Effects of laser energy density and path on residual stress of remanufactured key components for shield tunneling machine

Due to the abrasion and high cost of key components for shield tunneling machines, the failed or worn components are remanufactured by laser melting deposition (LMD) with paraxial powder feed. However, the residual stresses distributed in the cladding layer reduce the service life of remanufactured parts. In this paper, an experimental study is presented on residual stresses along the depth direction of cladding with varied laser energy density and deposition path. Residual stress in Fe-based coating and heat-affected zone (HAZ) is characterized by X-rays with the method of layer-removal. The microstructural evolution and the phase structure of laser deposited cladding layers are analyzed. The results indicate that the residual stresses, in the range of -624 to -86 MPa in the cladding layer, are mainly compressive while the tensile stresses (in the range of 200-550 MPa) are primarily in the heat-affected zone (HAZ). With the increase of the thickness of the cladding layer, the depth of the zero stress layer increases. The main phases in the cladding layer are alpha-Fe and gamma-Fe. The microstructure in the top layers of the cladding consists of fine, equiaxed grains while in the lower layers, the grains are distinctly cellular.