Characterization of Nano-Porous Si-Cu Composites to Enhance Lubricant Retention Impacting the Tribological Properties of Sliding Surfaces

As the expectations for modern machinery\u27s tribological and thermal performances continue to rise, the retention of lubricant on the contact surfaces of their sliding components becomes an increasingly important issue. Friction and wear cause heat-related failures which lead to catastrophic damage to machinery. Evaporation of a lubricant\u27s volatile constituents as well as lubricant migration leads not only to a reduction in lubricant quantity but also in its quality, thus facilitating component failures. In order to enhance component reliability, the surface should incorporate features that actively retain lubricants. The unique properties of nano-porous topographies such as their high surface area-to-volume ratio indicate they hold great potential to address these lubrication issues. Thermodynamics-based numerical models of smooth and nano-porous Si-Cu composite topographies were developed to predict the trends of lubricant retention. Photolithographic processes as well as physical etching and thin film deposition tools were utilized to fabricate smooth and patterned Si-Cu composite sample types. The nano-porous topographies incorporated various nano-pore geometries for determination of the optimum conditions for lubricant retention. Amorphous Si film was deposited on the samples using chemical vapor deposition which served as a surface chemistry modification to examine the film\u27s potential to enhance lubricant retention. Lubricant retention tests were performed using a custom-fabricated apparatus for evaporating lubricant from the sample types. Finally, the model\u27s predictions of lubricant retention trends were compared to actual testing results to examine the validity of those predictions. The predictions of the models were supported by the evaporation testing data obtained from the samples. It was found that surface nano-pores having the proper geometry, in combination with the dehydrogenated amorphous Si surface chemistry, could significantly enhance retention above the one micrometer fluid film thickness typically formed between interacting surfaces of machine components undergoing relative motion. The surface features show potential to prevent many types of mechanical failures, reduce maintenance costs, and achieve higher energy efficiency

Surface Wetting and Friction Studies of Nano-Engineered Surfaces on Copper Substrate

Nano-engineered-textures on a material surface can dramatically improve the wetting and non-wetting properties of a surface, and they also show promise to address friction issues that affect surfaces in contact. In this work, aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) was used to produce nano-textures on copper (Cu) substrates. A study was performed to examine the effects of changing the annealing conditions and a-Si thickness on nano-texture formation. The creation of various nano-topographies and chemically modifying them using octafluorocyclobutane (C4F8) was performed to control hydrophilicity, hydrophobicity, and oil affinity of nano-textured surfaces. A video-based contact angle measurement system was used to measure the surface wetting properties. Scanning electron microscopy (SEM) was employed to characterize the surface nano-topographies and provide a basis for qualitative and quantitative analysis of the nano-texture formations. Scratch testing was performed using a TriboIndenter to assess the potential of the nano-textured Cu substrates to lower the coefficient of friction (COF). It was found that the thicker a-Si layer generated larger textures overall which contributed to water contact angle (CA) results ranging between superhydrophilic and superhydrophobic, as well as increased oil affinity of Cu substrate. The nano-textured surfaces also achieved COF values that were 40 % lower than as-received (AR) Cu