Advancing structure − property homogeneity in forged Alloy 718 engine disks: A pathway towards enhanced performance

Abstract

Alloy 718 is widely used in critical temperature components of modern aircraft engines and gas turbines. However, its industrial-scale forging faces challenges around heterogeneous microstructures and properties in the final product. This has been attributed to inherent heterogeneous microstructures of the billet starting materials and/or the heterogeneous nature of deformation during hot forging itself, leading to heterogeneities and inferior mechanical performance during service.To overcome these challenges, a three-step TMP approach, denoted simply as TMP3, is introduced to unlock effective microstructure and homogeneity control, irrespective of the given billet microstructure. Using electron and atom probe microscopy, the through-process microstructure evolution is revealed, highlighting dependencies of homogeneity and superior properties on various dynamic recrystallization mechanisms and the δ-phase dissolution. The process affects the dislocation density, δ-phase characteristics, and solute distribution in the matrix γ-phase. This facilitates Nb redistribution, resulting in fractions and morphologies of γʹ and γ“ Co-precipitates during subsequent direct ageing. The final samples have a hardness of ∼ 500 HV, a ∼ 5 % improvement over previous methods, providing a reliable proxy for high-temperature yield strength, independent of the billet position. Our TMP3 approach can be scaled-up and will enable manufacturing of high-performance Alloy 718 parts ready for next generation aircraft engines.

Keywords

• Nickel-based superalloy
• Thermomechanical processing
• Dynamic recrystallisation
• Precipitation
• Strengthening