Effect of Long Time Stress Dwell on Cold Dwell Fatigue Behavior of Ti-6Al-4V

Abstract

Ti alloys are widely applied to jet engine components. Low cycle fatigue (LCF) strength of Ti alloys decreases with tensile stress dwell at room temperature (Cold Dwell Fatigue, CDF). CDF strength was influenced by stress level, microstructure, and dwell time. In order to study the effect of long time dwell for CDF properties, LCF test (0s dwell), CDF tests (120s~7200s dwell), and creep test were carried out. With increase of dwell time, fracture cycle decreased and fracture elongation increased. Fracture surface of long time dwell CDF tests corresponded to that of creep test. Additionally, strain accumulations during stress dwell at long time dwell CDF tests were similar to strain change of creep test. From SEM/EBSD analysis, inelastic strain was obviously increased after CDF tests and creep test, compared to LCF test. Hence, it was considered that long time dwell CDF was greatly influenced by creep deformation.