Surface lubrication of graphite fabric reinforced epoxy composites with nano- and micro-sized hexagonal boron nitride

In this work graphite fabric (GrF) as a reinforcement and epoxy matrix with high thermal stability (315 degrees C) as a binder were selected for developing high performance composites. Fibers of carbon or graphite are known to be inert with the matrices and hence possibility of composites with weaker interface always exists. Hence these are expected to be treated prior to the use as reinforcement. In this work GrF was treated with HNO3 as per standard practice. The composites with modified and unmodified GrF were developed using a solution impregnation technique followed by compression molding. Two more composites were developed with surface modification technique using these treated GrF. For surface designing a solid lubricant, hexagonal boron nitride-hBN also known as white graphite was used in two sizes {micron (approximate to 1.5 mu m) and nano-meter (approximate to 70 nm)} in different amounts. These composites were evaluated for adhesive wear performance under selected loads and speed by sliding against a mild steel disc (Ra approximate to 0.1 mu m). It was observed that the mu and specific wear rate (K-0) of a composite without modified GrF and without solid lubricated surfaces showed higher values as compared to composites with treated GrF and solid lubricated surfaces. Surface modification by nano-hBN proved most effective leading to a very low mu and K-0. Overall, mu and K-0 as low as 0.04 and 3 x 10(-16) m(3)/Nm were reported when tested under severe conditions which are treated as extremely good for antifriction materials. The thermo-mechanical stresses incurred in the fibers were examined using Raman spectroscopy by conducting long duration experiments. The film transfer on the disc which was responsible for this performance was studied using SEM-EDAX. (C) 2013 Elsevier B.V. All rights reserved.