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A continuous CO2 laser (10.6 µm wavelength) was adopted to investigate the influence of powder particle sizes on microstructural and morphological characteristics of laser claddings. To study the potential of powder in controlling the incident laser energy, different average particle sizes of Ni-base powder were deposited on an austenitic stainless steel X3CrNi18-10 substrate. The energy value necessary to melt a mass m of powder was calculated. The results indicate that this energy decreases with particle sizes. The claddings obtained with small particle sizes revealed a good morphological aspect and a low dilution of the cladding layer in the substrate, yet enough to create a very good metallurgical bond. The residual stress state was also influenced. Concerning modeling, we have elaborated residual stress model in the case of laser cladding by exploiting the response surface methodology (RSM), using a quadratic regression model. Combined effects of three laser cladding parameters on the residual stress is explored by a statistical analysis of variance (ANOVA). Results show that the residual stress is influenced principally by the power delivered by laser beam and by the scanning speed. It is also indicated that the size of powder particle is the dominant factor affecting the residual stress.

This study aims at developing an improved numerical simulation of the film boiling regime phenomenon to understand and visualize the growth of vapor bubble at a heated surface during low and high superheats. The simulation of the bubble dynamics including the bubble growth, departure, coalescence, rising, and frequency of detachment under different wall superheats is numerically investigated. The continuity, momentum, and energy equations are solved for the two immiscible fluids phases using the finite volume method. The phase change model and the results exhibited a good agreement with the theoretical models. The obtained results show that the velocity of bubble growth and its frequency of emission promotes heat exchange. It is found that the shape of a bubble has been influenced by the wall superheat. It is also found that the high superheat generates a large amount of steam in which the steam bubble takes the shape of a fungus. So, a clear correlation exists between heat transfer and the frequency of detachment. As long as the frequency is greater, the heat transfer increases. Most of the heat transfer is induced by the liquid movements associated with the vapor bubble detachment.