Effect of microstructure on high-cycle fatigue properties of Ti-6Al-4V alloy forging at cryogenic temperatures

Abstract

The effect of microstructure on the high-cycle fatigue properties of Ti-6Al-4V alloy forging at cryogenic temperature was investigated using four materials with different microstructure. One of them was α+β annealed and has bimodal microstructure which consists of equiaxed-α and α+β lamellar microstructure. Three other materials were water quenched (WQ), air cooled (AC) or furnace cooled (FC) after β-annealing. The β-annealed materials have lamellar microstructure and α lamellar width increase in the order of WQ, AC and FC materials. The fatigue test was done with uni-axial load-controlled and a stress ratio of R = σmin/σmax = 0.01 at 20 K (in gaseous helium), 77 K (in liquid nitrogen) and 293 K (in laboratory air). The 107-cycles fatigue strengths at 20 K decrease in the order of WQ, AC, FC and the α+β annealed material. Namely, the β-annealed Ti-6Al-4V alloys, which has lamellar α microstructures shows higher fatigue strengths than bimodal microstructure.