An investigation of XeCl laser ablation of polyetheretherketone (PEEK)-carbon fiber composite
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G. A. Oldershaw and D. Schudel School of Chemistry, The University of Hull, Hull HU6 7RX, United Kingdom (Received 8 June 1991; accepted 8 January 1992)
The XeCl laser ablation of a polyetheretherketone (PEEK)-carbon fiber composite (APC-2) is reported. Etch rates and measurements of the ablation products have been carried out, together with scanning electron microscope evaluation of the etch craters. Selective removal of the PEEK matrix occurs for fluences ~ 7 0 - 4 0 0 mJ cm"2. Net composite etching commences at ~420 mJ cm"2, with an etch rate above this value that is determined by the carbon fibers and is consistent with thermal vaporization at high temperature (>4000 K).
I. INTRODUCTION Over the past decade there has been much interest in the use of high power uv excimer lasers to ablate a wide variety of organic polymers.1 The extension of these studies to synthetic composite materials is of considerable importance, both as a means of helping to understand the ablative response of analogous biopolymers2 and for exploiting potential micromachining capabilities of excimer lasers. Previous reports have demonstrated that excimer lasers can be successfully employed for machining polymer-fiber composites containing polymer, glass, or carbon fibers and for epoxy-carbon fiber composites.3"5 In this paper we describe studies of the ablative etching of a PEEK (polyetheretherketone)-carbon fiber composite using the 308 nm XeCl laser. This material (APC-2, ICI pic, U.K.) has a high strength-to-weight ratio and excellent high temperature properties, and is expected to find an increasing range of applications in the future. UV laser etching of this composite is interesting as it combines an organic matrix (PEEK) which has been previously investigated6 with a refractory inorganic material in the form of graphitic carbon fibers. It is shown that the fibers raise the ablation threshold for the composite, though not dramatically, and that the etch rate is limited by thermal vaporization of the inorganic component occurring at temperatures ^4000 K. II. EXPERIMENTAL The experiments were carried out on ~200 /jm thick samples of PEEK-carbon fiber composite manufactured ^Present address: British Petroleum International Ltd., Sunbury Research Centre, Sunbury-on-Thames, United Kingdom.
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J. Mater. Res., Vol. 7, No. 5, May 1992 Downloaded: 17 Mar 2015
by ICI pic (APC-2/Hercules Magnamite AS4 carbon fibers). In this sheet form the continuous carbon fibers are unidirectional and occupy a volume fraction of 61% of the composite. The individual carbon filaments have diameters in the 6 - 9 fim range. The PEEK matrix is a linear polymer with the structural formula:
The composite was ablated using a XeCl laser (wavelength 308 nm), the output beam of which was spatially filtered using a small aperture to select a region of uniform fluence and then imaged onto the sample surface using a fused-silica lens. The laser pulse duration was 10 ns (full-width at half-maximum). In most cases the samples were irradi
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