A high-purity (HP) HOSP (Hollow Oven Spherical Process) PYSZ powder has been evaluated and compared to standard PYSZ powders. The main difference is these two powders is the starting raw material purity. Four TBC systems (2 standard types and 2 high purity versions) were Air Plasma Sprayed (APS) onto CMSX-4 substrates with APS CoNiCrAlY bond coats. Thermal shock testing was performed to 50 % spallation at 1135°C with 1 hour hot cycles with forced air cooling. The as-deposited coatings and those after thermal shock failure were characterized using X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The thermal cycling results show little difference in the thermal shock resistance of the coatings with all failing in an adhesive manner with failures occurring in excess of 180 hot cycles. XRD and Raman data is used to identify the levels of monoclinic and tetragonal phases present in each coating and SEM analysis used to identify differences between PYSZ with a broad particle size distribution and a tighter controlled PYSZ particle size distribution.

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