Dispersion and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure

The dispersion behavior and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure were investigated. The Si–C powders synthesized by a mechanical alloying (MA) process had a near‐spherical shape with an average particle size of 170 nm. A solid loading of 62 vol% was achieved using polyethyleneimine (PEI) as a dispersant. The optimum dispersant amount was 1 wt% based on zeta potential, sedimentation, and viscosity analysis data. The high zeta potential value (73 mV) compared with that of the commercially available SiC (65 mV) was caused by modified surface properties and consequent promotion of the cationic dispersant adsorption. A Si–Al–C slurry containing 6.5 wt% of sintering additives with a solid loading of 60 vol% was also prepared. The relative density of the dried Si–Al–C slurry was 63.3% without additional compaction, which could be densified at 1650°C at a pressure of 20 MPa using a spark plasma sintering furnace.     

Thermodynamic Behavior of Copper-Coated Silicon Carbide Particles during Conventional Heating and Spark Plasma Sintering

75Cu·25SiC (vol%) compacts were prepared using copper-coated SiC particles and spark plasma sintering (SPS). The preliminary thermal performance of the coated particles was determined using simultaneous DSC-TG-MS measurement. Characterization of compacts using XRD and SEM techniques was conducted to investigate the physical and chemical changes during the SPS operation. It was found that CuO decomposed at 850° and 500°C during conventional heating and SPS, respectively. Cu₂O facilitated the densification of Cu/SiC composites. The optimized sintering temperature of Cu/SiC composites using SPS was ∼730°C. The compacts showed improved hardness because of the SiC reinforcement.     

Erosive wear behavior of spark plasma-sintered SiC–TaC composites

Spark plasma sintering of SiC-10, 20, or 30 wt% TaC composites was performed at 1800°C. Microstructures of sintered composites revealed uniform dispersion of TaC particles in SiC matrix. With the increase in TaC content, hardness decreased from 25.75 to 23.30 GPa and fracture toughness increased from 3.48 to 3.85 MPa m^1/2. Erosion testing was performed to evaluate the potential of sintered composites at room temperature and 400°C by a stream of SiC particles impinging at different angles (30°, 60°, or 90°). The erosion rate varied from 25 to 166 mm³/kg, with change in TaC content, impingement angle, or temperature. The erosion rate increased as the angle of impingement and temperature increased, but reduced when the TaC concentration increased. Worn surfaces revealed that the material was dominantly removed via fracture of SiC grains and TaC particles pull-out. SiC-30 wt% TaC composites exhibited superior erosive wear resistance at low impingement angle and room temperature.     

High thermal conductivity of spark plasma sintered silicon carbide ceramics with yttria and scandia

A fully dense SiC ceramic with a room‐temperature thermal conductivity of 262 W·(m·K)^?1 was obtained via spark plasma sintering β‐SiC powder containing 0.79 vol% Y₂O₃‐Sc₂O₃. High‐resolution transmission electron microscopy revealed two different SiC‐SiC boundaries, that is, amorphous and clean boundaries, in addition to a fully crystallized junction phase. A high thermal conductivity was attributed to a low lattice oxygen content and the presence of clean SiC‐SiC boundaries.     

ZrB2-SiCpl复合陶瓷的SPS烧结行为及微观结构

利用放电等离子体烧结（spark plasma sintering,SPS）技术,在烧结温度、保温时间、压力和加热速率分别为1 600℃、5 min、30 MPa和100℃/min条件下制备硼化锆（ZrB2）–15%（体积分数）碳化硅晶片（SiCpl）复合陶瓷。研究ZrB2–SiCpl复合陶瓷的烧结致密化行为、微观结构...     

Does a True Fatigue Limit Exist for Continuous Fiber-Reinforced Ceramic Matrix Composites?

The high-cycle high-frequency fatigue behavior of a Nicalon-fiber-reinforced calcium aluminosilicate ceramic composite was investigated. A key goal of the room-temperature fatigue experiments was to determine if a true fatigue limit or endurance limit existed for this ceramic matrix composite. Although no fatigue failures occurred beyond 10⁷ cycles, the stress–strain hysteresis modulus and frictional heating continued to change up to 10⁸ cycles, at which point the 200 Hz experiments were terminated. This suggests that fatigue damage continued to evolve and that a true fatigue limit may not exist in ceramic matrix composites that have undergone interfacial frictional sliding.     

Fabrication of Continuous-SiC-Fiber-Reinforced SiAlON-Based Ceramic Composites by Reactive Melt Infiltration

A technique for fabrication of β'-SiAlON-based ceramics in three-dimensional woven fabrics of BN-coated SiC (Hi-Nicalon™) fibers was developed by reactive melt infiltration in a controlled N₂ atmosphere. β'-SiAlON was produced in situ by the reaction of β-Si₃N₄, AlN, and Y-Al-Si-O molten glass. The wettability of the fibers with the molten glass was improved by infiltration and pyrolysis of perhydropolysilazane, resulting in fully dense matrix composites. The reaction between the fiber and molten glass could be depressed by increasing the N₂ partial pressure during the melt infiltration. The inhibition of the interfacial reaction may be related to the formation of carbon and oxynitride on the SiC fiber, in agreement with thermodynamic calculations as a function of N₂ partial pressure. The fabricated composites had a high ultimate flexure strength and a large work of fracture at room temperature. Degradation of the mechanical performance of the composites was small, even at 1773 K in an argon atmosphere.     

Oxidation mechanisms of SiC-fiber–reinforced Si eutectic alloy matrix composites at elevated temperatures

SiC-fiber–reinforced binary Si eutectic alloy composites have been developed for aerospace applications using the melt infiltration method. In this study, the oxidation mechanisms of various binary Si eutectic alloys were evaluated at elevated temperatures. We suggest that the oxidation resistance of eutectic alloys could be predicted using the Gibbs energy change for the oxidation reaction. Based on these calculations, eutectic alloys of Si-16at%Ti, Si-17at%Cr, Si-22at%Co, Si-38at%Co, and Si-27at%Fe were prepared. These alloys produced uniform SiO₂ layers and showed the same oxidation resistance as Si at 1000°C under humid conditions. Therefore, SiC composites using Si alloys with excellent oxidation resistance can be predicted using thermodynamic calculations.     

Thermal Response and Oxidation of Tyranno™-Fiber-Reinforced Si-Ti-C-O Matrix Composites for a Thermal Protection System in High-Enthalpy Dissociated Air

The thermal response and oxidation of Tyranno™ Lox-M fiber-reinforced Si-Ti-C-O matrix composites in high-enthalpy dissociated air was investigated in an arc jet facility (an arc wind tunnel). The maximum surface temperature reached 1310–1670°C. Catalytic recombination of oxygen and nitrogen on the composite surface under dissociated air was not significant. Surface recession was insignificant below 1600°C surface temperatures and above 5 kPa of oxygen partial pressure at the stagnation point. Passive-to-active oxidation transition of the composite agreed with Balat's theory for monolithic silicon carbide. A glass sealant prevented active oxidation of the composite for short-time exposures.     

Intermediate temperature oxidative strength degradation of a SiC/SiNC composite with a polymer‐derived matrix

The article describes an experimental investigation of oxidative degradation in mechanical performance of a SiC fiber‐reinforced composite with a SiCN matrix produced by polymer infiltration and pyrolysis. Tensile stress rupture and retained strength tests were performed at 800°C in dry air and in water vapor. Fracture surfaces were examined to determine the degree of fiber pull‐out and constituent oxidation and to measure radii of representative fiber fracture mirrors. The results indicate that degradation in tows adjacent to cut surfaces occurs equally rapidly in water vapor with or without application of stress; regions in the composite interior and near as‐processed (uncut) surfaces appear far less affected. Similar effects are evident but less pronounced in dry air. Although oxidation of fiber coatings is observed in some cases, collectively the results suggest that fiber degradation is the main mechanism leading to reduced composite strength.     

Formation of Ti3SiC2 interphase coating on SiCf/SiC composite by electrophoretic deposition

To improve the oxidation resistance of SiC composites at high temperature, the feasibility of using Ti₃SiC₂ coated via electrophoretic deposition (EPD) as a SiC fiber reinforced SiC composite interphase material was studied. Through fiber pullout, Ti₃SiC₂, due to its lamellar structure, has the possibility of improving the fracture toughness of SiC_f/SiC composites. In this study, Ti₃SiC₂ coating was produced by EPD on SiC fiber; using Ti₃SiC₂‐coated SiC fabric, SiC_f/SiC composite was fabricated by hot pressing. Platelet Ti₃SiC₂ powder pulverized into nanoparticles through high‐energy wet ball milling was uniformly coated on the SiC fiber in a direction in which the basal plane of the particles was parallel to the fiber. In a 3‐point bending test of the SiC_f/SiC composite using Ti₃SiC₂‐coated SiC fabric, the SiC_f/SiC composite exhibited brittle fracture behavior, but an abrupt slope change in the strength‐displacement curve was observed during loading due to the Ti₃SiC₂ interphase. On the fracture surface, delamination between each layer of SiC fabric was observed.     

Cf/SiC复合材料的制备及性能的研究

采用料浆渗积-有机前躯体裂解工艺制备碳纤维增强碳化硅陶瓷基复合材料.制备材料的抗弯强度达283 MPa,断裂韧性达12.1 MPa·m1/2.     

连续纤维增韧碳化硅陶瓷基复合材料研究

采用化学气相浸渗法制造了连续碳纤维和碳化硅纤维增韧碳化硅陶瓷基复合材料,并对复合材料的显微结构和力学性能进行了研究,C/SiC／SiC复合材料的密度分别为2．1g/cm^3和2．5g/cm63,在断理解过程中表现出明显的非线性和非灾难性的断裂行为和规律,C／SiC和SiC／SiC弯曲强度分别为450MPa和850MPa,从室温至1600℃强度不发生降低;断裂韧性为20MPa.m^1/2和41．5MPa.m^1/2,断裂功为10kJ.m^-2和28．1kJ.m^-2,冲击韧性为62．0kJ.m^-2和36．0kJ.m^-2,C/SiC和SiC/SiC复合材料具有优异的抗热震性能,经1300℃→←3000℃,50次热震后,强度保持率高达96．4％,热震不是材料性能损伤的控制因素,而SiC/SiC复合材料优异的抗氧化性能,对温度梯度不敏感,得合材料喷管在液体火箭发动机上成功地通过了地面实验。     

放电等离子烧结工艺合成Ti3SiC2的研究

以元素单质粉为原料,当原料配比为n(Ti):n(Si):n(Al):n(C)=3:(1.2-x):x:2,其中：x=0.05-0.2时,在1200－1250℃温度下经放电等离子烧结成功制备了高纯、致密Ti3SiC2固溶体材料。原料中掺加适量Al能改善Ti3SiC2的合成反应并提高制备材料的纯度。当x=0.2时,所合成的固溶体形貌为板状结晶,分子式近似为Ti3Si0.8Al0.2C2,晶格参数a=0.3069nm,c=1.767nm。在1250℃温度下烧结,得到平均厚度达5μm,发育完善均匀的致密多晶体材料。材料Vickers硬度为3.5-5.5GPa,具有与石墨相似的加工性能。     

低温合成Ti3SiC2陶瓷

采用机械合金化和放电等离子烧结技术制备了纯度较高的Ti3SiC2陶瓷,研究了微量Al对Ti3SiC2的机械合金化和放电等离子烧结过程的影响.结果表明:添加适量的Al可以显著提高机械合金化及放电等离子烧结产物中Ti3SiC2的含量,并显著降低高纯度Ti3SiC2的烧结温度.机械合金化10h,成分为3Ti/Si/2C/0.2Al(摩尔比)的混合粉体,经850℃放电等离子烧结可获得质量分数(下同)高达96%的Ti3SiC2块体,烧结温度提高到1 100℃,可获得纯度为99.3%、相对密度高达98.9%的Ti3SiC2致密块体.     

碳纤维增强SiC陶瓷复合材料的研究进展

碳纤维增强SiC陶瓷基复合材料具有良好的高温力学性能,是航空航天和能源等领域新的高温结构材料研究的热点之一．本文回顾了增强体碳纤维的发展,对材料的成型制备工艺,材料的抗氧化涂层研究进展和现有的一些应用做了综述,并展望了碳纤维增强SiC陶瓷基复合材料以后的研究重点及发展前景．