Figure 17 shows a crosscut through a section of the blade tip. Fully epitaxial growth through severallayers is evident. The epitaxial material build-up results in matched thermo-physical propertiesbetween substrate and deposit and therefore in a longer blade lifetime. Due to the high cooling ratethe dendritic structure of the deposit is much finer than that of the substrate and this results in a morehomogeneous distribution of the coating elements. It can be also seen from Figure 17, that crack-freematerial build up can be achieved on the single crystal turbine blade, but this is dependent uponcareful choice (and control) of the process parameters and a suitable substrate-filler materialcombination. Under optimum conditions the single crystal microstructure of the deposit can beextended to the edges of the blade where polycrystalline material of the plasma sprayed MCrAlY11overlay coating may be present. Usually the top of the last layer solidifies with polycrystallinemicrostructure. This thin surface layer can be either transformed into single crystal material by a finalremelting step (without powder supply) or simply be machined away.
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