On conventional versus direct ageing of Alloy 718

F. Theska, A. Stanojevic, B. Oberwinkler, S.P. Ringer, S. Primig
Acta Materialia 156 (2018) 116-124.

We present a correlative microscopy approach to identify the detailed microstructural evolution during direct ageing versus conventional processing of alloy 718. The key finding reported here via the use of atom probe microscopy is a remarkable structuring within and between the nanoscale γ' and γ" precipitation. Not only do we find an increase in both the volume fraction and size of the γ" precipitates after direct ageing, we report a prevalence of stacked co-precipitation in various sequences depending on the nucleation condition. These microstructural changes are summarized in a qualitative microstructural model and attributed to yield strength increments.

Understanding the relationship between process, microstructure and properties may enable future improvements in superalloy design, required to cover growing demands by aerospace sectors.