Florida Institute of Technology professor emeritus Martin Glicksman’s latest research on metals and materials has implications for the foundry industry, but it also has a deep personal connection to the inspiration of two deceased colleagues. googletag.cmd.push(function() { googletag.display(‘div-gpt-ad-1449240174198-2′); });
Gliksman’s study “Surface Laplacian of the interfacial thermochemical potential: its role in the formation of the regime of solid and liquid phases” is published in the November issue of the joint journal Springer Nature Microgravity. The findings could lead to a better understanding of the solidification of metal castings, allowing engineers to build longer lasting engines and stronger aircraft, and to advance additive manufacturing.
“When you think about steel, aluminium, copper – all important engineering materials, casting, welding and primary metal production – these are multi-billion dollar industries of great societal value,” Glicksman said. “You will understand that we are talking about materials, and even small improvements can be valuable.”
Just as water forms crystals when it freezes, something similar happens when molten metal alloys solidify to form castings. Gliksman’s research shows that during the solidification of metal alloys, the surface tension between the crystal and the melt, as well as changes in the curvature of the crystal as it grows, cause a heat flux even at fixed interfaces. This fundamental conclusion is fundamentally different from the Stefan weights commonly used in the theory of casting, in which the thermal energy emitted by a growing crystal is directly proportional to its growth rate.
Gliksman noticed that the curvature of a crystallite reflects its chemical potential: a convex curvature slightly lowers the melting point, while a concave curvature slightly raises it. This is well known in thermodynamics. What is new and already proven is that this curvature gradient causes an additional heat flux during solidification, which was not taken into account in the traditional theory of casting. In addition, these heat flows are “deterministic” and not random, like random noise, which in principle can be successfully controlled during the casting process to change the microstructure of the alloy and improve properties.
“When you have frozen complex crystalline microstructures, there is curvature-induced heat flux that can be controlled,” Gliksman said. “If controlled by chemical additives or physical effects such as pressure or strong magnetic fields, these heat fluxes in real alloy castings can improve the microstructure and ultimately control cast alloys, welded structures, and even 3D printed materials.”
In addition to its scientific value, the study was of great personal importance to Glixman, thanks in large part to the helpful support of a late colleague. One such colleague was Paul Steen, professor of fluid mechanics at Cornell University, who died last year. A few years ago, Steen helped Glicksman in his research on materials in microgravity using space shuttle fluid mechanics and materials research. Springer Nature dedicated the November issue of Microgravity to Steen and contacted Gliksman to write a scientific article about the study in his honor.
“That prompted me to put together something interesting that Paul would especially appreciate. Of course, many readers of this research article are also interested in the area Paul contributed to, namely interface thermodynamics,” Gliksman said.
Another colleague who inspired Gliksman to write the article was Semyon Koksal, professor of mathematics, department head and vice president of academic affairs at Florida Institute of Technology, who died in March 2020. Gliksman described her as a kind, intelligent person who was a pleasure to talk to, noting that she helped him apply his mathematical knowledge to his research.
“She and I were good friends and she was very interested in my work. Semyon helped me when I formulated differential equations to explain the heat flow caused by curvature,” Gliksman said. “We spent a lot of time discussing my equations and how to formulate them, their limitations, etc. She was the only person I consulted and she was very helpful in formulating mathematical theory and helping me get it right.”
Further information: Martin E. Gliksman et al., Surface Laplacian of the interfacial thermochemical potential: its role in the formation of the solid-liquid mode, npj Microgravity (2021). DOI: 10.1038/s41526-021-00168-2
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