Cermets based on FeAl–NbC from composite powders: Design of composition and processing

The aim of this work is the design, processing and characterization of a metal&-ceramic composite (cermet) with an iron &- aluminum alloy as metallic matrix and NbC as ceramic phase. The cermet is obtained from a composite powder containing in situ formed NbC-rich precipitates on an iron rich metal matrix. The starting powder was supplied by CBMM (Brazil), and it was produced by a synthesis process under development which introduces other metals such as Al, Si and Ti to the composition. Due to the in situ process, good bonding is expected between the carbide and the matrix. However it is necessary to study the processability of those complex particles and the transformations occurring during sintering to get the final microstructure. Thermodynamic studies by means of ThermoCalc® software were performed to predict the phases stable with the starting composition and also the influence of Fe and C additions. Samples were produced by uniaxial pressing and vacuum sintering (PS), and also by Field Assisted Hot Pressing (FAHP). The processing parameters for PS processing, that is, sintering temperature and time were based on themodynamic simulations by ThermoCalc® software together with thermal analysis. The powders were characterized by measuring density, particle size, carbon content and chemical composition; and consolidated samples by density and Vickers hardness. The microstructure and morphology of the powder and consolidated samples was analyzed by SEM. The addition of Fe and both C and Fe to the starting cermet composition provided good results as the final microstructure consisted essentially of NbC and Fe matrix.