ENVIRONMENTAL EFFECTS ON HIGH TEMPERATURE CRACK GROWTH.

A brief review of the effect of environment on the high temperature crack growth behavior of several alloys under creep, fatigue and combined creep-fatigue conditions is presented. Environment can affect crack growth rates significantly depending on material and its microstructure, temperature, frequency or hold time, and load. In addition depending upon the load the environmental effect and creep effect can either augment one another thus accelerating crack growth or oppose each other thereby retarding the growth and sometimes even contributing to crack arrest. Furthermore, change in microstructure can change drastically the degree of environmental contribution to crack growth. The extent that these effects vary for different alloys is discussed in detail.