Cold Sprayed CoNiCrAlY Bond Coats for Thermal Barrier Coatings Applications

Using a high pressure cold spray equipment and N₂ as propelling gas, three different CoNiCrAlY powder cuts were investigated as feedstocks to produce bond coats (BCs) for thermal barrier coatings (TBCs). In general, all deposited coatings exhibited low values of porosity (i.e. 0.5±0.2% to 1.2 ±0.8%) with the lowest values obtained when the finest powder cut was used. Equally, CoNiCrAlY coatings obtained from the finest powder feedstock showed the highest cohesion/adhesion strength (e.g. 78 ± 7 MPa) prompting that powder and surface temperature have strong influences on the coating properties. Furthermore, air plasma spray 7wt.% YSZ  top coats were deposited on the cold sprayed bond coats to create full TBC architectures and to screen the thermally grown oxide (TGO) formation after thermal exposures, at 1100°C, for 100h isothermally and furnace cycle testing for 100 cycles. The microstructural and phase characteristics of the thermally exposed TBCs were assessed via scanning electron microscopy (SEM) and energy dispersive X-Ray (EDX). The TGO formation was analysed in conjunction with the CoNiCrAlY feedstock size distribution and the spray conditions employed and a comparison between the bond coats bevahiour is presented. It is concluded that cold gas dynamic spray has the potential to outperform other thermal spray processes for the production of MCrAlY bond coatings.