materials science concepts

laura001

hey,

i'm doing a course on materials science as part of an aerospace engineering degree. I'm just trying to gain a full understanding of some of the fundamental concepts involved. Would i be right in saying that, all processes that occur in metallurgy on an atomic scale (like recrystalisation, recovery, grain growth) are all driven by the systems tendancy to move towards equilibrium (i.e the minimum free energy)?

If that's correct, why does a system have this tendency to move towards equilibrium? What exactly is the driving force behind this, i guess it's a thermodynamic driving force, but does that mean that these processes actually 'feed' off of heat somehow? What is the source of that heat?

To take dislocation formation as an example of how the energy in a system increases, i understand that if you take a cyrstallite and bend it by some external force, then the energy assosciated with that elastic deformation can be stored by inserting a dislocation, i.e a defect. So as dislocations form, the free energy of a system increases... eventually the same process leads to grain boundaries to form.

But, then there's a reverse process, right? Say you've just plastically deformed a piece of metal, so it now has a high dislocation density... the system will then have an elevated internal energy right? So my limited understanding of what happens then is that processes begin which try to reduce this elevated internal energy i guess? Like recovery, recrystalisation and grain growth. In other words, the system tries to move towards equilibrium (minimum free energy).

Is that basic framework of understanding right or can you add any detalis that will help me understand this stuff? thanks.

PerennialII

Hi Laura,

I'd interpret the "abundance" of replies [ ] in such a manner that you're on the right track. Thermodynamical principles work on one way or the another to phenomena encountered in materials science & condensed matter problems, no matter at what level you're investigating your problem - and what are the variables under which your system is working in a particular case (always energy involved in one way or another - doesn't have to be heat like you ponder in your post). And the principles are the typical tools of investigating and understanding pretty much everything that goes on "down there" from typical phenomena of physical metallurgy to plasticity and beyond (and different 'phenomena' occur under a different set of "rules" (better understood thinking about the 'driving force' towards a 'change', towards an equilibrium), like your example of plasticity via dislocations, which again under conditions 'enabling' for example recrystallization can lead to such).