Fabrication and performance of graded ultrafine WC-Co cemented carbide tool by one/two-step spark plasma sintering

Ultrafine WC-Co cemented carbides with Co gradient were prepared by one-step (1300 degrees C/5 min) and two-step (1300 degrees C/3 min -> 1200 degrees C/5 min) spark plasma sintering. Effects of Co gradient and sintering process on the microstructure and mechanical properties were studied. The higher Co content of core layer provides the good fracture toughness and transverse rupture strength for graded cemented carbides, while the grain growth of surface caused by the migration of Co from the interior to the surface results in a slight decrease of surface hardness. Two-step sintering inhibits the grain growth and improves comprehensive mechanical properties of graded WC-4Co/WC-12Co/WC-4Co cemented carbide. Its surface grain size, hardness, fracture toughness and transverse rupture strength are 231 nm, 2080 kg/mm(2), 8.93 MPa.m(1/2) and 1829 MPa, respectively. In addition, the cutting performance of graded cemented carbides prepared by two-step sintering was investigated. The graded WC-4Co/WC-12Co/WC-4Co cemented carbide tool has a high wear resistance due to the high surface hardness, and its cutting edge has a good resistant capacity against breakage due to the high internal strength. It presents the longer tool life and higher machined surface quality than commercial YG8 tool.