Study Of Microstructures And Tribological Performance Of As-Milled Exfoliated Graphites

High energy ball milling is an effective method for changing material structure and improving material performance. In this thesis, exfoliated graphites (EGs) were obtained by high temperature expanding using natural flake graphites, and as-milled EGs were prepared by high energy ball milling. In addition, the structures and tribological performances for the as-milled EGs were investigated.The effects of expanding temperature and ball milling on the morphologies and structures of the EGs were characterized by using XRD, SEM and TEM, and the effect of added element B or Ni on the structures of the as-milled EGs were studied by using XRD and TEM. Furthermore, the tribological performances of the as-milled EGs as lubrication additives were investigated using a MMU-5G type friction and wear tester, and the morphologies of worn surfaces were examined by using SEM.The experimental results have shown that, the interlayer distances for the vermicular EGs resulting from natural flake graphites were markedly increased. In addition, the EGs show a multiple layer structure. When pure EGs were ball milled, their graphitization degrees and crystallite sizes decreased with ball milling time increasing. For the as-milled EGs added with B, the element B has two effects, i.e., catalytic graphitization or amorphism caused by grinding aid. When the Ni-added EGs were ball milled and annealed, element Ni shows an obvious catalytic graphitization effect. For the EGs milled for 100h, the C(002) interplanar distance was increased, and the crystal faces were bended for different angles. Furthermore, as lubrication oil additives, the EG has a more obvious antifriction effect than the flake graphite. When the B-added EGs were used as lubrication oil additives, friction coefficient dropped with ball milling time and testing load, but increased with testing temperature rise. When tested at 400℃and 400N, the B-added EGs as lubrication oil additives has a optimal antifriction and wear resistant performance. As lubrication oil additives, the Ni-added EGs have evident lubricating and antifriction effect, which, however, was effected greatly by ball milling time. The antifriction and wear resistant performance for the Ni-added EGs milled after 80 h was the most prominent.