High Temperature Oxidation of Turbine Materials
June 12, 2012
Dr. James L. Smialek, current Senior Technologist in the Research and Technology Directorate, presented his work to the NASA Glenn Space Academy students, other interns, faculty fellows, and Glenn employees, focusing on high temperature oxidation and corrosion. Since 1968, Dr. Smialek’s research has contributed to the advancement of science for materials in certain components of aircraft engines.
The presentation emphasized high temperature applications where oxidation and corrosion could possibly be an issue. More specifically, Smialek covered an overview of the effects on gas turbines. Gas turbine engines generally use high performance alloys, or superalloys, for the blades of the turbine engines. This would be due to, among other reasons, the mechanical strength and stability at high temperatures, and the oxidation and corrosion resistance. The oxidation and corrosion resistance of the superalloys are provided by elements such as aluminum and chromium. When said metals are exposed to oxygen, they form a thermal barrier coating (TBC), thereby protecting the rest of the material. Different types of silicides can be used for this coating as well, however, they are difficult to use due to the oxidation coatability, meaning that the silicidesallow and create cracks in the TBC.
In the lab, Dr. Smialek has tested many different types of TBC. Physical vapor deposition (PVD) TBC has been tested, for instance, in contact with water. Over a matter of a few seconds, the PVD TBC fails by cracking and breaking, shattering into many different pieces.
Further along in the presentation, Dr. Smialek discussed about hot corrosion and how it can also have serious effects on turbines. While dramatic failures do not happen all too often, sea salt, for instance, can react with the fuels in the gas turbines to form sodium sulfate gas. The sodium sulfate gas forms a liquid deposit on the blades, thereby dissolving them. The hot corrosion swells the material, making bulges, and essentially forces the material to fall apart. However, alloy regimes have been successfully implemented to help prevent this. Dr. Smialek is currently working on research to find out more about this topic area.
Dr. Smialek attended Case Institute of Technology for both his undergraduate and graduate studies, focusing on Metallurgy, specifically for his Master’s thesis, “The Transformation Temperatures of NiAl Martensite.” For his Ph.D. he studied at Case Western Reserve University, focusing on Material Science, under the topic, “The Microstructure of Al2O3 Scales.”