Nanocrystalline microstructure enhanced mechanical properties and cutting performance of WC-10Co-Ti(C, N) gradient cemented carbides

Cemented carbides are widely used in difficult-to-machine material tools. In this study, we investigated the effects of the nanocrystalline gradient cemented carbide gradient structure, solid solution, WC grain orientation, and internal alloy stresses on the mechanical properties and cutting performance. Scanning electron microscopy and electron probe microanalysis were used to analyze the microstructure of the cubic carbide-free layer (CCFL) layer, and electron backscatter diffraction was used to determine the WC grain size and reveal the WC grain orientation of the nanocrystalline cemented carbide. The results indicated that the thickness of the CCFL layer in nanocrystalline gradient cemented carbide reached 33-55 mu m, while the WC grain size ranged from 149.41 to 169.54 nm. The multiple of uniform density value of the WC grain {0001} texture was only 2.70, indicating that the nanocrystalline gradient cemented carbide is isotropic without a preferred orientation. The low kernel average misorientation and geometrically necessary dislocation values of the nanocrystalline cemented carbide indicated that the stresses were uniformly distributed within the alloy. In addition, a (W, Ti)(C, N) solid solution was formed at the phase boundary between WC and Co. Thus, the nanocrystalline gradient cemented carbide maintained excellent fracture toughness while possessing high hardness. With regard to cutting, the thick CCFL exhibited excellent toughness, while the nanocrystalline WC grains strengthened the substrate. The uncoated nanocrystalline gradient cemented carbide exhibited minimal tool wear in cutting Ti alloys up to 1000 m, with cutting wear depths as small as 0.096 mm.