Abstract
Grain boundary serration in the superalloy Inconel 600 was studied. Two microstructural variants, one with nonserrated and the other with serrated grain boundaries were generated by altering the heat-treatment conditions, while keeping other aspects of the microstructure unchanged. The effect on the creep response between 700 °C and 900 °C was measured, and the different failure modes and accumulated damage were quantified using high-angular resolution electron backscatter diffraction analysis in the scanning electron microscope and also by X-ray computed tomography. It is found that serration plays a more crucial role in the high-temperature/low-stress regime when an intergranular cracking mechanism involving cavitation is operative; here it plays a role in improving both creep life and creep ductility. Any effect of serration is less prevalent at low temperatures where transgranular failure is dominant.
Highlights
SERRATION of grain boundaries in metals and alloys, for example the nickel-based superalloys of the type studied here, is intriguing for various reasons
Refractory elements such as Ta, Mo, and W are absent; grain boundary MC-type carbides enriched with these elements have no contribution to microstructure; neither M23C6 nor M7C3 carbides could be formed from MC-carbide decomposition
The profiles of heat treatment that generated each type of grain boundary morphology are shown in Figures 1(a) and (b)
Summary
SERRATION of grain boundaries in metals and alloys, for example the nickel-based superalloys of the type studied here, is intriguing for various reasons. There is complexity arising from the inapplicability of the generally accepted picture of smooth or gently curved grain boundaries, as observed on the microscale. There is the fundamental question of why grain boundary serration arises in the first place. Effects of serration on the mechanical behavior of these materials are not well understood. What are the underlying fundamental effects which cause it? Detailed experimentation involving carefully controlled measurements and high-resolution characterization is needed
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