High Cycle Fatigue (HCF) Performance of Ti-6Al-4V Alloy Processed by Selective Laser Melting

TLDR

Selective laser melting (SLM) is a novel additive manufacturing process that can produce complex Ti‑6Al‑4V parts with quasi‑static properties comparable to wrought materials, yet its use in dynamic applications is limited by insufficient fatigue data, especially in aerospace and medical fields. The study investigates the high‑cycle fatigue performance of SLM‑produced Ti‑6Al‑4V parts by testing as‑built, polished, and shot‑peened samples. The authors conducted HCF tests on as‑built, polished, and shot‑peened Ti‑6Al‑4V specimens to assess SLM suitability. As‑built samples exhibited a markedly reduced fatigue limit because of rough surface quality, polishing raised the limit above 500 MPa—the typical value for wrought Ti‑6Al‑4V—and shot‑peening unexpectedly worsened performance, with fractography revealing that residual porosity below 0.4 % critically influenced fatigue behavior.

Abstract

Selective laser melting (SLM) is a relatively new additive manufacturing (AM) technology which uses laser energy for manufacturing in a layered pattern. The unique manufacturing process of SLM offers a competitive advantage in case of very complex and highly customized parts having quasi-static mechanical properties comparable to those of wrought materials. However, it is not currently being harnessed in dynamic applications due to the lack of reliable fatigue data. The manufacturing process shows competitive advantages particularly in the aerospace and medical industry in which Ti-6Al-4V is commonly used, especially for high performance and dynamic applications. Therefore, in this exploratory research, high cycle fatigue (HCF) tests were performed for as-built, polished and shot-peened samples to investigate the capability of SLM for these applications. As-built samples showed a drastic decrement of fatigue limit due to poor surface quality (R a ≈ 13 µm) obtained from the SLM process. Polishing improved the fatigue limit to more than 500 MPa, the typical value for base material. The effect of shot-peening proved to be antithetical to the expected results. In this context, fractographic analysis showed that very small remnant porosity (less than 0.4%) played a critical role in fatigue performance.