Effect of heat-treatment and heat-to-heat variations in the fatigue-crack growth response of alloy 718

The fatigue-crack growth behavior of seven heats of Alloy 718 was studied at five different test temperatures. These seven heats represented at least four different producers, four were tested in two different heat-treated conditions. Heat-to-heat variations were noted; these were most obvious in material given the conventional heat-treatment. Electron fractographic examination revealed that operative crack growth mechanisms were dependent on heat treatment, heat-to-heat variations, test temperature and prevailing crack-tip stress-intensity level. (author)