Processing and characterization of thermal barrier coatings with cryomilled bond coats
J.M. Schoenung, F. Tang, L. Ajdelsztajn
MATERIALS FORUM
Abstract
The objective of this research is to increase the life cycle times of thermal barrier coatings (TBCs) by modifying the bond coat microstructure and thus the thermally grown oxide (TGO). The effects of cryomilling the CoNiCrAlY and NiCrAlY powders that are used in the bond coat have been investigated. Cryomilling was selected because it results in agglomerates that have nanocrystalline grains, yet can be thermal sprayed, and because it results in an in-situ dispersion of nano-scale oxides and nitrides. For the CoNiCrAlY powder, nano-scale alumina particles have also been added to the system during the cryomilling step. Thermal spray processes including low-pressure plasma spray (LPPS) and high velocity oxy-fuel (HVOF) have been used to produce bond coats with different features. Air plasma-sprayed (APS) top coats have been applied. Performance has been evaluated under various conditions, including thermal cycling and static isothermal oxidation. Of particular concern has been the composition and morphology of the TGO. Although numerous factors can affect the performance, improved TBC lifetime has, indeed, been observed when cryomilled powders are used for the bond coats.
Key words: BOND COATS; THERMAL BARRIER; TBCs; TGO; top coats; cryomilling; CoNiCrAlY powder; LPPS; Thermal spray
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