Investigation of the effects of production parameters and post processes on residual stress, microstructure and mechanical properties of Ti6Al4V specimens produced by additive manufacturing

Selective laser melting; is a process whose importance is increasing day by day, capable of producing even parts with geometry that cannot be produced with other production methods, producing high-strength products quickly and close to a net shape. The process has some disadvantages as well as its advantages. Manufactured products generally result in lower ductility, higher porosity, higher residual stress and surface roughness values compared to wrought materials. Ti6Al4V alloy is a much-study alloy in academic and industrial applications in the production of parts by selective laser melting. In the first part of the study, a parameter study was carried out. At constant energy density, the effects of decreasing laser power and scanning velocity on the mechanical, microstructure, residual stress and relative density properties of the specimens were investigated by producing specimens in four different parameter sets. It was observed that decreasing laser power and scanning velocity at constant energy density did not have a linear effect on the decrease or increase in residual stress, tensile strength, percent elongation, and relative density values. In the second part of the study, specimens were produced in the parameter set which the best results were obtained in the first part; then machining, annealing, shot peening processes were applied on the specimens in different combinations and the effects of post-processes were investigated on the surface roughness, residual stress, fatigue, bending, microstructure and hardness properties of the specimens. As a result of the annealing, α+β transformation was observed in the microstructure. Traditional and multiple shot peening processes provided a significant increase in microhardness values of the specimens in the 0-250 µm depth range. Traditional and multiple shot peening ensured that the residual stress type was compression type in the depth range of 0-150 µm in the specimens. In terms of fatigue strength, the best results were obtained on the specimens that were machined after annealing.