Papers by Keyword: Laser Cladding

Abstract: In laser cladding process, generation of high temperature gradients significantly impacts the output coating parameters such as mechanical and microstructural properties. Buffer layer addition between hard alloys cladding shows reduction in crack formation and also dilution rates. The present study is on Insitu temperature monitoring in laser cladding of Stellite 6 alloy with addition of buffer layer, which were compared with direct deposition of Stellite 6. The results show about 17 - 20 % low substrate temperatures with a buffer layer, indicates more uniform cooling of the hard coatings than direct cladding. The increase in laser power measures 35 - 40 % higher temperatures in both the cases due to large heat addition at the clad region. The study provides an insight into the substrate temperature evolution in cladding with and without a buffer layer.

Abstract: Nickel-aluminum bronze coatings were deposited on high strength stainless steel SUS630 by laser cladding. The microstructure of the multi-layer structures was investigated. The OM results showed that steel-bronze bimetallic materials were successfully fabricated without any defects. The dilution rate of substrate can be adjusted by controlling the laser parameters. The main phases of the coating are α-Cu, Fe-rich dendrites and κ phases. Tensile tests were carried out and it was found that the upper specimen with fewer Fe-rich related components had better tensile strength properties.

Abstract: Copper is widely used in the power industry due to its good electrical conductivity. However, owing to its low hardness and resistance to abrasion, copper is prone to damage when working under harsh environmental conditions. In order to protect the power equipment and improve the surface strength of the material, this study explores the feasibility of using laser cladding technology to prepare a protective layer on the copper substrate. The phase, microstructure and element distribution of the cladding layer were analyzed, and the changes in the microhardness of the cross-section were measured. The wear resistance of the two cladding layers was tested and compared with the wear resistance of pure copper. The experimental results show that the cladding layer has uniform structure distribution, fine grains, and no element segregation; the hardness of the cladding layer is greatly increased, and the average hardness of the CuCr20 cladding layer is 155.8 HV, which can reach 2.2 times that of the substrate. The average hardness of the CuCr40 cladding layer is 254.4HV, which can reach 3.6 times that of the matrix. The wear resistance of the CuCr40 cladding layer is higher than that of the CuCr20 cladding layer, which can reach three times that of pure copper. Experiments have proved that the protective effect can be achieved by preparing a laser cladding layer on the surface of pure copper.

Abstract: The dilution ratio of the Ni coating prepared by the laser cladding under the assistance of the follow-up feeding pulsed current was optimized by combining back propagation (BP) neural network and genetic algorithm. The model was trained according to the results of the 6-factor 3-level orthogonal experiments. A BP genetic neural network forecast model between cladding parameters (laser power, scanning speed, powder feeding rate, pulsed current, pulse frequency and pulse width) and dilution ratio of coating was constructed. On this basis, technological parameters under the target dilution ratio of the coating were optimized by a genetic algorithm. Results demonstrated that the predicted results of the model are very close to the experimental results in term of dilution ratio of the coating, with a relative error no higher than 2.63%. This demonstrates that the model is reliable and effective. The optimal technological parameters are gained when the dilution ratio of the coating is 17.5%, including laser power=1926.3 W, laser scanning speed =·s^-1, powder feeding rate= ·min^-1, average pulsed current =, pulse frequency=445.6 Hz, pulse width= 108.4 μs.

Abstract: Pure niobium substrates were coated using laser cladding method. Pure molybdenum, Yttria Stabilized Zirkonia (YSZ) and corundum (Al₂O₃) powders were used as coating materials. Coatings were deposited on specimens as seperate paths with 3÷10mm width and 40mm of length. Two different laser power 3kW and 4kW were tested during deposition. In order to assess the quality of the Mo-YSZ and Mo-Al₂O₃ coatings, the light microscopy, Scanning Electron Microscopy (SEM), chemical analysis (EDS) and Vickers hardness test investigation were performed. The surface roughness and wear volume were also measured. As a result of YSZ-Mo powder cladding on the Nb substrate the composite layers were obtained without cracks and porosity not exceeding 1 μm. In addition, an increase in hardness of about 450 HV0.5 was revealed. As a result of Al₂O₃-Mo powder cladding on the Nb substrate the composite layers with many voids and cracks were obtained for each of the cladding variants.

Abstract: Laser cladding is an effective way to improve the surface hardness and wear resistance of titanium alloy. The powder materials and laser cladding process parameters have great influence on the properties of the wear resistant coating. In order to reduce the common defects including the cracks and pores of the coating, titanium alloy powder and self-melting alloy powder are selected to ensure the good adhesion between titanium alloy and wear resistant coating. In addition, the strengthening phase and self-lubricating phase were added to the laser cladding powder material to improve the micro hardness and reduce the friction coefficient, which bring in the improvement of the wear resistance of the coating. In the present work, the selection principle and application effect of powder materials for wear-resistant coatings are reviewed. the research status of the influence of laser technological parameters on coating properties is discussed. Meanwhile, the methods to reduce the defect of wear resistance coating by laser cladding are proposed.

Abstract: Laser based metal additive manufacturing (AM) is an emerging technology in various aerospace industries including aero-engine components and turbine manufactures. Laser cladding is a potential process for material deposition and surface enhancement technique that forms a strong metallurgical bond with the substrate. In the present study, Nickel based Inconel 718 (IN718) super alloy which maintains high strength working at elevated temperatures is used as the clad material. The study investigates the processing of Inconel 718 with powder morphology and microstructural properties and also two, three and four-layer deposition. This study explores the possibility of depositing IN718 using laser cladding that can be better considered as metal AM process.

Abstract: To investigate influences of multi-track overlapping on melting of preset MCrAlY coating during laser cladding plasma spraying, a three-dimensional finite element model of the continuously moving temperature field during multi-track laser cladding was constructed using the ANSYS parametric design language (APDL) based on the existing temperature field model during single-track laser cladding. According to analysis results of temperature field, temperature of samples increases gradually during laser cladding due to heat accumulation effect of laser scanning, and the molten pool expands gradually. There are evident differences among different scanning pathways. Therefore, it is impossible to get high-quality cladding coating with uniform melting and small dilution ratio. Molten pools with basically same sizes in different scanning pathways can be gained by decreasing laser power or increasing scanning speed in different tracks one by one. Similarly, differences of molten pools in different scanning pathways can be relieved effectively through preheating of samples. Through a closed-loop control over the highest cladding temperature, a more even cladding coating can be gained through adaptive control of laser power and / or scanning speed.

Abstract: A finite element model of thermal coupling stress field during laser cladding plasma spraying of preset MCrAlY coating was constructed based on the finite element model of temperature field by using the indirect thermal coupling method in ANSYS finite element software. Moreover, stress field during laser cladding was analyzed. Through the constructed model, variation laws of stress field with time during laser cladding and cooling process could be mastered. Based on the stress field, the formation mechanism of cracks in laser cladding coating and influencing factors were further analyzed and some solutions to cracks of laser cladding coating were proposed.

Abstract: A finite element model of temperature field for plasma spraying preset MCrAlY coating during laser cladding was constructed using ANSYS parametric design language (APDL) in accordance to characteristics of preset laser cladding. Influencing laws of laser cladding parameters on temperature field were analyzed. Results show that laser power influences temperature field of cladding samples more than laser scanning speed. Experimental results agree well with simulation results, which prove the accuracy and reliability of the constructed calculation model of temperature field. Heating and cooling laws in the laser cladding process could be mastered through this calculation model. Research conclusions provide some references to optimization parameters in preparing high-performance laser cladding coatings.