Influence of Different Surface- and Heat Treatments; Elevated Temperature, Orientation on the Fatigue Properties of Ti6Al4V Processed by L-PBF for Controlled Powder Properties

Abstract

While static mechanical properties of Laser Powder Bed Fusion (L-PBF) processed titanium alloy Ti6Al4V Grade 5 are sufficient and comparable to classic production processes (DebRoy et al. in Prog Mater Sci 92:112–224 [1]; Vrancken et al. in J Alloys Compd 541:177–185 [2]) the fatigue properties of L-PBF lack behind (Leuders et al. in Int J Fatigue 48:300–307 [3]; Nicoletto in Int J Fatigue [4]). However, the reason for this issue are not completely clear and uniquely assignable as combination of (sub surface) porosity, microstructure and surface roughness. This work aims to investigate the influence of several factors on the fatigue properties of controlled, single powder patch of Ti6Al4V. The use of a single patch eliminates the influences of mechanical and chemical powder properties. The investigated factors comprise mechanical and electrochemical polishing (EP) surface treatment, heat treatment (stress relief SR, furnace annealing FA, hot isostatic pressing HIP), print orientation (vertical and horizontal) and load cases (R = −1, R = 0.1). Additionally, a set of tests is performed at 80 °C. For both load cases HIP and machining show a positive impact with a higher influence of machining. For load case R = 0.1 HCF (σ_aD, 50%) for HIP and machined is around 400 MPa while the same surface treatment but FA reach 218 MPa and SR/EP samples at just 111 MPa. Elevated environmental temperature and horizontal orientation have a minor positive impact. For R = −1 the overall gap narrows to 300 for HIP/machined and 175 MPa for SR/EP respectively.