| Abstract: |
Different types of thermal spray systems, including HVOF (JP5000 and DJ2600-hybrid), APS (F4-MB and Axial III) and LPPS (Sulzer Metco system) were employed to spray CoNiCrAlY bond coats on Inconel 625 substrates. The chemical composition of the bond coat powder was the same in all cases; however, the particle size distribution of the powder employed with each torch, was that specifically recommended for the torch. For optimization purposes, these bond coats were screened based on initial evaluations of roughness, porosity, residual stress, relative oxidation, and isothermal TGO growth. A single type of standard YSZ top coat was deposited via APS (9MB) on all the optimized bond coats. The TBCs were thermally cycled by employing a furnace cycle test (FCT) (1080oC-1 h followed by forced air cooling). Samples were submitted to either 10, 100 or 430 cycles or cycled to failure. The behaviour of the microstructures, bond strength values (ASTM 633) and the TGO evolution of these TBCs were investigated for the as-sprayed and thermally cycled samples. The results showed that the bond strength values decrease significantly only when the TBC is about to fail (top coat spall off). Moreover, it was observed that lower levels of oxidation of the as-sprayed bond coat do not necessarily translate into an improved thermal cycle TBC life. The two best performing TBCs had their bond coats sprayed via HVOF (DJ2600-hybrid cycle to failure at 1800 cycles) and, surprisingly, APS (Axial III - cycle to failure at 1500-1700 cycles). The performance will be explained using the results of the analysis of both the as-sprayed and cycled TBCs.
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