Mechanical properties determined by nanoindentation tests of polypropylenemodified by He+ particle implantation

In this paper the changes are studied of the mechanical properties of polyp ropylene for various alpha irradiation fluences in nanoindentation tests. T he material's mechanical properties vary significantly for fluences above 5 x 10(13) He+ cm(-2), and increase sharply beyond 10(16) He+ cm(-2). The ha rdness and Young's modulus both increase in the first micrometer of the irr adiated sample. This behavior might be explained by reticulation of the amo rphous regions between the crystalline zones, The variations in both hardne ss and Young's modulus with fluence. and depth penetration were modeled as an equivalent hard thin film on a soft non-irradiated substrate. This allow ed us to estimate the hardness and Young's modulus for various penetration depths and fluences, describe the increase in hardness and Young's modulus versus the fluence, and report an exponential decrease versus penetration d epth. (C) 2001 Elsevier Science B.V. All rights reserved.