Concerning the speculation on warhammers: You could solve the problem of warhammers getting stuck in shields (or skulls, for that matter) by engineering a larger, flatter head, with a greater overall area. The damage done (and armour-destroying nature) could then be salvaged by employing either a "ball-peen" or blunt pyramid striking surface, or simply adding a short central stud or spike (or more than one), which would be kept from penetrating to a dangerous (for you, not them) depth into material, by the surrounding flat head.
This type of warhammer might actually be an improvement over a battleaxe, which has always had the problem of getting stuck into bone. Less maintenance required, as well.
The larger head should also make it a bit easier to strike the enemy, and wouldn't have to be horribly thick, reducing the overall weight.
Balance, by the way, is pretty important in a warhammer: You don't want to overextend yourself with a weapon, especially one that isn't very good at parrying or deflecting counterattacks. You also don't want to swing too hard and lose your grip, particularly considering that warhammers were often employed from horseback. Even if you have a method of retaining the weapon, badly losing your grip on it can still prove disadvantageous, to the point of being fatal.
P.S. Mercury cored platinum hammers with iridium hafts, tungsten spikes, and beryllium sweet spots are all well and good, but in real life, anything over 2-4 lbs (kilo, kilo and a half) gets really, really heavy after desperately swinging it for several hours, without a break. If anyone out there still doesn't consider this to be a bug along the lines of the gatling-crossbow, try it sometime and let us know how it goes*.
*I'm absolutely not suggesting anyone ever try the following, but if you really wanted to simulate the stress and life-and-death nature of a real battlefield, you'd try swinging that platinum hammer while floating-for a while, atleast-in the middle of a deep swimming pool. I hope your horse is a good swimmer.