| This study focused on Silicon Carbide (SiC) boundary lubrication. A variety of chemistries were tested for lubrication effectiveness using purified paraffinic oil as solvent. Many chemistries were identified that lubricate SiC including chlorine, phosphorous, oxygen, and sulfur containing compounds.; One additive, Molybdenum dithiocarbamate (DTC), produced very low friction. The load, speed, and temperature combinations which the low friction material formed was determined. The low friction product was molybdenum disulfide (MoS{dollar}sb2{dollar}). The mechanism involved decomposition of Molybdenum DTC to MoS{dollar}sb2{dollar}, forming the low friction product. When the contact temperature became too high, MoS{dollar}sb2{dollar} oxidized to MoO{dollar}sb3{dollar} and high friction resulted.; Another additive, benzyl phenyl sulfide (BPhS) was a very effective SiC lubricant. This additive formed very thick tribochemical film within the wear scar. The film formation was not influenced by sintering aids or impurities. Two competing processes controlled the concentration range which BPhS was effective. As the BPhS concentration increased to 8%, a protective film formed and the film thickness increased as additive concentration increased. At higher concentrations, severe damage occurred near the wear scar exit. The concentration which severe damage appears was controlled by material microstructure.; BPhS film characterization was performed using multiple analytical techniques. It was found that the film was tenacious, cohesive, comprised of high molecular weight material, comprised of C, H, S, and O, is organic in nature and binds to the surface through an oxygen atom bound to silicon. Both the solvent molecules and the chemical compound were essential constituents of the film.; A mechanism is proposed for SiC lubrication by BPhS and Phenyl Disulfide (PhDS) in paraffin oil in which both PhDS and BPhS participate in parallel reactions to function as antioxidants and antiwear agents. For BPhS, no antioxidant capacity was observed; therefore, BPhS forms effective antiwear film under argon and air atmospheres. PhDS was an effective antioxidant. Therefore, in air PhDS functions as an antioxidant and insufficient antiwear film is formed for PhDS to be effective. In argon, PhDS forms an equally effective antiwear film. A "dual film" process was found responsible for the SiC-BPhS film. |
