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In this research, carbon sources (Resin Phenolic, Carbon Black and Graphite) and Boron Carbide (B4C) were used to improve the mechanical properties of Silicon Carbide (SiC) composite. For this purpose, carbon sources of 0.5, 0.75, 1, 1.5, 2, 2.5, 3, and 5 wt% as well as 0.5 wt% B4C were added to SiC powder, respectively. The sample containing SiC—2.5 wt% Resin Phenolic—0.5 wt% B4C had the best properties with relative density, hardness, and fracture toughness values of 98.5%, 2820 GPa, and 3.9 MPa.√m, respectively. Examination of SEM images showed that by increasing carbon from 0.5 to 2.5 wt%, the fracture changes from intergranular to transgranular. [ABSTRACT FROM AUTHOR]

In this study, the effect of annealing treatment on microstructure and mechanical properties of the Nb-10Hf-1Ti wt.% produced by Spark Plasma Sintering (SPS) was investigated. Scanning electron microscope (SEM), optical microscopy, X-ray diffraction analysis, hardness, and uniaxial tension test were used to characterize the samples. Annealing treatment was carried out in a vacuum of 10-3 Pa at 1150 °C for 1, 3, 5, and 7 hours and in an argon atmosphere at 1350 °C for 5 hours. Internal oxidation and subsequent hafnium oxide formation causes the hardening of the C103 alloy and drastically increases the hardness and tensile strength. However, HfO2 particles formed at the grain boundary cause brittleness and cleavage fracture of samples. Volume fraction, particle size, and mean inter-particle spacing of oxides significantly change by annealing which affects the mechanical properties. The SPSed sample at 1500 °C is softened by annealing at 1150 C for 5 hours and its hardness and yield strength are reduced from 303 to 230 Hv and 538 to 490 MPa respectively. While annealing at 1350 °C for 5 hours increases hardness and yield strength increases to 343 Hv and 581 MPa respectively. [ABSTRACT FROM AUTHOR]

In this research, a SiC/ZrB2 coating was produced on graphite by reactive melt infiltration and plasma spraying method. The coating characterization was performed using XRD analysis, electron microscopy equipped with energy dispersive spectrometer (EDS), and supersonic flame ablation test at 2073 K. The results indicated that the dense C/SiC coating with good ablation resistance can be obtained at 1873 K. The coating thickness decreased with increasing infiltration temperature. The results of ablation test showed that by increasing the infiltration temperature and holding time, weight loss and mass ablation rate decreased from 22.63% to 9.83% and 3.63 × 10−3 g cm−2 s−1 to 1.34 × 10−3 g cm−2 s−1, respectively. The results showed that by using the ZrB2 as outer coating the ablation resistance improved remarkably. The weight loss and mass ablation rates for the SiC/ZrB2 coating were 12.79% and 1.857 × 10−3 g cm−2 s−1, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured C/SiC/ZrB2–SiC oxidation protective gradient coating was prepared by a two‐step reactive melt infiltration method. In order to reduce production cost, ZrB2 phase was synthesized by the in situ reactive that included low‐cost ZrO2 and B2O3 powders as raw materials. High‐temperature oxidation behavior of coatings was evaluated by isothermal oxidation test at 1773 K in air for 10 hours. Thermodynamical behavior of the coatings at various temperatures during oxidation test and coating process was predicted by HSC Chemistry 6.0 software. Compressive residual stresses of 36.9 MPa and 41 MPa were calculated for in situ and ex situ coatings by Williamson‐Hall method. After 10 hours of isothermal oxidation at 1773K, in situ and ex situ coatings showed 12.84% and 15.69% of weight losses with oxidation rates of 1.87 × 10−2 g cm−3 h−1 and 0.91 × 10−2 g cm−3 h−1, respectively. These results indicated that the oxidation protection ability of the coating produced by the in situ method was very close to ex situ coating. [ABSTRACT FROM AUTHOR]

In this study, a functionally graded SiC layer was prepared on a graphite substrate by a pack cementation method with Si, C, and AlO powders. Then a SiC-ZrB coating was developed by an in situ reaction method through a novel pack cementation technique at 1873 K with Zr, Si, and BC powders to improve the oxidation protection ability of SiC-coated graphite. The phase compositions, microstructure, and element distribution of the coating were identified by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. The isothermal oxidation test of the coated samples was accomplished at 1773 K in air for 10 h. According to the results, a 550-μm thick graded C-SiC layer was detected at the graphite-coating interface and a SiC-ZrB coating was formed on the first coating. The SiC-ZrB coating could efficiently enhance oxidation resistance of graphite with a mass gain of +1.1 %, as compared with a −1.2 % mass loss of the first step coating. The excellent protection ability of SiC-ZrB coating could be ascribed to the high thermally stable ZrSiO. [ABSTRACT FROM AUTHOR]

Abstract: Al2O3 is a major reinforcement in aluminum-based composites, which have been developing rapidly in recent years. The aim of this paper is to investigate the effect of alumina particle size, sintering temperature and sintering time on the properties of Al–Al2O3 composite. The average particle size of alumina were 3, 12 and 48μm. Sintering temperature and time were in the range of 500–600°C for 30–90min. A correlation is established between the microstructure and mechanical properties. The investigated properties include density, hardness, microstructure, yield strength, compressive strength and elongation to fracture. It has been concluded that as the particle size of alumina is reduced, the density is increased followed by a fall in density. In addition, at low particle size, the hardness and yield strength and compressive strength and elongation to fracture were higher, compared to coarse particles size of alumina. The variations in properties of Al–Al2O3 composite are dependent on both sintering temperature and time. Prolonged sintering times had an adverse effect on the strength of the composite. [Copyright &y& Elsevier]

Abstract: The effect of Al addition on pressureless sintering of B4C ceramic was analyzed in the present work. Different amounts of Al, from 0 to 5wt.% were added to the base material and pressureless sintering was conducted at 2050 and 2150°C under argon atmosphere. Microstructure, crystal phases and density evolution were studied and correlated to Al additions and firing temperature. Density and grain size of sintered samples, increased significantly with Al load while less evidence is the effect of sintering temperature; 94% dense material was obtained by adding 4wt.% Al regardless of the maximum firing temperature. [Copyright &y& Elsevier]