I know that you need a special nozzle to extrude abrasive filament (carbon fibre, copper, ...). I do have such a nozzle (coated steel) and am printing carbon fibre and copper filament. Last time I used it to print carbon fibre PLA. It worked well, however when I removed the nozzle from the hotend I realized that I could no longer screw the non-abrasive nozzle in (the dirt cheap 0.1$ china nozzles that work well enough for most materials) and the thread of the hotend was completely loosened up.
I had been working on a few other things with my printer, so I am not entirely sure what caused the thread to become loose, but I was wondering, are there some requirements to the hotend excluding the nozzle when printing abrasive filament?
The filament path, aka Coolend. It consists of the heartbreak, cooling solution and anything up from it.
The heater block, that holds everything together
The nozzle, in which the filament melts and is pushed out.
The part of the hotend assembly that gets to be in the most contact with the particles that are inside the abrasive filament is the nozzle through which the molten polymer gets out. Unless you have heat creep and the filament melts in the heartbreak, it is the only part that ever will encounter the abrasive particles even.
Since even the most abrasive filaments come as rather smooth filaments, only the nozzle needs to be special. Hardened Steel will hold some kilos, while people printing a lot of carbonfiber filled material swear on ruby nozzles.