Residual Stress in Stellite 6 Layers Deposited on Austenitic Stainless Steel Substrate using GMAW-WAAM

Abstract

This thesis describes an investigation of the deposition of Stellite 6 on SS316L stainless steel substrates using a Gas Metal Arc Welding (GMAW) based Wire Arc Additive Manufacturing (WAAM) system. The primary aim of this research was to optimize the deposition process with a focus on reducing heat input and understanding the development of residual stress, a critical factor in the performance of hardfacing materials. The project utilized a zigzag toolpath deposition strategy requested by adaptation from current manual operation, aiming to achieve low heat input while maintaining layer integrity.
The experimental methods involved finite element analysis (FEA) to simulate the deformation of the sample for a better understanding of the material thermo-mechanical responses to the zigzag deposition strategy used. The deformation simulation agrees with the measured deflection. The model, however, computed very large residual stresses. To have a better evaluation of the residual stress resulted from the deposition process, Incremental Central Hole Drilling (ICHD) method was used for residual stress analysis. Residual stresses were introduced in the samples by depositing one or two layers, with different clamping configurations. The measured residual stresses together with the observations noted during the experiments were analysed, compared, and discussed. The results show that double layer deposition can reduce residual stress gradients and provide a more stable stress profile along the thickness of the deposited layer. Furthermore, although single-sided clamping allowed for a higher freedom of thermal expansion and contraction during the deposition process, which leads to a more balanced stress distribution, it also increases deformation. Therefore, the use of uniform clamping during deposition of Stellite 6 should be implemented for actual application case. Additionally, depending on the desired thickness of Stellite 6, a multi-layer deposition strategy can be implemented to minimize residual stress build up.
The research concluded that defect-free Stellite 6 layers can be successfully deposited using the GMAW-based WAAM process. The residual stress measurement showed that preheating and reducing the thermal gradient can effectively reduce the residual stress within the deposited material. The obtained results can be helpful for the further development of automated toolpath generation and the integration of 3D vision control systems for more efficient and reliable WAAM processes.