Modified surface morphology in surface ablation of cobalt-cemented tungsten carbide with pulsed UV laser radiation

Surface ablation of cobalt-cemented tungsten carbide hardmetal has been car ried out in this work using a 308 nm, 20 ns XeCl excimer laser. The influen ce of ablation rate, surface roughness, surface micromorphology as well as surface phase structure on laser conditions including laser irradiance and pulse number have been investigated. The experimental results showed that t he ablation rate and surface roughness were controlled by varying the numbe r of pulses and laser irradiance. The microstructure and crystalline struct ure of irradiated surface layer varied greatly with different laser conditi ons. After 300 shots of laser irradiation at irradiance of 125 MW/cm(2), th e surface micromorphology characterizing a uniform framework pattern of "hi ll-valleys". With the increment of laser shots at laser irradiance of 125 M W/cm(2), the microstructure of cemented tungsten carbide transformed from o riginal polygon grains with the size of 3 mum to interlaced large and long grains after 300 shots of laser irradiation, and finally to gross grains wi th the size of 10 mum with clear grain boundaries after 700 shots. The crys talline structure of irradiated area has partly transformed from original W C to beta -WC1-x, then to alpha -W2C and CW3, and finally to W crystal. At proper laser irradiance and pulse number, cobalt binder has been selectivel y removed from the surface layer of hardmetal. it has been demonstrated tha t surface ablation with pulsed UV laser should be a feasible way to selecti vely remove cobalt binder from surface layer of cemented tungsten carbide h ardmetal. (C) 2001 Elsevier Science B.V. All rights reserved.