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7443 |
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Wednesday, May 04, 2022, Hall D 3:45 PM Young Professionals Session |
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Effects of powder feedstock pre-heating on polymer cold spray deposition |
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Tristan Bacha* / Rowan University, United States of America Joseph Stanzione / Rowan University, United States David Brennan/ Rowan University, United States Ülar Tiitma/ Rowan University, United States Francis Haas/ Rowan University, United States |
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The feasibility of processing various polymers by cold spray has been exemplified by depositions with low porosity and material properties comparable to the bulk. However, cold sprayed polymers are generally deposited with low deposition efficiency compared to extensively studied metal sprays. Low efficiencies in polymer sprays are attributed to characteristic differences in material properties between metals and polymers. Notably, the thermophysical properties of polymers limit heat transfer and promote intra-particle thermal gradients that develop in-flight inside polymer particles as they are subject to a hot gas stream in a nozzle. These properties (e.g., thermal conductivity, heat capacity, density) and low deposition efficiencies demand alterations to the cold spray process equipment beyond the state of the art for metal sprays. Herein, a custom powder feeder is used to pre-heat powder to temperatures below the melting point before contacting the high velocity carrier gas in the nozzle. Pre-heating the powder feedstock is demonstrated to be a viable means of increasing particle temperature upon impact that has not been utilized in the cold spray of polymers on commercial systems. Simulations of in-flight particle temperature indicate that the bulk averaged temperature of a polymer particle upon impact with a substrate increases linearly with particle pre-heat temperature. Simulation results motivate this study of pre-heat temperature of the powder feedstock as a control variable in polymer cold sprays. The effects of particle pre-heat temperatures on deposit strength are determined by ASTM C633 mechanical testing. Microstructural differences between deposits are elucidated by electron microscopy. Results indicate that deposition efficiency increases with increasing particle preheat temperature. Based on microstructural analysis, deposit compaction does not always increase with particle pre-heat temperature. This discontinuity is attributed to several modes of deformation occurring due to the interaction of a particle’s average temperature upon impact with its impact velocity. |