Ni60 alloys exhibit high hardness, strong wear, and corrosion resistance. However, based on existing theoretical and practical research, it has been determined that the Ni60 alloy exhibits a high crack sensitivity, which seriously restricts its engineering applications. Orthogonal experiments on laser cladding under non-preheating conditions are conducted, and a multiple regression prediction analysis is adopted to predict the quality of the cladding layers and optimize the process parameters of the laser cladding. High-quality Ni60 cladding layers are beneficial for the wear and corrosion resistance of machine parts fabricated from 316L stainless steel. This study aims to prepare a crack-free Ni60 alloy coating on the surface of 316L stainless steel to promote the application of the Ni60 alloy in the green remanufacturing field.

Cracks are mainly caused by residual internal stresses in the cladding layers. They can be avoided by controlling the process parameters, which essentially means controlling the laser energy during the cladding process. Single-layer single-pass and single-layer multipass orthogonal experiments on laser cladding were conducted without preheating. In the experiments, the influences of the powder feeding rate, laser power, and scanning speed on the quality of the cladding layers were examined. The main factor affecting the crack density was obtained via range analysis. Additionally, the effects of the powder feeding rate, laser power, and scanning speed on the dilution rate and forming coefficient were determined based on the geometric morphology of the cladding layers. Multiple regression prediction models were established, which considered the laser power, scanning speed, and powder feeding rate as input factors and the forming quality parameters, such as crack density, dilution rate, and forming coefficient, as optimization goals. Consequently, optimized process parameters for laser cladding were obtained. A crack-free Ni60 alloy coating was prepared using the optimized process parameters. Subsequently, the effect of the overlap rate on the cladding layer was analyzed. Finally, the microstructures and microhardnesses of the coatings were examined.

By analyzing the experimental results of the first single-layer single-pass orthogonal experiments, it is determined that the influence of the laser power and powder feeding rate on the crack density of the cladding layer is greater than that of the scanning speed. By increasing the laser power and decreasing the powder feeding rate and scanning speed, the number of cracks can be reduced. Based on the cross-sectional morphology of the cladding layers obtained in the second orthogonal experiment, it can be seen that the dilution rate increases as laser power increases and decreases as powder feeding rate increases. Additionally, the forming coefficient decreases as laser power increases and increases as scanning speed increases. Multi-objective regression prediction and parameter optimization are performed based on the data obtained from the experiments. The predicted results are highly consistent with the experimental results. The optimal process parameters are as follows: laser power of 1405 W, scanning speed of 5.7 mm/s, and powder feeding rate of 0.4 r/min. To verify the effectiveness and repeatability of the optimized process parameters, three single-pass cladding tests are conducted. Dye inspection of the cladding layers illustrates that the cladding layer is smooth, without crack defects, and the process repeatability is good. Single-layer multipass laser cladding experiments are conducted to determine the overlap ratio. According to the dye inspection and morphology observation of the cladding layers, a 45% overlap rate satisfies the requirements, and 50% overlap rate is optimal for cladding.

In this study, the process parameter optimization for laser cladding Ni60 alloy powder on the surface of 316L stainless steel was examined. Orthogonal experimental methods combined with multiple regression prediction methods are used. The effects of process parameters, such as laser power, powder feeding rate, and scanning speed, on the crack density, dilution rate, and forming coefficient are determined. High-quality cladding layers are successfully prepared using the optimized process parameters. By observing the metallographic structure of the cladding layer via a metallographic microscope, it is determined that the microstructure transitions from planar crystals and dendritic crystals to equiaxed dendritic crystals from the bonding zone to the surface of the cladding layer. The upper part of the cladding layer is composed of small and disordered equiaxed crystals and equiaxed dendrites. This illustrates that the Ni60 alloy powder forms a dense metallurgical bond with the 316L stainless steel substrate. Microhardness measurement experiments show that the hardness of the Ni60 alloy coating was approximately 2.8?3.4 times that of the 316L stainless steel substrate. The surface strengthening of the substrate was significant.