HR: 08:30h
AN: V21A-03    [PDF]
TI: The effect of shear deformations on the transition onset pressure of the bcc to hcp pressure induced martensitic phase transformation in iron.
AU: * Caspersen, K
EM: kcasper@chem.ucla.edu
AF: University of California Los Angeles, Department of Chemistry and Biochemistry Box 951569 UCLA, Los Angles, CA 90095 United States
AU: Lew, A
EM: lewa@aero.caltech.edu
AF: California Intitute of Technology, Graduate Aeronautical Laboratories California Intitute of Technology, Pasadena, CA 91125 United States
AU: Ortiz, M
EM: ortiz@aero.caltech.edu
AF: California Intitute of Technology, Graduate Aeronautical Laboratories California Intitute of Technology, Pasadena, CA 91125 United States
AU: Carter, E
EM: eac@chem.ucla.edu
AF: University of California Los Angeles, Department of Chemistry and Biochemistry Box 951569 UCLA, Los Angles, CA 90095 United States
AB: At a pressure of approximately 13 GPa iron undergoes a martensitic phase transition from ground state ferro-magnetic \emph{bcc} to a non-magnetic \emph{hcp} structure. The exact transformation varies between experiments and is postulated to have a strong dependence on shear stresses during the loading process. To study this shear dependence we have developed a multi-scale model of iron, in which we employ a quantum mechanics based free energy, a kinematically compatible spinodal decomposition of phases, and a dependence on the \emph{bcc}{$\leftrightarrow$}\emph{hcp} transition path(s). Using this model we see that that the predicted transformation pressure for pure hydrostatic compression is much higher than expected, however with the inclusion of small initial shear deformations we see the predicted transformation pressure drop considerably and into the experimentally determined pressure range.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 3200 MATHEMATICAL GEOPHYSICS (New field)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting