Applications of Quasicrystalline materials as Thermal Barriers in Aeronautics and Future Perspective ofUse for these Materials

Abstract

Quasicrystalline materials (QCs) have very interesting properties which make them good candidates to be used as coatings resistant to wear, high temperature oxidation, corrosion, etc. the potential application of AI71Co13Fe8Co8 (QC1), a quasicrystalline approximant alloy, as a thermal barrier coating (TBC) for components of aeronautical and power generation turbines was explored in our laboratories and the results are presented in this paper. QC1 is stable at I 1000°C and has a thermal conductivity similar to that of yttria stabilized zirconia (YSZ), the most commonly used material for TBCs. QC1 powders were low pressure plasma sprayed on IN100 superalloy and coatings of excellent quality were obtained after a series of optimization experiments. the “as deposited” coatings were characterized by XRD, SEM and TEM and the results indicated that the coatings retained the same microstructure and phase composition as the bulk material. However, when coated specimens were heat treated at 950°C, interdifussion between coating and substrate took place resulting in the transformation of the QC approximant phase. To avoid or retard this process, the effect of several diffussion barrier layers, deposited between substrate and coating, was studied and the results showed that some of these barriers were quite efficient in slowing the diffusion process. Extensive cyclic oxidation and hot corrosion studies were carried out, showing promising results for this new type of TBC coatings. A short term ground engine test was carried out with coated blades.