Effect of stress ratio on long life fatigue behavior of Ti-Al alloy under flexural loading

来源期刊：中国有色金属学报(英文版)2008年第3期

论文作者：薛红前 陶华 邵忍平 B. CLAUDE

文章页码：499 - 505

Key words：bending fatigue; cycles fatigue; S—N curve; Ti-Al alloy; surface roughness

Abstract: A new ultrasonic three-point bending fatigue test device was introduced to investigate fatigue life ranging up to 1010 cycles and associated fracture behavior of Ti-Al alloy. Tests were performed at a frequency of 20 kHz with stress ratio R=0.5 and R=0.7 at ambient temperature in air. Three groups of specimens with different surface roughness were applied to investigate the effect of surface roughness on fatigue life. Furthermore, optical microscopy(OM) and scanning electron microscopy(SEM) were used for microstructure characteristic and fracture surface analysis. The S—N curves obtained show that fatigue failure occurs in the range of 105 -1010 cycles, and the asymptote of S—N curve inclines slightly in very high cycle regime, but is not horizontal for R=0.5. Fatigue limit appears after 108 cycles for R=0.7. Surface roughness (the maximum roughness is no more than 3 μm) has no influence on the fatigue properties in the high cycle regime. A detailed investigation on fatigue fracture surface shows that the Ti-Al alloy studied here is a binary alloy in the microstructure composed of α₂-Ti₃Al and γ-Ti-Al with fully lamellar microstructure. Fractography shows that fatigue failures are mostly initiated on the surface of specimens, also, in very high cycle regime, subsurface fatigue crack initiation can be found. Interlamellar fatigue crack initiation is predominant in the Ti-Al alloy with fully lamellar structure. Fatigue crack growth is mainly in transgranular mode.

基金信息：the National Natural Science Foundation of China
the Natural Science Foundation of Shaanxi Province, China