High Resolution 3D Strain and Orientation Mapping within a Grain of a Directed Energy Deposition Laser Additively Manufactured Superalloy

TL;DR

This study employs Dark Field X-ray Microscopy to non-destructively map 3D microstructure, orientation, and strain within a grain of a laser additively manufactured superalloy, revealing heterogeneity and deformation patterns.

Contribution

It introduces a novel application of DFXM for 3D intragranular mapping in LAM superalloys, providing detailed insights into microstructure development and residual stresses.

Findings

Revealed highly heterogenous 3D microstructure within the grain.

Identified strain variations up to 5×10^{-3} and orientation differences <0.5°.

Compared DFXM results with EBSD to validate microstructure observations.

Abstract

The industrialization of Laser Additive Manufacturing (LAM) is challenged by the undesirable microstructures and high residual stresses originating from the fast and complex solidification process. Non-destructive assessment of the mechanical performance controlling deformation patterning is therefore critical. Here, we use Dark Field X-ray Microscopy (DFXM) to non-destructively map the 3D intragranular orientation and strain variations throughout a surface breaking grain within a directed energy deposition nickel superalloy. DFXM results reveal a highly heterogenous 3D microstructure in terms of the local orientation and lattice strain. The grain comprises $\approx$ 5$\mu$m-sized cells with alternating strain states, as high as 5 $\times 10^{-3}$, and orientation differences <0.5{\deg} . The DFXM results are compared to Electron Backscatter Diffraction measurements of the same grain from its cut-off surface. We discuss the microstructure developments during LAM, rationalising the development of the deformation patterning from the extreme thermal gradients during processing and the susceptibility for solute segregation.