CRACK-GROWTH RATE BEHAVIOR OF A TITANIUM ALUMINIDE ALLOY DURING ISOTHERMAL AND NONISOTHERMAL CONDITIONS

Observations of isothermal fatigue, isothermal fatigue with superimpos ed load hold times, and thermomechanical fatigue (TMF) crack growth ra te behavior of Ti-24Al-11Nb are presented and compared with results fr om previous studies on titanium and nickel-base superalloys. Elevated- temperature crack growth mechanisms in this alloy, which involve fatig ue, oxidation and creep, and the influence of frequency, temperature, and hold-time are discussed. These mechanisms are used to interpret th e observations of TMF crack growth. The limitations of current crack g rowth rate models based on the linear-elastic fracture mechanics param eter, K, are addressed.