Wear of sintered composites based on bearing steel at boundary friction with current collection against copper

The possibility of creating a composite of steel-graphite by  sintering using the simplest technology has been studied at temperature lower than 1000  °C in the electric furnace without vacuum.  The main research aim was to estimate ability of such composite  to show high wear resistance at sliding against copper counterbody  under the influence of electric current with a contact density higher  than 100  A/cm². Powder steel has been obtained by recycling of  grinding wastes of bearing production. Composites had low mechanical properties and high specific electric resistance. The high  through porosity was shown by optical metallography. Tribotechnical loading of composites has been carried out according to the  contact scheme “pin-on-ring” with a sliding velocity of 5  m/s and  with a contact pressure of 0.09  MPa. It has been noted that dry  friction of these composites has caused transfer layer emergence  on the sliding surface of copper counterbody. As a  result there was  reduction of sliding electric contact conductivity and increase in  the general copper sliding surface roughness. Impregnation by industrial oil of composites porous framework led to significant increase in specific surface contact electric conductivity and to linear  wear intensity decrease comparing with the same characteristics of  dry contact. Catastrophic wear under these conditions began at the  contact current density of 150  –  200  A/cm². It has been shown that  the placing of lead plate and composite in the specimen holder and  implementation of their joint sliding under the influence of electric  current caused additional contact electric conductivity increase and  wear intensity decrease to values of 3  –  11  μm/km at the contact  current density about 250  A/cm². Catastrophic wear in the presence  of a lead plate and industrial oil in contact zone began at the contact  current density of 250  –  300  A/cm². Contact characteristics dependence on graphite concentration was not evidently observed. It has  been established that every friction mode did not lead to copper  sliding surface deterioration. It was concluded that the use of the  restored bearing steel has the perspective for creation of current  collection materials demonstrating high wear resistance under the  influence of electric current of high contact density.

sliding electric contact,  surface layer,  contact voltage drop,  specific contact electric conductivity,  stress relaxation,  sintered composite,  pores space,  self-lubricating friction

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