Deformation Substructure in Cemented WC-Co Materials

Abstract

The cemented refractory carbides represent one of the basic classes of materials used in machine cutting and rock drilling tools. These multiphase materials (a refractory carbide compact with a metallic binder phase) provide a good combination of hardness, toughness, and abrasion resistance which leads to long tool life. The present study investigates the microstructure of several cobalt-based cemented WC materials in response to different types of mechanical loading.The materials were hot isostatically pressed sintered compacts of WC and blends of cobalt and nickel metal powders (∼17 wt %). Three blends of metal powders were used: Co-1, Co-2, and Co-3 (in increasing nickel content). During the high-temperature sintering process, the metallic binder was molten, aiding the sintering reaction and also dissolving some WC into solution. Specimens were examined in the ORNL Hitachi HU-1000 high voltage electron microscope in the undeformed state and following different conditions of mechanical treatment: low (2.1 GPa) and high (3.4 GPa) stress compressive monotonic loading, and low (1.0 GPa) and high (2.1 GPa) stress compressive cyclic loading. The high penetration power of the HVEM allowed the examination of the microstructure of the dense WC grains and thicker binder regions where the dislocation structure would be representative of that in the bulk.