Ultrafine grained metastable Ti6Al4V5Cu alloy with high strength and excellent low-cycle fatigue property

Abstract

The insufficient low-cycle fatigue properties of titanium alloys under cyclic heavy loading are regarded as a challenge for their security in service. In recent years, a large number of studies have found that the transformation induced plasticity (TRIP) effect could hinder the propagation of fatigue cracks, which significantly improved the low-cycle fatigue properties of titanium alloys. However, the coarse β-phase grains and the soft phase transformation product α″ phase in TRIP titanium alloys impair their tensile strength, which restrict their applications in engineering. To this end, a Ti6Al4V5Cu alloy with TRIP effect was developed in this work. It was proposed to use the mutual restraint between the α and β phases in the material to refine the grains, and through composition optimization, the phase transformation product would be the α' phase, which has a higher strength than the α″ phase. Thus, the strength of the Ti6Al4V5Cu alloy can be improved. The results showed that the tensile strength and elongation of the TRIP Ti6Al4V5Cu alloy was 1286 MPa and 22%, which was 23.7% and 46.7% higher than that of the traditional Ti6Al4V alloy, respectively. Besides, under the same strain amplitude, the fatigue life of the Ti6Al4V5Cu alloy was 2–5 times longer than that of the Ti6Al4V alloy. Furthermore, we clarified the mechanisms of improving the tensile strength and fatigue properties of the Ti6Al4V5Cu alloy, which would lay a research foundation for the development of high-performance titanium alloys.