Quantifying the role of APB tubes on the work-hardening of ordered phases

Anti-phase boundary (APB) tubes are linear defects that are 2-5 nm in height and width and up to several microns long that can be generated in some ordered alloys when they are deformed. The APB tubes have a strain field associated with them that can interact with gliding dislocations during deformation. The aim of this project is to quantify the contribution of APB tubes to the strength both of ordered alloys and of ordered phases in high entropy alloys (HEAs).

In this project we will: (1) determine the APB tube formation mechanisms via transmission electron microscope (TEM) in situstraining experiments; (2) perform tensile tests to various strains and measure both the APB tube and dislocation density using a combination of TEM, calorimetry, and possibly electron channeling contrast imaging in a scanning electron microscope at each strain, and use these data to model the work-hardening rate; (3) anneal out the APB tubes (but not the mobile dislocations) from strained specimens and determine the effect on the subsequent flow stress and work-hardening rate in order to provide insight into the mechanisms of APB tube strengthening; (4) relate synchrotron X-ray diffraction measurements of APB tube density to the flow stress continuously usingin situdeformation experiments; and (5) examine the chemistry of the APB tubes in a HEA using atom probe tomography. 

The outcome will be to have directly observed APB tube formation mechanisms; determined the strengthening mechanism associated with these APB tubes using TEM in situstraining experiments coupled with annealing studies; and to have used the experimental information obtained to quantitatively model the effects of APB tubes on the work hardening in a “traditional” B2-structured intermetallic compound; a new L12-structured HEA; and a novel strong, ductile, two-phase HEA consisting of both B2 and L12phases.

This project is funded by the U.S. Department of Energy.

Faculty contact: Ian Baker