Effect of high layer thickness on surface quality and defect behavior of Ti-6Al-4V fabricated by selective laser melting

Abstract

High layer thickness has been used to improve the building efficiency in Selective Laser Melting (SLM), but its application is limited due to the poor component accuracy and performance. In order to eliminate the process instability and improve forming precision at high layer thicknesses, the effects of 100 μm and 200 μm layer thickness on surface quality, density, microstructure, defect behavior and tensile properties of Ti-6Al-4V fabricated by SLM were investigated in this work. It was found that high layer thickness seriously deteriorated surface roughness rather than density and tensile properties during SLM process. Specifically, all of the generated samples had relatively coarse surfaces (Sa > 45 µm), especially for the 200-µm layer thickness samples (Sa > 95 µm), which could be smoothed over (Sa = 13 µm) by the surface re-melting process. Moreover, when the layer thickness was 100 µm, the optimal ultimate tensile strength, yield strength and elongation were 1200 MPa, 1100 MPa and 10.2%, respectively; which were consistent with those at the thin layer thicknesses used in previous researches because of the similar density and microstructure. In comparison, samples fabricated at 200 µm layer thickness exhibited lower values of 1130 MPa, 1040 MPa and 7.57%, respectively; this was due to the existence of defects, such as pores, incomplete fusion defects and slag inclusions, and the formation of different microstructures, i.e., martensite and widmanstatten.