Correlative statistical microstructural assessment of precipitates and their distribution, with simultaneous electron backscatter diffraction and energy dispersive X-ray spectroscopy

TL;DR

This study combines EDS and EBSD techniques to statistically analyze the distribution and chemistry of precipitates in Ni-based alloys, revealing differences related to their location and processing methods, with implications for material performance.

Contribution

It introduces a combined EDS and EBSD methodology for microstructural assessment, providing new insights into precipitate chemistry and distribution in Ni alloys.

Findings

Chemistry varies between precipitates in different microstructural locations.

Precipitate distribution differs between wrought and powder metallurgy alloys.

Statistical analysis highlights boundary-related differences in precipitate chemistry.

Abstract

Modern engineering alloys have bespoke microstructures, where features such as precipitates are used to control properties. In many Ni-based alloys, carbo-nitride precipitates are introduced to strengthen and improve performance. These precipitates can be distributed throughout the microstructure and niobium rich carbides are often found at grain boundaries. In this work, we used combined energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) to characterise the population of these precipitates. Processing of the EDS signal is used to label the Mo/Nb-rich precipitates, and their size and location are measured from maps using a circular Hough transform. This label map is combined with the grain boundary network (from EBSD analysis). Statistical analysis, using ANOVA testing, reveals differences in chemistry between carbides found in Ni-rich matrix grain interiors, on random high angle boundaries and on special boundaries ({\Sigma}3 and {\Sigma}9). These results are compared between wrought and power metallurgy product forms. These distributions are discussed in the context of their performance within demanding environments, such as reactor core internals.