Scanning Microscopy


The phenomenon "High Temperature Corrosion" (HTC) is described; three different types (pure oxidation, high temperature hot corrosion, low temperature hot corrosion) are defined. HTC is demonstrated taking gas turbine blades as an example. The results of laboratory HTC tests under defined conditions were compared with those of long time engine experience; the agreement is very satisfactory.

Metallurgical investigations with scanning electron microscopy and EDX-/WDX-analytical techniques gave explanations for the behaviour of protective coatings . The corrosion mechanism of a NiCrAlY-plasma spray coating is explained as consequence of Cr- and Al-oxidation. A special analytical technique - the "integral layer profile analysis" is introduced to ameliorate concentration profile methods. By examining IN 738 LC specimen with CoCrAlY-plasma spray coating, stressed by hot gas at 900°C, the limits of this system are shown.

The aim of the present work is to demonstrate how the analytical techniques mentioned can contribute to the selection of materials and protective coatings leading to higher rentability, higher output and durability of the plant.

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