Thierry A. Blanchet - US grants

9457596 Blanchet An NYI award will support research on the formation of high temperature carbon solid lubricants directly on bearing surfaces from the decomposition of carbonaceous gases. Process models incorporating kinetics and thermodynamics of the processes will be developed and validated experimentally. The feasibility of controlling the deposition process will be assessed. ***

9975691
Schadler

This award will provide partial support for the acquisition of a micro Raman spectrometer (MRS) for use of applications including: micro-mechanical behavior of materials, tribology, nanotube technology, biomaterials, and microelectronics. Students from materials engineering, mechanical engineering, and biomediacal engineering will be the primary users of the proposed equipment, but it will be available to other users as well. This instrument will provide research capability currently not available at Rensselaer. It will strengthen many current research programs and provide numerous opportunities for developing new programs. The MRS is a state-of-the-art central facility with an order of magnitude faster count times and better spatial resolution than the technology currently available at Rensselaer.

The MRS will do more than impact individual projects. It: (1) will contribute to the infrastructure in Rensselaer's developing center of excellence in nano-structured materials; (2) will help advance the field of micromechanical behavior (i.e., MRS is the only technique capable of directly probing the strain in fibers embedded in a polymer composite), and ; (3) will be used for innovation in studying materials for microelectronic applications and tribology, and bone implant materials.

MRS is becoming a standard analytical technique, and RPI students in many areas of study need experience in Raman spectroscopy. The facility will be available to our microscopy for undergraduate research projects. The Department also teaches a course in nanostructured materials in a seminar format. Thus, as new developments are uncovered using micro Raman spectroscopy, they will be included in this course through the guest lectures and/or student projects.
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This is a unique investment which is expected to advance fundamental knowledge, and provide excellent training for students at all levels.
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This research project proposes to explore and demonstrate a new approach to adaptive high-temperature lubrication. Self-organized nanopores within wear-resistant coatings are exploited to guide lubricant flow to the sliding contact surface. As a model system, this project uses sputter deposited CrN-Ag nanocomposite coatings where nanoporous CrN acts as a hard wear-resistant matrix which contains Ag, a low- and high-temperature solid lubricant. The project focuses on (a) understanding the nanopore formation mechanism, based on atomic shadowing effects and surface diffusion processes, by studying nanopore dimensions and Ag distribution as a function of deposition angle, growth temperature, ion-irradiation flux, (b) developing a kinetic model for lubricant-diffusion through 1-nm-wide nanopores, including geometrical constraints for transport and agglomerate formation within the coating, using annealing experiments and compositional mapping, and (c) studying the adaptive lubrication mechanisms at elevated temperatures, by mapping friction and wear over a space of temperature, contact pressure, and sliding speed.

This research program will provide a fundamental scientific understanding, including coating deposition, lubricant transport, and tribological mechanisms, for the investigated new approach for self-lubrication. The new approach uses self-assembled 1-nm-wide pores, that form in transition-metal nitride hard-coatings, as channels that guide the diffusive transport of solid lubricants. During high-temperature operation, a solid lubricant which is contained in the hard matrix will move through the pores to replenish a lubricious surface-layer. This new strategy is applicable to a range of coating systems and has the potential to become a breakthrough technology by providing low friction surfaces in various environments and during multiple temperature cycles ranging from 0 to ~1000 C. Applications include hard wear-resistant lubricious coatings for high-temperature bearings in fuel-efficient jet-engines and gas-turbines, solid-lubrication in cyclic air-vacuum environments for space applications, and oil-free air-foil bearings in gas compressors for fuel cells.

This research effort focuses on a new approach to high-temperature self-lubrication, using wear-resistant nanoporous coatings. The key idea is to control and guide the flow of easily-sheared solid lubricant inclusions through nanopore channels within the hard matrix of a composite coating towards its sliding contact surface. It is envisioned that the lubricant flow can be controlled by (i) the original lubricant agglomerate size, (ii) the channel width, and (iii) a thin barrier-layer that allows diffusion only exactly where wear indicates lubricant depletion. The primary advantage of this approach over isotropic or multilayered adaptive composite coatings is the much smaller amount of wear that is required to initiate the supply of additional lubricant to the surface, resulting in less abrasive wear debris and, in turn, greatly enhanced coating life-time.

While specifically exploring silver solid lubricant inclusions within a chromium nitride nanoporous matrix, this new strategy is applicable to a range of coating systems and has the potential to become a true breakthrough technology by providing low friction surfaces in various environments and during multiple temperature cycles ranging from 0 to ~1000°C. Applications include hard wear-resistant lubricious coatings for high-temperature bearings in fuel-efficient jet-engines and gas-turbines, solid-lubrication in cyclic air-vacuum environments for space applications, and oil-free air-foil bearings in gas compressors for fuel cells and hydrogen storage. The research effort will also provide the dissertation experience of one graduate student through completion of the doctoral degree, as well as a mind-broadening experience for several undergraduate students to also be involved in the research laboratories. Finally, a hands-on friction and wear sliding test involving solid lubricant-containing materials will be performed by over 200 mechanical engineering undergraduate students per year in their required junior-level Mechanical Systems Laboratory course, providing them direct exposure to the field of engineered multi-functional adaptive materials.

The objective of this grant is to elucidate the fundamental mechanisms that are responsible for the suppression of wear in graphene-polymer composites. Our goal in this project is to develop an in-depth understanding of the enhanced ability of graphene additives to resist wear in polymers. Graphene is interesting from the point of view of wear suppression since it has in-plane sheet dimensions of the order of several microns coupled with nanometer scale sheet thickness. The microscale dimensions of the graphene sheets enables it to effectively interfere with debris generation processes in polymers, while the nanometer scale thickness, low density and planer sheet geometry of graphene enables a huge interfacial contact area with very large number density of graphene platelets in the matrix. Moreover, the sliding of individual graphene planes within graphene platelets is expected to enhance the lubrication effect and reduce the friction levels in addition to the material wear rates.

If successful, the proposed work will provide the fundamental understanding necessary to enable the rational design of wear-resistant graphene polymer composites. The excellent wear suppression ability of graphene fillers coupled with their potentially low production cost makes this technology very promising for industrial applications. Such composites offering reduced friction and wear have a wide range of applications in the aerospace, medical, chemical, automotive and electronics industries. Outreach activities include demonstrations to students from New York State's New Visions high school program. This will help to popularize science and to attract underrepresented groups to careers in science and engineering.

NON-TECHNICAL DESCRIPTION: Glasses have many important applications because they are transparent, low cost, light-weight, and can be produced in large quantities and rapidly. They have one drawback: a lack of high mechanical strength. There are some methods to make glasses stronger such as rapid cooling called tempering which is used to make stronger window glasses or the ion-exchange method which is used to make stronger touch screen for smart phones. However, these methods are not applicable to all glasses and cannot be used, for example, to make stronger silica glass optical fibers. A new glass strengthening method, which can be used for all types of glasses, is explored.

TECHNICAL DETAILS: Water vapor in the atmosphere can affect the glass surface characteristics. When a glass is subjected to a tensile stress below the critical stress which can break the glass, at an appropriate temperature below the glass transition temperature, some of the surface tensile stress is relaxed by the influence of moisture. When the applied tensile stress is removed, the surface of the glass acquires a residual compressive stress. The resulting glass sample is stronger than before, because a greater tensile stress is required, in order to overcome the generated surface compressive stress, to break the glass. By clarifying mechanism by which water promotes surface stress relaxation and controls the kinetics of surface residual stress generation, an optimum temperature, time, tensile stress, and moisture content can be chosen to produce high strength glasses. Specifically, the magnitude of a sub-micrometer thick surface residual stress in silica glass optical fiber, produced by heating under a tensile stress and water vapor, can be estimated by using both the bending of sliced fibers as well as FTIR reflection spectroscopy and the result compared with the measured mechanical strength of the fibers. Furthermore, the proposed mechanism of glass strengthening can explain some long-standing mysteries in glass science. For example, a crack in a glass can grow under a low tensile stress. However, when the glass was first subjected to a low tensile stress, one which does not cause crack growth, and then subjected to the original tensile stress, the crack does not grow. Apparently, the glass became stronger by a sub-critical tensile stress application, but no convincing explanation exists at the present. In this research two graduate students and two undergraduates are trained on this research topic which combines exploration of the science and technology of glasses.

Non-Technical Description: A trace amount of water vapor in the atmosphere can have large effects on mechanical strength of oxide glasses. One important step of this effect is the fast elimination of the surface stress. This surface stress removal can cause weakening of strengthened glasses. At the same time, the phenomenon can be used to make glass mechanically stronger. The present research can clarify how a trace amount of water can cause these seemingly contradictory phenomena. Research results are discussed in the formal Glass Science course during the academic year, as well as in a "pop-up' short course that includes a broader audience beyond science and engineering during summer sessions. Students - both women and men, and both undergraduates and graduates -trained in this research become valued employees for US high technology companies.

Technical Details: In comparison to bulk glass, oxide glass surfaces (of the same composition) exhibit faster stress relaxation realized by moisture in air. This phenomenon is used to make mechanically stronger glass fibers by building the surface compressive stress caused by the fast surface stress relaxation. The phenomena can also explain long-standing mysteries related to mechanical strength of glasses such as the strength degradation of ion-exchange strengthened glasses, and static fatigue limit. The phenomenon of the fast surface stress relaxation is expected to be important in all amorphous oxides with large surface areas such as thin films, nano-particles and curved surfaces, which readily interact with a trace amount of water vapor. One main objective of the present research is to clarify the scientific origin of the fast surface stress relaxation. The second objective is to optimize the fiber strengthening process and clarify various anomalous features such as anomalous oxidation kinetics of Si with small radius of curvature. During this proposed research, two graduate students and four undergraduate students per year are trained in the glass science field.