A 3D finite element analysis of thermally induced residual stress distribution in stainless steel coatings on a mild steel by laser hot wire cladding

Large residual stresses in a laser-cladded surface coating over a metal part are detrimental to its mechanical integrity and fatigue life. In this study, a three-dimensional uncoupled thermo-mechanical finite element model was developed to predict (a) the evolution of the temperature field in a direct diode laser hot-wire multi-track cladding process and (b) associated thermally induced residual stress distribution in laser-cladded 316L stainless steel coatings on the A36 mild steel substrate. The thermal analysis of the finite element model of the laser cladding process was first validated by the time-resolved temperature measurements using thermocouples placed on the mild steel surface near the clad layer. The stress analysis of the finite element model during the cooling stage was then validated by the spatially-resolved X-ray diffraction measurements of residual stresses in the clad layer. The experimentally validated finite element model was then applied to investigate the effect of laser power, material properties (Young's modulus, yield strength, and coefficient of thermal expansion), and the number of clad tracks on the residual stresses in the clad layer. It was found from the numerical simulations that the magnitude of residual stress components increases with increasing Young's modulus, yield strength, and coefficient of thermal expansion of the clad material. A higher temperature gradient located in the molten pool induced a higher concentration of thermal stresses and eventually a higher residual stress level in the clad samples. Higher tensile residual stress was generated with an increasing number of clad tracks although the residual stress in the existing clad tracks was relaxed somewhat during the subsequent cladding process of new tracks. Specifically, high tensile transverse residual stress formed in the overlapped region and on both sides of the clad layer, whereas higher longitudinal and von Mises equivalent residual stresses were developed in the last clad track. The finite element analysis results presented in this study may provide useful guidance for reducing the residual stresses in clad layers by optimizing the multi-track laser cladding processing parameters.