Effect of nitrogen introduction methods on the microstructure and properties of gradient cemented carbides

Gradient cemented carbides with the surface depleted in cubic phases were prepared following normal powder metallurgical procedures. Gradient zone formation and the influence of nitrogen introduction methods on the microstructure and performance of the alloys were investigated. The results show that the simple one-step vacuum sintering technique is doable for producing gradient cemented carbides. Gradient structure formation is attributed to the gradient in nitrogen activity during sintering, but is independent from nitrogen introduced methods. A uniform carbon distribution is found throughout the materials. Moreover, the transverse rupture strength of the cemented carbides can be increased by a gradient layer. Different nitrogen carriers give the alloys distinguishing microstructure and mechanical properties, and a gradient alloy with ultrafine-TiC_0.5N_0.5 is found optimal.