Thomas W. Scharf - US grants

Moving mechanical assemblies (MMA), such as miniature rolling element bearings, gears and other precision components, must function reliably and predictably in device operation. Advancements in MMA products have required a reduction in the dimensions of these devices, thereby increasing the influence of dynamic tribological surface interactions on performance and reliability. Presently, there are several shortcomings and challenges, including nanoscale conformality and uniformity of coatings on buried surfaces/interfaces, application of new routes to coating synthesis on fully assembled MMA, accurate characterization of complex coating microstructures and tribochemically-modified interfaces under shearing loads, and site-selective deposition of coating on critical tribological surfaces. UNT and Timken propose a two-fold research strategy to address these issues. First, novel coating synthesis techniques will be developed utilizing atomic layer deposition (ALD), with the goal of depositing nanocomposite and nanolaminate solid lubricants, especially lubricious oxides and metal nitrides/sulphides, on fully assembled MMA devices. In addition, the fundamental structure and properties of nanocomposite tribological films deposited with plasma-discharge vapor deposition systems will be examined, including films containing nanoscale metal carbides in mixed sp3/sp2 carbon matrices. Second, the research will address the composition/structure dependence of tribological thin films on performance and explore the mechanisms of film modification by tribo-chemical reactions in MMA applications. Desired outcomes include correlations of film initial nanostructure and properties to macro-scale friction and wear performance, increasing scientific understanding of these phenomena and supporting the development of predictive models. To accomplish these goals, new diagnostic tools and methods at UNT will be utilized to study interfacial composition, periodicity, and morphological changes occurring at the surface and in the subsurface regions, as well as tribochemical reactivity under varying contact stress and environments with focused ion beam cross-sectional SEM, analytical high resolution TEM, and local electrode 3-D atom probe (LEAP) tomography.

This proposal will address educational activities with integration of Materials Science and Engineering between UNT and Timken. During the tenure of this program, one undergraduate and one graduate student will be provided a thorough background in the processing, structure and property interrelationships of tribological coatings applicable to current surface engineering issues. This will provide the students the opportunity to externally collaborate on issues critical to future industry needs. A number of the PI's current and future students include minorities and women, and they will participate in the collaborative external interaction. This cooperative venture will help bridge the gap in transferring technology from research to commercial application. Outreach programs to local K-12 levels will also be implemented in the summer with educational and hands-on 'Materials Camp' programs.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

This award supports the renovation and modernization of approximately 2,900 square feet of space within the University of North Texas' (UNT) Center for Advanced Research and Technology (CART), located in the university's Discovery Park (about 4.5 miles north of the main campus). As part of CART, UNT will create a modern, model facility, called the UNT Nanofabrication Analysis and Research Facility (NARF), which is to be an open-access "one-stop-shop" for advanced device fabrication and analysis across multiple length and time scales. The renovations will consolidate currently spatially distributed, advanced characterization and analysis instruments; upgrade the space to include high speed cyber connectivity permitting remote access and control of these instruments; and integrate this space with a clean room and technology incubator.

Intellectual Merit: NARF will use "open system design" architecture to maximize collaboration and shared use of equipment, "integration for fabrication" to maximize entrepreneurial activities characterized by co-location of a clean room and technology incubator, and a "community/school-friendly" setting, where researchers share results and explain their work in real-time or via distance to visitors. The facility will host a unique trio of tools consisting of a dual-beam focused ion beam instrument, a high resolution transmission electron microscope, and a local electrode atom probe, capable of true atomic scale analysis of the structure and chemistry of materials, as well as many other advanced instruments, into direct proximity of one another. NARF will foster fundamental research involving nanoscale characterization and analysis applied to a wide variety of materials systems and devices, and will allow for the first time at UNT, true 3D characterization of the nanoscale structure and composition of specific components and failure sites in semiconductor devices, as well as interfaces in hybrid materials for aerospace, biomedical, and energy-related applications.

Broader Impacts: One of the primary impacts enabled by NARF will be the research training of graduate and undergraduate students, as well as post-docs and external researchers from industry, in the use of sophisticated characterization and analysis equipment. NARF will provide researchers a range of different equipment under one roof and allow them to appreciate the novel research possibilities afforded by these various techniques. Such an impact is not possible if the equipment is isolated and located at geographically scattered locations across the campus, as it is currently.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

The objective of this Major Research Instrumentation (MRI-R2) award is to acquire a high resolution x-ray tomography apparatus. A parallel computing cluster with associated software is acquired as part of the system for fast three-dimensional structure re-generation to accommodate the use by multiple researchers. A cooling stage will provide a constant temperature environment. A loading stage will allow in-situ observation of a sample under load.

The instrument will be accessed by multiple users on projects that require the ability to use non-destructive techniques to determine the microstructures as well as their evolution under deformations. The instrument will be made available to all users at the university, and industry in the region as well as in the nation. The equipment will help enhance the training of graduate and undergraduate students, including a substantial number of under-represented minority and women students, and will also support student projects at nearby high schools.

The research objective of this award is to understand the mechanisms of how defect structure in ceramic coatings (transition metal oxides and in situ formed carbides) determines the thermal/oxidative and friction/wear properties in cellular solids, such as carbon-based composites and foams. Specifically, this project will explore (a) how interstitial carbide and oxide phases, such as ZrC and ZrO2, provide thermal and oxidation resistance to carbon, and (b) how lubricious, nanocrystalline layered ceramics, such as high basal stacking fault density ZnO, and low crystallographic shear, oxygen deficient Magnéli phases, such as TiO2-x, mitigate friction and wear. In conjunction, classical molecular dynamics simulations and ab initio Density Functional Theory calculations will be implemented to study the interfacial behavior of C/ZrC/ZrO2 as well as to characterize the defect chemistry, thermodynamic properties, and mechanical/tribological behavior of the layered, low crystallographic shear ceramic coatings. This research will help answer two important questions: (1) Can the coating systems be processed with thermodynamically and kinetically stable oxide and carbide phases and interfaces? (2) How will the defect structure (planar stacking faults and vacancies/interstitials) of these phases be able to accommodate interfacial shear while providing sufficient hardness and elastic modulus?

If successful, the results of this research could also be applied and have broader impact to other refractory oxide coatings that form in situ interstitial carbide phases. Further enhancement in operating temperatures of carbon-based composites and foams for aerospace and other industries is expected with these protective coatings that require minimal processing and undergo in situ modifications during use to improve mechanical and tribological properties. Educational activities for graduate students will involve experimental and modeling components aimed to understand the fundamental thermochemical mechanisms of carbide and oxide formation and their oxidative, thermal and high temperature properties. Additionally, undergraduate students will be actively involved in this research through senior design projects. The project will introduce ceramic science and surface engineering research to high school sophomores attending the Texas Governor's School, a summer academic enrichment camp at UNT. Broader impact will also be realized through contributions to an NSF-funded cyberinfrastructure dedicated to friction: Atomic-scale Friction Research and Education Synergy Hub (AFRESH).