Speaker
Description
The excellent mechanical properties up to 650°C make Alloy 718, a Ni-based superalloy, a common material used in low-pressure turbine discs of commercial airplanes. A major contribution to the high mechanical strength is attributed to the presence of nanoscale γ' and γ" precipitates. Different ageing treatments, such as conventional or direct ageing cause variations in the volume fraction, size, and configuration of co-precipitates which can improve the mechanical properties [1]. During direct ageing, the presence of dislocations accelerates the formation of γ" precipitates due to pipe diffusion of Nb [2]. However, a systematic comparison between ageing treatments from the onset of clustering through the early stages of precipitation remained unexplored.
Atom probe microscopy (APM) is a powerful characterization technique that provides sub-nanometre resolution [3] which is critical to explore the formation of clusters of atoms prior to ageing, as well as the early stages of precipitation. In this work, we correlate hardness testing with APM to investigate the evolution of γ' and γ" precipitates during conventional versus direct ageing. Dislocations are already decorated with γ" precipitates after rapid water quenching from hot forging. This shows that dislocations shift γ" precipitation towards temperatures higher than predicted by time-temperature-transformation diagrams [4].
[1] F. Theska, A. Stanojevic, B. Oberwinkler, S.P. Ringer, S. Primig, Acta Mater. 156 (2018) 116–124.
[2] F. Theska, K. Nomoto, F. Godor, B. Oberwinkler, A. Stanojevic, S.P. Ringer, S. Primig, Acta Mater. 188 (2020) 492–503.
[3] B. Gault, M.P. Moody, J.M. Cairney, S.P. Ringer, Atom Probe Microscopy, Springer Science & Business Media, 2012.
[4] L. Renhof, C. Krempaszky, E. Werner, M. Stockinger, Proc. Int. Symp. Superalloys Var. Deriv. (2005) 261–270.
| Speaker Country | Australia |
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