Date of Award
Master of Science (MS)
Garrett J. Pataky
Paul F. Joseph
Enrique Martinez Saez
The understanding of microstructural damage mechanisms is the foundation of better understanding existing materials and future material development. There are significant challenges to measuring these damage mechanisms in-situ as continuous observation of the state of the microstructure is difficult or impossible for many experimental setups. This thesis presents a method for measuring grain boundary sliding (GBS) and local strain concentrations in-situ via a Heaviside function based algorithm. GBS is the shearing of two grains along their shared grain boundary and is a common damage mechanism in creep which presents as a discontinuity that can be measured with a Heaviside function.
Multi-principal element alloys (MPEAs) have potential to be the future of alloy design as there are limitless compositions possible which could exceed the capabilities of conventional alloys. MPEAs are a new class of alloys with a loose definition that they are made of multiple principal elements, generally with ≥5 at% of each principal element. Ti80(AlCrNb)20 is the alloy used in this thesis due to its potential as a lightweight MPEA (LMPEA) and its solid solution β titanium phase composition which is well suited for strong creep resistance. High resolution digital image correlation (HRDIC) enabled creep tests are performed to measure the GBS and other localized slip of Ti80(AlCrNb)20.
The GBS analysis code developed in this thesis utilizes the HRDIC creep data captured via optical microscope to measure GBS. Microstructural maps from electron backscatter diffraction (EBSD) are aligned with HRDIC creep imaging using fiducial markers to identify grain boundary locations, and the discontinuity across the grain boundary due to GBS was measured via a Heaviside function based algorithm. Measurement of GBS in-situ using an optical microscope is an advancement over existing methods by providing continuous data. This method also requires significantly less scanning electron microscope (SEM) time and access as the only SEM usage is an initial EBSD scan to identify the microstructure. Current methods utilize multiple or continuous SEM scans that can require the creep test to be stopped temporarily. As creep testing is typically at elevated temperatures, this induces thermic cycling in the sample which prevents a pure creep test. Being able to run a pure creep test without thermic cycling or interruptions while taking continuous measurements will improve the data analysis capabilities and informativity of future testing on microstructure damage.
Elbrecht, Benjamin, "Creep Behavior of a Ti-based Multi-Principal Element Alloy" (2022). All Theses. 3861.