Maybe this question doesn't go too far, but when reading about liquid metal type materials like those that can harden with electricity or magnetism, I was kind of thinking of something there. For those who have read through stuff about developments in smart materials, is there a known material that could be made to harden and flatten like some kind of shield or harden and extend to a sharp point?
That is not a great idea. If your enemy has access to the same technology they probably can send another current at contact and destabilise your shield/blade, making them useless. It is probably easier to cause the material to return to liquid than to keep it in shield form so unless you are using it against someone you know doesn't have the technological level to do it you are giving the enemy an advantage.
For shields it would likely be doable with a magnetic, non-newtonian fluid.
The magnetic part would let you manipulate the shape a bit, although probably only to keep it stuck to the surface of some rigid material unless you have really good field control and a lot of power to spare.
Non-newtonian fluids are basically like silly-putty. They flow to some extent under slow, constant pressure, but harden if struck sharply. Some of the newest body armour today uses them to allow flexibility, while still hardening during an impact to be almost as strong as a traditional strike plate. Modern armour does it by saturating an absorbant, carbon-fiber mesh with the fluid rather than magnets, but compact power sources and precisely controlled electromagnets wouldn't be a ridiculous thing to find in a sci-fi setting.