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The aim of this paper is to study both the mechanical and chemical properties of a new material composed of B4C doped with 3% volume of CoCrFeNiMo HEA by the spark plasma sintering technique. Scanning electron microscopy and microhardness were used to characterize the composite microstructure and hardness. Corrosion behavior was studied by corrosion potential, corrosion rate and electrochemical impedance spectroscopy, where the equivalent circuit was obtained, characterized by the presence of the Warburg element. The addition of HEA resulted in a more compact microstructure, filling pores and inhibiting ceramic grain growth. A microhardness statistical analysis revealed that the sample followed a normal distribution, which suggests that the sample has a homogeneous structure. The doped material exhibits excellent corrosion resistance in artificial seawater, where its chemical interaction occurs in two steps, with an important diffusional component. This study highlights the potential for use in environments where both corrosion resistance and mechanical strength are critical factors. [ABSTRACT FROM AUTHOR]

The influence of two different spark plasma sintering (SPS)-based processing routes (i.e., reactive SPS [RSPS] and nonreactive SPS) on the properties of TaB2-TaC composites was investigated. Ta2O5 and B4C powders were used as starting materials in the RSPS method, and synthesis and densification of TaB2-TaC composites were accomplished in a facile single step. The effect of sintering temperature and time on the microstructure and densification of the in-situ RSPS were investigated. The obtained results were compared with nonreactive spark plasma sintered TaB2-TaC composites. The highest densification (~99.5%) was achieved for the TaB2-TaC composite with 6.64 vol.% TaC after reactive sintering at 1550° C under 40 MPa with a 5 min holding time. Although lower SPS temperature was used in the RSPS method, better densification and higher Vickers hardness were obtained compared to the nonreactive SPS. While platelet-shaped TaC formation was observed in both processes, the average grain size was smaller in the RSPS method. On the other hand, no significant difference was detected in the oxidation behavior of the composites produced by RSPS and nonreactive SPS. [ABSTRACT FROM AUTHOR]

Monolithic NbB2, NbB2-SiC, and NbB2-SiC-GNP samples were produced by spark plasma sintering (SPS), and the effects of additives on the mechanical and thermal properties, microstructures, and oxidation behavior of the samples were investigated. The addition of SiC up to 30 vol% decreased the Vickers hardness of the binary composites due to microcrack formation. The fracture toughness and oxidation resistance of NbB2 were improved with the incorporation of SiC. Fracture toughness was higher for all the composites in comparison to monolithic NbB2, moreover the highest value of ~5.2 MPa·m1/2 exhibited by 3 vol% GNP-containing composite. A strong interface and homogeneous distribution of GNPs enhanced the thermal transfer properties and improved the oxidation resistance of selected NbB2-SiC ceramics in oxidation studies at 1200°C. A combination of high mechanical properties, high thermal conductivity, and low mass gain was achieved for the NbB2-SiC-GNP samples with 1 and 3 vol% GNPs. [ABSTRACT FROM AUTHOR]

The aim of this study was to prepare and to characterize the structure of Al2 O3-3 YSZ composites with 5% Ti O2 addition as well as the surface modification upon treatments with Sn F2 and Na BF4, respectively. SEM micrographs showed the controlled densification of the composites as an effect of 3 YSZ and Ti O2 addition to alumina matrix. By FTIR and XRD, the characteristics of Al- O and Zr- O vibrations, respectively, the diffractions lines related to α-corundum and zirconia in tetragonal phase were discussed. Qualitative and quantitative results obtained by XPS and ATR FTIR demonstrated that the proposed materials are more sensitive to Sn F2 than to Na BF4 treatment. [ABSTRACT FROM AUTHOR]

Tetragonal ZrO2 polycrystalline (TZP) ceramics with varying yttria and ceria content (2–3 mol%) and distribution (coated or co-precipitated), and varying second phase content Al2O3 were prepared and investigated by means of microstructural analysis, mechanical properties, and hydrothermal stability, and ZrO2-based composites with 35–60 vol% of electrical conductive TiN particles were developed. The effects of stabilizer content and means of addition, powder preparation, sintering conditions, and grain size have been systematically investigated. Fully dense Y-TZP ceramics, stabilized with 2–3 mol% Y2O3, 2 wt% Al2O3 can be achieved by hot pressing at 1,450 °C for 1 h. The hydrothermal stability increased with increasing overall yttria content. The jet-milled TiN powder was used to investigate the ZrO2–TiN composites as function of the TiN content. The experimental work revealed that fully dense ZrO2–TiN composites, stabilized with 1.75 mol% Y2O3, 0.75 wt% Al2O3, and a jet-milled TiN content ranging from 35 to 60 vol% could be achieved by hot pressing at 1,550 °C for 1 h. Transformation toughening was found as the primary toughening mechanism. The decreasing hardness and strength could be attributed to an increasing TiN grain size with increasing TiN content, whereas the decreasing toughness might be due to the decreasing contribution of transformation toughening from the tetragonal to monoclinic ZrO2 phase transformation. The E modulus increases linearly with increasing TiN content, whereas the hydrothermal stability increases with addition of TiN content. [ABSTRACT FROM AUTHOR]

In this study, the effect of TiO2 addition as a nucleating agent on the crystallization and machinability of potassium mica and fluorapatite base glass ceramics were investigated. Glass compositions were prepared and casted at predetermined temperatures. Differential thermal analysis and XRD methods were applied to characterize phase precipitation sequence and identification of phases. Disc and cylindrical shaped samples were prepared to determine microstructural and mechanical properties in terms of microhardness and machinability. FEG-SEM was used to characterize variation of microstructural constituents depending on the amount of nucleating agent. The results indicate that optimum microstructure and machinability can be obtained in machinable glass-ceramic by the addition of 1 wt% TiO2 for the composition having 3:7 weight ratio of fluorapatite to potassium mica. [ABSTRACT FROM AUTHOR]