Thermal cycle characteristics and flow field evolution law of multi-layer laser cladding on 45 steel surface

Abstract In multi-pass and multi-layer laser cladding, significant thermal accumulation occurs in the clad layers. This thermal accumulation causes substantial fluctuations in the molten pool’s temperature field. It also induces significant variations in the flow field. Consequently, these changes affect the microstructure, formation quality, and mechanical properties of the clad layer. This study develops a finite element model that integrates heat transfer, fluid flow, and free surface dynamics to simulate the multi-layer deposition of IN718 alloy onto a 45 steel substrate. The model reveals the dynamic evolution of the temperature and flow fields under the influence of thermal accumulation during multi-layer deposition. Numerical results demonstrate that interlayer thermal accumulation exerts a more substantial influence than multi-pass overlapping. A continuous decrease in temperature gradient is observed throughout the entire process. After the first pass, the gradient measures 1.53 × 10 6 K m −1 . It then declines sharply during interlayer deposition. The gradient ultimately reaches 8.5 × 10 5 K m −1 by the end of cladding. This represents a total reduction of 44.4%. The molten pool flow velocity exhibits an initial increase from 0.42 m s −1 to 0.45 m s −1 , followed by a decrease and eventual stabilization at 0.37 m s −1 . With progressive deposition, insufficient edge support leads to increasingly severe gravity-driven pool inclination, particularly evident in the final pass of each layer. The average error between the temperature measurements and the simulation results is 4.42%. Furthermore, the simulated pool morphology aligns closely with experimental cross-sections, confirming the model’s reliability.