Numerical simulation research on multifield coupling evolution mechanism of IN625 laser cladding on nodular cast iron

Nodular cast iron has the strength and toughness which are close to steel and is widely used in industrial fields. The repair and modification of nodular cast iron based on laser cladding can effectively improve the service life, corrosion resistance, and wear resistance of parts. However, nodular cast iron cladding is prone to cracks and hole defects, severely limiting the promotion and application of this technology. The evolution mechanism of multi-field coupling in the spheroidal graphite cast iron laser cladding is the key to quantitatively reveal the improvement of cladding quality. In this paper, moving Gaussian heat source, the influence of temperature change on material physical parameters, the Marangoni effect of molten pool surface tension, and buoyancy on the molten metal flow were considered. A multifield coupling three-dimensional numerical model of IN625 powder laser cladding on nodular cast iron by disk lasers was established. The calculation reveals the transient evolution law of the cladding temperature field, flow field, and plastic stress field. The microstructure morphologies of the cladding layer were observed by Zeiss sigma HD field emission SEM to verify the effectiveness of the model. The results show that the substrate heat input and heat loss reached equilibrium at 0.8s, and the highest temperature reached 1979.7K. There was apparent Marangoni flow in the molten pool, resulting in a small flow velocity in the center and large edges, and the maximum flow velocity was 0.203m/s. When the molten pool was air-cooled to ambient temperature in 1000s, the maximum residual stress was 429MPa. The micromorphology from the bottom to the top of the molten pool is planar crystals, cell crystals, columnar crystals, and equiaxed crystals, which are consistent with the numerical calculation results.