UC Merced

As we strive to increase the energy efficiency of mechanical systems, it is necessary to find different avenues to reduce energy losses. Sliding contacts are part of most mechanical systems, and they are a major source of energy dissipation due to friction and wear. Sliding friction and wear can be mitigated using a multitude of strategies, including advanced surface modification techniques, new materials that exhibit better mechanical properties and novel lubricants (both liquid and solid). In this dissertation, new approaches to each of these strategies were studied using tribological experiments at application-relevant conditions. In the advanced surface modification strategy, surface properties of Ultrasonic Nanocrystalline Surface Modified (UNSM) Ti6Al4V alloy were characterized, revealing improved scratch resistance. Also, wear tests on Electropulsing-assisted UNSM treated NiTi alloy revealed improved wear resistance compared to untreated alloy. In the new materials strategy, the friction and wear performance of 60NiTi, a relatively new material exhibiting excellent hardenability, elastic recovery, and corrosion resistance, especially suited for space applications, was studied and its performance was characterized in the presence of various greases. This study provided a necessary first step to a complete evaluation of the friction and wear performance of self-mated 60NiTi contacts. In the liquid lubricants approach, novel liquid lubricants with low molecular weight polyalkylmethacrylate additives functioning as viscosity index improvers, friction modifiers and anti-wear additives were studied for their tribological performance. Their friction performance was found to be on par with two commercial benchmarks, an anti-wear additive and a fully-formulated oil, obviating the need to add dedicated friction modifiers, potentially leading to cheaper lubricants. And, lastly, in the solid lubricants approach, the wear life of undoped and Ni-doped sputtered MoS2 coatings was investigated in ambient air conditions. Ni-doped MoS2 coatings outlasted their undoped counterpart particularly at low pressures, where a delamination-driven debris formation was found to favor longer wear life in Ni-doped coatings. Also wear evolution during run-in revealed that both undoped and Ni-doped MoS2 appear to wear through the coating thickness at the center of the contact very early on, but microstructural studies revealed that new lubricious debris generated from the sides of the wear track provided continuous lubrication until the coatings failed much later. Overall, this research evaluated the performance and investigated the mechanisms of novel techniques to improve friction and wear behavior of tribological contacts using experimental methods. The results demonstrated viability of these techniques for enabling better energy efficiency in many different possible applications.