“Carbon fiber barrels are thin steel barrels wrapped with carbon fiber. You will never be able to print them.”
What of a ceramic bore?
Betcha that could stand more throat erosion than a chromed steel barrel.
Yes, it could, but why bother? Ceramics are brittle. The first time you dropped a ceramic barrel, it would probably shatter or break.
There are already 3D printers that are making complex shapes from for-real alloy steel and stainless steel. The process is called “direct metal laser sintering,” and the Germans are in the lead on the technology (and the machines). Right now, the machines are ferociously expensive and they require a fair bit of power, but they make for-real metal parts that handle high temps to tight specs.
Once you have a chrome-moly alloy steel barrel, you just salt bath nitride it and it will have a case hardened layer that’s harder than the hinges of hell.