Fatigue and corrosion-fatigue behavior of the β-metastable Ti-5Al-5Mo-5V-3Cr alloy processed by laser powder bed fusion

Abstract

We performed rotating bending tests and axial (tension-compression) load-increase and constant amplitude high-cycle fatigue tests in air and Hanks' balanced salt solution (HBSS) on the β-metastable titanium alloy Ti-5Al-5Mo-5V-3Cr, processed by laser powder bed fusion (LPBF-M), solution-treated and aged, and shot-peened. Rotating bending loading in air revealed a strong influence of process-induced flaws on fatigue endurance. Especially in the high-cycle fatigue range and the transition region, the stochastic distribution of the flaws and flaw sizes led to a high scatter of the number of cycles to failure. The axial load-increase tests yielded a good fatigue life estimation, with a negligible difference between air and HBSS. The cyclic deformation behavior in HBSS was also strongly influenced by the local microstructure and defect distribution, and, thus, by crack formation and propagation. Plastic deformation and microcrack growth interact, and their relative amount resulted in different progressions of the plastic strain amplitude over the number of cycles for different specimens. Changes in the free corrosion potential and the corrosion current were highly sensitive indicators for fatigue-induced damage on the rough surfaces, which was correlated to the microscopic examination, fracture surface features, and the fatigue crack development.