Dynamic solidification process during laser cladding of IN718: Multi-physics model, solute suppressed nucleation and microstructure evolution

The solidification microstructures directly determine the mechanical properties of the laser cladding. At present, the investigation of the dynamic evolution of the microstructures during the laser cladding process is still limited. In this study, a multi-physics model was established to analyze the complex microstructure evolution process during the laser cladding of IN718. The model consists of heat and mass transfer process, polycrystalline solidification process, heterogeneous nucleation process with solute suppressed nucleation. The accuracy of the model was verified by comparing the profile of the molten pool calculated by the heat and mass transfer model and the solidification microstructures of the molten pool calculated by the polycrystalline solidification model with the experimental results. The results show that thermal convection is the main heat transfer mode in the molten pool. The decrease of the line energy decreases the flow velocity pool and weakens the thermal convection in the molten pool. Columnar grains are composed of epitaxial growth grains and elongated grains nucleated between the primary branches. The columnar-to-equiaxed transition (CET) is affected by the size of "active nucleation zone (ANZ)", and the size of equiaxed grain is affected by the size of "inhibited nucleation zone (INZ)". The decrease of line energy leads to the decrease of the area of both the ANZ and INZ, which leads to the increase of the area of the columnar grain zone, but the decrease of the equiaxed grain size.