Research Viewpoint on Performance Enhancement for Very-High-Cycle Fatigue of Ti-6Al-4V Alloys via Laser-Based Powder Bed Fusion

Additive manufacturing (AM) or 3D printing is a promising industrial technology that enables rapid prototyping of complex configurations. Powder Bed Fusion (PBF) is one of the most popular AM techniques for metallic materials. Until today, only a few metals and alloys are available for AM, e.g., titanium alloys, the most common of which is Ti-6Al-4V. After optimization of PBF parameters, with or without post processing such as heat treatment or hot isostatic pressing, the printed titanium alloy can easily reach tensile strengths of over 1100 MPa due to the quick cooling of the AM process. However, attributed to the unique features of metallurgical defects and microstructure introduced by this AM process, their fatigue strength has been low, often less than 30% of the tensile strength, especially in very-high-cycle regimes, i.e., failure life beyond 107 cycles. Here, based on our group’s research on the very-high-cycle fatigue (VHCF) of additively manufactured (AMed) Ti-6Al-4V alloys, we have refined the basic quantities of porosity, metallurgical defects, and the AMed microstructure, summarized the main factors limiting their VHCF strengths, and suggested possible ways to improve VHCF performance.