Densification and Phase Formation Kinetics in Composite Materials of WC Embedded in an Fe-Matrix

Abstract

This paper presents results corresponding to the densification of WC-Fe composites. Commercial WC (4NPO H.C.Starck) was mixed with iron (Fe) added from a precursor obtained via sol-gel route. Results of the kinetics of phase formation in materials obtained via this sol-gel route, which involves several precursors of W, Fe and C, plus the addition of colloidal alumina (Al 2 O 3 ) are also reported. Samples with different concentrations of Fe were studied using a vertical dilatometer up to 1230ºC with 10% H 2 -Ar gas flow up to 800°C, and then in vacuum of 30mTorr until the final temperature. Densification is discussed in terms of kinetics analysis of selected experimental data to identify the different mechanisms involved. These samples were subjected to Xray diffraction to identify the resulting phases, where WC and W were the main phases. On the other hand, samples prepared from a sol-gel route containing Fe and alumina were treated under an atmosphere of 10% H 2 -Ar, in order to analyze the transformations produced in the temperature range 500 to 800°C. XRD studies indicated the formation of different phases, such as WC (of primary interest), and the subcarbide M 6 C type: W 3 Fe 3 C, among others. The analysis of all diffractograms indicates the evolution of the system as a function of temperature, leading first to oxidation (formation of FeWO 4 ) and reductions (formation of Fe) in the system. Simultaneous mass losses of this system are shown in the same range of 500-800°C.

Ti(C,N)-Fe15Ni10Cr cermets as alternative hard materials: Influence of the processing route and composition on their microstructure and properties

“…For example, Cr content in the alloy may be compromised by its affinity to Cleading to formation of secondary carbidesor its evaporation when vacuum-sintered [21]. Another well-known problem to be overcome is the oxidation tendency of Fe when used as alternative binder in WCbased and cermet systems [22][23][24]. Moreover, it is of vital importance to know the effects of the manufacturing process regarding the sample composition, especially with respect to C content [25].…”

Phase diagrams in alternative hard materials: Validation of thermodynamic simulation through high temperature x-ray diffraction, differential thermal analysis and microstructural characterization

“…For example, Cr content in the alloy may be compromised by its affinity for C -leading to formation of secondary carbides -or its evaporation when vacuum-sintered [176]. Another well-known problem to be overcome is the oxidation tendency of Fe when used as alternative binder in WCbased and cermet systems [28,177,178]. This is also the case of Al, as stated before, which is prone to form Al-oxides because of its high affinity for O [44,84,85,179].…”