With the right material, you could print the gear and then sinter it, resulting in actual metal gears. However, 80 % metal-filled PLA is at the lowest border to achieve this, and a lot of that technology is patented.
FilametTM is a Virtual Foundry product that contains around 80-92 % metal powder of 100-400 µm particle size, suspended in a carrier. The carrier material is supposedly PLA or at least functionally similar. The resulting filament is highly abrasive, requiring stainless steel1 to print more than short sections. The high metal content also gives the material a memory of its spooled-up shape. This demands extra special treatment during printing to prevent snapping the filament in the shape of a pre-heater to get it spooled off properly. The same company also offers similar products for ceramics. After printing, the models are burned-out and sintered in an oven at very high temperatures. This sintering is done in a crucible filled with carbon and alumina, burning out the PLA carrier while retaining the shape. Their material-making process is patented (patent itself) and covers all their metal, ceramic, and glass materials.
1 - or something even more hardy, like an Olsson Ruby by 3DVerkstan
The MetalXTM system by Markforged uses a special printer and proprietary Bound Powder Metal Filament that contains an unknown plastic binder. A lot of this machine and surrounding peripheries are patented and information spare. Among others, their method of creating composite filaments and their binder material, support material & sintering process are only described in patents. From their advertisement I could deduce the following process: The MetalX printer prints the item with unknown print settings, resulting in a raw item containing metal and the binder. After wash-cleaning using a liquid known as OpteonTM SF79 (Datasheet) to remove the specialty binder, the sintering happens in a free oven at 1300 °C, leaving behind a metal product. Free oven means here, that the printed part is not embedded in a filled crucible like with FilametTM.
Disclaimer: I am not affiliated with either Virtual Foundry, Markforged, 3DVerkstan, any of their products or affiliates.