Study On Dwell Fatigue Behavior Of Ti60 Titanium Alloy

Titanium alloy has been widely used for fan disc,compressor disc,blade and other components in areo-engine,owing to low density,high specific strength,excellent corrosion resistance and thermal resistance.It is an important material to reduce weight and increase the thrust-to-weight ratio of aero-engine.Titanium alloy exists a failure mode during service as dwell fatigue,which can reduce the fatigue life significantly.This issue effects the safety of aero-engine.Therefore,dwell fatigue of titanium has become a hot topic of research.In this paper,Ti60 titanium alloy was tested with bimodal structure and lamellar structure.Microhardness,microstructure,fracture morphology,microtexture,tensile property,low cycle fatigue(LCF)property and low cycle dwell fatigue(LCDF)property of Ti60 titanium alloy were studied using microhardness tester,metallographic microscope(OM),field emission scanning electron microscope(SEM),electron backscatter diffraction(EBSD),tensile testing machine and hydraulic servo fatigue testing machine and other testing equipments respectively.First,the basic mechanical properties were measured by tensile test of two typical structures.The results show that the strength of bimodal structure is less than that of lamellar structure,but the plasticity of bimodal structure is greater than that of lamellar structure,and the strength and plasticity decreases and increases with increasing of the temperature.Secondly,the influence of factors such as microstructure,peak stress,temperature and holdong time on fatigue properties of Ti60 titanium alloy were investigated by fatigue test.The results show that the fatigue life tends to decrease and the plastic strain accumulation trends to increase with increasing of the peak stress and holding time.The plastic strain accumulation of LCDF is higher than that of LCF.The dwell fatigue sensitivity of the bimodal structure is greater than that of the lamellar structure at room temperature.However,the dwell fatigue sensitivity of the bimodal structure is less than that of the lamellar structure at 440?.The dwell fatigue sensitivity at 440? is lower than that of at room temperature significantly.Finally,the fatigue fractures were observed by SEM.It was observed to found that crack initiates on the surface of the sample of LCF,which was with a single crack source.And the cracks originate interior of the sample by multiple sources of LCDF at room temperature.All the fatigue cracks initiate from the surface of the sample by multiple sources at 440?.There were quasi-cleaved facets on the surface of the fatigue fracture.