A New Method for Making Functionally Graded WC-Co Composites via Liquid Phase Sintering

摘要

Functionally graded WC-Co is a new research area which is focused on optimizing the structure-property relationships of WC-Co composites. However, during consolidation of functionally graded WC-Co using liquid phase sintering, the flow of liquid phase can easily occur and a gradient in the liquid phase is easily eliminated. This makes the processing of functionally graded WC-Co composites difficult. In this paper, a new approach, which involves modifying the composition of functionally graded WC-Co composites in the green state prior to liquid phase sintering, is used to create a continuous gradient in cobalt metal binder phase. The carbon content in one layer is reduced below its stoichiometric value while the carbon content in the other layer is increased above its stoichiometric value. Carbon content will homogenize across layers during liquid phase sintering. It was found that cobalt will migrate in the same direction of carbon diffusion which leads to a continuous gradient of cobalt content within the microstrucrure. Phase reaction processes which occur during homogenization of carbon across the layers are believed to cause the redistribution of the cobalt phase across the structure. The effectiveness of using this method to produce fully dense functionally WC-Co with continuous cobalt gradient starting with different layer compositions is considered. The mechanism of binder gradient formation during liquid phase sintering of functionally graded WC-Co is discussed.