Investigation of the orientation relationship between nano-sized G-phase precipitates and austenite with scanning nano-beam electron diffraction using a pixelated detector

TL;DR

This study uses scanning nano-beam electron diffraction with a pixelated detector to determine the orientation relationship of nano-sized G-phase precipitates within an austenite matrix, revealing FCC to BCC transformation characteristics.

Contribution

It introduces a novel application of pixelated detector-based nano-beam electron diffraction to analyze orientation relationships of nano-precipitates with complex structures.

Findings

G-phase precipitates show FCC to BCC orientation relationships.

The technique resolves faint diffraction spots from small precipitates.

Nano-beam electron diffraction is effective for complex nano-precipitate analysis.

Abstract

Scanning nano-beam electron diffraction with a pixelated detector was employed to investigate the orientation relationship of nanometer sized, irradiation induced G-phase (M$_6$Ni$_{16}$Si$_{7}$) precipitates in an austenite matrix. Using this detector, the faint diffraction spots originating from the small G-phase particles could be resolved simultaneously as the intense matrix reflections. The diffraction patterns were analyzed using a two-stage template matching scheme, whereby the matrix is indexed first and the precipitates are indexed second after subtraction of the matrix contribution to the diffraction patterns. The results show that G-phase forms with orientation relationships relative to austenite that are characteristic of face-centered cubic (FCC) to body-centered cubic (BCC) transformations. This work demonstrates that nano-beam electron diffraction with a pixelated detector is a promising technique to investigate orientation relationships of nano-sized precipitates with complex crystal structures in other material systems with relative ease.