Uniform 1 micron thick protective mullite coating on a 15 micron diameter SiC fiber

Microstructure of typical plasma sprayed thermal barrier coating showing a distribution of microcracks and pores

Undergraduate Research Opportunities in Manufacturing Engineering

Engineered Materials and Processing
Soumendra Basu, Professor
http://people.bu.edu/basu/RAindex.html
basu@bu.edu

Environmental Barrier Coatings for Advanced Gas Turbines
Silicon-based ceramics such as silicon carbide and silicon nitride are found in microturbines and are used in on-site power generation systems. These ceramics can withstand higher operating temperatures than the conventional superalloys, leading to improved efficiency and environmentally cleaner byproducts. However, when exposed to corrosive environments containing high-pressure steam at elevated temperatures, these silicon-based ceramics are susceptible to hot-corrosion and recession. We are currently developing functionally graded chemically vapor deposited mullite environmental barrier coatings with excellent corrosion, recession and thermal shock resistance. These environmental barrier coatings are expected to substantially improve the service lifetimes of these silicon-based ceramic components.

Undergraduate projects:

• Modeling the thermal shock in the coatings during cyclic oxidation and testing the coatings under these conditions.
• Studying the phase stability in the coatings by x-ray diffraction after high temperature exposure.
• Studying the hot-corrosion resistance of the coatings.

Engineering Microcracks in Thermal Barrier Coatings
Plasma sprayed coatings are commonly found in hot-sections of gas turbines. These coatings, due to their low thermal conductivity, keep the surface temperature of the blade cooler than the ambient, thereby increasing their lifetimes. One important feature of these plasma sprayed coatings is microcracks, which can serve to decrease the thermal conductivity of the coatings, thereby improving its performance. However, these microcracks can also lead to coating
spallation, which exposes the blade surface to higher temperatures and reduces their service lifetimes. Our research focuses on
understanding the mechanism of microcrack formation during deposition of these coatings, and in developing a feedback control system that allows us to engineer the microcrack distribution across the coating thickness that leads to optimal coating performance and lifetimes.

Undergraduate projects:

• Writing a program to measure the important surface roughness features in the coatings that effect the stress distribution and microcrack formation.
• Studying the effect of controlled deposition parameters on microcrack structure.