Dislocation structure and crystallite size distribution in lath martensite determined by X-ray diffraction peak profile analysis

Abstract

Abstract X-ray diffraction peak profiles obtained from 18Ni lath martensite were analyzed in accordance with the modified Williamson – Hall and modified Warren – Averbach methodologies, aided by supplemental optical and transmission electron microscopy. After instrumental broadening removal, structural peak broadenings were determined for diffraction lines. Consequently, a log-normal size distribution with a mean size of about 156 nm was determined, corresponding reasonably to the lath width illustrated by means of transmission electron microscopy. Further, a dislocation density of 0.723 × 1016 m– 2 along with a near equal proportion of edge and screw dislocations were identified. Determination of the dislocation arrangement parameter revealed a weak dipole and thus, weak screening action of dislocation strain fields.