Selective removal of cobalt binder in surface ablation of tungsten carbide hardmetal with pulsed UV laser

A novel method using pulsed laser ablation to selectively remove cobalt binder from the surface layer of cemented tungsten carbide hardmetal is proposed in this paper. A 308-nm, 20-ns XeCl excimer laser was used as the light source in this process. The dependence of surface morphology and XRD spectra on laser conditions have been investigated, respectively. The experimental results showed that the microstructure and crystalline structure of the irradiated surface layer varied greatly with laser conditions. After 300 shots of laser irradiation at fluence of 2.5 J/cm(2), the surface morphology is characterized by a uniform framework pattern of 'hills-valleys'. With the increment of laser shots at a laser fluence of 2.5 J/cm(2), the microstructure of cemented tungsten carbide was transformed after 300 shots of laser irradiation from the original polygon grains with a size of 3 mum to interlaced large and long grains, and finally, after 700 shots, to gross grains with a size of 10 mum and clear grain boundaries. The crystalline structure of the irradiated area has partly transformed from: the original WC to beta -WC1-x; then to alpha -W2C and CW3; and finally to W crystal. It was demonstrated that, at proper laser fluence and pulse numbers, cobalt binder could be selectively removed from the surface layer of hardmetal. (C) 2001 Elsevier Science B.V. All rights reserved.