Subject: The Forces Responsible for Shape Memory Alloys

In a previous post, someone asked about how shape memory alloys do their 
thing.  In the response to that post, the analogy was made of how the 
transition from liquid water to ice can create a force.  In the solid 
state phase transition from the martensitic phase to the austenitic phase a 
force is created as well.  

I understand that the force created when water freezes is due to the fact that 
as the water molecules crystallize, they fall into a highly ordered structure 
that is more open than what is present in the random 'structures' of the 
liquid.  All of this has to do with hydrogen bonding.  As this more organized 
solid structure forms, the liquid expands, and as it expands, it exerts a force 
on anything around it.  So the key thing here is the hydrogen bonding between 
the molecules while in the liquid phase, and how these bonds are responsible 
for the liquid actually being of a higher density than the solid.

How does this compare to shape memory alloys?  What interaction is there 
between the atoms in an alloy that generate this force?  Please be as specific 
as possible...a lot of explanations I've found just kind of do some hand waving 
at this point and say, "A force is generated."  How?  As the atoms move past 
one another when the metal is deformed, how do they find their way back to 
their original location?  

Re: The Forces Responsible for Shape Memory Alloys