Effect of composition and microstructure on the fatigue and creep-fatigue behaviour of Allvac 718Plus alloy

ATI Allvac has recently developed Allvac\uae 718Plus\u2122 (718Plus), a new class of nickel-base superalloy to be used in high temperature turbine engine applications. This new alloy has an in-service temperature capability that is 55\ub0C (100\ub0F) higher than Inconel 718 and has better processing characteristics, thermal stability, and lower raw material cost compared with other superalloys such as Waspaloy. The fatigue and creep-fatigue behaviour of three different microstructural conditions of 718Plus were investigated; the standard fine grain (ASTM 8 \ub11) microstructure produced by the standard heat treatment, the standard fine grain microstructure after long term thermal exposure (732\ub0C for 1000 h), and a fine grain microstructure with modified \u3b4-phase particles. All three conditions of 718Plus showed a significantly improved threshold for fatigue crack propagation over the widely used disc material, Waspaloy. This is an important material property for damage tolerant engine design as it indicates that 718Plus has a potentially higher application stress range for which cracks or defects are effectively non-propagating. Waspaloy showed better creep-fatigue crack growth resistance than the 718Plus materials but prolonged thermal exposure does improve this property considerably, making it comparable to Waspaloy.Peer reviewed: YesNRC publication: Ye