Zhixing Guo

Adherent coating on gradient cemented carbide with ultrafine Ti(C0.5,N0.5)

Gradient cemented carbide is usually employed as the substrate for coated carbide insert. In this work, gradient cemented carbide with ultrafine Ti(C0.5,N0.5) was prepared and its microstructure and properties were researched. Moreover, this novel substrate was coated to investigate cutting performance. It is found that the average WC grain size in the gradient zone is larger than that in the bulk. Owing to ultrafine Ti(C0.5,N0.5) introduction, gradient cemented carbide prepared by vacuum sintering exhibits full densification. By contrast, the gradient cemented carbide with ultrafine Ti(C0.5,N0.5) shows higher transverse rupture strength (TRS) and hardness than the homogenous one. Gradient cemented carbide suffers small TRS reduction after coating, and the bonding between coatings and gradient substrate is tidy and compact. The coated gradient cemented carbide shows much better endurance and impact resistance than the coated homogenous one. It confirms the superiority of gradient cemented carbide when used as the substrate for coating inserts.

Microstructure and Properties of Gradient Cemented Carbide with Nano-TiN

Gradient cemented carbides with nano-TiN were prepared by the common powder metallurgical procedure. The formation of gradient zone and the microstructure, properties of the alloys were investigated using scanning electron microscope(SEM), energy dispersive spectroscopy(EDS) and other performance testing apparatus. Moreover, the effect of nano-TiN on the gradient cemented carbide was studied. It is found that gradient zone width increases slightly with nano-TiN introduction. Both cobalt and titanium concentrations reach the maximum near the gradient border. Tungsten concentration shows fluctuation from the surface to the bulk. (Ti,W)C phase grains are refined for nitrogen introduction. Core-rim structure has been observed under the SEM back-scattered mode. The core appears as dark due to more titanium in it and the rim with more tungsten appears as grey. In addition, the hardness and transverse rupture strength of gradient cemented carbide are enhanced with nano-TiN introduced.