Surface and subsurface characterization of epoxy-mesoporous silica composites to clarify tribological properties

As-synthesized and calcined DAM-1 (Dallas Amorphous Material-1) mesoporous silica were used as particulate reinforcements in an epoxy matrix. The mesocomposites showed enhanced tribological properties over the base epoxy. The particles were introduced as both as-synthesized and calcined forms to evaluate the effect of porosity on tribological behavior. Epoxy-DAM1 as-synthesized (DSE) mesocomposites exhibited the longest duration low coefficient of friction (COF) values during the run-in regime as well as the lowest COF values in the higher friction regime. These results were attributed to the low cross-linking density envelope around the as-synthesized particles and their plate-like morphology which work together to form friction-lowering transfer films. Subsurface HRSEM imaging using focused ion beam (FIB) cross-sectioning inside wear tracks showed that shear band formation is the mode of deformation in DSE, while for Epoxy-DAM1 calcined (DCE) mesocomposites and pure epoxy, it was determined to be surface fatigue resulting from brittle cracking. This study shows that the as-synthesized particles increase the toughness of the epoxy by altering the mode of deformation and wear debris formation.