The Study Of Preparation And Electrical Wear Properties Of Cu-MoS₂-G Composites

Molybdenum disulfide and graphite are both good lubricants because of their hexagonal crystal system. The previous studies indicated that MoS2 reacts with matrix into new compounds during sintering process in Fe and Cu based composites, but the friction and wear properties of the samples had not been studied in detail. Electrical sliding contact exsits between the brush and the commutator in the system of electrical brush and rotor, so it is desirable for the materials to have high wear resistance and good conductivity when the currents pass. We will join molybdenum disulfide and graphite in copper substrate to achieve this goal.The Cu-MoS2-G composites were prepared by powder metallurgy method in H2 protective atmosphere with seven kinds of components in this paper. The phases, microstructures, morphologies of worn surface and surface roughness of composites were detected by some material analysis test methods, such as XRD, SEM, EDS and surface roughness measuring instrument. The research was made on the effects of MoS2 and G content changing on the physical,mechanical properties and conductivity of composites. Besides, the influences of content change and current density on the friction and wear properties of Cu-MoS2-G composites in the presence of electric current were studied by means of changing the content of MoS2 and G and current density in the electrical sliding contact.The results show that graphite has no change and MoS2 reacts with Cu into some complex compounds containing Cu, Mo and S.Larger content of MoS2 and lower content of graphite result in higher density, hardness, bending strength and resistivity.The law that both the contact voltage drop and the friction coefficient gradually increase with the increase of MoS2 and the decrease of graphite is found after the experiment of electric wear. The contact voltage drop sharply increases and the electric spark appears when MoS2 is up to 10wt%. When the content of MoS2 and graphite are both 7.5wt%, the brush will have proper hardness and conductance and its wear mass loss reaches to the minimum.The contact voltage drop of Cu(85wt%)-MoS2(7.5wt%)-G(7.5wt%) composite only have a little change when current density changing from 5 A/cm2 to 25 A/cm2, but the friction coefficient increases. Both the mechanical and electrical wear mass loss increase to a certain extent, so the total wear mass loss is proportional to current density. The brush will produce abnormal wear with the appearing of the electric spark when overload current passes.