Fundamental aspects of phase formation in WC-based cemented carbides containing FeMn-based binders

Abstract

The hardmetal industry is continuously seeking for (Co, Ni)-free binder alternatives. Several attempts have been made to use FeMn binders, Mn being a very effective austenite stabilizer. Substitution of Co binders for FeMn based binders comes along with many challenges such as: narrow carbon windows, evaporation of Mn during sintering or the formation of stable Mn-oxides. This work presents an overview on the phase formation in hardmetals with different carbon contents prepared from FeMn, FeMnSi and FeMnNi binders. Due to the efficient role of Mn as cementite stabilizer, it was not possible to avoid the presence of eta-carbides and cementite under the conditions studied, and samples with intermediate carbon contents presented both eta-carbides and cementite in the microstructure. Only after the addition of 25 wt% of Ni to the binder it was possible to observe materials with two phase microstructures. The challenges related to Mn evaporation and formation of stable oxides can be overcome by a proper selection of the starting materials and the sintering conditions. It is thus proved that the main challenge posed by these materials is the difficulty to obtain microstructures without detrimental phases.