Novel hardmetals with nanograin reinforced binder: Structure, properties and applications

Abstract

Conventional (first-generation) hardmetals with binders reinforced by hard W-Co-C nanoparticles, which are obtained by a special heat-treatment technology, having a brand name of MasterGrade™ were developed and implemented in industry about 20 years ago. Although they have significantly improved performance, conducting the heat-treatment is expensive and the nanoparticles are thermally unstable; their precipitation process is suppressed by impurities present in secondary raw materials employed in the manufacture. There is therefore a need to develop alternative hardmetals with nanograin reinforced binder obtained using another approach. As a result of basic research, a new phenomenon with respect to WC-TaC-Co hardmetals was discovered and reported in the literature. It was established that small amounts of TaC added to WC-Co hardmetals form an oversaturated solid solution in cobalt when solidifying the liquid binder during cooling from sintering temperatures. This solid solution decomposes when further cooling in the solid state resulting in the formation of (Ta,W)C nanoprecipitates in the binder. Based on this phenomenon novel hardmetal grades with binder reinforced by the (Ta,W)C nanoprecipitates designated as the “second-generation MasterGrade™“were developed and implemented in the manufacture. The nanoprecipitates form when cooling the hardmetals from sintering temperatures, allowing the need for consequent heat-treatment to be eliminated. The novel hardmetals are characterized by improved performance in comparison with standard WC-Co materials and the first-generation MasterGrade™ in laboratory performance tests on percussive drilling and concrete-cutting. The high temperature creep resistance of the submicron second-generation MasterGrade™ grade is significantly greater than that of the conventional grade with nearly the same WC mean grain size. Results of a lab test on subjecting walker module cubes, which belong to a special type of cubic anvils, to a high temperature and ultra-high pressure for a long time indicated that the deformation rate of the novel hardmetal is nearly half of that of a conventional submicron grade. The manufacture process of the novel hardmetals with nanograin reinforced binder is more economical and sustainable compared to that of the first-generation MasterGrade™.