Fracture Toughness of Cemented carbide WC-Co

摘要

Rotating fatigue test was carried out using the cemented carbide WC-Co in ultra-long life. A sintered alloy has many defects (pore=porosity) on the boundary. A crack initiates from these defect, propagates belong the boundary. Fatigue limit does not exist. Because the cemented carbide alloy like ceramics obeys to weakest link. The boundary slips easily, and is weak to sharing force. The fatigue crack propagation rate (da/dN) cannot calculates. But, fracture toughness K{sub}(IC) can calculate from relationship Fractal dimension or Hurst number and yield area. The yield area of fracture in ultralong N{sub}f=2.05×10{sup}7 broad along on the surface. The surface defect is origin of fracture. When K{sub}(IC)>K{sub}(max) in surface stands up; the crack in the plane stress propagate. The fatigue strength of WC cemented carbide is obeyed to weakest link model of defects. Because, even if it supposes that it was worked the cyclic stress over the fatigue strength, the fatigue fracture did not always happen.