Fabrication And Properties Of High Performance Wear Resistant Graphite/bronze Matrix Composites

As a kind of self-lubricating composite,graphite/bronze has a good application prospect in the fields of brake pads and sliding bearings,the hardness and wear resistance of graphite/bronze composites can be improved by adding hard phase.The research preparedβ-Si₃N₄ whisker and ferrochrome doped graphite/bronze matrix composites by powder metallurgy,and optimized the material system from the aspects of interface and composition,the friction and wear properties were tested in different environmental media.Finally,the research tried to use the high temperature self-propagating to introduce titanium carbide as hard phase,which can not only improve the interfacial bonding between graphite and matrix,but also improve the mechanical and tribological properties of composites.Theβ-Si₃N₄ whisker has remarkable anti-wear effect,which can obviously reduce the size of wear debris and wear rate,meanwhile improve the stability of the friction coefficient under different normal loads.The combination of ferrochrome alloy and matrix is good,so the ferrochrome particles are not easy to fall off during friction,which can improve the stability of friction coefficient at different rotating speeds and avoiding the possibility of increasing wear rate at high rotating speeds.The friction coefficient of the bronze matrix composite containing 12.5 vol%β-Si₃N₄whisker and 2.5 vol%ferrochrome alloy particles was stable at about 0.45 under different loads and rotating speeds.The wear rate was 67%lower than that of pure bronze,and the variation coefficient of the friction coefficient was 50%lower than that of the sample with only silicon nitride whisker,showing good comprehensive performance.The interface bond between the whisker and the bronze matrix was improved after electro-less nickel plating,the vickers hardness and bending strength of the composite increased by 103%and 62%respectively.The improvement of mechanical properties of composites is accompanied by the improvement of tribological properties.The wear rate decreased by 83%compared with pure bronze and 69%compared with the sample without surface treatment of whiskers.The friction coefficient of the composites is more stable than that of pure bronze no matter in the atmosphere,rain water or seawater.Rainwater and seawater have both corrosive and lubricating effects on the composites.After the surface modification of whiskers,the reduction of pores can reduce the corrosive effect of the medium.The flake corrosion products are mainly metal oxides and chlorides.These products adhere to the friction surface and can protect the friction surface to some extent.When the mass ratio of titanium to graphite in the raw materials was 3:1,the Vickers hardness,bending strength and compression strength of the composites were up to 122,250 MPa and 459 MPa,respectively,which were improved by 85%,20%and 128%compared with the unpretreated graphite/bronze composite materials.Moreover,the generated titanium carbide protects the matrix during the friction process,reduces the size of wear debris and wear rate,meanwhile improves the stability of friction coefficient.