Warm spraying—a novel coating process based on high-velocity impact of solid particles

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 needed to form a coating can be significantly lowered by heating, (2) the degradation of feedstock powder such as oxidation can be significantly 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.

Metallization of ceramic materials based on the kinetic energy of detonation waves

“…Detonation spraying is based on the controlled detonation of a mixture of gases, such as an energetic gas (most often acetylene and propane) and oxygen, triggered by an electric discharge between the electrodes of a sparking plug. The detonation of the energetic gas generates a shock wave, which heats up the individual particles of the coating material and accelerates them in the barrel of a special gun to velocities of about 900 m/s [29][30][31][32]. Thanks to their high kinetic energy, the hot coating particles shot towards the substrate form on it a coating with a multi-layered, homogeneous, and compact structure.…”

“…The thickness of the ceramic substrate was 200 µm. The temperature of the particle moving in air after the detonation was adopted, according to the literature reports [31,35], to be 2773 K and its maximum velocity to be 850 m/s. Fig.…”

Observation of High Resolution Microstructures in Thermal Sprayed Coatings and Single Deposited Splats Using Ion Beam Milling

“…32,33) The spraying process to prepare single splats and coatings is described in detail elsewhere. 34,35) In the process, a mixture of kerosene and oxygen ignited in a combustion chamber and was mixed with nitrogen in a mixing chamber to lower its temperature. Then, nickel powder was fed into the final mixture of supersonic gases passing through a convergentdivergent nozzle.…”

Electron beam evaporation of alumina ceramics at forevacuum pressure range

“…There are several methods of deposition of conducting and dielectric materials: thermal spraying, vacuum arc deposition, and cathodic arc deposition [1][2][3]. However, most of these methods require bulky and expensive equipment or provide low efficiency due to rather low coating growth rates.…”