I know that solid water (ice) sublimes ("evaporates" straight from solid to dissolved gas) in air. On the other hand, some metal objects seem to last forever (e.g. gold, stainless steel and other metals that don't tarnish, rust, etc.) So, does solid metal sublime? And if not, why not, darn it!
[Physics] Does metal sublimate
material-science
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The answer is that in principle yes, the removal of defects will increase the density. The question is by how much.
You specifically ask about forging. The forging process doesn't remove dislocations but instead moves them until they become pinned, which is what causes the work hardening. Well, that's an oversimplification since some defects will be removed but on the other hand fresh defects will be created. So whether forging will change the density, and if so by how much, is a hard question to answer.
The extreme version of removing defects would be to compare the densities of crystalline and amorphous metal. However I'm not sure that the common metals can be prepared in well characterised amorphous forms. If you compare that most common of amorphous solids, silica glass, then the density of the amorphous form is about 10% lower than the density of quartz.
I did have a Google for the effect of forging on density (I'm sure you did too) but I couldn't find anything that looked reliable. I did find this paper that reports a density decrease, but the authors suggest this is due to formation of small cracks. I think it would be a hard experiment to do as there are other variables that are hard to control.
From Wikipedia:
Hardening is a metallurgical and metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain. A harder metal will have a higher resistance to plastic deformation than a less hard metal.
Link to original reference: Hardening Metal
Ductility is reduced after hardening, but you don't say which metal or alloy you have in mind and, because of the varying crystal structure, it's a property that varies with the metal.
Again from Wiki:
There are several ways in which crystalline and amorphous materials can be engineered to increase their yield strength. By altering dislocation density, impurity levels, grain size (in crystalline materials), the yield strength of the material can be fine tuned. This occurs typically by introducing defects such as impurities dislocations in the material. To move this defect (plastically deforming or yielding the material), a larger stress must be applied. This thus causes a higher yield stress in the material. While many material properties depend only on the composition of the bulk material, yield strength is extremely sensitive to the materials processing as well for this reason.
Yield Strength Factors From Wikipedia
Best Answer
They do actually, but in normal conditions you can not observe this. The sublimation rate will depend on temperature and energy of sublimation, which is different for different metals. Also in normal conditions you will have some kind of equilibrium - some of the particles that leave the surface will condensate back. But in vacuum techniques you need to take this to account - there are metals with low sublimation energy - such as Zinc, Magnesium, Cadmium e.t.c. You can see them here, here, for example, in the list of non-suitable for vacuum equipment. As an extreme case you can imagine a piece of metal, which is heated from inside and put into deep space, if its mass is small and gravitation attraction can be neglected, it will evaporate.