Abstract
The high-temperature crack-growth behaviour of Nimonic PE16 has been studied at 650°C under cyclic, static, and combined loads, and the results are compared with those of Alloy 718. Crack-growth rates in vacuum under continuous cycling are the same in both alloys, but the rates differ significantly in air. A 1min hold has no effect on the growth rate offatiguecracks in Nimonic PE16, but has a large effect in Alloy 718 in air. This difference is due to the difference in their time-dependent crack-growth behaviour. In Alloy 718, time-dependent crack growth occurs readily at low stress intensities. However, in Nimonic PE16, high stress intensities are required to induce crack growth. Furthermore, the crack-growth rates in the two alloys differ by nearly three orders ofmagnitude. The higher growth rate in Alloy 718 is due largely to environmental effects. Time-dependent crack growth in Nimonic PE16, however, is mostly due to creep, and environment has a negligible effect on the growth. The results indicate that Nimonic PE16 has better resistance to time-dependent crack growth than Alloy 718. Therefore Nimonic PE16 would be expected to perform better than Alloy 718 at high temperatures under cyclic load, particularly at low frequencies, or with hold times as well as under static load.
Get full access to this article
View all access options for this article.