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7455 |
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Friday, May 06, 2022, Hall G1 2:20 PM Cold Gas Spraying IV |
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Effects of powder preconditioning on flowability and deposition in polymer cold spray |
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David Brennan* / Rowan University, United States of America Joseph Stanzione / Rowan University, United States Tristan Bacha/ Rowan University, United States Ular Tiitma/ Rowan University, United States Francis Haas/ Rowan University, United States |
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The cold spray process is sensitive to variations in feedstock and requires consistent powder properties, particularly flowability, to produce uniform structures. Poor powder flow causes a cascade of effects beginning with erratic feeding, generating deposits with void spaces, and inconsistent geometries. These issues result in deposits which are not suitable for testing and prevent sample replication, hindering experimental evaluation of deposits. Powder flowability is largely affected by material properties, manufacturing methods, and storage conditions; with flowability directly affecting the deposit properties of deposition efficiency, porosity, and surface finish. In this study, the flowability and deposit quality of fluoropolymer is evaluated with changing pretreatment conditions. Powder mass flowrate(g/s) is determined as outlined in ASTM(D1895-17), the angle of repose is measured, and the Hausner ratio is calculated. Flowability is evaluated for fluoropolymer powders as received, after sieving(45-100um), with drying at elevated temperature(80?C), with inert gas purging(0%RH), and after 72hrs. in a humidity chamber(95%RH). Powders exposed to humid conditions are dried under vacuum to remove moisture and retested to determine the effectiveness of reconditioning. Preconditioned, free-flowing powders are sealed in metal containers, stored under humid conditions(95%RH) for one week and reevaluated to determine the ability to protect materials from exposure to undesirable conditions. Finally, effect of preconditioning on cold spray deposit quality of fluoropolymer is evaluated. The choice of spray conditions is informed by simulation of particle velocity and temperature distribution at impact using one-dimensional compressible flow modeling. The deposition efficiency is determined gravimetrically, surface roughness is evaluated using a profilometer, and microstructure porosity is evaluated under SEM. The ability to evaluate these properties before use in the manufacturing process will save both time and money compared evaluating powder suitability by trial and error. Overall, we found that free flowing powders deposited with higher efficiency, lower porosity, and reduced surface roughness. |