At the picture above you can see the pair of gears of the high pressure stage of the fuel pump without the support bearings. Note the significant wear of the gears due to the cavitation effect. They are made of steel alloy.

At the picture above you can see one of the gears of the high pressure stage of the pump together with it’s supporting bearings. The damage to the gear teeth is obvious, being the main reason for the erratic operation of the pump, (low pressure output, noise, increased friction).