Effect of iron addition on the structure and properties of copper-based friction powder material used under friction conditions with lubrication

Machines and mechanisms contain units responsible for their movement and stopping, and such units use friction materials. These units include oil-cooled brakes, hydromechanical transmissions, and clutches. They use mainly copper-based friction materials providing the high coefficient of friction and wear resistance. These materials feature by effective heat dissipation since a large amount of heat is released in these areas for a short period of time. The paper presents the results of studies into the effect of iron addition into a frictional powder material based on BrO6 and BrO12 bronze on its structure, mechanical and tribotechnical properties. It was shown that the introduction of iron contributes to an increase in the coefficient of friction from 0.034 to 0.055 for the BrO6-based friction material and from 0.042 to 0.073 for the BrO12-based friction material. It was determined that the ultimate compression strength of the BrO12-based friction material is 340 MPa without iron addition, 310 MPa at 10 vol.% of iron, and 180 MPa at 50 vol.% of iron. This is due to the fact that the iron content of more than 30 vol.% results in the change of the frame structure of the material to the matrix one having a sintering temperature higher than the temperature used in the paper for friction material sintering. It was found that for the BrO6-based friction material there are both rounded and elongated inclusions in the copper phase up to 2.5 μm in size with the iron content of 30–50 %. In the BrO12-based material there are more iron inclusions in the copper phase and their size are much larger, the length of inclusions reaches 20 μm, and the iron content in them is 49–73 %.