Numerical and Experimental Investigation of Cold Spray Gas Dynamic Effects for Polymer Coating
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JTTEE5 21:852–862 DOI: 10.1007/s11666-012-9743-4 1059-9630/$19.00 Ó ASM International
Numerical and Experimental Investigation of Cold Spray Gas Dynamic Effects for Polymer Coating Abdulaziz S. Alhulaifi, Gregory A. Buck, and William J. Arbegast (Submitted September 20, 2011; in revised form January 8, 2012) Low melting temperature materials such as polymers are known to be difficult to deposit using traditional cold spray techniques. Computational fluid dynamics (CFD) models were created for various nozzle geometries and flow conditions. A schlieren optical system was used to visualize the density gradients and flow characteristics in the free jet impingement region. Based on the CFD models, it was determined that a diffuser placed into the carrier gas flow near the nozzle exit not only leads to lower particle impact velocity required for polymer deposition, but also provides for appropriate application of compression heating of the particles to produce the conditions necessary at impact for successful coating adhesion of these materials. Experiments subsequently confirmed the successful deposition of polyethylene powder onto a 7075-T6 aluminum substrate. Using air as the carrier gas, polyethylene particles of 53-75 lm diameter and 0.94 g/cm3 density, were cold spray deposited onto the aluminum substrate, with a critical impact velocity of 191 m/s. No apparent melting of the polymer particles was observed. Refinements to these concepts are currently under investigation and a patent disclosure for the idea is pending.
Keywords
CFD, cold spray, polymer coating
1. Introduction The cold spray process was discovered in the mid-1980s at the Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences (Ref 1). The advent of cold spray technology has permitted the spray coating of a wide variety of new materials on a host of different substrates previously not possible (Ref 2). Typically, inert gasses such as helium or nitrogen are used as carrier gasses to accelerate the spray particles of 1-100 lm in size to very high velocities, in the range of 500 to 1200 m/s, in a free jet. This high velocity jet subsequently impacts the substrate, and through the conversion of particle kinetic energy to plastic strain energy, a strong bonded coating is created. High gas costs (particularly for helium and nitrogen), often dictate the use of heated compressed air in place of an inert gas, which can also be used to attain the requisite high gas velocity. A key feature of the process nonetheless, is that particle temperAbdulaziz S. Alhulaifi, Gregory A. Buck, and William J. Arbegast, Department of Mechanical Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701 and Arbegast Advanced Materials Processing Center, South Dakota School of Mines and Technology, Rapid City, SD 57701; Abdulaziz S. Alhulaifi, Department of Mechanical Engineering, Yanbu Industrial College, Yanbu Alsinayiah 21477, Kingdom of Saudi Arabia. Contact e-mail: [email protected].
852—Volume 21(5) Septem
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