Improved wear properties of high energy ion-implanted polycarbonate
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R. Bhattacharya and A. W. McCormick UES, Inc., 4401, Dayton-Xenia Road, Dayton, Ohio 45432 (Received 28 February 1994; accepted 14 September 1994)
Polycarbonate (Lexan™) (PC) was implanted with 2 MeV B + and O + ions separately to fluences of 5 X 1017, 1 X 1018, and 5 X 1018 ions/m 2 , and characterized for changes in surface hardness and tribological properties. Results of tests showed that hardness values of all implanted specimens increased over those of the unirradiated material, and the O + implantation was more effective in improving hardness for a given fluence than the B + implantation. Reciprocating sliding wear tests using a nylon ball counterface yielded significant improvements for all implanted specimens except for the 5 X 1017 ions/m 2 B+-implanted PC. Wear tests conducted with a 52100 steel ball yielded significant improvements for the highest fluence of 5 X 1018 ions/m 2 for both ions, but not for the two lower fluences. The improvements in properties were related to Linear Energy Transfer (LET) mechanisms, where it was shown that the O + implantation caused greater ionization, thereby greater cross-linking at the surface corresponding to much better improvements in properties. The results were also compared with a previous study on PC using 200 keV B + ions. The present study indicates that high energy ion irradiation produces thicker, more cross-linked, harder, and more wear-resistant surfaces on polymers and thereby improves properties to a greater extent and more efficiently than lower energy ion implantation.
I. INTRODUCTION Polycarbonate (PC) is a tough engineering polymer widely used in industry in various technological applications. The combination of transparency, toughness, flame retardancy, and heat-distortion resistance make it a very useful and attractive polymer for use in the automotive and electrical industries as well as for business equipment, and as protective transparent windows. However, components made from polycarbonate are soft and easily scratched, typical of most thermoplastic polymers, particularly in abrasive environments. The potential for applications of polycarbonate can be significantly increased if the scratch resistance and wear properties can be improved. Ion implantation can significantly alter surfacesensitive properties of polymers.1 Recent studies at Oak Ridge National Laboratory (ORNL) have shown that ion implantation of polymers can improve surface hardness, wear, and other surface-sensitive properties, sometimes dramatically.2"4 In one study,3 polycarbonate was implanted with 100 and 200 keV B + ions to fluences of 0.26, 0.78, and 2.6 X 1019 ions/m 2 . The ion beam treatment improved hardness for all the implanted specimens, and for the highest fluence of 200 keV B + implantation, hardness improved by a factor of nearly 190
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10. It was also observed that wear properties of the polymer, sliding against nylon spheres of 9.53 mm diameter, improved after the ion beam treatment, and for the 200 keV, 0.78 X 1019 ions/m 2 implanted
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