| In order to improve the wear-resistance and heat-resistance of carbon tool steel, a study of tungsten surface alloying by the irradiation of CO₂laser was carried out. Mixtures of tungsten and cobalt powders were applied directly on specimens by coating a powder slurry suspended in a alchohol to the thickness of 70㎛. Surface alloyed layers were obtained by single and overlapping laser tracks at 900 W. Microhardness test, microstructural observation, X-ray diffraction analysis and EPMA test were carried out on each specimen. Well developed tungsten surface-alloyed layers were produced on tool steel. The thickness of these layers was about 250㎛ and the hardness was 1000 Hv Tungsten was distributed homogeneously throughout the alloyed layer by well-intermixing of components, and its concentration was about 10%. The microstructure of this layer consisted of martensite in equiaxed grains. Mixtures of W +5% Ce increased the depth and width of the lasermelted zone. A futher increase of Co in mixture decreased the depth of allayed layer. When a specimen was annealed at 1100℃ for 5 hours, a large amount of tungsten carbides (WC) precipitated in the alloyed layer When a large surface is to be alloyed by overlapping laser tracks, the degree of overlapping should be at least within a half of that of single laser pass to obtain homogeneous alloyed layer. |
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