Abstract
Low pressure of inert gas in the vacuum chamber significantly affects the transfer of plasma particle velocity onto powder particles, residence time of powder particles in plasma and the kinetic energy of molten particles before the collision with the substrate. In addition to low pressure of inert gas in the vacuum chamber, the size and mass density of powder particles, together with plasma arc power, have the biggest impact on the average velocity of powder particles. To measure the velocity of powder particles in the vacuum chamber at low pressure, a laser speedometer is applied.The average velocity of molten powder particles V=s/t is calculated when the length of the path of powder particles that pass between two focus distances of the laser beam is divided by the time of particle passage between the two focuses. Measurements are done for vacuum chamber pressure, the values of which are usually from 6.7 to 80 kPa. The paper describes the relationship between the average velocity of Al2O3 and W powder particles and the vacuum chamber pressure, granulate distribution, mass density and plasma arc power. It was found that, for powder of lower mass density, the average velocity of particles can increase for 200 m/s with a decrease in chamber pressure.The effect of pressure on W particles of larger mass density is lower but still important, because a decrease in pressure increases the average velocity of particles up to 50%. Reducing plasma arc power reduces the maximum velocity of both types of powder particles. .
Highlights
The velocity of powder particles is an important variable size of the VPS process which affects particle melting, coating density and cohesive / adhesion strength
In order to examine the influence of the process parameters on the velocity of powder particles in the vacuum plasma system applying a laser speedometer, it was found that there is a significant relationship between the velocity of particles and the process parameters such as powder particle size, particle mass density, pressure in the chamber, plasma arc power, and electrode geometry
A large number of powders are deposited at atmospheric pressure, but requests for high-quality coatings have led to the development of powder deposition in the vacuum chamber, which is maintained at a pressure of an inert gas, usually from 1.9 to 6.7 kPa (Muehlberger, 1974, pp.245-256), (Hamatani et al, 2002, pp.79–92)
Summary
FIELD: Chemical technology ARTICLE TYPE: Original scientific paper ARTICLE LANGUAGE: English. Summary: Low pressure of inert gas in the vacuum chamber significantly affects the transfer of plasma particle velocity onto powder particles, residence time of powder particles in plasma and the kinetic energy of molten particles before the collision with the substrate. In addition to low pressure of inert gas in the vacuum chamber, the size and mass density of powder particles, together with plasma arc power, have the biggest impact on the average velocity of powder particles. Measurements are done for vacuum chamber pressure, the values of which are usually from 6.7 to 80 kPa. The paper describes the relationship between the average velocity of Al2O3 and W powder particles and the vacuum chamber pressure, granulate distribution, mass density and plasma arc power.
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