A Numerical Investigation into Residual Stress Characteristics in Laser Deposited Multiple Layer Waspaloy Parts

Abstract

This paper reports an investigation into the residual stress generated with the laser direct metal deposition (LDMD) process and particularly that which arises from the deposition of a multiple-layer wall of Waspaloy on an Inconel 718 substrate. These Ni-based superalloys possess excellent strength and creep resistance at relatively high temperatures. These are attributes contributing to their extensive utilization in various applications in modern industry and particularly in the aerospace sector. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stress generated in the combined use of these materials in an LDMD process affect interfacial bonding and structural integrity during the process, and it can also cause unpredicted in-service failures. Prediction of its distribution in the deposited structure is vital toward enhancing process optimization that could lead to its control. Using the ANSYS finite element package, this study investigated the residual stress characteristics in a 6 mm wide and 14 mm high Waspaloy wall that was built from the deposition of 20 layers each consisting of 6 parallel tracks. The predicted results were validated by published experimental data and showed very good agreement. The results indicated that irrespective of the position in the height of the wall, the stress along the length of the wall oscillates about a stress-free state. Along the height of the wall, the stress was found to vary with position. The wall is near stress-free close to the substrate, while, at positions close to the free surface, the stress was uniaxially tensile. The largely tensile stress in the beam scanning direction in the deposited wall increases with number of layers while the stress in the build-up direction in the wall is close to zero.