Prediction and characterization of variant electron diffraction patterns for Υ' and δ precipitates in an INCONEL 718 alloy

摘要

A universal theoretical method has been developedin this article to predict and characterize electron diffractionpatterns (EDPs) which contain various variants of precipitate(s)with a matrix. The plane and direction transition matrices forthree γ"-phase variants and 12 δ-phase variants precipitatedfrom a y matrix in the INCONEL 718 alloy were deduced, fromwhich the EDPs for seven low-index zones of γ matrixcontaining γ" precipitates were predicted by plotting and werefound to be consistent with transmission electron microscopy(TEM) observations, showing that some of the results reportedby Quist et al. should be corrected. Meanwhile, three variants ofδ phase, precipitated from any one of four { 111 } matrices in 12possible orientational variants, were also predicted andconfirmed by EDPs. Different from Paulonis' conclusion, ourtheoretical calculations indicated that the {1/2 10}-typesuperlattice reflections in the <100> zone of the γ matrixpermitted detection of both γ"- and δ-phase precipitates, but notof γ"-phase precipitates. Therefore, the precipitates shown indark-field images using these superlattice reflections cannot beunambiguously determined to be γ" phase. A unique approachfor identification of γ" precipitates in the alloy has been proposed.