Nov_Dec_AMP_Digital

iTSSe TSS A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 0 4 7 iTSSe TSS while maintaining stable deposition efficiency and coating mi- crostructural properties (e.g., porosity, vertical crack density). In contrast, many commercially available legacy plasma spray torches would require hardware maintenance after 40 hours or less. Any drift in plasma conditions could lead to changes in microstructures, resulting in coatings with different properties than what were originally designed. This technology alsooffers applicators the ability to spray complex parts at longer spray distances (75-120 mm) and still achieve similar, acceptable coating microstructures. This benefit is critical, as it significantly reduces potential robotic restrictions that are often encountered when coating turbine components with segmented TBC structures. The ability to spray segmented TBCs depends on many factors. Torch power, enthalpy, heat transfer to powder parti- cles, particle size distribution of powders, particle velocity and temperature before deposition, spray distance, application rate, and deposit efficiency are examples of factors that are crucial to the formation of acceptable coatings in a cost-ef- fective, repeatable, and efficient manner. Many of the legacy low-power plasma torches have power limits of 40 kW or be- low. These limitations restrict themaximumpowder feed rates that can be used while still obtaining the desired microstruc- tures, resulting in lower coverage rates. In contrast, coating processes that use torches with higher power and/or cascaded arc technology allow for fast- er coating production through improved application rates. The continuously evolving TBC market is incorporating these high-enthalpy and more efficient plasma systems for the fu- ture production of segmented TBCs. Figure 4 compares the coverage rate (a value that captures the overall efficiency of the entire process) of various plasma torches while targeting seg- mented microstructures with similar crack densities. Results Fig. 4 — Coverage rates of various plasma torches. Fig. 5 — Advanced thermal barrier coating systems have been designed through new chemistries and coating architectures. FEATURE 11