INFLUENCE OF PROCESSING CONDITIONS ON GEOMETRICAL FEATURES OF LASER CLADDINGS OBTAINED BY POWDER INJECTION

The influence of processing conditions on the geometrical aspects of laser claddings is studied. Attention is drawn to the following laser-processing parameters: laser-power interaction time, surface of the irradiated zone, powder-feed rate. Different Ni-Cr-Co-Fe base powders are deposited on an austenitic stainless steel. It is observed that the mass of powder participating in the clad layer - which is proportional to the effective cross-section S of the layer - increases linearly with irradiance and interaction time. However, threshold values are detected; they are due to the existence of a minimum energy value required to melt the powder particles. The influence of the powder-feed rate, F, is more complicated. For low values, S is directly proportional to F, while beyond a critical value, F*, the powder injected in the laser beam acts as a screen, the opacity of which increases due to the multiple scattering phenomenon; energy absorption is more and more efficient and process efficiency is enhanced. However, this increase is limited to a maximum value, since the energy delivered by the laser source is also limited and since cladding requires melting of the particles. A simple explanation is proposed, based on mass- and energy-transfer governing equations.