Automated indentation-based slip trace analysis for bcc and B2 intermetallic plasticity

Abstract

Intermetallics are a key material class toward high-temperature applications, as monolithic materials such as B2 NiAl, or when used as a precipitate reinforcing phase within Ni fcc-superalloys or nascent bcc-superalloys and refractory high entropy superalloys. There is large variability across B2 ordered-bcc intermetallic compounds in terms of strength and ductility, which is underpinned by variability in their dominant slip systems. Here we have developed an automated indentation-based slip trace analysis method, designed to accelerate the assessment and quantification of favoured slip systems. The methodology uses microhardness indentation and imaging of the resultant surface slip traces, paired with local crystal orientations determined by Electron Backscatter Diffraction (EBSD). Our newly developed code for automated detection of slip trace orientations then uses image segmentation, Hough transform line detection, and a scoring procedure that evaluates how likely detected lines are to be aligned with real slip traces. This simply applied methodology is validated on fcc nickel, and then used to determine the slip behaviours of four bcc/B2 materials, finding unambiguous evidence of ½<111> {112} and/or {123} type slip in bcc Fe and B2 Ti₂AlNb, compared to slip predominantly on {110} in B2 TiFe and Ti₂AlMo, which correlates to their respective apparent ductile/brittle behaviours. The methodology can readily be adapted to other testing techniques (e.g. nanoindentation, tensile), and to gain deformation behaviour insights for other crystal structures (e.g. hcp and complex intermetallics).