INFLUENCE OF MULTI-MICROSTRUCTURE INTERACTION ON FATIGUE CRACK GROWTH RATE OF GH4738 ALLOY

The effects of microstructure on the fatigue crack growth behavior of hard-to-deformed GH4738 superalloy have been studied by a number of researchers. However, most of these studies are confined to a single factor, such as the effect of grain size on the fatigue crack growth rate, and show the effect of single factor which do not reflect the combined impacts of multi-microstructure factors. Therefore, there is a need to develop a quantitative approach to predict the effects of multi-microstructure on fatigue crack growth behavior in the design of GH4738 alloy with high damage-tolerant microstructure. A new multi-microstructure factors interaction equation is proposed for the prediction of the effects of grain size, gamma' size and carbide size on fatigue crack growth rate of GH4738 alloy in this work. Different microstructures of GH4738 alloy are produced by different heat treatments (HT) for this equation. The fatigue crack growth experiments are carried out under constant stress ranges on compact tension (CT) specimens at 650 degrees C in air. Subsequently, the effects of grain size, gamma' size and grain boundary carbides size on the fatigue crack growth rate of GH4738 alloy are analyzed by using the interaction equation of multi microstructure factors. The results show that the equation can well predict the fatigue crack growth rate of GH4738 alloy under different microstructures. The growth rate of fatigue crack in GH4738 can be decreased with increasing grain size and reducing gamma' size and carbide size. The effect of grain size on fatigue crack growth rate is more noticeable than that of gamma' and carbide sizes.