  The serration of grain boundaries in Inconel 600 caused by heat treatment is
studied systematically. A new method based on Fourier transforms is used to
analyse the multiple wave-like character of the serrated grain boundaries. A
new metric -- the serration index -- is devised and utilised to quantify the
degree of serration and more generally to distinguish objectively between
serrated and non-serrated boundaries. By considering the variation of the
serration index with processing parameters, a causal relationship between
degree of serration and solution treatment/cooling rate is elucidated.
Processing maps for the degree of serration are presented. Two distinct
formation mechanisms arise which rely upon grain boundary interaction with
carbides: (i) Zener-type dragging which hinders grain boundary migration and
(ii) a faceted carbide growth-induced serration.
