The Grain Size of Binder-Phase in WC-Co Alloy

Abstract

The methods of revealing grain-structures of binder-phase (γ-phase) in WC-Co alloy, effects of various factors on the grain size of γ-phase, the composition changes near the grain boundary of γ-phase and the mechanical properties affected by the grain size were in detail investigated. The results obtained were as follows; (1) The grain-structure of γ-phase in WC-Co alloy was confirmed to be succesfully revealed by either chemical etching or thermal etching under a certain suitable condition. The reasons why the γ-phase grain could be revealed by these methods were discussed. The surface-pattern of as-sintered alloy was also confirmed to reflect well the γ-phase grain. (2) The grain size of γ-phase increased with increasing cobalt contents and mean grain size of WC in the alloy, and increased with decreasing carbon contents and cooling rates. (3) The grain-structure of γ-phase consisted of equiaxed grains regardless of cooling rates or cobalt contents so that any kinds of anisotropy due to solidification did not exist in the cemented carbide. (4) The region deficient in cobalt contents (or execs in WC contents) existed near γ-phase grain boundary. The amount of this segregation increased with increasing cobalt contents in the alloy and grain size of γ-phase. (5) The strength of the alloy increased, in particular in high cobalt alloy, with decreasing grain size of γ-phase.