Investigation on the Formation of Graded Structure in WC-Co Hard Alloy

摘要

Recently, cemented carbides with graded structure have attracted great attention of materials scientists and industry entrepreneur. In this work, a cemented carbide with apparent graded structure was made, and the relationship between the processing parameters and the microstructure was studied. Firstly, WC-6Co alloy with a carbon content lower than equilibrium was presintered to introduce a η-phase-containing homogenous microstructure. Then the hard alloy was carburized in a carbon atmosphere to form cobalt-gradient structure with thickness of several micrometers. The thickness of the cobalt-gradient was found in this work to be closely related to such factors as carbon content, sintering temperature, holding time etc. A moderate carbon diffusion rate, which was induced by a relatively higher carbon content and low sintering temperature would be essential for the formation of gradient structure. The gradient structure does good to the mechanical properties of hardmetals, and simultaneous increase of the hardness and the fracture strength can be obtained.