Evolution of nanoscale precipitates during common Alloy 718 ageing treatments

Improving mechanical properties of the Ni-based superalloy Alloy 718, commonly used in turbine discs, is of vital importance to commercial aviation. The need for higher efficiency will push materials to the limit. Modifications in the processing routes of this alloy can be more easily implemented in industry than changes in the alloying elements. Variations in ageing treatment or cooling rate from hot forging can produce a wide variety of mechanical properties. These are mostly caused by changes in the nanos-cale precipitates responsible for strengthening. The effects of different common ageing treatments such as conventional and direct ageing on clustering, size, volume fraction, morphology, configuration, and chemical composition of y0-and y00-precipitates are still largely unknown. We investigate these aspects of the precipitates with atom probe microscopy and correlate them with hardness. The flux of the main chemical elements in the formation of co-precipitates such as duplets and triplets is remarkably different in conventionally and directly aged materials. Dislocation rich structures also inflict in unexpected rapid formation of y00-precipitates at temperatures more than 90 degrees C higher than predicted by time-tempera ture-transformation diagrams. Water quenching from forging impedes precipitates formed along disloca-tions to coarsen during ageing, considerably impacting hardness, in comparison to air cooling. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Superscript/Subscript Available

Automated summary

Improving mechanical properties of Ni-based superalloy Alloy 718 is crucial for commercial aviation, with modifications in processing routes impacting material performance. Various ageing treatments lead to different nanoscale precipitates, affecting hardness significantly.