碳含量对反应熔渗法制备SiC晶须增强碳化硅陶瓷性能的影响研究

以SiC晶须作为增强体,通过酚醛树脂高温碳化裂解获得碳包覆的SiC晶须,与纳米碳化硅粉体、炭黑混合均匀形成复合陶瓷乙醇浆料.经过干燥、造粒、成型和排胶后获得SiCw-C-SiC素坯,利用反应熔渗法制备高体积分数的SiC晶须增强SiC陶瓷基复合材料.研究了碳黑含量对复合材料力学性能与显微结构的影响.通过扫描电镜照片显示,碳包覆的SiC晶须经高温反应熔渗后仍保持表面的竹节状形貌,且晶须与碳化硅基体间形成适中的界面结合强度,材料断口处有明显的晶须拔出;当炭黑含量为15wt％时,抗弯强度和断裂韧性达到最高值分别为315 MPa和4.85 MPa·m1/2,比未加晶须的SiC陶瓷抗弯强度提高了25％,断裂韧性提高了15％;当炭黑含量为20wt％时,复合材料中残留部分未反应的炭黑,制约其力学性能的提高.     

反应烧结制备碳化硅-氮化铝复合材料

采用硅作为熔渗剂,利用真空反应烧结的工艺,在1600℃烧结制得了结构致密、密度低的碳化硅-氮化铝(SiC/AlN)复合材料,分析测试了所制得的复合材料的物相、微观结构和力学性能.结果表明,氮化铝的添加量由2wt％增加到10wt％时,复合材料的力学性能出现先增加后减小的趋势,当AlN含量为6wt％时,得到复合材料的力学性能最高,其抗弯强度为256 MPa,显微硬度为2660 HV.加入AlN后,复合材料的孔隙率略微有点上升,烧结体的密度在2.95 ～3.01 g/cm3之间.复合材料的主要组成相为SiC、AlN和Si.     

凝胶-注模成型技术制备碳纤维/HA复合材料的研究

本文研究了pH值、分散剂、有机单体和碳纤维含量对碳纤维/HA陶瓷浆料粘度的影响,观察了复相陶瓷浆料的凝胶固化过程,研究了烧结温度和碳纤维含量对复合材料烧结密度、抗弯强度和断裂韧性的影响.研究结果表明:当pH =9、有机单体含量为10wt％、分散剂含量为5wt％、固相含量为50wt％的碳纤维/HA陶瓷浆料具有良好的分散性.随引发剂、催化剂含量的增加,复相陶瓷浆料的凝胶固化时间缩短.复合材料的烧结密度、抗弯强度和断裂韧性均随烧结温度的升高而升高.复合材料的抗弯强度和断裂韧性均随着碳纤维含量的增加呈现先增加而后降低趋势.当碳纤维含量为2wt％和2.5wt％时,凝胶注模成型所制备的复合材料的抗弯强度和断裂韧性分别为80.6 MPa和1.87 MPa·m1/2,较干压成型样品提高了24.9％和19.8％.     

BNNTs/SiC陶瓷复合材料的制备与性能研究

以SiC为基体,Y_2O_3和Al_2O_3为烧结助剂,氮化硼纳米管(BNNTs)为增韧补强剂,采用喷雾造粒和干压成型方法,通过真空无压烧结工艺制备了BNNTs/SiC陶瓷复合材料。讨论BNNTs添加量和烧结工艺对BNNTs/SiC陶瓷复合材料的致密度、微观结构和力学性能的影响。实验结果表明:采用单因素法得到BNNTs的最佳添加量为1.5 wt.%和压制压力为100 MPa,确定了最佳烧成制度为:最高温度2050℃,保温时间2.5 h。采用阿基米德排水法测试样品密度,其相对密度达到99.0%,通过三点弯曲法和压痕法分别测试了样品的抗弯强度、断裂韧性和维氏硬度。BNNTs/SiC的抗弯强度、断裂韧性和维氏硬度分别达到了546.3 MPa、6.53 MPa·m~(1/2)和26.8 GPa。     

SiC_p/B_4C复合陶瓷的热压烧结及组织性能

以Si粉为烧结助剂,SiC颗粒为增强剂,采用真空热压烧结工艺制备了SiCp/B4C陶瓷基复合材料。研究了SiCp对复合材料力学性能的影响。借助X射线衍射、扫描电镜等分析了复合材料的物相组成和微观结构。研究表明:添加的SiCp中粒径小的颗粒被包裹在主晶相中,粒径较大的颗粒分布在晶界上,形成"晶内-晶间"混合型复合陶瓷。当SiCp含量为4wt.%时,复合材料的弯曲强度和断裂韧性分别达到431MPa和5.41MPa.m1/2。复合材料力学性能的提高主要是由于残余应力引起的晶界强化以及断裂方式的转变。     

YAG对TiCN陶瓷刀具材料力学性能及烧结工艺的影响

以钇铝石榴石(YAG)为添加相,采用热压烧结法制备YAG–TiCN复合陶瓷。研究了不同YAG添加量对复合陶瓷的物相、显微结构、力学性能的影响。结果表明:热压烧结过程中TiCN和YAG不发生反应;YAG第二相明显改善了TiCN的烧结性能,并有助于提高YAG–TiCN复合陶瓷的硬度、抗弯强度和断裂韧性;YAG含量在10%(质量分数)时复合陶瓷的致密度达到99.3%,并且Vickers硬度、断裂韧性、抗弯强度均达到最高,分别为:20.48GPa、7.27MPa·m1/2、570.36MPa,远远超过TiCN单相陶瓷的致密度以及力学性能:88.04%、9.33GPa、5MPa·m1/2、204.45MPa。YAG作为添加相可显著提高TiCN等难烧结陶瓷的致密度和力学性能。     

YAG对TiCN陶瓷刀具材料力学性能及烧结工艺的影响

以钇铝石榴石(YAG)为添加相,采用热压烧结法制备YAG–TiCN复合陶瓷。研究了不同YAG添加量对复合陶瓷的物相、显微结构、力学性能的影响。结果表明:热压烧结过程中TiCN和YAG不发生反应;YAG第二相明显改善了TiCN的烧结性能,并有助于提高YAG–TiCN复合陶瓷的硬度、抗弯强度和断裂韧性;YAG含量在10%(质量分数)时复合陶瓷的致密度达到99.3%,并且Vickers硬度、断裂韧性、抗弯强度均达到最高,分别为:20.48GPa、7.27MPa·m1/2、570.36MPa,远远超过TiCN单相陶瓷的致密度以及力学性能:88.04%、9.33GPa、5MPa·m1/2、204.45MPa。YAG作为添加相可显著提高TiCN等难烧结陶瓷的致密度和力学性能。     

AlN-Pr2O3液相烧结SiC陶瓷

以AlN、Pr2O3做为SiC陶瓷液相烧结的复合助剂,选定不同的助剂含量(5wt％～ 20wt％)和不同的助剂摩尔比例(Pr2O3/AlN=1/3、1/1、3/1),在1800～2000℃温度下,采用热压和无压烧结的方法制备SiC陶瓷样品,并对这些陶瓷样品的性能进行了研究.实验结果表明,助剂比1/3组的样品显示出更有效地促进SiC陶瓷致密化,该组样品无压烧结最大相对密度为87％,热压烧结具有最高的相对密度96.1％、维氏硬度23.4 GPa、抗弯强度549.7MPa、断裂韧性5.36 MPa·m1/2,显微结构中可观察到晶粒拔出现象,断裂模式为沿晶断裂.     

热压烧结石墨烯/B4C复合材料的制备与性能研究

采用真空热压烧结工艺,在2150℃及30 MPa压制压力条件下,保温30 min制备了石墨烯/B4 C陶瓷基复合材料.采用拉曼光谱仪、X射线衍射仪和扫描电镜分析了复合材料的物相组成和显微结构,通过测量陶瓷的相对密度、硬度和弯曲强度,研究了氧化石墨烯添加量对B4C烧结行为和力学性能的影响.结果 表明:复合材料的相对密度随着石墨烯含量的增加先增加而后降低.当氧化石墨烯含量为3.0wt％时,复合材料的力学性能达到最大值,其抗弯强度为547 MPa,断裂韧性为4.50 MPa·m1/2,裂纹偏转以及石墨烯拔出是材料力学性能提升的原因;与此同时,该复合材料的电导率达到1.0 S/m以上,达到了电加工所需的电导率水平.     

碳化硅/石墨复合陶瓷密封材料的显微结构与性能

以碳化硅微粉为原料、石墨为固体润滑添加剂,采用无压烧结技术制备碳化硅/石墨复合陶瓷密封材料,研究了石墨添加量对复合陶瓷密封材料烧结性能、显微结构、力学性能和摩擦性能的影响。结果表明,加入的石墨能以片状颗粒形态均匀分布在碳化硅陶瓷基体中;随着石墨添加量增加,复合陶瓷密封材料的体积密度、抗弯强度、弹性模量、断裂韧性、硬度均逐渐降低,但干、湿静摩擦系数则随之减小;当石墨添加量达到20%(质量分数)时,复合陶瓷的相对密度仅为90.6%,弯曲强度降至189 MPa,弹性模量降至295 GPa,断裂韧性为1.82 MPa·m1/2,Vickers硬度为19.2 GPa,而干、湿摩擦系数则分别减小到0.14和0.10。综合考虑复合陶瓷的力学性能和摩擦性能,石墨添加量控制在10%~15%之间为宜。     

Thermophysical and Mechanical Properties of a Three-Dimensional Hi–Nicalon/SiC Composite

Key thermophysical and mechanical properties of a three-dimensional Hi-Nicalon™/silicon carbide (SiC) composite were tested. The relationship between the thermal expansion coefficient and temperature of the composite from room temperature (RT) to 1400°C was similar to that of chemical vapor deposition SiC. The thermal diffusivity of the composite could be well fitted by a logarithmic function. The composite exhibited excellent mechanical properties at RT and high temperature in vacuum. At RT, the flexural strength and flexural modulus were 1193 MPa and 255.6 GPa, respectively. Above 1200°C, the value of the flexural strength and flexural modulus at high temperature in vacuum decreased as the temperature increased, while the fracture toughness increased as the temperature increased.     

The influence of different SiC amounts on the microstructure,densification, and mechanical properties of hot-pressed Al2O3-SiC composites

The hot pressing process of monolithic Al₂O₃ and Al₂O₃-SiC composites with 0-25 wt% of submicrometer silicon carbide was done in this paper. The presence of SiC particles prohibited the grain growth of the Al₂O₃ matrix during sintering at the temperatures of 1450°C and 1550°C for 1 h and under the pressure of 30 MPa in vacuum. The effect of SiC reinforcement on the mechanical properties of composite specimens like fracture toughness, flexural strength, and hardness was discussed. The results showed that the maximum values of fracture toughness (5.9 ± 0.5 MPa.m^1/2) and hardness (20.8 ± 0.4 GPa) were obtained for the Al₂O₃-5 wt% SiC composite specimens. The significant improvement in fracture toughness of composite specimens in comparison with the monolithic alumina (3.1 ± 0.4 MPa.m^1/2) could be attributed to crack deflection as one of the toughening mechanisms with regard to the presence of SiC particles. In addition, the flexural strength was improved by increasing SiC value up to 25 wt% and reached 395 ± 1.4 MPa. The scanning electron microscopy (SEM) observations verified that the increasing of flexural strength was related to the fine-grained microstructure.     

Microstructure and mechanical properties of hot pressed Al2O3/SiC nanocomposites

Al₂O₃/SiC micro/nano composites containing different volume fractions (5, 10, 15, and 20 vol.%) of SiC were prepared by mixing a sub-micron alumina powder with respective amounts of either micro- or nano-sized silicon carbide powders. The powder mixtures were hot pressed 1 h at 1740 °C and 30 MPa in the atmosphere of Ar. The effect of SiC addition on the microstructure and mechanical properties, i.e. hardness, fracture toughness, and room temperature flexural strength were investigated. The flexural strength increased with increasing volume fraction of silicon carbide particles. The maximum flexural strength (655 ± 90 MPa) was achieved for the composite containing 20 vol.% of coarse-grained SiC, which is more than twice as high as in the Al₂O₃ reference. Hardness and fracture toughness were also moderately improved. The observed improvement of mechanical properties is mainly attributed to alumina matrix grain refinement and grain boundary reinforcement.     

Three-Dimensional Carbon/Silicon Carbide Composites Prepared by Chemical Vapor Infiltration

Continuous-carbon-fiber-reinforced silicon carbide composites (C/SiC) were prepared by chemical vapor infiltration in which the preforms were fabricated with the three-dimensional braid method. The mechanical properties and microstructures were investigated. For the composites with no interfacial layer, flexural strength and fracture toughness increased with density of the composites, and the maximum values were 520 MPa and 16.5 MPa·m^1/2, respectively. The fracture behavior was dependent on the interfacial bonding between fiber/matrix and fiber bundle/bundle which was determined by the density of the composites. Heat treatment had a significant influence on the mechanical properties and fracture behavior. The composites with pyrolysis interfacial layers exhibited characteristic fracture and relatively low strength (300 MPa).     

Mechanical properties of SiCf/SiC composites with alternating PyC/BN multilayer interfaces

Alternating pyrolytic carbon/boron nitride (PyC/BN)_n multilayer coatings were applied to the KD–II silicon carbide (SiC) fibres by chemical vapour deposition technique to fabricate continuous SiC fibre-reinforced SiC matrix (SiC_f/SiC) composites with improved flexural strength and fracture toughness. Three-dimensional SiC_f/SiC composites with different interfaces were fabricated by polymer infiltration and pyrolysis process. The microstructure of the coating was characterised by scanning electron microscopy, X–photoelectron spectroscopy and transmission electron microscopy. The interfacial shear strength was determined by the single-fibre push-out test. Single-edge notched beam (SENB) test and three-point bending test were used to evaluate the influence of multilayer interfaces on the mechanical properties of SiC_f/SiC composites. The results indicated that the (PyC/BN)_n multilayer interface led to optimum flexural strength and fracture toughness of 566.0?MPa and 21.5?MPa?m^1/2, respectively, thus the fracture toughness of the composites was significantly improved.     

Mechanical properties and microstructure of biomorphic silicon carbide ceramics fabricated from wood precursors

Silicon carbide-based, environment friendly, biomorphic ceramics have been fabricated by the pyrolysis and infiltration of natural wood (maple and mahogany) precursors. This technology provides an eco-friendly route to advanced ceramic materials. These biomorphic silicon carbide ceramics have tailorable properties and behave like silicon carbide based materials manufactured by conventional approaches. The elastic moduli and fracture toughness of biomorphic ceramics strongly depend on the properties of starting wood preforms and the degree of molten silicon infiltration. Mechanical properties of silicon carbide ceramics fabricated from maple wood precursors indicate flexural strengths of 344±58 MPa at room temperature and 230±36 MPa at 1350 °C. Room temperature fracture toughness of the maple based material is 2.6±0.2 MPa√m while the mahogany precursor derived ceramics show a fracture toughness of 2.0±0.2 MPa√m. The fracture toughness and the strength increase as the density of final material increases. Fractographic characterization indicates the failure origins to be pores and chipped pockets of silicon.     

Strengthening and toughening of CNTs-reinforced B4C-SiC ceramic composite material via spark plasma sintering

For addressing the issue of low relative density, poor fracture toughness of boron carbide ceramics, carbon nanotubes (CNTs)-reinforced B₄C-SiC ceramic composite material was prepared via spark plasma sintering (SPS), and the impact of CNTs on the strengthening and toughening of the composite was studied. The evidence revealed that an appropriate amount of CNTs can enhance the discharge effect and improve the compactness. As the CNTs content increased, the flexural strength and fracture toughness took on a tendency to first rise and then drop. After mixing .5 wt.% CNTs, the flexural strength and fracture toughness were 499 MPa and 5.38 MPa·m^1/2, which increased by 59.4% and 28.4%, respectively. The transformation of fracture mode, grain refinement, bridging and pulling-out of CNTs efficiently enhance the mechanical properties.     

The Role of Infiltration Temperature in the Reaction Bonding of Boron Carbide by Silicon Infiltration

The present paper is concerned on the effect of infiltration temperature on the components, microstructure, and mechanical properties of reaction‐bonded boron carbide (RBBC) ceramics. RBBC ceramics were fabricated by reactive infiltration of molten silicon (Si) into porous preforms containing boron carbide (B₄C) and free carbon. It has been found that infiltration temperatures have significant influence on the infiltration reactions involved and therefore the evolution of different phases formed in the RBBC ceramics. An increase in grain size of boron carbide particles through the coalescence of neighboring grains was observed at certain infiltration temperatures. The morphology of silicon carbide (SiC) phases developed from discontinuous and cloud‐like SiC to continuous and integrated SiC zones with the increase of infiltration temperatures. With increasing temperatures up to 1600°C, the hardness, flexural strength, and fracture toughness all increased. When the temperatures exceeded 1600°C, while the hardness and flexural strength decreased, the fracture toughness continued to increase.     

Development of Silicon Carbide Reinforced Jute Epoxy Composites: Physical,Mechanical and Thermo-mechanical Characterizations

The aim of the present study was to investigate the physical and thermo-mechanical characterization of silicon carbide filled needle punch nonwoven jute fiber reinforced epoxy composites. The composite materials were prepared by mixing different weight percentages (0–15 wt.%) of silicon carbide in needle punch nonwoven jute fiber reinforced epoxy composites by hand-lay-up techniques. The physical and mechanical tests have been performed to find the void content, water absorption, hardness, tensile strength, impact strength, fracture toughness and thermo-mechanical properties of the silicon carbide filled jute epoxy composites. The results indicated that increase in silicon carbide filler from 0 to 15 wt.% in the jute epoxy composites increased the void content by 1.49 %, water absorption by 1.83 %, hardness by 39.47 %, tensile strength by 52.5 %, flexural strength by 48.5 %, and impact strength by 14.5 % but on the other hand, decreased the thermal conductivity by 11.62 %. The result also indicated that jute epoxy composites reinforced with 15 wt.% silicon carbide particulate filler presented the highest storage modulus and loss modulus as compared with the unfilled jute epoxy composite.     

低压化学气相渗透法制备2.5维SiCf/SiC复合材料

采用低压化学气相渗透法制备了具有和不具有热解炭界面层的2.5维连续SiC纤维增强的SiC复合材料(SiCf/SiC).SiC纤维的体积分数为30%和41%.所制备复合材料的气孔率为20%左右.当纤维为30%时,沉积有0.1 μm热解炭界面层的复合材料的弯曲强度由未加热解炭界面层的232MPa增加到328MPa,而且材料由灾难性断裂转变为非灾难性断裂.在同一制备条件下,纤维体积分数为41%的SiCf/SiC比30%的SiCf/SiC具有更高的气孔率.纤维为41%时,热解炭界面层厚度为0.1 μm的SiCf/SiC的弯曲强度只有244MPa,但是它具有更高的韧性和更长的纤维拔出长度.