Anthony G. Evans - US grants

This research is on pressure consolidation of powders into advanced ceramic, metallic, and intermetallic composites. The goal of the research is to develop an ability to predict densification that will enable the selection of optimal temperatures and pressures for processing these advanced materials. Analytical and numerical modeling will be carried out for both homogeneous and composite materials. Related experiments will be conducted to provide insight into the important physical processes of consolidation. Emphasis will be placed on densification of powder around reinforcing fibers. Accordingly, experiments will be done to investigate the incidence of fiber failure during consolidation. Models will also be developed for fiber failure and for the effect of such failure on the final mechanical properties of the consolidated composite material. The science and technology developed in this project will make it possible to process advanced composites with the desired densified net shape and mechanical properties.

9805188 Evans This GOALI project will relate the results of quantum mechanical calculations to macroscopic adhesion measurements made on the same oxide/metal interfaces with the long range goal of understanding and improving coatings for automotive applications. Greater reliance is being placed on these coatings to serve thermomechanical functions. Functions such as thermal and abrasion protection have already been realized, but the coatings have yet to achieve their full potential because of limited basic understanding about their cohesion and adhesion. Most coatings are non-equilibrium assemblages of metals and oxides, with their interfaces exerting a dominant influence on performance. Segregants have a dramatic effect on the adhesion of such interfaces. Segregant-free interfaces are typically ductile and tough, whereas segregants of carbon, sulfur, etc. can lead to weak, brittle interfaces. The interactions that cause segregant embrittlement have yet to be clarified and understood. The research has two synergistic elements: 1) It puts in place the linkages needed to connect the physics of bond rupture with continuum level interface fracture mechanics. This would be done through a combination of measurements performed on metal/oxide interfaces relevant to coatings, in conjunction with first principles bonding calculations, coupled with crack growth simulations; and 2) The results would have direct relevance to coating technology through the laboratory and field testing conducted at GM in both their Research Laboratory and Powertrain Division. %%% The GOALI research would exploit new capabilities in first principles bonding calculations to develop a basic understanding of the adhesion of interfaces having technological importance for coatings used in the automotive industry. It would involve a collaboration between the PI and J. R. Smith of General Motors, as well as with Hutchinson (Harvard) and Ruhle (Stuttgart). The GOALI collaboration will inclu de quarterly meetings involving the industrial and academic researchers, the graduate student spending time between semesters at the GM research facility, and Dr. Smith acting as co-advisor to the graduate student. In addition, GM will provide a summer internship for an undergraduate to conduct projects at GM. This project is co- funded by the Ceramics Program of the Division on Materials Research and the Office of Multidisciplinary Activities of the Mathematical and Physical Sciences Directorate. ***

Abstract: 0099695
Univ. of Santa Barbara
Carlos G. Levi

A multidisciplinary scientific team will undertake a collaborative program to investigate the dynamics of layered, multifunctional surfaces. The focus is on coating systems that provide both thermal insulation and oxidation/corrosion protection for thermostructural components. The overarching intellectual challenge is establishing a science-based protocol for optimizing functionality while integrating thermomechanically and thermochemically disparate materials that experience large temperature extremes. These systems are inherently metastable and evolve via morphological changes, diffusional interactions and thermomechanically-induced stresses that generally degrade performance and limit durability. The program aims to develop a fundamental understanding of the underlying mechanisms that could provide a basis for designing superior, durable surfaces. The scientific themes involve phase equilibria between oxides and intermetallics, diffusive and thermal transport phenomena in oxides, fundamental mechanisms of deformation and basic mechanistic aspects of oxide growth. Specific objectives seek to elucidate (a) the role of composition on the mechanisms of surface diffusion in fluorite-structured oxides, as well as boundary diffusion in intermetallics; (b) the thermomechanical behavior of individual layers, as they relate to chemistry and microstructure, and complexities associated with their interaction; (c) the interplay between processing and material parameters via microstructural modifications; and (d) the mechanisms governing thermal transport in porous multicomponent oxides. The materials systems of interest are ceramics based on zirconia and rare earth oxides, as well as Ni-based intermetallics alloyed with platinum group metals. The synthesis technologies are predominantly vapor-based, with precursor methods and melt processing used in generating model specimens. Thermodynamic, kinetic and mechanics modeling activities will be an essential complement of the experimental activities.
The program offers a balanced set of educational, scientific and technological benefits. The technological motivation derives from the drive to expand the limits and durability of structural materials, wherein durable multifunctional surfaces represent a materials challenge of highest priority. These material systems are essential to the pursuit of improved efficiency and reduced environmental impact for gas turbines, a predominant source of power for global electrification, aircraft and marine transportation, as well as numerous industrial processes. The societal and economic benefits are thus self-evident but are presently limited because of insufficient scientific understanding to guide needed improvements in materials design, processing and performance. The complexity and richness in fundamental issues associated with the dynamics of these layers provide the scientific motivation as well as the need for an interdisciplinary research approach. The team assembled has an unprecedented combination of expertise and available facilities to undertake this research. They are all closely involved in working with students and motivated by the unique educational opportunity afforded by the NSF-EC program. Accordingly, the projects will be defined to foster collaboration among American and European students. Mechanisms will be provided for extended reciprocal visits of students working together on a given topic, to experience first hand how research is done at the partner institution. By working on a broad

The International Materials Institute (IMI) at the University of California-Santa Barbara, named the International Center for Materials Science, builds upon the extensive materials expertise at UCSB and the various materials-related Centers at the University, such as the MRSEC, the Institute for Theoretical Physics and the California NanoSystems Institute. The IMI covers a broad spectrum of materials science, including photonic and electronic materials, self-assembled materials, nanomaterials and multifunctional materials. The IMI serves as umbrella for existing and to be developed world-wide networks of collaborations, both at the individual and institutional levels. The IMI international activities focus on Asia and the Americas, with a special emphasis on developing countries in those regions, but the IMI includes participants from across the world. The IMI supports an annual visitors program that convenes leading scientists from the US and abroad for a 3-month period and includes substantial participation from scientists from developing countries in Asia and Latin America. The visitors program focuses on a central materials research theme that changes from year to year and comprises seminars, discussions and active research with UCSB faculty. In addition, the IMI provides fellowships for students, postdoctoral associates and young faculty for overseas research visits. The IMI also supports annual international workshops and an annual international summer school aimed at graduate students, postdoctoral associates, and junior researchers. This award is co-funded by the Division of Materials Research and the Office of International Science and Engineering.

Models for the Performance of Layered Thermal Barrier Systems
Abstract Thermal barrier systems of columnar porous zirconia will be used for developing a general simulator that can be utilized to predict the thermomechanical evolution and performance of highly nonlinear multilayers. Microscale characterization tools will identify key phenomena, guide construction of models and provide benchmarks for hierarchical approaches. Methods ranging from first principles schemes to phenomenological continuum mechanics will be utilized with length-scale linkages, and applicability to other materials and systems will be demonstrated. The broader impacts will include a better understanding of thermal barrier systems, the development of better products for thermal protection and improved performance and efficiency of gas turbine engines. This will open avenues for improved design, performance and reliability for thermal barrier systems at higher than current temperatures. A graduate student, undergraduates and high school students will gain experience in research in an important interdisciplinary area encompassing mechanical engineering and materials science.

NON-TECHNICAL DESCRIPTION: An interdisciplinary academic/industry team has been convened to perform research on fundamental aspects of layered multifunctional systems used for the thermal and environmental protection of gas turbine components. These material systems offer quantum-leap improvements in engine efficiency with attendant benefits to the economics and environmental impact of the national energy and transportation sectors, as well as to the global competitiveness of the US industry. Fulfillment of this promise is currently hindered by inadequate understanding of how these multi-material non-equilibrium systems evolve over time upon exposure to one of the harshest environments encountered in modern technology. The research team aims to advance this understanding by focusing on the fundamental connections between the chemistry, internal structure and morphology of the layers and interfaces, their evolution over time, the impact on properties and the relevance to mechanisms that eventually compromise the integrity of the system and lead to failure. The program provides unique educational opportunities by (i) motivating students to learn the scientific foundation of their discipline within the context of a technologically important problem, (ii) working as members of an interdisciplinary team that includes scientists from a world leading company in this area (General Electric) collaborating with academics with diverse background and expertise, and (iii) having access to internships at a premier corporate research center (GE-Global Research). As research becomes increasingly global, it is deemed invaluable for students to have experiences in doing research abroad. This program offers such opportunities at collaborating institutions in Europe, Latin America and Pacific Rim countries, including GE-GRC in Bangalore. The program will benefit from the excellent outreach infrastructure of the participating universities, and the proven record of the investigators involving undergraduates and members of underrepresented groups in their research. The fundamental nature of the program, its prospective impact on a technology of critical importance to the US economy, and the educational enrichment experiences available to students are fully consistent with the goals of NSF and its sponsoring programs.
TECHNICAL DETAILS: The overarching objective of this program is to develop a fundamental understanding of the dynamics of structure evolution in layered systems subject to the extreme environments typical of gas turbine engines, and how these influence system performance. Establishing the fundamentals governing the physico-chemical phenomena within and between layers will enable the design of improved protection concepts for next generation turbine systems that operate at higher temperature. The information generated will also facilitate validation and refinement of system-level models used for design and durability assessments. The research aims to distil phenomena having crucial impact on a technologically important system by integrating component/layer functionalities with the evolutionary processes that lead to their degradation. Because of the complexity of the system and the scale of the layers, new high-resolution probes occupy a central role. Scientific advances are envisaged within the following five themes. (a) Phase evolution in refractory oxides caused by the decomposition of metastable phases and of clustering in multi-doped systems. (b) Surface diffusion in oxides, including its dependence on dopants, and its effects on the sintering of textured columnar structures. (c) The evolution of stresses and deformations induced by the thermal growth of alumina. (d) The effects of inter-diffusion between layers on phase evolution, on volumetric strains and on stress-inducing transformations; including the behavior of structurally compatible diffusion barriers. (e) The effects of structural evolution on the critical properties, especially the toughness of the various layers and interfaces, the constitutive behavior at high temperature, and the optical and thermal properties of the oxides. Projects are designed to foster collaboration, especially among students and post-docs, and to promote co-advising. Extramural experiences, especially at GE-GRC, allow students to have access to unique facilities and the interaction with industrial scientists contributes to developing an appreciation of how their dissertation research contributes to the overall effort and the progress of the field.
FUNDING: This project is co-funded by the Office of International Science and Engineering, the Engineering directorate, and the Ceramics Program within the Mathematical and Physical Sciences directorate.

This work adopts an interdisciplinary approach to examine trust, a topic with far reaching consequences. Knowing when to trust others is an essential skill, but little is known about the mental processes that lead to trust. This research introduces a model to explain the decision making process underlying trust. There are two critical factors a person considers when deciding to trust: the potential outcomes (the costs and benefits of trusting) and the perspective of the trusted party (how these people are likely to act if I trust them). The central assumption of the model is that decision making is primarily egocentric: people focus on the potential outcomes while perspective-taking plays a limited or secondary role.

Two experiments examine both trusting behavior and the process of decision making. Participants will play a series of economic trust games. The relevant information in these games will be initially concealed and participants will need to actively search in order to learn the consequences of their decisions. The researchers record and analyze the order and duration in which people search for different types of information. The first experiment will test if the decision making process is egocentric; the second experiment will attempt to reduce this egocentrism using a perspective-taking manipulation.