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7445 |
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Wednesday, May 04, 2022, Hall D 4:10 PM Young Professionals Session |
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Effects of polymer crystallinity on deposition efficiency and porosity in cold spray of PEKK |
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Madison Kaminskyj* / Rowan University, United States of America Joseph Stanzione / Rowan University, United States Matthew Schwenger/ Rowan University, United States David Brennan/ Rowan University, United States Francis Haas/ Rowan University, United States |
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An experimental study was conducted to examine the effects of polymer feedstock degree of crystallinity (D) on cold sprayed deposits of polyether-ketone-ketone (PEKK, Arkema), a thermoplastic used in aerospace and other high-performance applications. Polymers consist of long chains forming crystalline regions with higher strength and lower ductility compared to the amorphous regions interspersed around them. The strong intermolecular attractions of the crystalline regions require more energy to deform compared to amorphous domains. As deposition relies on the plastic deformation of the impacting particle, polymers with high D may inhibit deposition, reducing deposit quality. This study evaluates three PEKK grades produced using different ratios of terephthalic (T) to isophthalic (I) moieties (T/I = 1.5, 2.3, 4.0). These ratios control D, with higher proportions of T monomers corresponding to higher crystallization rates and degrees of crystallinity. A parametric study was completed to evaluate functional process setpoints of system carrier gas temperature and powder mass flow rate. Using operational parameters common between PEKK grades, spray cycles were completed for each material and quantitative responses to variation in crystallinity were evaluated through a suite of analyses. Deposition efficiency of the materials was assessed gravimetrically, deposit porosity was evaluated by scanning electron microscopy, and thermophysical changes to the feedstock during the spray cycle were determined by differential scanning calorimetry and x-ray diffraction. Overall, we found that cold spray processing of powders of lower D formed less porous deposits with a higher deposition efficiency than measured for more crystalline powders sprayed at the same process conditions. PEKK grades with lower T/I ratios achieved deposition efficiencies in the range of 75-80%, whereas more T-rich grades only reached approximately 10% deposition efficiency. |