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Phase Field Theory Of Surface- And Size-Induced Microstructures, Valery I. Levitas, D.W. Lee, D. L. Preston
Phase Field Theory Of Surface- And Size-Induced Microstructures, Valery I. Levitas, D.W. Lee, D. L. Preston
Valery I. Levitas
New surface- and size-induced microstructures are found as analytic solutions to a phase field theory of first-order phase transformations. A recently developed exact stability criterion, based on most destabilizing fluctuations, is used to analyze the stability and physical interpretation of each microstructure. Conditions for barrierless surface nucleation, i.e. relationship between surface energy, driving force for the transformation and sample size, are found. If they are met, some of these microstructures are destroyed resulting in the barrierless transformation to alternative phases.
Ginzburg-Landau Theory Of Microstructures: Stability, Transient Dynamics, And Functionally Graded Nanophases, Valery I. Levitas, D. L. Preston, Dong Wook Lee
Ginzburg-Landau Theory Of Microstructures: Stability, Transient Dynamics, And Functionally Graded Nanophases, Valery I. Levitas, D. L. Preston, Dong Wook Lee
Valery I. Levitas
The stability, transient dynamics, and physical interpretation of microstructures obtained from a Ginzburg-Landau theory of first-order phase transformations are studied. The Jacobi condition for stability fails numerically, thus an alternative exact stability criterion, based on critical (most destabilizing) fluctuations, is developed. The degree-of-stability parameter is introduced to quantify the physical stability of long-lived unstable microstructures. For nanofilms, the existence of functionally graded nanophases is demonstrated. Numerical simulations indicate that graded nanophases can be produced by dissolving material from both surfaces of a nanofilm. Stability under finite fluctuations and post-bifurcation microstructure evolution are investigated numerically.
Strain-Induced Disorder, Phase Transformations, And Transformation-Induced Plasticity In Hexagonal Boron Nitride Under Compression And Shear In A Rotational Diamond Anvil Cell: In Situ X-Ray Diffraction Study And Modeling, Valery I. Levitas, Yanzhang Ma, Javad Hashemi, Mark Holtz, Necip Guven
Strain-Induced Disorder, Phase Transformations, And Transformation-Induced Plasticity In Hexagonal Boron Nitride Under Compression And Shear In A Rotational Diamond Anvil Cell: In Situ X-Ray Diffraction Study And Modeling, Valery I. Levitas, Yanzhang Ma, Javad Hashemi, Mark Holtz, Necip Guven
Valery I. Levitas
Plastic shear significantly reduces the phase transformation (PT) pressure when compared to hydrostatic conditions. Here, a paradoxical result was obtained: PT of graphitelike hexagonal boron nitride (hBN) to superhard wurtzitic boron nitride under pressure and shear started at about the same pressure(∼10GPa) as under hydrostatic conditions. In situ x-ray diffraction measurement and modeling of the turbostratic stacking fault concentration (degree of disorder) and PT in hBN were performed. Under hydrostaticpressure, changes in the disorder were negligible. Under a complex compression and shear loading program, a strain-induced disorder was observed and quantitatively characterized. It is found that the strain-induced disorder suppresses …