Possible to see a variety of structural features in the raft that also occur in real crystal structures, such as grainīoundaries, vacancies, dislocations and solute 'atoms'.Ī grain boundary in a 2D lattice is the interface between two regions of crystalline order. The forces between the bubbles mimic the forces between atoms in a crystal. Dislocations in 2DĪ 'raft' of equally sized bubbles floating on the surface of a liquid is a good large-scale model of a single plane ofĪtoms in a crystal structure. In the final part of this package, we consider some of the observations one can make that were first used to verify the presence of dislocations in real crystals. The structure of a dislocation in 3D can be more difficult to visualise. ![]() In real crystals, dislocations are three-dimensional. (Click on image to view a larger version.) These can be tremendously instructive, and we use video clips and still pictures to demonstrate how plastic deformation occurs via dislocation motion.Ī bubble raft. Much of the early work on dislocations was done using simple models such as bubble rafts. The first section of this package deals with dislocations in the simplest way - in two dimensions. It took another ten years before electron microscopy techniques were advanced enough to show dislocations moving through a material. Not until 1947 was the existence of dislocations experimentally verified. Materials work-harden: when a material has been plastically deformed it subsequently requires a greater stress.The stress required to plastically deform a crystal is much less than the stress one calculates from considering a defect-free.The concept of the dislocation was invented independently by Orowan, Taylor and Polanyi in 1934 as a way of explaining two key observations about the plastic deformation of crystalline material: It should be possible to make use of the package even without knowledge of these concepts. Miller index notation for specification of crystal planes and.However, some of the more detailed explanations use the following: Most of this package assumes no prior knowledge. be aware of the methods that can be used to reveal dislocations in a crystal structure.appreciate the motion of a dislocation under an applied stress. ![]() understand the nature of dislocations both conceptually and in a real crystal structure.
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