Laser cladding, as one of the most promising surface modification technologies, is being widely applied in industry to improve the wear and corrosion resistance of components. The high energy input and high cooling rate during the cladding process lead to severe metallurgical reactions that determine the microstructure and properties of the cladded layer. In this study, a 3-dimensional (3-D) finite element (FE) model was developed to study heat transfer during laser cladding of 420 stainless steel+ 4% molybdenum on mild steel A36. In this model, the effects of laser-powder interaction, temperature-dependent material properties, latent heat, and Marangoni flow were considered. A method based on mass balance was adopted to predict the clad geometry. The thermal results such as the temperature history, temperature gradient, and solidification rate were investigated. Based on the simulated thermal results, the microstructure and Mo distribution in the clad layer were studied. In order to verify the established model, a series of experiments was conducted by using an 8-kW high-power direct diode laser (HPDDL). Thermocouples and a CCD camera were used to monitor the temperature history and molten pool size. The predicted clad height and width showed a good agreement with the experimental results.
In laser cladding, the performance of the deposited layers subjected to severe working conditions (e.g., wear and high temperature conditions) depends on the mechanical properties, the metallurgical bond to the substrate, and the percentage of dilution. The clad geometry and mechanical characteristics of the deposited layer are influenced greatly by the type of laser used as a heat source and process parameters used. Nowadays, the quality of fabricated coating by laser cladding and the efficiency of this process has improved thanks to the development of high-power diode lasers, with power up to 10 kW. In this study, the laser cladding by a high power direct diode laser (HPDDL) as a new heat source in laser cladding was investigated in detail. The high alloy tool steel material (AISI H13) as feedstock was deposited on mild steel (ASTM A36) by a HPDDL up to 8kW laser and with new design lateral feeding nozzle. The influences of the main process parameters (laser power, powder flow rate, and scanning speed) on the clad-bead geometry (specifically layer height and depth of the heat affected zone), and clad microhardness were studied. Multiple regression analysis was used to develop the analytical models for desired output properties according to input process parameters. The Analysis of Variance was applied to check the accuracy of the developed models. The response surface methodology (RSM) and desirability function were used for multi-criteria optimization of the cladding process. In order to investigate the effect of process parameters on the molten pool evolution, in-situ monitoring was utilized. Finally, the validation results for optimized process conditions show the predicted results were in a good agreement with measured values. The multicriteria optimization makes it possible to acquire an efficient process for a combination of clad geometrical and mechanical characteristics control.Keywords Laser cladding . High power direct diode laser . Response surface methodology (RSM) . Multi-response optimization Lasers Manuf. Mater. Process.
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