Fabrication, characterization, and post-processing machinability aspects of additively manufactured titanium alloys: A review of industrial challenges and cleaner strategies

Additive manufacturing (AM) of titanium alloy is emerging in various aerospace, marine, automobile, and medical implants applications because of high strength-to-weight ratio, enhanced mechanical, biocompatibility, wear, and corrosion resistance properties. AM processes are meant for near-net-shape components with higher mechanical properties due to difference in microstructure and lacks ductility. Optimization of additively manufactured (Amed) process parameters (laser power, scan speed, and layer thickness etc) and post-processing techniques such as stress relief heat treatment and sustainable machining are essentially required to achieve required microstructure, mechanical properties, and surface quality to meet the strict industrial tolerances. Micro-textured tools used with MQL improved the machinability of AMed Ti-6Al-4V reducing chip-tool contact by 38%, feed force by 28.9%, and surface roughness by 10.4% respectively. Reduction of crater wear for cryogenic machining than dry is 58% for direct metal laser sintering and 80% for both heat-treated DMLS and wrought Ti6Al4V alloys. Substantial improvements in drilling performance of Ti-6Al-4V have been observed under hybrid hBN-GNP nanofluids i.e. reductions in energy consumption by 28.8% (wrought) and 24.36% (wire arc additive manufacturing [WAAM]), along with improvement of surface finish by 48.57% and 49.47% respectively. Machining wrought Ti-6Al-4V yields 39.52% higher CO 2 emission than WAAM alloy as revealed from sustainability assessment under nanofluids application. It is worthwhile to analyse machining performance of AMed Ti-6Al-4V under novel sustainable cooling and lubrication environments such as nanofluids as it enhances thermo-physical characteristics and beneficial for sustainable manufacturing. Therefore, this paper reviews the fabrication, characterization, and sustainable machinability aspects of novel additive manufactured Ti-6Al-4V followed by challenges, research gaps, and future scopes.