Surface micro-cracks and microstructures of Ti6Al4V alloy fabricated by high-layer thickness multi-laser directed energy deposition additive manufacturing process

Implementing a high-layer thickness additive manufacturing (AM) can significantly reduce the manufacturing time. With this, the cracking phenomenon and microstructure of the additively manufactured parts should be controlled. This paper investigates the surface micro-cracks and microstructures of Ti6Al4V alloy manufactured by high layer thickness laser-based directed energy position additive manufacturing process. No cracks were visibly present under the naked eye. Solidification cracking within a disposition boundary was present on some parts of the as-printed Ti6Al4V surface. Trans-deposition boundary cracks were visible under the optical microscope as liquation cracking. After polishing, the cracks were almost eliminated, with small isolated cracks on the polished surface. These cracks and concentrated C depositions confirmed with SEM-EDX can act as stress concentration points and crack initiation sites. SEM images showed α-lath structures with Widmanstätten pattern, and α+β Ti grains were observed. Post-processing methods such as removing the topmost crack surfaces, shot peening, laser shock peening and heat treatment can be adopted to reduce the cracks and enhance the performance of the as-deposited parts.