Microstructure Evolution, Properties, and Damage Mechanisms in Ti-6Al-4V Manufactured By Laser Engineered Net Shaping

Laser Engineered Net Shaping (LENS) is an Additive Manufacturing (AM) technique able to build 3D functional parts directly from computer models, using metal powders. Its computer aided design and near-net-shape capabilities offer superior geometrical flexibility, shorter manufacturing lead time, less material waste, and lower energy consumption than conventional manufacturing methods. These benefits make LENS a promising technique for aerospace applications. It has been proven that this process is able to fabricate fully dense, defect-free metallic components, and is especially compatible with Ti alloys. Applying it to structural aerospace applications, however, requires a fundamental understanding of the microstructure, static properties and dynamic performance of the LENS-fabricated materials. In this study, LENS Ti-6Al-4V alloys were made using two power levels, and were investigated in both as-fabricated and post-LENS heat treated conditions. First, the effects of processing parameters and heat treatment on microstructure and tensile properties were systematically studied. Next, room temperature fatigue crack growth tests at different stress ratios were performed in different orientations (with respected to the deposition direction), in order to establish the crack growth mechanisms at microstructural scale of the materials at different growth stages. The results will be presented and discussed from both the material/process optimization, as well as design and life prediction perspectives.