一种TiAl合金高温低循环疲劳性能及失效机理

通过对TiAl合金进行总应变范围控制的高温(750℃)低循环疲劳实验,研究双态(Duplex,DP)和全片层(Fully Lamellar,FL)组织形态对TiAl合金低循环疲劳性能和寿命的影响,并采用总应变幅-寿命方程对两类组态TiAl合金低循环疲劳寿命进行预测。结果表明:在相同温度和应变条件下,DP组态TiAl合金稳态迟滞回线对应的平均应力明显低于FL组态TiAl合金稳态迟滞回线对应的平均应力;采用总应变幅-疲劳寿命方程能够准确预测两种组态TiAl合金在750℃下的疲劳寿命,预测寿命基本位于试验寿命的±2倍分散带以内;另外,DP组态TiAl合金的疲劳源区位于试样的近心部,而FL组态TiAl合金的疲劳源区位于试样的次表面,两类组态TiAl合金的高温疲劳失效机理存在明显差异。

High Temperature Low Cycle Fatigue Properties and Failure Mechanism of a TiAl Alloy

Total strain range controlled low cycle fatigue (LCF)experiments were conducted at 750 ℃ to investigate the effects of the duplex and fully lamellar microstructure on fatigue behavior and life of a TiAl alloy,and the total strain range-life equation was em-ployed to predict LCF life of the alloy.The results show that the mean stress produced at hysteresis loop of TiAl alloy with DP is less that of TiAl alloy with FL at the same temperature and applied strain.The total strain range-life equation is able to predict the fatigue life of the alloy,and the predicted life is located between ±2 scatter band of the experimental life.In addition,the fatigue source of TiAl alloy with DP is located near center of the specimen while that of TiAl alloy with FL is located on subsurface of the specimen,and the failure mechanisms are obviously different between the two types of the TiAl alloy.