And finally in the lecture we'll see the mechanisms for creep deformation, specifically in metals and ceramics when they're used at really high temperatures. Well how does this additional plastic deformation occur? In metallic alloys one of the common possibilities is so called dislocation climb. And what we're saying here is remember how we're basically classically deforming materials by moving dislocations along. Here's our simple edge dislocation schematic. We're really combining some of the concepts from our discussion of defects in solids and saying that, okay, if we are increasing the number of point defects, so, let's say, vacancies, by heating the material up to higher and higher temperatures. And we're doing that by an Arrhenius mechanism. Exponentially increasing the number of vacancies as we are putting more such vacancies in the system than we're allowing for the possibility of some atomic motion and atoms that might happen to be in the lower edge of this extra half-plane of atoms that defines the edge dislocation. Some of those atoms could pop into adjacent vacancies. And if that happened enough remember of course this is an extra half plane of atoms so there's a whole two dimensional plane going into the board, or into the screen here that all of those leading edge atoms would have to move out of there, but with the increasingly high number of such vacancies, that's a real possibility. So again, what's happening is that you're giving yourself alternate routes so if this, if there had been some obstacle over here, a solute atom or another dislocation that was gonna keep this dislocation under the shearing action for moving along and providing a plastic deformation overall, you can simply move around that obstacle by again, this so-called dislocation climb. So it's just like taking a detour. You're moving up to this next plane, so as long as the dislocation is now moved upward, this has climbed up that one atomic unit. It then has the potential of climbing around the strange field of whatever obstacle is over here, again, whether it's another dislocation or a Solute atom creating some significant strain field. In ceramic materials, again because they're relatively brittle and this kind of plastic deformation doesn't occur, it's more likely that the mechanism for a creep is coming from just simply the sliding of grains past each other. So, grain sliding is much more likely in those brittle materials.