My name is Michael Lastovich, and I’m a fifth year PhD candidate in the Materials Science Program. I work with Dr. Bharat Gwalani in the Lab for Agile Manufacturing and Rapid Characterization (LaMARC). Our group’s research is heavily focused on the development of metallic materials for extreme environments and multifunctional applications. We take advantage of the localized solid state nature of techniques like Friction Stir Processing and High Pressure Torsion to produce composites which might otherwise be limited by high phase reactivity or mechanical incompatibility. My current career goal is to pursue work in the National Lab system. When I’m not in the lab or in a self-imposed exile writing papers, you’ll probably find me in my kitchen making a batch or three of ice cream, gaming with friends, or out in a field somewhere sparring with my historical fencing group.

What instruments are you using for your research and why do you like them?

During solid state processes like hot working or friction stir, the microstructural evolution is determined by a multiscale progression of nanoscale defects and chemical changes into macroscale deformation structures and phases. The ThermoFisher Hydra G5 dual beam pFIB has been an absolute work horse with the combination of high resolution electron column, EDS detector, EBSD detector, and FIB column for S/TEM sample prep all in the same instrument. SEM-EDS and EBSD provide broad characterization of chemical partitioning and macroscale deformation structures, which can then be made into highly targeted site specific S/TEM samples with the attached Ion column. Taking these samples to the Talos F2000 TEM, and previously to the aberration-corrected Titan, extends our understanding of the deformation mechanisms down to the nanoscale. The combination of high resolution dislocation and interfacial imaging with S/TEM EDS chemical mapping provides directly interpretable results on the stability of defect networks and the nature of the chemical changes. The entire combined workflow enables exploration of the dominant microstructural evolution pathways while removing ambiguity between length scales.

What have you been researching?

My dissertation research focuses on the role of combined chemical and structural instabilities in governing the microstructural evolution of metallic systems, with a focus on systems which display a miscibility gap. These systems, which in my case take the form of a single phase BCC FeCrCo alloy and a mixed FCC+BCC AlCoCrFeNi(CuTiZr) High entropy alloy (HEA) system, will typically undergo phase separation from a solid solution into multiple compositional domains via spinodal decomposition. Spinodal microstructures evolve through a continuum of compositions, producing quasi-periodic structures with extremely high interfacial areas as a result, which can produce significant changes to the mechanical and magnetic properties of the material. Dislocations, through a combination of long range strain effects and local pipe diffusion, have been shown to have a marked impact on the driving force for spinodal separation as well as the resulting morphology. I’m using a combination of controlled mechanical, thermal, and thermomechanical treatment within the two systems to highlight the conditions under which these dislocation-spinodal interactions dominate macroscale behavior of the alloys, evaluating the multi-length scale behavior using EBSD, FIB, and S/TEM EDS.

Due to the fundamental nature of Spinodal Decomposition, the interactions and behaviors I aim to uncover will hopefully provide guiding insights to a large portion of the metallurgy community.
– Michael Lastovich

Within the more specific context of the systems I’m interrogating, dual phase HEA’s are growing as one of the more promising candidates for next generation high temperature structural applications, predominantly in energy sector applications such as turbines and reactor walls. The mixture of multiple phases and inherent chemical complexity of HEAs does mean this alloy class is prone to highly complex deformation and phase transformation behavior which must be understood to guarantee material performance under extreme conditions. For FeCrCo spinodal alloys, the focus shifts to the semi-hard magnetic properties, which are highly dependent on the size scale and shape of the spinodal morphology, and are much less thermally sensitive than magnets which rely on magneto-crystalline anisotropy. In the case of these materials, the goal is to expand on deformation processing as a means of enhancing the functional properties of these alloys to push the boundaries of their performance.

What have you learned from your experience at AIF?

Through my time at AIF, I’ve learned a lot about the operation of various instruments, none more so than the S/TEMs. My thesis direction would hardly be possible without the AIF, as the facilities here enable me to look at my materials to depth which likely would’ve been unavailable to me anywhere else.

Best thing about AIF in 5 words or less?

I am free to explore

Is there a staff member at AIF that has helped you?

First and foremost, I want to thank Chris Winkler for being not only my introduction and guide through the early choppy waters of learning STEM, but also has been an invaluable resource and source of support through the last 4 years of research I’ve done. Despite the inherent headaches which accompany managing such persnickety instruments, he has remained someone I can pretty universally rely on when I need it.

I would also like to extend gratitude to Roberto Garcia and Jenny Forester for putting up with my various shenanigans on the FIBs and XRD when I was first working with the AIF, and Toby Tung for always seeming to show up the second I need his help fixing something.