Iron Manganese Nickel Binders for WC Cemented Carbides

Abstract

In the cemented carbide industry, the research for alternative binders to cobalt has emerged as a real challenge. Scarcely any of the produced alternative binders succeeded in competing with the well-established WC-Co hardmetal. Nevertheless, since cobalt is considered a critical raw material and in addition has been classified as deleterious on human health by the REACH program of the EU, the existing obstacles must be surmounted. Nickel and iron have themselves proven to be good partial substitutes for cobalt but the likewise high toxicity of nickel forces the content of this element to be minimized. The work in this thesis which was conducted at the TU Wien aimed at discovering an appropriate composition of an alternative binder consisting of a manganese-iron-nickel alloy. Previous work stated that in case of theWC-FeMn system with a binder content of 20 % the already rather narrow two-phase region (WC + FeMn) is completely ”roofed” by the three-phase region (WC + Liq. + M6C). By Addition of nickel, the twophase region should be broadened to successfully produce a two-phase cemented carbide. After calculating different possibilities of composition with the CALPHAD method, two MnFeNi systems were chosen for production by the means of powder metallurgy. For each system various specimen with different carbon contents and a binder content of 20 wt.% were manufactured to determine the carbon contents which yield cemented carbides without precipitation of any third phases such as eta-carbides or cementite (Fe3C). After sintering, the samples were metallographically prepared and analyzed by light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and differential thermal analysis (DTA). The results showed that by adding nickel to a FeMn binder system respectively varying the Ni content, the two-phase region can be sufficiently broadened to successfully produce a two-phase material. It was further established that for FeMnNi binder systems of WC-based hardmetals the CALPHAD method with the currently available databases is convenient to acquire an initial understanding. Although both investigated alloy systems show a two-phase region in the calculated phase diagram, however, only one experimentally prepared composition achieved a WC binder cemented carbide without third-phase precipitates. The produced samples were further analyzed for mechanical property hardness.