Abstract

Reactive Plasma Spraying (RPS) with a hydrocarbon gas has been studied as a method to improve the mechanical properties of a commercially available 80:20 Ni/Cr alloy and subsequently as a method to reduce the oxygen content of MCrA1Y coatings. A conventional d.c. plasma torch has been modified by attaching a conical graphite tube (reactor) onto the end of the gun. The powder is then sprayed through the reactor with injected reactive hydrocarbon gas. The reactor shrouds the plasma flame from the external atmosphere and contains the desirable inner atmosphere necessary for RPS. When using a reactor and reactive gas the plasma environment is changed significantly, making it necessary to alter the spraying parameters from those recommended by the manufacturer for a particular powder. Work has been carried out to establish the effect various spray parameters have on the final coating such that new parameters can be selected which maximise the coatings quality and performance. Significant improvements have been achieved in terms of both objectives with hardnesses being doubled for the 80/20 Ni/Cr alloy and an order of magnitude reduction in the oxygen content for the MCrA1Y alloy.

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