Residual stress characterisation of Laser Metal Deposition of Ti-4Al-6V powder over different length scales

Circularity in aerospace manufacturing is a growing priority. One way to reach this is to improve material utilization through weld repair of larger casted components such as blades or vanes. Laser Metal Deposition powder (LMDp) is an emerging technique for such repairs, yet its impact on residual stresses is not well known today. This study investigates residual stress evolutions along with the key process steps; as-built, heat treated, and finish machined for different substrate thicknesses.

The results demonstrate a significant impact from the LMDp process, which induces high tensile stresses in the LMDp layer and interface, along with low compressive stress in the substrate. The stress magnitudes increase with thickness of the samples due to higher heat input resulting in both phase transformation and deformation, i.e., pronounced bending of the samples especially observed for the thickest sample. Although heat treatment substantially reduces the stress magnitudes below ± 100 MPa, there is potential for further optimisation of the heat treatment process. Finish machining introduces compressive stresses but with a limited impact depth (0.1 mm.

Notably, the stresses induced in these samples occurs at both a macro and micro scales, necessitating the use of different measurement techniques. These findings suggests that the selection of verification methods for future applications should consider both requirements (e.g. non-destructive) and types of stresses induced (I-III, i.e., micro-macro).