MULTI-LAYER RESULTS
Two layer simulation - No upper surface tension force
Downloadable .avi file (4.54 MB)
In the first simulation, there is no offset surface tension force on the grain boundary in the second layer; it is simply a boundary. The grain boundary in the first layer, however, has a driving force at the ground, so it moves to the right. As the groove forms in the bottom layer, the atoms diffuse out of the boundary and along the surface between the two layers, causing a wind-like effect on the grain boundary in the top layer. This “wind” pushes the grain boundary to the left, deforming the shape greatly from the original orientation. The diffusion mechanics are well highlighted here, as the flow of atoms causes a great change in the shape of the upper grain boundary.
Two layer simulation - With upper surface tension force
Downloadable .avi file (3.02 MB)
In the second video, a difference in surface tension has been created across the bottom of the grain boundary in the second layer: the surface tension the right is greater than the surface tension to the left. This effect counteracts the wind-like flow of atoms out of the groove in the bottom grain boundary, and causes the grain boundary in the second layer to remain stationary. Instead of moving left or right, the groove on the top and bottom of this upper grain boundary becomes deeper and deeper. Eventually, if the simulation were allowed to continue long enough, the two grooves would have evolved across the height.