Reactive plasma spraying

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 nickel-chromium alloy, and subsequently as a method to reduce the oxygen content of sprayed MCrAlY 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 spraying using a reactor and reactive gas the plasma environment is changed significantly. 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 Reactively sprayed 80: 20 Ni/Cr coatings have been produced with an in- stiu carbide reinforcing phase, leading to greatly improved wear properties compared with conventionally sprayed coatings. Reactively sprayed MCrAlY coatings have been deposited with an order of magnitude reduction in oxide levels, leading to considerably fewer line defects such as oxide stringers and delarninations. An attempt has been made with the aid of computational fluid dynamics software, to model phenomenon occurring inside the reactor section as a method to appraise reactor design and suggest further design improvements.