Papers by Keyword: Reaction Sintering

Abstract: Improvement of fuel efficiency and reduction of carbon dioxide emission are important issues in the automotive and aviation industries. To achieve these issues, materials that are lightweight and have excellent heat resistance are required. For this reason, various alloys have been proposed. Among them, TiAl intermetallic compounds have excellent low specific gravity and high strength at high temperature. However, TiAl is difficult for machining and easily oxidized, so casting is difficult. For this reason, a method using reaction sintering has been studied, though it is difficult to obtain low oxygen concentration TiAl alloy powder. Therefore, the process to produce TiAl parts from Ti powder and Al powder is studied. However, in this method, when a mixed powder of Ti and Al is sintered, a phenomenon called ignition with a rapid temperature increasing may occurs, and ignited parts are swelling and becomes high porosity.

Abstract: SiC/B₄C composite was obtained using the reaction sintering method with Si infiltration, which exhibited excellent mechanical properties. The dynamic compressive response was investigated using a Split Hopkinson pressure bar at high strain rates ranging from 0.4×10³ to 1.2×10³ s^-1. The results show that the dynamic strength of the SiC/B₄C composite obtains a peak value at a strain rate of 1000/s, while its strain increased continuously with increasing strain rate. The dynamic loading mode of SiC/B₄C composite exhibited three deformation regions, including an inelastic deformation region, rapid loading region and failure region. The dynamic failure mode of SiC/B₄C composite depended upon the strain rate.

Abstract: The paper presents the results of obtaining silicon carbide SiC ceramic from organic raw materials by the reaction spark plasma sintering (SPS). Annealed rice husks are used as an organic raw material. A feature of the batch preparation for sintering is annealing in an inert atmosphere. Thus, the carbon source C for further reaction with silicon dioxide SiO2 to form SiC is the organic part of the rice husk. This way let to achieve the most uniform reacting components mixing directly at the stage of annealing the husks and to exclude the mixing stage from the technological process. The reaction SPS method was used for the first time for the production of ceramic material from such a raw material. The results of a comprehensive study of the obtained material by various methods are presented in the article: scanning electron microscopy, Raman spectroscopy, X-ray phase analysis, strength analysis, and others.

Abstract: High hardness, high strength, high fracture toughness and low density are required for novel bulletproof materials. B₄C/SiC composite ceramic is one of the most potential candidates. In this study, B₄C/SiC composite ceramic was prepared by reaction sintering. The influence of B₄C content, species and content of carbon, sintering temperature on the mechanical properties of B₄C/SiC composite ceramic were studied. A high performance B₄C/SiC composite ceramic was sintered at 1750°C for 30 min. Phenolic resin and carbon black were both chosen as carbon sources, whose favorable contents were 10wt%, 5wt%, respectively. The density of sintered bodies reduces with B₄C content increases. To some extent, fracture toughness, bending strength improve initially and then deteriorate with the increase of B₄C content whose optimal amount is 30wt%. The optimal fracture toughness and bending strength of the B₄C/SiC composite ceramic are 5.07MPa·m^1/2 and 487MPa, respectively. Meanwhile, the Viker-hardness of the sintered body is 30.2GPa, the density is as low as 2.82g/cm³.

Abstract: Ceramics with formula (1-x-y)[Na_0.515K_0.485]_0.94Li_0.06(Nb_0.99Ta_0.01)O₃ (NKLNT) xMnO₂ yCuO (when x, y = 0, 0.005 and 0.01) were prepared by a reaction sintering method. The effects of doping level on sinterability and properties of NKLNT ceramics were studied. The results indicated that the co-doping of MnO₂ and CuO was effective in promoting the densification of ceramics. Grain growth during secondary recrystallization was also affected, leading to larger grain size with x, y = 0.01 sample. X-ray diffraction data showed that the orthorhombic tetragonal morphotropic phase boundary existed in all the samples. At room temperature, the dielectric properties of NKLNT ceramics were improved by doping of appropriate MnO₂ and CuO content. The temperature dependence of dielectric constant showed a decrease slightly in Curie temperature (T_C) with increasing MnO₂ and CuO content. The composition with x = 0.005, y = 0 exhibited favorable properties for the promising lead-free piezoelectric candidate material.

Abstract: Experimental program and preparation technology of highly densified reaction bonded silicon carbide resistance materials with different resistivity were investigated by using alumina or silicon nitride as aids for improving of the volume resistivity. The microstructure of the materials was observed by scanning electron microscope. According to the experimental results, the resistivity of the material could be controlled by the particle size and the content of the aids. Besides, alumina could reduce silicon penetration and increase resistivity greatly, and 10wt.% of alumina could satisfy the requirement of resistance. In addition, different particle size of matrix materials had a great impact on the resistivity. Compared with the coarse silicon carbide, the room temperature resistivity value by using the fine silicon carbide could increases for six times.

Abstract: Reaction-bonding sintering silicon carbide (RB-SiC) toughened by 10vol% short carbon fibers were produced by Gel-casting method using water soluble epoxy as gel former and then reaction sintering at 1750°C under vacuum atmosphere for 2 h . SEM showed that short carbon fibers could disperse uniformly in the preforms and sintered carbon fiber reinforced silicon carbide composites (C_f/SiC). The mechanical test results showed that the strength decrease from 286 MPa for RB-SiC to 231 MPa for C_f/SiC, however, the fracture toughness of Cf/SiC increased from 3.65 MPa m^1/2 to 5.28 MPa m^1/2 compared with RB-SiC. The strength decrease of the C_f/SiC should be ascribed to the chemical reaction between the addition of short fibers and matrix, and the increase of the fracture toughness could be attributed to fiber debonding, fiber pull-out and crack deflection .

Abstract: Based on industrial silicon and carbon black as starting materials,β-SiC bonded SiC materials were prepared. The microstructure of such material and the silicon/carbon reaction were analyzed and investigated by XRD, SEM and other tools. The results indicate that the synthesis of β-SiC at 1400°C can be achieved through gas-phase mass transfer, liquid dissolution as well as in-situ reaction. While gas-phase mass transfer is the dominant reaction during the sintering of the material, in which β-SiC exists mainly as nanowhisker. The formation of β-SiC nanowires is believed to be the mechanism of reaction sintering.

Abstract: Al₂TiO₅-Si₃N₄ composites were prepared by reaction sintering process using Al₂TiO₅ and α-Si₃N₄ powders as raw materials. The effect of sintering temperature, soaking time and Si₃N₄ content on the sintering properties of the composites was studied. The results showed that the best sintering temperature and soaking time were 1550 °C and 2 h, respectively. The samples with 15 wt% of Si₃N₄ addition had good sintering properties, and its mechanical strength was 28.96 MPa, which was 2 times of the one of the samples without Si₃N₄ addition.

Abstract: Reaction sintering B₄C/SiC ceramics with high density were manufactured. The effect of the carbon content in green bodies on the microstructure and mechanical properties of the ceramics has been studied. Results showed that the carbon content and the value of carbon relative density (ρ_CRD) in the green bodies were the major factors affected the composition, that is, the free silicon and carbon contents and mechanical behaviors of sintered specimens. The optimal value of ρ_CRD was gotten at 0.85 g/cm³. The fracture toughness, flexural strength, and hardness of the composites increased with increasing carbon content up to 20 wt.%. The maximum values of fracture toughness of 3.8 MPa∙m^1/2, flexural strength of 475 MPa, and hardness of 32.0 GPa were obtained under the following process parameters: value of ρ_CRD in the green bodies was about 0.85 g/cm³; carbon, B₄C and SiC contents in green bodies were 20 wt.%, 30 wt.% and 50 wt.%, respectively; compact pressure was 75 MPa and sintering temperature was 1600°C.