Abstract
Nanoscale solute segregation to or near lattice defects is a coupled diffusion and trapping phenomenon that occurs in superalloys at high temperatures during service. Understanding the mechanisms underpinning this crucial process will open pathways to tuning the alloy composition for improving the high-temperature performance and lifetime. Here, we introduce an approach combining atom probe tomography with high-end scanning electron microscopy techniques, in transmission and backscattering modes, to enable direct investigation of solute segregation to defects generated during high-temperature deformation such as dislocations in a heat-treated Ni-based superalloy and planar faults in a CoNi-based superalloy. Three protocols were elaborated to capture the complete structural and compositional nature of the targeted defect in the alloy.
Highlights
Correlative microscopy, i.e., the combined utilization of a range of microscopy techniques on a single specimen, is increasingly deployed to understand fundamental aspects in material science
These nanoscale defects critically impact the mechanical performance of high-temperature engineering alloys
The strength of these approaches is to enable both structural and compositional information on the same object, which is necessary to unveil the mechanisms controlling the mechanical response of the material under investigation
Summary
Correlative microscopy, i.e., the combined utilization of a range of microscopy techniques on a single specimen, is increasingly deployed to understand fundamental aspects in material science. APT had previously revealed details of the composition of structural imperfections,[15] the presence of which were confirmed by field ion microscopy[16] or TEM.[11,17,18] Here, we introduce methodologies to aid target features of interest for correlative TEM/APT investigation by exploiting advanced scanning electron microscopy (SEM) techniques in deformed Ni- and CoNi-based superalloys, one of the most important classes of engineering materials for temperatures above 1000°C Their high temperature stability is attributed to the uniform distribution of L12-ordered c¢ precipitates coherently embedded in an fcc solid solution c matrix.
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