MICROSTRUCTURAL EVALUATION AND HEAT-TREATMENTS OF ADDITIVE MANUFACTURED TITANIUM ALLOYS

The additive manufactured (AM) titanium alloys that are produced by powder bed fusion process show different microstructures and mechanical properties compared to the conventional wrought alloys. During the AM process about three fine powder metal layers are fusing together and undergo solidification stage. In addition, each layer is exposed to cyclic heating and cooling in different rates. The results are anisotropic grains with fully unusually martensitic structure. The objective of this research is to study the microstructural evaluation of Ti-6Al-4V during the AM process by simulation of the cyclic thermal paths and by comparison with wrought titanium alloys . Series of cyclic heat-treatments with various damped waves of thermal paths were performed on wrought Ti-6Al-4V in order to investigate the evaluated structure in the AM process. The microstructure, chemical composition and mechanical properties of the specimens were determined using optical microscopy, scanning electron microscopy (LV-SEM), energy dispersive X-ray spectroscopy (EDS) and hardness tests. The results were compared with the AM specimens prepared by powder bed fusion with electron-beam energy source. The study led to develop a thermal model, based on phase diagrams, of the microstructural evaluation during the AM process.