What are the disadvantages of replacing metals with ceramics?

Answer 1

Ceramics do not perform well with tension or torsional loads.

Metals can be joined (and repaired) by welding.

Metals are easier to form into different shapes (bend, fold, draw, extrude, stamp, etc.)

Answer 2

Depends on your application. I'm assuming structural, though, since it should be obvious why replacing metal with ceramics for, say, electrical wires is a bad idea: ceramics aren't conductors.

Basically, the main structural disadvantages are with two of the properties ceramics generally have: brittleness and weakness in tension. Ceramics don't bend much, and when they break, instead of slowly pulling apart the way metals will, they generally snap. Also, they have a tendency to shatter when something hits them hard - as opposed to metals, which generally will just get dented or bent.

The other disadvantage is that ceramics are strong in compression, but weak in tension. I believe the rule of thumb with concrete is that its tensile strength is one tenth its compressive strength. So, a concrete column that can hold a thousand pounds on top of it can only hold one hundred pounds hanging beneath it. In fact, that's why we use reinforced or pre-stressed concrete: because part of every beam and girder's going to be in tension while part's in compression, and the part in tension would fail otherwise.

Now, that's not to say ceramics shouldn't ever be used. Brick and stone - which is essentially ceramics - have been construction materials for millenia - and things built with them are still standing after millenia. Not to mention, there's some applications where you flat-out can't use metals. High-temperature applications, for instance. After all, when metals get smelted, all that liquid metal is held and heated inside of... very non-melted ceramics.

There's also things like weight and fatigue considerations, but those will vary according to which metal and which ceramic you're talking about.

Answer 3

Cost, cost, cost is one reason.
Which is largely why we even invented
AI, Internet, UPC, email, Microprocessors,
fiber optics, CD, Flat Screen Displays,
NAVSAT, and GPS.
Since that my itself gets rid of the need
for a billion long tons of both metals and ceramics.