Effects of initial particle size distribution and sintering parameters on microstructure and mechanical properties of functionally graded WC-TiC-VC-Cr3C2-Co hard alloys

Abstract Functionally graded WC-TiC-Co cemented carbides with a Co content gradient and not comprising the η-phase were prepared employing hot-pressing sintering technique by introducing pre-designed both gradients of Co contents and WC grain sizes. The effects of initial hard phase particle size distribution and sintering parameters on the microstructure and mechanical properties of functionally graded cemented carbides were investigated by fabricating coarse-particle, fine-particle and hybrid-particle (combining coarse-particle and fine-particle) functionally graded cemented carbides employing hot-pressing sintering technique. Various hot sintering temperatures (1325 ℃, 1350 ℃, 1375 ℃ and 1400 ℃) and soaking times (15 min, 30 min, 45 min, 60 min) were tested in order to determine the optimal parameters of hybrid-particle functionally graded WC-TiC-Co cemented carbides with the assistance of VC and Cr 3 C 2 as grain growth inhibitors and PVP as dispersant. The experimental results showed that excellent mechanical properties are achieved for sintering at 1375 ℃ soaked for 45 min with a hardness of 1986 kgf/mm 2 , a TRS of 1752 MPa and a fracture toughness of 13.05 MPa m 1/2 . Hybrid-particle functionally graded WC-TiC-Co cemented carbides generated a good liquid-phase sintering at 1375 ℃ soaked for 45 min. Specimens sintering for 1325 ℃ and 1350 ℃ maintained the pre-designed Co gradient, whereas the specimens sintering for 1375 ℃ maintained a smaller Co gradient and the specimen sintering for 1400 ℃ had no Co gradient. The excessive grain growth of fine-grained WC resulted the WC size difference disappear of coarse-grain and fine-grain, which weaken the Co phase migration pressure from surface layer to core layer. Furthermore, Co liquid phase distribution behavior is normally related with temperature, soaking time and pressure. The five-layer structure developed in this paper provides the surface with exceptional combination of high wear resistance and high toughness, which is favorable for the application as metal cutting tools.