Nucleation of a Modulated Phase in Ordering Alloys: Labyrinths or Columns?
Nicholas Angelo Gross
Department of Science and Mathematics, College of General Studies
Department of Physics, Oakland University
Department of Physics, Brandeis University
Relaxation dynamics is used to study the nucleation of the modulated phase of CuAu from systems prepared in the disordered and ordered phases.
Binary alloys are made by mixing two species of metals; in this case: Copper and Gold. If the two species are of roughly the same size then simple phase ordering will take place; that is to say at high temperatures (but still below the melting point of both species so there is still a crystalline structure) the two types of atoms are distributed randomly on the crystalline lattice while at low temperatures the two types of atoms will order in an alternating structure. In many alloys however the two species are of different sizes and the ordering is accompanied by a structural change in which the lattice size changes. This structural change induces an additional phase between the high temperature disordered phase and the low temperature ordered phase. This third phase is a modulated phase where the ordering of the atoms oscillates in space between the two types. These video sequences will explore the formation of the modulated phase. The two sequences represent 2D simulations of a system which is prepared with two different initial conditions and then quenched to the temperature regime where the modulated phase is dominant. In the first sequence the system is prepared in the disordered regime while in the second sequence it is prepared in the ordered phase. The modulated phases which form from these different initial conditions have different structure and time evolution.
Quench from the Disordered Phase – 2D slice
Quench from the Disordered Phase – 3D volume
Quench from the Ordered Phase – 2D slice
Quench from the Ordered Phase – - 3D volume
Isosurface of Idealized Modulated Phase
A larger and slower 1.9 megabyte MPEG version is also available.
Hardware: 18 processor SGI Power Challenge.
Software: Fortran 90, simpim imaging tools (2D), IDL (3D isosurface), AVS (ray-traced volumes)
Graphics programming and video production: 2D segments by Kathleen Curry, 3D ray-traced segments by Kathleen Curry, Scientific Computing and Visualization Group, Boston University; 3D isosurface by Erik Brisson, Scientific Computing and Visualization Group, Boston University.