The study on the high cycle fatigue performance and life prediction of Ti–6Al–4V alloy fabricated by laser engineered net shaping

Abstract

Three-dimensional characterization of internal defects in Ti–6Al–4V alloy fabricated by Laser Engineered Net Shaping (LENS) was conducted by utilizing synchrotron X-ray imaging technology. Subsequently, the statistical analysis of defect size, quantity, and morphology characteristics was performed. Additionally, high cycle fatigue tests were conducted to analyze the high cycle fatigue performance of LENS Ti–6Al–4V alloy and elucidate the causes of its anisotropic behavior. Furthermore, based on the multi-stage crack growth model, the high cycle fatigue life of LENS Ti–6Al–4V alloy was predicted. The results showed that the quantity and size of internal defects were small, with defects predominantly spherical pores and no lack of fusion defects detected. Longitudinal specimens exhibited significantly higher fatigue life at high stress levels compared to transverse specimens. The anisotropic behavior of high cycle fatigue performance of LENS Ti–6Al–4V alloy at high stress levels was mainly attributed to the anisotropic distribution of its microstructure, and defects had no impact on the fatigue performance of LENS Ti–6Al–4V alloy. As stress levels decreased, the fatigue life of both types of specimens approached each other, with fatigue strengths of 650 and 656 MPa at 2 × 10⁶ cycles for longitudinal and transverse specimens respectively, showing minimal difference. In addition, the predictions from the multi-stage crack growth model aligned well with experimental results, effectively predicting the high cycle fatigue life of LENS Ti–6Al–4V alloy.