1. Introduction
Wire arc spraying is an efficient and economical coating
technique, which has a wide range of applications in industry
(Ref 1-3). Some of its principal attractions are its operational
simplicity and the low cost for the wire feedstock. However, this
simplicity does not exclude that minor modifications of the
equipment design features can strongly influence the coating
properties. Because of the resurgent interest in this process, a
number of new developments in improving the equipment have
been initiated and introduced. This is particularly true for the
way the atomizing gas is delivered to the wire tips. In the wire
arc spray process, the arc between the tips of two continuously
advancing wires melts the material, and the molten metal is removed
and blown toward the substrate by a high-velocity gas
stream. This gas stream is responsible for forming the initial
droplets after removal of the molten material from the wire tips
(primary breakup), for atomizing the larger droplets (secondary
breakup), and for accelerating them toward the substrate. Higher
gas velocities will result in the generation of finer droplets,
which are accelerated to higher velocities. A detailed description
of these effects has been presented by Steffens (Ref 4).
In this article, the results of a systematic investigation of the
influence of different nozzle and shroud configurations on the
coating properties is presented, including the effects on particle
size distribution, particle velocities, coating microstructure and
composition, and coating adhesion. The nozzle configurations
investigated are shown schematically in Fig. 1 and can be characterized
as follows: A is the standard nozzle with a straight