. • Defect characteristics and change mechanisms were analyzed. • Overlap rate and defects on corrosion resistance of coating mechanism were analyzed. [ABSTRACT FROM AUTHOR]

• Fe-based alloy coatings were prepared by an integrated process of laser cladding and laser remelting. • Increasing the laser remelting speed can significantly refine the microstructure and release residual stresses. • The coating exhibited peak hardness and abrasion resistance at a higher laser remelting speed of 40 mm/s. In this work, Fe-based alloy coatings were prepared on ductile iron substrates by laser cladding and laser remelting was used to further improve the abrasion resistance of the coatings. The result shows that increasing the remelting speed can gradually refine the microstructure and fully releases the residual stresses, and the inter-dendritic mesh structure becomes finer and denser. Compared with the original coating, remelted coatings have a significant increase in hardness and hardness uniformity. At the higher remelting speed of 40 mm/s, the coating had the highest hardness and abrasion resistance, 113.08 % and 157.55 % of the original coating, respectively. [ABSTRACT FROM AUTHOR]

In this paper, laser cladding technology coated the ductile iron surface with austenitic stainless steel. To improve the wear resistance of the coating, consider a heat treatment way to strengthen it. The effects of temperature and time on microstructure, hardness, and wear resistance of austenitic stainless steel coating were investigated. The results show that the martensitic phase was added to the samples at different times of 950 ℃, and the carbide precipitated phase was the main change in the microstructure. At 1050 ℃, the samples also changed from austenite to martensite at different deal times, and the microstructure mainly changed between dendrites. The hardness and abrasion resistance of the 1050 °C/2 h process improved with a hardness of 40.6 HRC, an increase of 26.1%, and a maximum relative abrasion resistance improvement of 84.63%. Which strengthening mechanism was mainly coating dendrites coarse and uniform diffusion occurs, martensite uniform phase transition presented on the surface, coating austenite grain size 9.08 µm smaller, martensite recrystallization and larger grain size of 28.57 µm, the coating as a whole in the uniform phase transition and dendritic crystal strengthening synergistic effect, hardness increased, resistance to wear became stronger. [ABSTRACT FROM AUTHOR]