Revealing 3D Strain and Carbide Architectures in Additively Manufactured Ni Superalloys

TL;DR

This study uses advanced 3D X-ray diffraction to non-destructively analyze the complex microstructure, strain, and carbide distribution in additively manufactured Ni superalloys, revealing how processing affects material properties.

Contribution

It provides the first detailed 3D non-destructive analysis of microstructure, strain, and carbide architecture in Ni superalloys produced by laser additive manufacturing.

Findings

Carbides are spatially associated with cellular sub-grain networks.

Solute-rich regions have higher elastic modulus and influence residual stress.

The study links solidification segregation, deformation, and carbide architecture.

Abstract

Fast directional solidification during Laser Additive Manufacturing (LAM) produces a complex microstructure in nickel-based superalloys, comprising columnar grains with cellular sub-grain structures and carbides. Using non-destructive Scanning 3D X-ray Diffraction (S3DXRD), we reveal spatially complex orientation and intergranular strain relationships that couple strongly to processing-induced cellular sub-grain networks and a primary cubic metal carbide (MC) phase. We have examined 3D orientation and elastic strain tensor fields across 82 $\gamma$ grains together with the spatial distribution of over 37,000 MC carbides in an ABD-900AM alloy sample manufactured by the Directed Energy Deposition (DED) LAM process. Carbides are spatially associated with the cellular sub-grain network with a weak but present orientation relationship with their parent $\gamma$ grains. The MC carbides, known to be Ti, Ta and Nb rich, form in regions of high solute segregation, resulting in a significant volumetric lattice parameter patterning in the associated $\gamma$ phase regions. These chemically distinct solute-rich regions possess a higher associated elastic modulus compared to intercellular regions and determine the local residual stress patterning. These results provide the first non-destructive 3D study of the relationship between rapid solidification-induced segregation, deformation heterogeneity and carbide architectures in an additively manufactured Ni-based superalloy. The insights provide crucial detail to rationalise LAM process parameter optimisation and the coupled spatially governed structural performance.