Microstructure and residual stress in Ti-6l-4V parts made by different additive manufacturing techniques

Additive manufacturing (AM) or additive layer manufacturing, direct digital manufacturing and 3D printing, is rapidly growing as an advanced manufacturing technology. Powder bed fusion (PBF) and directed energy deposition (DPD) are two main groups of AM techniques available at present. The material’s mechanical properties, residual stress level and surface quality are the major limitations preventing the uptake of the technology to produce components for demanding engineering applications. The objective of this study is to obtain more in-depth knowledge of microstructure and residual stress developments in Ti-6Al-4V cylindrical parts made by different AM techniques, and compare the results with parts made through traditional manufacturing practices. For this purpose, direct comparisons are made between the materials made by AM techniques and those made by a forging process route. Five different components of the same material made through different manufacturing routes, including traditional forging and AM methods: electron beam melting (EBM), direct metal laser sintering (DMLS), and laser metal deposition (LMD), were analysed. These include microstructure characterisation and residual stress measurements by x-ray diffraction (XRD) and a hole-drilling technique based on electronic speckle pattern interferometry (ESPI). The material produced by AM techniques was compared with the mill-annealed condition of conventionally forged material.