Contribution of ultrasonic surface rolling process to the fatigue properties of TB8 alloy with body-centered cubic structure  

作　　者：Dan Liu Daoxin Liu Mario Guagliano Xingchen Xu Kaifa Fan Sara Bagherifard 

机构地区：[1]College of Civil Aviation,Northwestern Polytechnical University,Xi'an 710072,China [2]Department of Mechanical Engineering,Politecnico di Milano,Milan 20156,Italy

出　　处：《Journal of Materials Science & Technology》2021年第2期63-74,共12页材料科学技术（英文版）

基　　金：the support of National Natural Science Foundation of China(51771155);National Science and Technology Major Project(2017-VII-0012-0107);Equipment Pre-research Field Fund(61409220202)。

摘　　要：The effect of ultrasonic surface rolling process(USRP) as a severe plastic deformation technology was investigated on the evolution of microstructure, residual stress and surface morphology of TB8 alloys with body-centered cubic structure. Stress-controlled rotating-bending fatigue tests indicated increased fatigue strength in USRP samples prepared using different number of passes compared to the base material, which was attributed to the presence of gradient structure surface layers. Five subsequent USRP passes resulted in the highest fatigue strength, due to the optimal surface properties including higher extent of grain refinement, larger compressive residual stresses, "smoother" surface morphology and increased micro-hardness. However, the effect of USRP technology on improving fatigue strength of TB8 alloy was not significant in comparison with that of other titanium alloys(for example, Ti6 Al4 V), which was attributed to the notable surface residual stresses relaxation revealed from measurements on postfatigued USRP samples. Electron backscatter diffraction analysis confirmed that fatigue crack initiation occurred in the larger grains on the surface with high Schmid factor. Small cracks were found to propagate into the core material in a mixed transgranular and intergranular mode. Further analysis indicated that grain growth existed in post-fatigued USRP-treated TB8 samples and that the average geometrically necessary dislocations value reduced after fatigue loading.

关 键 词：Ultrasonic surface rolling process Gradient structure layers Fatigue crack Rotating-bending fatigue TB8 alloys 

分 类 号：TG146.23[一般工业技术—材料科学与工程]