Prof. Ersan Üstündag

Assistant Professor of Materials Science

The main focus of our group is ceramics and ceramic-based composite materials. Our approach is to gain a fundamental understanding of microstructure evolution during processing and to relate this knowledge to materials properties. The ultimate aim in this approach is to obtain microstructure-property relationships and to use that information to modify the processing conditions so that the desired materials property is achieved.

We use a variety of processing techniques to produce our materials: Classical ceramic processing (hot pressing, sintering, etc.); partial reduction reactions of mixed oxides; displacement reactions which are reactive phase transformations; and sol-gel processing. The characterization tools we employ in our studies include electron microscopy (scanning, transmission and analytical), X-ray diffraction, neutron scattering and diffraction, and a number of mechanical testing methods (fracture toughness by bending and indentation, hardness, tensile and bending strength, and creep testing).

An important issue that frequently arises during the processing of ceramics is a solid state phase transformation or reaction that involves a volume or crystal shape change. In this case, residual stresses often develop that can lead to deleterious consequences such as cracking and spalling. We are studying such reactions and phase transformations using an integrated approach that includes stress measurements (both in and ex situ) with X-rays and neutrons, microstructure characterization with electron microscopy, reaction kinetics measurements, andof mechanical testing. Our goal is to investigate the evolution of these residual stresses and relate them to the microstructure and processing conditions. Once a fundamental knowledge about stress evolution is obtained, it will also be possible to manipulate these stresses to enhance materials properties.

As metal-ceramic composites are being used in an increasing number of applications, it is important to understand the effect of the metal-ceramic interface strength and structure on the mechanical properties of these materials. Recent studies have suggested the importance of a "strong" interface to obtain a high fracture toughness for the composite. The strength of the interface also determines the "best" morphology for the metal phase. We are working on a number of metal-ceramic composites investigating these issues and trying to optimize the processing parameters to obtain the maximum contribution from the metal phase.

Recent Publications

1. E. Üstündag , R. Subramanian, R. Vaia, R. Dieckmann and S. L. Sass, Acta Metall., 41 [7], 2153 (1993).

2. E. Üstündag , R. Subramanian, R. Dieckmann and S. L. Sass, in: In Situ Composites: Science and Technology, M. Singh and D. Lewis (eds.), TMS, Warrendale, Pennsylvania, (1994), p. 97.

3. E. Üstündag , R. Subramanian, R. Dieckmann and S. L. Sass, Acta Metall., 43 [1], 383 (1995).

4. R. Subramanian, E. Üstündag , R. Dieckmann and S. L. Sass, Solid State Ionics, 75, 241 (1995).

5. E. Üstündag , R. Subramanian, R. Dieckmann and S. L. Sass, "In Situ Formation of Ductile Phase Toughened Ceramics by Partial Reduction Reactions in the Ni-Al-O System" in: Advances in Ceramics Matrix Composites II, N. P. Bansal and J. P. Singh (eds.), Ceram. Trans., 46 (1995), p. 439.

6. E. Üstündag , P. Ret, R. Subramanian, R. Dieckmann and S. L. Sass, Mat. Sci. and Eng., A195, 39 (1995).

7. R. Subramanian, E. Üstündag , R. Dieckmann and S. L. Sass, Mat. Sci. and Eng., A195, 51 (1995).

8. E. Üstündag , P. Ret, Y. Shapiro, R. Subramanian, R. Dieckmann and S. L. Sass, in: Ceramic Matrix Composites - Advanced High-Temperature Structural Materials, R. A. Lowden et al. (eds.), MRS Symposium Proceedings, vol. 365, MRS, Pittsburgh, Pennsylvania, (1995), p. 125.

9. R. Kolhe, E. Üstündag , C.-Y. Hui and S. L. Sass, Acta Mater., 44 [1], 279 (1996).

10. E. D. Rodeghiero, E. Üstündag , M. Wutherow, S. L. Sass and E. P. Giannelis, in: Advances in Ceramic Matrix Composites III, N. P. Bansal (ed.), Ceram. Trans., 74 (1996), in press.

11. E. Üstündag , K. E. Sickafus, Y. He, R. B. Schwarz, P. Panda and R. Raj, in: Advances in Ceramic Matrix Composites III, N. P. Bansal (ed.), Ceram. Trans., 74 (1996), in press.

12. E. Üstündag , E. D. Rodeghiero, H. J. Yoo and A. T. Zehnder, to be submitted to Acta Mater., (1996).

PATENTS

1. E. Üstündag , R. Dieckmann and S. L. Sass, "In Situ Metal-Ceramic Microstructures by Partial Reduction Reactions in the Ni-Al-O System and the Role of Dopants," patent pending.

2. E. Üstündag , J. E. Trancik and S. L. Sass, "The Generation of Controlled Residual Stresses in Solids by Partial Reduction Reactions," patent pending.

3. S. L. Sass, M. O. Thompson, E. P. Giannelis and E. Üstündag , "Metal-Ceramic Thin Films for Magnetic Storage Applications Produced by Partial Reduction Reactions," patent pending.

4. E. Üstündag , K. E. Sickafus and R. B. Schwarz, "Processing of Metal-Ceramic Composites for Hostile Environments Using Displacement Reactions," patent pending.