Effects of selected nanoadditives on the friction and wear performance of carbon–carbon aircraft brake composites

Abstract Nanomaterials are being produced in large volumes for the development of advanced new materials. Composites can easily make use of the nanomaterials because of the small size of the particle. With the large surface area of nanomaterials very small quantities are needed to observe significant friction altering effects as observed by numerous researchers. Specifically, when the nanomaterials become part of the friction layer they will increase the nominal area of contact, the mechanical properties and typically increase or stabilize the coefficient of friction and reduce wear. Nanomaterials were added (nanoadditives) to commercial C/C composites using ultrasonics attempting to fill in some of the open porosity. The nanoadditives used were Si, SiC, and SWCNT's. Two different concentrations of each nanoadditive in isopropyl alcohol were attempted. A total of 6 pairs of nanoadditive disks and 1 baseline pair were made. The finished 2.75 in. (69.85 mm) diameter disks were tested on a LINK ring-on-ring subscale aircraft brake dynamometer. A series of braking engagements simulating an aircraft taxiing to the runway, landing, and taxiing back to the terminal were performed totalling 50 landings. Wear was measured as mass and thickness changes of the original disks. It was found that Si and SiC had significant effects on the friction performance in the “hot” taxi after a landing with very small weight percentages. The presence of Si led to chemical changes of the friction layer and the formation of carbides. These changes would occur when the interface reaches a temperature high enough to activate the chemical process. As a consequence, the dominating oxidative wear mechanism changed to mild abrasion. Friction and wear performance is shown and discussed. Analysis of the friction layer was performed using SEM and polarized light microscopy and is presented.