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Crystal-Amorphous And Crystal-Crystal Phase Transformations Via Virtual Melting, Valery I. Levitas
Crystal-Amorphous And Crystal-Crystal Phase Transformations Via Virtual Melting, Valery I. Levitas
Valery I. Levitas
A new mechanism of crystal (c)–amorphous (a) and c-c phase transformations (PTs) and internal stress relaxation via virtual melting (VM) induced by internal stresses was justified thermodynamically and kinetically. VM removes interface friction, reduces kinetic barrier, increases atomic mobility, and can reduce thermodynamic melting temperature. We combine VM and nonequilibrium PT diagrams to develop new scenarios of c-a and c-c PTs. Results are applied for a new interpretation of c-c and c-a PT mechanisms in ice Ih and are also applicable for other materials.
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting: Additional Confirmations, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting: Additional Confirmations, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Valery I. Levitas
Recently, we predicted a mechanism of solid-solid phase transformation (PT) via virtual melting at 121K below the melting temperature. We report additional experimental and theoretical results for PTs among three polymorphs of the energetic material HMX, α, β, and δ that support this mechanism. In particular: (a) the predicted velocity of interface propagation for β→δ PT and overall kinetics of δ→β PT are in agreement with experiment; (b) the energy of internal stresses is sufficient to reduce the melting temperature from 520to400K for δ→β PT; (c) the nanocracking that appears during solidification does not change the PT thermodynamics and kinetics …
Transformation-Induced Plasticity And Cascading Structural Changes In Hexagonal Boron Nitride Under High Pressure And Shear, Valery I. Levitas, Yanzhang Ma, Javad Hashemi
Transformation-Induced Plasticity And Cascading Structural Changes In Hexagonal Boron Nitride Under High Pressure And Shear, Valery I. Levitas, Yanzhang Ma, Javad Hashemi
Valery I. Levitas
In situx-ray diffraction study and modeling of the degree of disorder, s, and phase transformation (PT) in hexagonal hBN were performed. It was proven that changes in s are strain-induced and that s can be used to quantify plastic strain. During the strain-induced hBN→wurtzitic wBN PT, the transformation-induced plasticity (TRIP) was exposed and quantified. TRIP exceeds conventional plasticity by a factor of 20. Cascading structural changes were revealed. Strain-induced disorder explains why PT under hydrostatic and nonhydrostatic conditions started at the same pressure∼10GPa. For the same disorder, plastic shear reduces PT pressure by a factor of 3–4.