Warm spraying—a novel coating process based on high-velocity impact of solid particles
Seiji Kuroda, Jin Kawakita, Makoto Watanabe
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS
Abstract
In recent years, coating processes based on the impact of high-velocity solid particles such as cold spraying and aerosol deposition have been developed and attracting much industrial attention. A novel coating process called warm spraying has been developed, in which coatings are formed by the high-velocity impact of solid powder particles heated to appropriate temperatures below the melting point of the powder material. The advantages of such process are as follows: (1) the critical velocity n...Moreeeded to form a coating can be signicantly lowered by heating, (2) the degradation of feedstock powder such as oxidation can be signicantly controlled compared with conventional thermal spraying where powder is molten, and (3) various coating structures can be realized from porous to dense ones by controlling the temperature and velocity of the particles. The principles and characteristics of this new process are discussed in light of other existing spray processes such as high-velocity oxy-fuel spraying and cold spraying. The gas dynamics of particle heating and acceleration by the spraying apparatus as well as the high-velocity impact phenomena of powder particles are discussed in detail. Several examples of depositing heat sensitive materials such as titanium, metallic glass, WC Co cermet and polymers are described with potential industrial applications.
keywords:Thermal spray; Coating; Titanium oxide; Titanium; Metallic glass; WC–Co; gas dynamics; high-velocity impact; ultrahigh-molecular-weight polyethylene
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