Structure and properties of WC/HS6-5-2 gradient tool materials

The goal of this work is to obtain gradient materials based on a high-speed steel HS6-5-2 reinforced with tungsten carbide (WC). The material presented in this paper has layers at one side consisting of the high-speed steel, characterized by a high ductility and at the other side the carbide-steel characterized by a higher hardness. The materials were fabricated using the conventional powder metallurgy method. The layers inside the material are mixes of the high-speed steel powders with the WC ones in various proportions. The uniaxial pressing consisting in compacting the powder in a closed die, and subsequent sintering. Density and hardness of the obtained materials were measured. The sintered test pieces were also examined using the scanning electron microscope (SEM) equipped with the back-scatter electrons detector (BSE) and the dispersive energy analyser (EDAX D4). It was observed that the properties of as-sintered gradient materials are strongly affected by the tungsten carbide content and sintering parameters. The density of the test pieces grows along with the sintering temperature increase. The porosity grows along with the WC content growth in the particular layers. It was observed that also the sintering time has an effect on the porosity growth. The longer the sintering time is, the higher the porosity is. The hardness of the compacted and sintered test pieces, measured using the Rockwell method, grows along with the sintering temperature increase. It was noted that application of a longer sintering time results in slight HRA hardness lowering. It was found out, basing on the comparison of tructures and properties of the compacted and sintered test pieces, that in structures of all examined test pieces in the sintered state fine carbides occurred, distributed homogeneously in the high-speed steel layer. Developed material can be applied to manufacturing cutting tools. Forming methods were developed for high-speed steel and WC powders, making it possible to obtain materials with seven layers in their structure.