Testing and Prediction of Thermal-Mechanical Fatigue Crack Growth Rates in Ni₃Al Superalloy

In this paper,the experimental study and the analysis about the behavior of thermal mechanical fatigue (TMF) crack growth were conducted in Ni 3Al superalloy,with thermal cycle of 450℃ to 990℃.The effects of phase angle,load hold,temperature and frequency on thermal mechanical fatigue crack growth rate in Ni 3Al superalloy,respectively,were studied.A predictable model about thermal mechanical crack growth rate in Ni 3Al superalloy is proposed.The key results drawn from this study are as follows:Increasing temperature and decreasing frequency accelerate crack growth rate;The crack growth rate of in phase thermal mechanical fatigue is much larger than that of out phase thermal mechanical fatigue and both of them are between the crack growth rates of 450℃ isothermal and 990℃ isothermal tests;Load hold also accelerates crack growth.A linear summation model is proposed about thermal mechanical fatigue crack rate in Ni₃Al superalloy based on these experimental results.This model is composed of cycle dependent component and time dependent component.And two proof tests were conducted to verify this model.The results predicted by this linear summation model agree well with experimental data.