Metallurgical Challenges in Producing Large Scale Airframe Components by Additive Manufacture

Wire arc-based additive manufacture (WAAM) is a high deposition rate process suitable for building large-scale aerospace components. However, the large heat source and relatively thick layer height leads to much lower cooling rates and can cause significantly greater microstructural heterogeneity and anisotropy, compared to in components produced by smaller-scale powder bed processes.

In particular, titanium materials deposited by high deposition rate AM can have very coarse primary grain structures and significant texture, and overlap of the thermal field from sequential passes leads to the formation of more severe heat affected zone banding. A fuller understanding of these issues is presented and the potential for using process modification to improve the deposited materials is discussed, based on in-depth analysis of the material response. The research presented includes detailed results, involving automated microstructure quantification over large sample areas and using in-situ experiments, on the effect of thermal banding and texture on the micromechanical behaviour of titanium, the limitations of process parameters in reducing the primary beta grain size and the benefits of combining AM with deformation to refine the grain structure.