Oxygen-induced intergranular cracking of a Ni-base alloy at elevated temperatures—an example of dynamic embrittlement Original Research Article

The brittle intergranular cracking of Alloy 718 at temperatures between 550 and 650°C and at oxygen pressures from atmospheric to 10−5 torr has been studied by the use of single-edge-notched specimens loaded in pure bending at fixed displacement. The cracking rate was calculated from the load relaxation and a compliance–calibration curve. Rates in the range 10−9 to 10−5 m/s were observed, depending on temperature and oxygen pressure. The phenomenon appears similar to the oxygen effects observed by others in cyclic loading and also to the dynamic embrittlement observed in other materials and environments. The mechanism recently modeled for dynamic embrittlement can be applied here directly, and the special characteristics of polycrystalline (as opposed to bicrystalline) behavior, as well as the effects of varying the oxygen pressure, can be explained.