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 NbCrich 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.
Abbreviations
PS -Pressing and Sintering FAHP -Field Assisted Hot Pressing
The present study aimed to produce and characterize FeNbC coatings deposited on AISI 1020 steel using flame spray process (FS) evaluating the influence of powder granulometry, standoff distance, powder feed rate and substrate preheating. FS process parameters variations produce coatings with different properties. Taguchi experimental design based in the L9 orthogonal array and ANOVA statistical analysis were performed. Coating morphology was evaluated using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the present phases were identified by x-ray diffraction (XRD). Coatings microhardness was evaluated using Knoop hardness test. The coatings corrosion resistance was measured through monitoring the open circuit potential and potenciodynamic polarization in 3.5% NaCl solution. The results indicate that coatings with microhardness average of 1084 HK 0.3 and dispersion of the measured values were associated with heterogeneity and interlamellar oxides formed in the microstructure. All control factors investigated showed significant influence on microhardness. Substrate preheating was the most important factor, followed by the powder granulometry; powder feed rate and standoff distance. The FeNbC coating presented a reduction in the substrate corrosion rate, but the presence of defects in the microstructure, such as porosities, voids and cracks compromised the barrier effects of these coatings.
This study presents the development of niobium carbide cermets bound to nickel and Ni-12Al (wt%). The use of and Ni aims to replace strategic elements such as cobalt (Co) utilized in tungsten carbide-based cermets. Cermets of different compositions were processed by conventional powder metallurgy. Microstructural analysis with semi-quantitative chemical analysis by EDX, Vickers microhardness and density measurement were performed to evaluate the influence of high energy milling application and sintering temperature on the properties of these cermets. A milling time of 20 min in a planetary mill and sintering temperatures of 1420 ºC or 1450 ºC resulted in homogeneous microstructures, densities close to 90% and hardness of around 1000 HV 1 , showing a potential for use of this material in cutting tools.
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