جستجوی مقالات مرتبط با کلیدواژه « zrb2 » در نشریات گروه « مواد و متالورژی »

In this research, the effect of adding silicon carbide nanoparticles, zirconium carbide, and carbon nanofibers at different sintering temperatures and times on fracture toughness and hardness of ZrB2 ceramics has been investigated. Due to the high number of required samples (four variables in three levels) to optimize the fracture toughness and hardness, the design of the experiment (DOE) by the Taguchi method was used. The hardness and fracture toughness of the composites fabricated by spark plasma sintering (SPS) were evaluated by macro-Vickers and crack length measurement methods respectively. The results showed that sample 8 with the chemical composition of ZrB2-25Vol%SiC-15ZrC-10CNF sintered at 1875°C for 7 minutes has the maximum amount of HV hardness (400±33) and fracture toughness (7.3±0.4) Mpa.m1/2. Also, analysis of variance (ANOVA) indicated that temperature and time are the most effective variables on fracture toughness (with contributions of 84% and 10.5% respectively) and hardness (with contributions of 74.3% and 15.9% respectively).

Ceramic borides, carbides and nitrides with high melting point, relatively good resistance to oxidation and corrosive environments are considered by many researchers in various high temperature industries, which is known from the family of materials as high temperature ceramic (UHTC). To be. All UHTCs have very strong bonds that give them structural stability at high temperatures, and among them diboride compounds offer the highest degree of oxidation resistance, which compared to carbides and nitrides, diborides have high thermal conductivity and their strength Increases against heat shock. Further studies on diborides, especially zirconium diboride (ZrB2), were selected as the most promising candidate for use in high temperature applications. This review article discusses their mechanical and thermal properties, especially ZrB2, and also focuses on the effect of additives such as SiC to improve mechanical or thermal properties and / or to improve oxidation resistance in harsh environments at temperatures above 2000 ° C.

In the present study, ZrB2 nano powders were synthesized using sol-gel method. Zirconium alkoxide was used as the source of zirconium and boric acid as the source of boron. The size of precursor nanoparticle was controlled using the pH parameter inside the sol, and the formation of primary nuclei of ZrB2 phase and their crystallized amount were investigated using the temperature parameter. To evaluate the mechanism of product formation during the sol-gel process, DLS analysis showed that the size of precursor particle inside the sol at pH less than 5 was below 10 nm. Mixing of precursor particles at molecular level inside the sol was one of the important reasons in reducing the synthesis temperature of ZrB2 particles. FTIR analysis on chemical bonds showed that Zr-O-B bond was formed inside the gel powder.DTA analysis showed that the primary nuclei of ZrB2 particles were formed at a temperature of about 1400 °C. XRD observations proved that the primary nuclei of the ZrB2 phase crystallized and grew at a temperature of about 1500°C. Surface research revealed that the specific surface area of the synthesized ZrB2 particles is equivalent to 115 m2/g, and also the surfaces of these particles are porous, and the size of these porosities is in meso range. SEM analysis showed that the particle size of ZrB2 having homogeneous morphology is about 50 nm. TEM microstructural analysis revealed that ZrB2 particles were formed uniformly and orderly in very fine dimensions.

In this research, the effective parameters on the oxidation of ZrB2 ceramics were investigated. Temperature, time and pressure in addition of different additives (SiC, Cf, MoSi2, HfB2 and ZrC) were investigated. Taguchi method was applied for experimental design. Oxidation test was conducted on box furnace at 1600 C for one hour. It was cleared that the HfB2 resulted to better oxidation resistance. At the presence of ZrC, oxidation resistance was damaged. SiC improves the oxidation resistance by borosilicate layer formation. Finally, among the SPS parameters, temperature is the most.

In the present paper, ZrB2-SiC nanocomposite was developed by pressureless sintering method. Micro sized AlN powder and SiC powderes at nano and micro-sized scale were used as additive. In order to produce composite samples, the primary powders were milled and blended in planetary ball mill apparatus with rotational speed of 200rpm and then processed using hot pressing (80?C and 100MPa), cold isostatic press and sintering at 2150?C. The values of relative density and porosity of samples were measured to evaluate the effect of presence of micro-sized SiC and SiC nano particles simultaneously on the pressureless sintering behavior of ZrB2-SiC. In order to compare the microstructure and mechanical properties of samples Scanning Electron microscopy (SEM), equipped with EDS spectroscopy, XRD analysis, hardness and toughness tests were used. The results show that as the volume percentage of nano SiC decreases to 15 vol.% and AlN increases to 7.5 vol.% the hardness (17.1 GPa), toughness (5.7 MPa.m1/2) and relative density (98.1%) increase.

ZrB2 is a ultra-high temperature ceramic (UHTCs) with a high melting point of over 3040 ° C with unique properties. Of the major problems with ZrB2 is its weakness of sinterability, that in this study adding SiC in micron and nano as a secondary phase and B4C as an additive tried to overcome this problem. Systematic studies were performed on the pressureless sintering of ZrB2–SiC nanocomposites. At first changes in particle size were investigated as a result of different milling times and optimization of this time. Then the effect of different weights of SiC micron and nano with addition of B4C was investigated. Samples were pressurelessly sintered at 2050 ° C, 2100 ° C, 2150 ° C and 2200 ° C for one hour. ZrB2–SiC nanocomposites with 10%wt nano SiC and 3%wt B4C have an average hardness of 14.85± 0.5 GPa and toughness around 3.8 MPam1/2. At the final stage, the samples were oxidized at 1500 ºC in the air atmosphere and appearance and weight variations were investigated. The results showed that the addition of B4C is not only useful for sintering but also useful for oxidation resistance.

ZrB2 base composites containing SiC, MoSi2 and AlN have good sinterability and mechanical properties. In this study, 20 vol% nanometric SiC and 4wt% micrometric MoSi2 with different amount of AlN whiskers (0-10%vol) added to ZrB2. After mixing, composite samples were formed by cold isostatic press (CIP) with 200MPa pressure, and then samples were fired at 2100°C/1hr in Ar atmosphere with heating rate of 10°C/min. After firing bulk density, open porosity, microhardness, toughness, microstructural and phase analysis were determined. The results showed that optimum properties obtained at 7.5%vol AlN whiskers with relative density (96.3%), open porosity (1%vol), Vickers hardness (18.5 GPa) and fracture toughness (4.37 MPa.1/2). The SEM+EDS and XRD analysis showed that SiC and AlN solid solution and formation of Zr2Al3C4 phases due to probably high vapour pressure of AlN at 2100°C were promoted sintering and improvement of properties of composites.

In this study، ZrB2-HfB2 composite was produced by pressureless sintering method. MoSi2 B4C and SiC particles were used as reinforcement. ZrB2 powder was milled in planetary ball mill apparatus and then reinforcement particles were added to the milled powder. The composite powders were then CIPed and sintered at 2100oC and 2150oC. Scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDS)، flexural test، and resonance frequency method were used to compare the added particle effects on mechanical properties and pressureless sintering behavior of ZrB2-HfB2 composite. The analysis showed that the ZrB2-HfB2-MoSi2-SiCnano composite displays the largest gain in flexural strength. Furthermore، increasing the sintering temperature leads to an increase in flexural strength of samples.