chapter  5
40 Pages

Diffusion and Plastic Deformation

It is important to understand some of the basic management techniques for the control of metallic properties. How atoms move and how to retard or prevent this movement is key to getting a material to perform as planned. The mechanisms of diffusion and plastic deformation in crystalline materials are dependent on the presence of imperfections in the lattice. In a material, if all the atoms were in place and all the bonds were 100% active, the material would be very strong and nearly impossible to form into a marketable product. We know, however, that deformation processing is a common occurrence in the manufacturing world. Imagine, if you will, zipping your jacket; then when it comes time to take it off, you grab the lapels and pull perpendicular to the axis of the zipper to open the jacket. We all know the cloth will most likely tear before the zipper is separated (assuming it is a good metallic zipper), and it will take a high level of effort to accomplish this task. However, if we take the zipper pull and unhook each of the zipper teeth one at time, in the normal manner, the zipper is opened with little effort and the garment stays intact. In a perfect lattice, movement and deformation will require large forces, but with defects in the structure this force is reduced to a manageable level.