Preliminary investigation on tensile and fatigue properties of Ti6Al4V manufactured by selected laser melting

Abstract

Selective laser melting (SLM) is a promising additive manufacturing method that falls under the category of powder bed fusion (PBF) technology. It has many advantages such as material versatility, efficiency, and the ability to print complex parts without additional machining. However, its surface quality and fatigue properties have been found to be inferior to traditional manufacturing methods. Process-related defects such as pores, incomplete fusion, and un-melted powders give rise to areas of stress concentrations, which lead to mechanical inferiority such as poor fatigue strength. This study aims to investigate and optimize the printing process parameters for Ti6Al4V fabricated by SLM to reduce process-related defects and to investigate their relative density, tensile, and fatigue properties. Ti6Al4V specimens were printed in both 30- and 130-μm layer thicknesses using SLM280 and subjected to tensile and fatigue testing according to ASTM standards. The relative density of Ti6Al4V samples built by 30-µm layer thickness is 99.97 ± 0.02 % (n = 8). The relative density of Ti6Al4V samples built by 130-µm layer thickness is 99.96 ± 0.02 % (n = 8). The average ultimate tensile strength (UTS) of specimens with 30-μm layer thickness is 1152.8 ± 23.8 MPa (n = 4). The average UTS of specimens with 130-μm layer thickness is 1075.5 ± 46.8 MPa (n = 4). S/N curve of the fatigue performance of Ti6Al4V samples printed by 30-μm layer thickness was also obtained. Possible factors impacting the tensile property of SLM-produced parts, such as layer thickness, build orientation, and post-process, are discussed in this paper. Furthermore, crack propagation and surface quality were observed using optical microscopes, laser scanning microscopes, and scanning electron microscopes. The findings of this study will contribute to the improvement of SLM-printed Ti6Al4V parts, which can be potentially applied in the aerospace industry, where fatigue strength is critical to ensuring safety.