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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 …
A Microscale Model For Strain-Induced Phase Transformations And Chemical Reactions Under High Pressure, Valery I. Levitas
A Microscale Model For Strain-Induced Phase Transformations And Chemical Reactions Under High Pressure, Valery I. Levitas
Valery I. Levitas
A simple strain-controlled kinetic equation for strain-induced phase transformations and chemical reactions is thermodynamically derived. This model is applied to explain various mechanochemical phenomena observed under compression and shear of materials in diamond or Bridgman anvils. In particular, it explains zero-pressure hysteresis and the appearance of new phases, especially strong phases, which were not obtained without shear. Also an explanation was obtained as to why a nonreacting matrix with a yield stress higher (lower) than that for reagents significantly accelerates (slows down) the reactions. Some methods to characterize and control strain-induced transformations and reactions are suggested.