Research Makes a Case for Cracks
Cracks in a coating system could be a good thing, with the potential to improve insulation properties and coating life when carefully manipulated, researchers in Sweden have found.
Researchers at University West (Högskolan Väst) in Trollhättan, Sweden, say they have developed methods to improve the surface coatings on gas turbines by playing with the size of pores and cracks.
The turbines receive a surface coating consisting of two layers: one of metal, to protect against oxidation and corrosion; and one of ceramic, to provide thermal insulation.
Controlling the Cracks
The researchers have used a computer simulation to investigate the connection between a coating's structure and its heat-insulating properties. Coating structures, which vary greatly, are made up of pores and cracks.
By controlling the shape, number and size of the cracks, a more effective surface coating can be produced, according to the team.
"We have been able to confirm the results from the computer simulation through experiments, too," says Mohit Gupta, who presented a doctoral thesis on the subject.
"One important result is that larger pores that are interconnected with cracks can give the surface coating layer much better thermal insulation and longer lifespan."
System Stress & Lifespan
The team also investigated the relationship between the surface structure of emerging oxidation and the stresses formed between the two layers as a result of oxidation.
The researchers have used this information to design a system of layers with a longer lifespan.
|©iStock.com / Mallivan
"One important result is that larger pores that are interconnected with cracks can give the surface coating layer much better thermal insulation and longer lifespan," says Mohit Gupta.
Gupta says he had designed models to study the spread of oxidation, and these models can be used to calculate the stresses between layers.
The results show that these advanced models are "a powerful tool for designing new types of coating, with properties that are far superior to those used industrially today," the university says.
GKN Aerospace, an aircraft manufacturer, and Siemens Industrial Turbomachinery, a gas turbine manufacturer, collaborated on the research. Both companies are interested in using the new coatings.