Performing Member Contact:

Professor Carlos G. Levi

University of California, Santa Barbara
Materials Department, College of Engineering
1361D Engineering II
Santa Barbara, CA, 93106-5050
805-893-2381/FAX 805-893-8486
levic@engineering.ucsb.edu

• Thermal Barrier Coatings Sensors, Process Control Catalysts, Active Control of Aeroengines

• Materials, Advanced Coatings, Nonlinear Control, Risk Assessment

• EB-PVD System, Materials Research Laboratory, Composite Center

University of California, Santa Barbara

The University of California , Santa Barbara (UCSB), is the site of leading research programs on Materials and Controls closely linked to advanced gas turbine technology. While much of this research evolved from problems in aero-engine design and performance, growing interactions with the stationary gas turbine industry have motivated an expansion of activities toward the latter. Advanced materials and control systems are recognized as enabling elements of technological progress in both aero and stationary turbines. A well-integrated perspective in research can serve both areas well as attested by the rich history of technology transfer between these sectors.

Since the establishment of its Materials Department in 1985 UCSB has been a center of excellence for interdisciplinary research in advanced structural materials. The early emphasis was on the mechanics of high temperature/high performance composites, and the implementation of the resulting understanding into mechanism-based design and processing methods. A major topic within this area has been the development and study of all-oxide continuous fiber ceramic composites (CFCCs) that exhibit damage tolerance without the use of fiber coatings (Levi, Zok, McMeeking, Lange). While these activities are still continuing, the major growth in materials research related to gas turbine engines has been in Thermal Barrier Coatings. The broader theme is the evolution of microstructure and damage during processing and service, the underlying mechanisms, and the implications for the life of the coating system. Current major activities include an ONR/MURI program on the Science Underpinning Prime Reliant Coatings and an NSF/EC International Collaboration program on the Dynamics of Layered, Multifunctional High Performance Coatings (HIPERCOAT). Five faculty members are involved at UCSB (Bennett, Clarke, Evans, Levi, McMeeking) with 14 additional PI's at 11 other institutions in the US and Europe . UCSB also participated actively in the prior AGTSR program but does not presently have UTSR funding.

Additional UCSB strengths of direct interest to the gas turbine industry include world class expertise in ultralight multifunctional materials and structures (Evans, Zok, McMeeking), structural ceramics with improved properties and reliability (Evans, Lange, Clarke, Zok), advanced alloys for hostile environments (Odette, Lucas), risk studies and safety (Theofanous), and thermostructural design (Evans, Kedward, McMeeking, Yang). UCSB also has outstanding faculty working on catalysts for cleaner combustion systems (Cheetham), which can couple with expertise on materials and thermostructural design to assist in the efforts to develop improved emission controls for gas turbine based systems.

UCSB is the home of the AFOSR-PRET Center for Robust Nonlinear Control of Aeroengines, 2 directed by Professor Kokotovic and Khamash. The program focuses on the development of active control strategies to prevent surge and stall instabilities of compression systems in jet engines. Improved understanding of these instabilities is critical to the safe performance of jet engines. Their control has become essential in the drive to improve efficiency since jet engines are currently forced to operate in non-optimal conditions (relatively large mass flow) in order to stay clear of the aforementioned instabilities. The UCSB team (Mezic) has reformulated the axial compression system models in a form suitable for dynamical systems analysis. This reformulation has led to the identification of nonlinear modes that are currently guiding the active control research and place UCSB at the forefront of this field.

UC Santa Barbara has outstanding processing, characterization and testing facilities for the study of materials relevant to gas turbine engines. Of particular significance is the availability of a high rate electron-beam system dedicated to the deposition of Thermal Barrier Coatings, developed by Professor Levi's group. Ceramic coatings can be deposited using a continuously fed ingot source, 25 mm in diameter, onto stationary or rotating substrates heated to temperatures up to ~1150°C. The system can operate at pressures up to 10 mtorr with regulated oxygen injection, and deposit conventional and novel TBCs materials at rates up to 15 µm/min on a stationary substrate, or about 1/3 of that value for a rotating substrate. The system is equipped with a two color imaging pyrometer, a gas analyzer and the necessary pressure and temperature controls. In spite of its high rate deposition capabilities, this system was designed so that it could be used directly by students (after reasonable training) following our philosophy of providing the students with the best possible combination of theoretical and hands-on experiences.

A major experimental asset at UCSB is the Optical Piezospectroscopy Microprobe Facility, under the direction of Professor Clarke. Piezospectroscopy is a non-contact, non-destructive optical spectroscopy technique for the measurement of stresses. UCSB has the capability of obtaining piezospectroscopic information from regions as small as 1 µm across. The principal instrument in the facility, the optical microprobe, consists of a high resolution (better than 0.01 cm -1 ), 1 m optical spectrometer attached to an optical microscope. Spectroscopy is performed using either an argon ion laser or a HeNe laser source, and the signals detected with either a liquid nitrogen cooled CCD or a photomultiplier. Use of the microscope enables regions on a sample to be identified in the optical microscope, the laser beam focused onto those regions and then their optical spectra recorded. Two principal forms of spectroscopy are exploited in determining local stress in a sample, photostimulated luminescence (fluorescence) and Raman. The former is particularly suited to stress measurement in oxide scales and thermal barrier coatings whereas the latter has proved to be most useful in analyzing stresses in electronic circuits. A variety of in-situ, testing capabilities in the microprobe are available including the ability to cool samples, apply mechanical loads and local heating. The stress in any shaped sample that can fit under the optical microscope can be analyzed, including whole turbine blades. Larger sized objects can be analyzed using a fiber-optic extension.

In addition to the EB-PVD facility dedicated to TBCs, the Materials Processing Laboratory includes two additional EB-PVD systems for the deposition of metallic coatings for bond coat studies. There is also extensive equipment for alloy preparation and heat treatment under inert or controlled atmospheres; equipment for ceramic powder processing and densification; and a system for the fabrication of continuous-fiber oxide composites. Particularly relevant to the AGTSR research are laboratories for lithography and thin-film deposition within the superb microelectronics facilities that have earned UCSB the designation as a key node in the National Nanofabrication Users Network (NNUN). There are also facilities for measuring thermal conductivity using lasers (Clarke, Bennett, Zok) and third harmonic (Clarke) techniques.

Extensive mechanical testing equipment for ambient and elevated temperatures is available, including all the ancillary instrumentation required for research on the behavior and properties of composites and coatings. This is complemented by extensive computational facilities for performing finite element computations involving plasticity and fracture mechanics. This unusual suite of facilities is complemented by extensive characterization laboratories for X-ray, electron microscopy (SEM, TEM), atomic force microscopy (AFM), SIMS, and NMR spectroscopy, many of which are part of the NSF sponsored Materials Science Research and Engineering Center at UCSB.

http://www.materials.ucsb.edu/TBC/index.php
http://www.ece.ucsb.edu/ccec/pages/research2.htm
http://www.materials.ucsb.edu/MURI/index.htm
http://www.materials.ucsb.edu/~nsf/