Tensile and Fatigue Properties of Ti-6Al-4V Alloy Fabricated by Laser Powder-Bed Fusion Process

Additive manufacturing (AM) of metals and high entropy alloys offers new possibilities for producing complex structures with properties comparable to conventionally manufactured parts. As an effective and flexible AM process, laser powder-bed fusion (L-PBF) can fabricate ultra-light-weight yet high-energy-density solid state parts vastly suitable for electro-mechanical, automotive, space, and aerospace applications. The widespread industrial applications of L-PBF process demand for an extensive investigation on the tailored properties of the high-strength alloys as the scanning strategy, powder metallurgy, remelting, and heat dissipation of the L-PBF process have significant effects on the microstructure, strength, hardness, precipitation behavior, and fatigue life of the alloy. While producing components by the L-PBF process, a comprehensive understanding of the material and mechanical behavior is required to optimize the process parameters effectively and predict the reliability of the finished parts under different thermal and loading conditions. Therefore, the purpose of this study is to investigate the thermal and mechanical properties of L-PBF processed specimens at room and elevated temperatures while varying the loading conditions. The study covers experimental analysis and finite element (FE) modeling of L-PBF processed Ti-6Al-4V specimens aiming the tensile and fatigue tests at room and high temperatures. The L-PBF processed specimen used for the study is a heat-treated and post-machined customized dog-bone structure. The tensile and fatigue tests of the specimens are conducted by mechanical testing equipment covering both low cycle fatigue (LCF) and high cycle fatigue (HCF) tests. The FE modeling for the fatigue analysis of the Ti-6Al-4V specimen is conducted for both fully-reversed and zero-based cyclic loads at different frequencies. The experimental and numerical results show that the fatigue life decreases as the load increases. It is also found that the fatigue life does not vary with the change of the test frequency under a specific fatigue load. The effects of build orientation, hot isostatic pressing, and surface roughness on the crack initiation and fatigue life of the Ti-6Al-4V parts are also studied with microstructure analysis. The performance of the L-PBF processed specimens is compared to conventionally manufactured Ti-6Al-4V parts to outline the fatigue resistance and microstructural properties. Results for tensile strength, elongation, thermal stress, and fatigue life of the Ti-6Al-4V build-part obtained at different temperatures under both LCF (up to 10⁴ cycles) and HCF (up to 10⁷ cycles) conditions provide a detailed understanding of the thermal, metallurgical, and mechanical properties of this alloy. The overall study also provides a guide to investigate fatigue properties of other functional materials used in the L-PBF process.