Influence of Spray Materials and Their Surface Oxidation on the Critical Velocity in Cold Spraying

Abstract

The critical velocity is an important parameter in cold spraying, which determines the deposition efficiency under a given spray condition. The critical velocity depends not only on materials types, but also on particle temperature and oxidation conditions. In the present paper, three types of materials including copper, 316L stainless steel, Monel alloy were used to deposit coatings by cold spraying. The critical velocities of spray materials were determined using a novel measurement method. The oxygen content in the three powders was changed by isothermal oxidation at ambient atmosphere. The effect of oxygen content on the critical velocity was examined. It was found that the critical velocity in cold spray was significantly influenced by particle oxidation condition besides materials properties. The critical velocity of Cu particles changed from about 300 m/s to over 610 m/s with the change of oxygen content in powder. It is evident that the materials properties influence the critical velocity more remarkable at low oxygen content than at high oxygen content. The results suggest that with a severely oxidized powder the critical velocity tends to be dominated by oxide on the powder surface rather than materials properties.

Experimental Verification of Statistically Optimized Parameters for Low-Pressure Cold Spray Coating of Titanium

“…If the velocities of the particles are higher than critical velocity, there will be strong erosion as a result of hydrodynamic penetration. The optimum velocity for efficient deposition and good quality bonding lies between these two velocities [18]. The optimum velocity obtained from the statistical calculation is in good agreement with the value obtained from the CFD at temperature of 500˝C (773 K).…”

“…Basically, the velocity of the particle is always less than that of the carrier gas. Therefore, the velocity of the carrier gas must be substantially above the critical velocity for deposition of high quality coating [18]. Li et al [33] reported that particle temperature affects critical velocity.…”

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Stainless Steel 316L Coatings Produced by Cold Spray for Biomedical Applications

“…Limited research has been performed on 316L stainless steel coatings using cold spray (Ref [18][19][20][21][22][23][24]. The formation of recrystallized, nanoscale grains near particle interfaces in the as-sprayed 316L coating (N 2 and He-sprayed) was observed through TEM analysis (Ref 18) while EBSD analysis revealed a fully recrystallized microstructure after annealing (compressed air-sprayed coatings) (Ref 23).…”

The Influence of Powder Particle Velocity and Microstructure on the Properties of Cold Sprayed Copper Coatings

“…The influence of Cu particle velocity (measured in situ during the coating process) on deposition efficiency and bonding has been evaluated ( Ref 9,12,16). The DeLaval nozzle design has also been optimized on the basis of maximizing the particle velocity for a given input conditions ( Ref 17).…”