Studies of thermal distortion and residual stresses of an Inconel 718 part fabricated by the laser powder deposition process

Laser powder deposition is essentially a thermal process involving rapid phase changes and high temperature gradients. Thermal stresses generated during rapid cooling have critical impacts on the geometric accuracy and material properties of a laser deposited part. Thermal control is critical for obtaining consistent deposition conditions and in limiting thermal deformation and stress induced cracking during the deposition process. In this work, thin-walled Inconel 718 parts were fabricated by laser powder deposition with different laser energy inputs and cylindrical wall curvatures similar to the aeroengine compressor blade geometries. The asdeposited parts were scanned by a CMM laser probe in order to examine the distortions of these parts. Residual stresses on the thin-walled parts were measured by the X-ray diffraction method in a transmission mode. Measurement results show that no significant distortions in the laser deposited thin-walled samples were detected. For single row deposition, residual stresses increases with linear energy input. Curved walls are found to have reduced residual stresses than the flat walls. Tensile stresses are only found in the build up direction at the edges of the flat thin-walled parts.