Study on Process Optimization of Cold Gas Spraying
- PDF / 1,654,800 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 18 Downloads / 221 Views
JTTEE5 20:608–620 DOI: 10.1007/s11666-010-9564-2 1059-9630/$19.00 ASM International
Study on Process Optimization of Cold Gas Spraying H. Tabbara, S. Gu, D.G. McCartney, T.S. Price, and P.H. Shipway (Submitted April 23, 2010; in revised form September 14, 2010) Cold gas dynamic spraying is a relatively new spray coating technique capable of depositing a variety of materials without extensive heating. As a result the inherent degradation of the powder particles found during traditional thermal spraying can be avoided. The simplicity of this technique is its most salient feature. High pressure gas is accelerated through a convergent-divergent nozzle up to supersonic velocity. The powder particles are carried to the substrate by the gas and on impact the particles deform at temperatures below their melting point. Computational modeling of thermal spray systems can provide thorough descriptions of the complex, compressible, particle-laden flow, and therefore can be utilized to strengthen understanding and allow technological progress to be made in a more systematic fashion. The computational fluid dynamic approach is adopted in this study to examine the effects of changing the nozzle cross-section shape, particle size and process gas type on the gas flow characteristics through a cold spray nozzle, as well as the spray distribution and particle velocity variation at the exit.
Keywords
3D, CFD, cold nozzle, helium
spray,
convergent-divergent
1. Introduction Developed in the mid-1980s at the Russian Academy of Science (Ref 1), cold gas dynamic spraying (CGDS) is a relatively new spray coating technique. From the outset it was demonstrated that pure metals, metal alloys, and composite powders can be deposited without extensive heating. As a result the inherent degradation of the powder particles due to overheating, which are commonly found in traditional, high-temperature thermal spraying can be largely reduced. These include: high-temperature oxidation, phase changes, crystallization, and residual tensile stresses due to solidification shrinkage (Ref 1, 2). CGDS is renowned for its simplicity. High pressure gas is accelerated through a de Laval nozzle, and depending on the type of gas, pressure, and temperature the gas velocity can exceed 1000 m/s. The powder particles which range in size from 1 to 50 lm (Ref 1) are accelerated to the substrate by the gas at temperatures below their melting point. In order to achieve adhesion on impact the particles deform in their solid state, characterized by high strain rates through the material (Ref 3). The particle velocity on impact is one of the dominant factors conH. Tabbara, and S. Gu, Energy Technology Research Group, School of Engineering Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, UK; and D.G. McCartney, T.S. Price, and P.H. Shipway, Department of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK. Contact e-mail: [email protected].
608—Volume 20(3) March 2011
trolling the
Data Loading...
