Dr. Sohn’s research group focuses on identifying failure mechanisms, developing non-destructive inspection (NDI) techniques, and improving durability/reliability of thermal barrier coatings (TBCs). TBCs, consisting of ceramic coating, thermally grown oxide (TGO), metallic bond coat and superalloy substrate offer thermal protection for hot components in gas turbine engines. The materials phenomena involved in failure of TBCs are complex, and include micro-mechanics, phase transformation, sintering, multicomponent diffusion, oxidation, creep, fatigue and fracture. Practical engineering solutions for quality control and life-remain assessment by NDI techniques are also important for industrial users of TBCs. NDI techniques such as photostimulated luminescence spectroscopy (PSLS) and electrochemical impedance spectroscopy (EIS) are being developed. In addition, improvement in durability and reliability of next-generation TBCs is being sought through innovative materials design and processing.

Professor Sohn is also active in research involving multicomponent diffusion, commonly encountered in most of the commercial materials systems at high temperatures and nuclear reactor environment. The development of multicomponent alloys also requires control of microstructure involving phase transformation and surface modification, where interdiffusion processes play a major role. Diffusion studies for multicomponent systems include experimental and analytical studies of intrinsic and interdiffusion, diffusion structures and diffusion paths, multiphase interface stability and microstructural evolution kinetic, and thermodynamic interactions among the diffusing species for metallic alloys, intermetallics and bulk metallic glasses. Experimental and analytical studies in multicomponent systems are also extended to the phenomena of thermotransport and electromigration, where diffusion occurs due to multiple gradients including concentrations, temperature and electrical potential.

Research activities by Professor Sohn also include design and development of innovative structural materials, coatings and composites for a variety of applications such as resistance against wear, impact, and oxidation.

Selected Recent Publications

Y.H. Sohn, A. Puccio, M.A. Dayananda, “Diffusion Structures and Diffusion Paths of Selected Multiphase Couples in the Fe-Ni-Al System,” Metallurgical and Materials Transactions A, 36A (2005) pp. 2361.

Y.H. Sohn, "Diffusion in Metals", Smithells Metals Reference Book 8th Edition, W.F. Gale and T.C. Totemeier, Eds., Elsevier Butterworth-Heinemann, and ASM International, 2004, pp. 13:1.

Y.H. Sohn, et al., "Non-Destructive and Microstructural Characterization of Thermal Barrier Coatings," Journal of Metals, 56 (2004) 53-56.

B.W. Kempshall, et al., "An Observation of Nearly Failed Electron Beam Physical Vapor Deposited Thermal Barrier Coating with Grit Blasted (Ni,Pt)Al Bond Coat," Thin Solid Films, 466 (2004) pp. 128.

B. Jayaraj, et al., "Electrochemical Impedance Spectroscopy of Porous ZrO2 – 8 wt.% Y2O3 and Thermally Grown Oxide on Nickel Aluminide," Materials Science and Engineering A, A372 (2004) pp. 278.


Professional Services

Chair of Atomic Transport Committee, ASM International-MSCT

Member of Alloy Phase Diagram Committee, ASM International/TMS

Member of High Temperature Materials Committee, TMS

Member of Academic Advisory Committee, University Turbine Systems Research, USDOE

Modern Turbine Blades are Coated with Ceramic Thermal Barrier Coatings by
(a) Air-Plasma Spray or (b) Electron-Beam Physical Vapor Deposition