SOME TRENDS IN IMPROVING WC–Co HARDMETALS
I. HYBRID AND COARSE-GRAINED HARDMETALS

Abstract

The paper provides an overview and analysis of the areas for improving WC–Co hardmetals. One of the areas was initiated by Grygorii Samsonov in the mid-1950s and has proved to be relevant up to now. It deals with the development and study of hardmetals with inhomogeneous structure resulting from nonuniform distribution of the carbide phase in samples with a cobalt binder. Samsonov showed in 1956 that the materials representing granules of the VK3 hardmetal in a VK15 hardmetal matrix had very high wear resistance, exceeding the wear resistance of uniform VK3 and VK15 hardmetals by 8–10 times. Similar hardmetals but with a cobalt matrix were created in the 2000s in the USA and were called ‘hybrid’ or ‘double’ hardmetals and later, in Ukraine, ‘mesostructural’ hardmetals. At a given level of hardness, such hardmetals show increased fracture toughness that determines their high wear resistance. Along with hybrid or mesostructural hardmetals, research efforts focusing on coarse-grained and extra-coarse-grained hardmetals, which also ensure high wear resistance through increased fracture toughness and plastic work of deformation, have been resumed. Additional increase in the wear resistance of coarse-grained hardmetals was reached in Germany due to hardening of the cobalt matrix, specifically thick layers of cobalt, by nanosized hard inclusions such as complex Co₂W₄C carbide (θ phase). Comparative wear resistance tests of the coarse-grained and ultrafine-grained hardmetals show that those with coarse WC particles are much more preferable. At the same time, the high wear resistance of ultrafine-grained hardmetals has been found in abrasive wear tests at low loads.