Fighting erosion of thermal barrier coatings
Thermal barrier systems are key materials employed in gas turbine technology due to their excellent chemical and thermal properties. The HIPERCOAT project focused on shedding some light in the complex scientific aspects of the design, performance and durability of thermal barriers. Electron beam physical vapour deposited (EB-PVD) thermal barrier coatings that are widely used in gas turbines often lead to malfunctions. These failures are mainly caused by different, highly complicated mechanisms and include damage induced by erosion or foreign object impact with the columnar EB-PVD ceramic. Concentrating on this complex mechanism the HIPERCOAT project researchers extensively investigated the role of chemistry and microstructure on the complex mechanics of surface damage. Erosion due to small particle impact results in cracking of the individual columns in the near surface region of the thermal barrier. During the impact, elastic stress waves propagate through the columns, interact with imperfections of the coating material within each column and cause damage. Key factors that affect the damaging process include the column diameter and inclination, the impact physical parameters (particle size, velocity, angle of impact), temperature and the ceramic composition. Foreign object impact causes extended damage and material loss down to the ceramic bond coat interface, which may weaken the thermal protection capabilities of the material. The phenomena were found to be more intense in the case of large particles (greater than 200 micro-metres) impacting with a high velocity (in excess of 100 m/s). The temperature level also affects the type of damage, being either shear cracking or column buckling results. For more information click at: http://www.materials.ucsb.edu/~nsf/
