In-situ observation and simulation of melt pool evolution and single-track formation in laser cladding

Melt pool and single-track are fundamental units in laser additive manufacturing and surface treatment, and their characteristics critically determine final quality of parts and surface. In this work, A high-speed camera was integrated for observation of instantaneous melt pool, coupled with finite element simulation to elucidate underlying thermal and flow behavior in laser cladding. The effects of laser power, scanning speed, and powder feeding rate on melt pool area and single-track (width, microstructure, microhardness) were analyzed. The results indicated that elevated heat input induces periodic oscillations of the melt pool free surface, attributable to thermo-capillary instability under high thermal gradients. Powder particles do not instantaneously immerse but remain temporarily suspended on the surface due to dominant surface tension forces. High laser power or low scanning speed promotes the increase in single-track width, while powder feeding rate has only a marginal influence on width, underscoring that energy density-rather than powder flux-is the dominant factor controlling track geometry. Under high laser power or low scanning speed conditions, large columnar grains develop due to elevated thermal gradient and reduced cooling rates. Elevated microhardness of the single track is promoted by high laser power and high scanning speed. Lower powder feeding rates produce mixed grains with high hardness, whereas excessive feeding rate promotes equiaxed grains via powder shielding, yet exhibits negligible hardness variation. This work reveals the correlation between processing parameters, melt pool and single-track, and thereby providing critical insights into multi-physics phenomena that determine cladding layer and parts quality.