Decomposition and ordering in the Fe-Ga bcc alloys: atomic phase field modeling and diffuse scattering study
Speaker: Julien Boisse, Rutgers Materials Science and Engineering
Date & Time: November 3, 2009 - 12:10pm
Location: CCR 201
The Fe-Ga bcc alloys within the 15-20 at% Ga composition range have abnormally high magnetostriction. There is growing evidence that this effect is associated with the formation of a dispersion of nanoscale ordered particles in the bcc lattice, which undergo cubicàtetragonal displacive transformation transforming these particles into three orientation domains of the tetragonal phase, and the reorientation of these domains under the magnetic field is responsible for a large magnetomechanic effect. We investigated the structural and ordering and clustering processes within this composition range by using the computer modeling in the Atomic Density Field approximation. The nearest and next-nearest atomic interaction model was used. The parameters of this model were fitted to the known solubility limits of the bcc and DO3 ordered phases. The computer modeling of the equilibration of the compositionally homogeneous bcc solid solution resulted in a heterogeneous microstructure consisting of atomically ordered B2 and DO3 nanoparticles. The geometry of this nanostructure is in excellent agreement with that observed in the TEM and HREM images. Using the kinematic theory of the x-ray scattering and the microscopic crystal lattice statics, we calculated diffraction patterns of the diffuse scattering generated by such a nanostructural state for the cases wherein the nanoparticles undergo the cubicàtetragonal confined martensitic transformation. These cases were compared with the experimental observations.
2003-2005: Master of theoretical physics option: nanosciences and semiconductors, university of Marseille, France.
2005-2008: PhD and teaching in the University of Rouen in France in the laboratory GPM (Materials Physics Group). PhD title: "Phase field modelisation of precipitation kinetic in Ni-Al, Al-Sc et Al-Zr-Sc alloys". PhD obtained in September 29, 2008.
Member of The research groups (GDR) Phase Field and TransDiff (phase transition and diffusion) in France.
Actually work on Shape-memory Ferro-magnetic alloys.
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