TiAl合金高周弯曲疲劳研究  

HIGH-CYCLE FATIGUE OF A TiAl ALLOY IN THREE POINT BENDING TEST

作　　者：薛红前[1,2] 陶华[1] C．Bathias 

机构地区：[1]西北工业大学机电学院,西安710072 [2]Department of Mechanical Engineering,CNAM/ITMA,2 rue Conte,Paris 75003,France

出　　处：《机械强度》2008年第1期112-116,共5页Journal of Mechanical Strength

基　　金：国家自然科学基金(50775182);西北工业大学留学人员科研启动基金资助项目~~

摘　　要：应用压电超声疲劳试验技术，开发20kHz频率下的三点弯曲疲劳试验系统，完成室温下TiAl合金超高周弯曲疲劳试验。结果表明，在疲劳循环大于10^7周时，试样仍会发生疲劳断裂。S-N曲线显示，当应力比R=0．7时，在10^7周后会出现疲劳极限，表面粗糙度对疲劳性能没有明显影响。当R=0．1及R=0．5时，在10^5～10^10周之间疲劳强度随循环次数的增加连续下降，S-N曲线未出现水平。光学显微观察发现，TiAl合金由α2-Ti3Al和γ-TiAl组成（γ＋α2钛铝合金），具有全片层状显微结构。疲劳破坏主要起源于试件表面承受应力最大处，层状晶体内层间裂纹萌生是TiAl合金主要的裂纹萌生方式，疲劳裂纹主要以穿晶方式扩展。在超高周循环条件下，疲劳裂纹也会从试样近表层处的铸造缩孔萌生。Experimental investigation of the ultra-high cycles fatigue llfe and associated fracture behavior of the TiAl alloy subjected to bending fatigue deformation has been conducted. Tests have been performed at stress ratio R = 0.1, R = 0.5 and R = 0.7 and ambient temperature in air. The three-point bending ultrasonic fatigue technique at a frequency of 20 kHz was developed to study the very high.cycle fatigue properties of TiAl alloy. The S-N curves obtained shows that between 10^5 and 10^10 cycles, there are specimens cracked. The asymptote of S--N curve is inclined gently, but not horizontal for R = 0.1 and R = 0.5, fatigue limit appears after 10^7 cycles for R = 0.7, surface roughness has no influence on the fatigue properties. TiAl alloy studied here shows two phases in micrastmcture composed of α2-Ti3Al and γ-TiAl with near lamellar microstructure. The fractographic study showed that fatigue failures are mostly initiated at the surface of the test specimens. Interlamellar fatigue crack initiation is predominant in the Ti-Al alloy with near lamellar structure, fatigue crack growth is mainly in transgranular mode. In the very high cycle regime subsurface fatigue crack initiation can been found.

关 键 词：弯曲疲劳 超高周疲劳 S-N曲线 TIAL合金 20kHz 应力比 

分 类 号：O346.2[理学—固体力学] O346.4[理学—力学]