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 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.