Prediction and validation of residual stresses generated during laser metal deposition of γ titanium aluminide thin wall structures

The focus of the current work is to predict and validate residual stresses developed during Laser Metal Deposition (LMD) of Gamma Titanium Aluminide (gamma-TiAl) alloy by using a combination of numerical modeling and experimental methods. Laser Engineered Net Shaping (LENS), which is one of the commercially available LMD techniques, was used to fabricate gamma-TiAl alloy thin wall structures at various processing conditions. These deposits are expected to develop residual stresses due to the rapid heating and cooling cycles involved in the LMD process. 3D transient thermomechanical finite element analysis was used to simulate the LMD process. Thermal gradients and residual stresses were predicted from the thermomechanical models. It was found that the magnitude of thermal gradients increases with the addition of each deposited layer. Tensile residual stresses were observed at the edges of the thin-wall, while compressive residual stresses were observed at the center of the wall as well as in regions away from the edges. Residual stresses in the deposited samples were also measured using the x-ray diffraction technique. Reasonable agreement was observed between the predicted and measured values of residual stresses.