A study at the University West (Högskolan Väst) investigated the shape and number of cracks in gas turbine coating and found that not all cracks are bad.
The surface coating used on gas turbines to increase lifespan, consists of two layers – one of metal to protect against oxidation and corrosion , and a ceramic one for thermal insulation. The structure of the coating varies, with pores and cracks of different sizes, which determine the efficiency of the thermal insulation and the length of the coating life-span.
Using computer simulation, they investigated the connection between the structure of the coating and its heat-insulating properties. By controlling the shape, number and size of the cracks in the coating, they have been able to produce a more effective surface coating. They also investigated the relationship between the surface structure of emerging oxidation and the stresses that are formed between the two layers as a result of oxidation, to design a system of layers with a longer life-span.
"One important result is that larger pores that are interconnected with cracks can give the surface coating layer much better thermal insulation and longer life-span," says Mohit Gupta who has presented a doctoral thesis on this subject.
Models he designed for studying the spreading of oxidation can be used to calculate the stresses between the layers that is caused by oxidation. The results show that these models can be used to design new types of coating, with superior properties to those used today.
The research was in collaboration with GKN Aerospace and Siemens Industrial Turbomachinery.
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