METALLURGICAL ASPECTS OF ADDITIVE MANUFACTURED TITANIUM COMPONENTS VS. WELDED COMPONENTS

The additive manufactured (AM) titanium alloys, that are produced by powder bed fusion process, are actually made up of hundreds of microscopic welding process where about three fine powder metal layers are fusing together and undergo solidification stage. In addition, each layer is exposed to cyclic heating in the solid-state and cooling in different rates. Both in welding and AM process involve fusion zone, solidification and heat-effected zone as well as different cooling rates depending on the distance from the melting zone. Therefore, it was likely to find identical microstructures in both processes, including defects and resultant mechanical properties. However, the defects created during AM are different from those in the wrought welded alloys because the micro-scale of the powders/layers process. The objective of this research is to characterize the Ti-6Al-4V AM defects by fractographic analysis and by investigation of the metallurgical aspects compare with wrought titanium welded alloy. Thermal simulation were made by finite element method to define AM resulting micro-structure. The specimens were broken by tensile and fatigue tests and were characterized in the fractographic and metallographic forms, using scanning electron microscopy (LV-SEM). The results of some samples show differences in the discontinuous defect caused by a non-solidified surfaces or lack solidification between the layers. The imperfection can damage the ductility and fatigue required in aviation components. In addition, the poor surface roughness obtained by AM may accelerate the formation and the propagation of the fatigue or corrosion cracks. One of the fundamental problems arising from the above defects is how to solve the non-destructive testing when standard methods fall. It is important to look for effective NDT methods before the technology is applied to load-bearing structural materials.