An Iowa State professor and his PhD student are gaining global recognition for their work on surface-induced phase transformations.
Valery Levitas, Schafer 2050 Challenge Professor and faculty member of aerospace engineering and of mechanical engineering, along with PhD student Mahdi Javanbakht were published in Physical Review Letters (PRL, 2011, Vol. 107, 175701), the world’s foremost physics journal.
The researchers have advanced our understanding of surface-induced phenomena and the Ginzburg-Landau theory for their description in the paper “Surface-Induced Phase Transformations: Multiple Scale and Mechanics Effects and Morphological Transitions.”
Through their paper, Levitas and Javanbakht revealed strong, surprising, and multifaceted effects of the width of the external surface layer and internal stresses on surface-induced pre-transformation and phase transformations. To be able to study surface-induced phenomena, they further developed the Ginzburg-Landau theory and computational approach.
They found that above some critical thickness of the surface layer, a morphological transition from fully transformed layer to lack of surface pre-transformation occurs for any transformation strain. It corresponds to a sharp transition to the universal (independent of transformation strain), strongly increasing relationship of the critical thermodynamic driving force for phase transformation on the width of surface layer.
For large transformation strain and below the critical width, this dependence unexpectedly oscillates. Oscillations are caused by several morphological transitions (i.e., sharp change in geometry) of transformed surface nanostructures. Obtained results open new doors for controlling surface-induced phase transformations and nanostructures.
Similar developments can be applied for internal surfaces (grain boundaries) and for various types of phase transformations and chemical reactions. This is the second PRL article for Javanbakht during his two years of study at Iowa State.
Another paper by Levitas with his other PhD student Kamran Samani was recently published as Rapid Communications in Physical Review B (PRB, 2011, Vol. 84, No. 14, 140103(R)). Rapid Communications in PRB satisfy all the same stringent criteria as PRL papers, but with specialization in condensed matter and materials physics.
In their paper “Coherent interface with stress relaxation in phase-field approach for melting-solidification,” they developed an advanced Ginzburg-Landau approach to melting-solidification coupled with mechanics. This approach allowed them to describe complex relaxation processes and surface stresses at solid-liquid interface.
As a result, they obtained good correspondence with known experimental results on size-dependence of the melting temperature and temperature-dependence of the thickness of molten layer, as well as with molecular dynamic results on surface stress distributions. A similar approach can be applied for sublimation-condensation, amorphization-vitrification, diffusive transformations and chemical reactions.
This work is a continuation of their paper published in Nature Communications in April 2011.