| Résumé | Four microstructural variants of ATI 718Plus® Alloy (718Plus) are produced via modified heat treatments to elucidate the effects of grain size, precipitate size, morphology, and phase fraction (δ and γ′), on the mechanical properties of low cycle fatigue (LCF) life, fatigue crack growth rate (FCGR) properties, and Dwell FCGR behaviour at both 649ºC (1200ºF) and 704ºC (1300ºF) under 100s dwell and non dwell conditions. Similar tests are also performed on Waspaloy in two comparative microstructural conditions. FCGR results show that at both test temperatures, all microstructural conditions of 718Plus and Waspaloy exhibit identical behavior in the steady state regime, except that 718Plus exhibits a much higher threshold stress intensity (∆KTH). However, the Dwell FCGR results show that Waspaloy displays better steady state crack growth resistance under dwell conditions; with an optimized precipitate microstructure of 718Plus showing considerable improvement. LCF test results demonstrate that all four microstructural conditions of 718Plus have superior life compared to Waspaloy under all test conditions. |
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