Investigation of the effects of process parameters and secondary thermal treatments on the microstructure and mechanical properties in electron beam melting additive manufacturing of Ti6Al4V alloy

In the first part of this thesis, the effects of parameters such as maximum beam current, speed function, focus offset, minimum beam current, reference current, and reference scan length on factors such as porosity formation, part density, microstructure, hardness, and dimensional accuracy were investigated in the additive manufacturing of Ti6Al4V alloys using the electron beam melting (EBM) method. The findings indicate that incorrect selection of these parameters affects energy input, leading to increased porosity, dimensional inconsistency, and a loss of hardness. In the second part, the effects of secondary thermal processes, such as solution treatment, aging heat treatments, and hot isostatic pressing (HIP), on the microstructure and mechanical properties of parts produced with standard parameters were examined. The results showed that HIP significantly reduced internal porosity (by 58%), while heat treatments had no significant effect on density. It was observed that solution treatment alone caused a reduction in strength by up to 13%, but this decrease was compensated by subsequent aging. HIP applied at low temperatures and high pressures was found to increase material ductility by up to 104% without loss of strength, while increasing HIP temperature resulted in a significant decrease in strength (12%). The effects of the secondary thermal treatments on mechanical properties were attributed to changes in the microstructure.