近净成形制备SiC/Al复合材料Ⅰ:SiC预成形坯的制备

以微米级的碳化硅粉和石墨粉为原料,采用氧化结合法制备出不同孔隙含量的、适合液态铝无压渗透的SiC预成形坯。研究SiC多孔陶瓷的低温烧结机理和石墨添加量对SiC陶瓷骨架烧结密度和尺寸变化的影响。结果表明：在1 100℃烧结时,碳化硅和石墨粉同时发生氧化反应;SiC氧化产生的结晶态SiO2膜将SiC粉体粘结成陶瓷骨架,石墨氧化去除后形成孔隙;SiC粉体间本征孔隙和石墨去除后留下的孔隙构成三维互连通状态;因SiC氧化导致陶瓷骨架产生4%左右的线膨胀,但坯体不发生形状改变;通过调整石墨含量,能获得孔隙率从0.47-0.63的SiC陶瓷骨架。     

低温常压烧结SiC陶瓷的结构与性能

采用Al2O3-Y2O3-CaO烧结助剂体系,低于1600℃无保护气氛条件下常压烧结制备SiC陶瓷。研究了粘结剂含量、压制压力、SiC原料粒径级配、烧结温度、烧结助剂含量等对SiC陶瓷结构与性能的影响,优化低温常压烧结SiC陶瓷工艺参数。结果表明,在SiC陶瓷烧结过程中,烧结体中的助烧熔体能充分填充孔隙,并在随后的冷却过程中大多转化为晶态氧化物,有效促进SiC陶瓷的烧结致密化,并赋予其良好的结构与性能。采用3.5μm和0.5μm粒径的粉体按3∶1质量比级配,烧结助剂含量为30%(质量分数),1575℃烧结制备的SiC陶瓷的密度为2.93 g/cm3,抗弯强度为359 MPa。     

Si含量对放电等离子烧结制备(1-x)Ti3SiC2+xSiC复合材料的影响

以钛粉、硅粉和石墨粉为原料,制备出(1-x)Ti3SiC2+xSiC(x=0.1～0.8)复合材料,并利用X射线衍射仪对样品进行相组成分析.结果表明经1300℃放电等离子烧结15min后,可以得到纯净的0.9Ti3SiC2-0.1SiC和含有 微量石墨的0.2Ti3SiC2-0.8SiC复合材料,0.9Ti3SiC2-0.1SiC和0.2Ti3SiC2-0.8SiC复合材料的显微硬度分别为8.8和10.5GPa,均明显高于Ti3SiC2的(4GPa).随着SiC含量的增加,复合材料的硬度也增加,但杂质(石墨)和孔洞的含量也增多,成分为0.5Ti3SiC2-0.5SiC的复合材料在烧结过程中有少量Si流出;而当SiC含量增加到0.2Ti3SiC2-0.8SiC时,烧结过程中大量的Si流出使得复合材料无法成功烧结.     

改性SiC粉体添加量对球墨铸铁性能影响的研究

通过在球墨铸铁铸造熔炼中加入不同含量的改性SiC粉体,研究球墨铸铁微观组织和力学性能变化。试验结果表明,改性SiC粉体添加量为0.1%时,抗拉强度提升了6%,延伸率提升65.4%,冲击功提升了16.67%,石墨球化率提升了16.06%,石墨球数量提升了45.38%.与其他添加量相比,添加0.1%改性SiC粉体时,铁素体含量最高,晶粒细化效果最好,珠光体含量最低,对球墨铸铁综合性能的强化及组织的改善效果最好。     

CNTs/SiC/Cu复合材料制备及性能

以碳纳米管(CNTs)、碳化硅(SiC)粉体、锌(Zn)粉和CuSO_4·5H_2O为主要原料,用化学镀的方法制备CNTs /Cu复合粉体,再采用非均相沉淀法制备CNTs/SiC/Cu复合粉体.在750 ℃、100 MPa的制度下进行真空热压烧结后制得CNTs/SiC/Cu复合材料,其中Cu的含量(体积分数,下同)为70%,CNTs的含量(体积分数, 下同)分别为0,3%,5%,8%,12%.利用XRD、SEM分析样品的物相组成和显微结构;利用阿基米德排水法、显微硬度计、三点弯曲法测试了复合材料的密度、显微硬度和抗弯强度.结果表明,随着碳纳米管含量的增加,CNTs/SiC/Cu复合材料的密度、显微硬度和抗弯强度等性能发生相应变化,其中,抗弯强度呈现逐渐升高趋势.与未添加碳纳米管的30SiC/70Cu复合材料相比,添加12%CNTs的12CNTs/18SiC/70Cu 样品,抗弯强度提高了21.45 MPa.     

反应热压烧结Al4SiC4陶瓷的合成及力学性能

以铝粉、石墨粉和有机物聚碳硅烷(PCS)为原材料,采用预裂解及原位反应热压烧结的方法制备了Al4SiC4块体陶瓷.通过XRD,SEM,TEM及力学性能分析等测试手段对材料的结构及性能进行了分析研究.原料预裂解粉的XRD分析结果表明原料在预裂解后,反应产品主要为Al4C3和SiC的混合粉末.将预裂解后的Al4C3和SiC混合粉进行热压烧结,烧结产品经XRD分析表明最终物相主要为Al4SiC4相.Al4SiC4陶瓷的微观组织观察表明,Al4SiC4粒子形貌为板片状,在{0001}基面上分布有大量的层错.Al4SiC4陶瓷的室温弯曲强度随烧结温度的升高而增加,而断裂韧性则随烧结温度的升高而降低.     

SiC晶片增韧ZrB_2复合陶瓷材料的制备与性能

研究了以氮化铝(AlN)为助烧剂的碳化硅晶片(SiC_(pl))增韧二硼化锆(ZrB_2)复合陶瓷材料的制备工艺,并测定其抗弯强度、断裂韧性、致密度和显微硬度.利用扫描电子显微镜(SEM)观察了样品的表面及断面形貌.复合陶瓷中SiC晶片的添加量分别为5%, 10%, 15%以及20%(体积分数, 下同),AlN作为烧结助剂添加量为3%.结果表明:适量SiC晶片的添加提高了SiC_(pl)/ZrB_2复合陶瓷的烧结致密度;SiC_(pl)/ZrB_2复合陶瓷的力学性能比纯ZrB_2陶瓷有所提高,抗弯强度和维氏硬度在5%SiC晶片添加量时达到最大,分别为(625.34±21.46) MPa和(14.60±0.84) GPa;断裂韧性在15%SiC晶片添加量时达到最大值(8.35 ± 0.26) MPa·m~(1/2).断口形貌观察表明主要增韧机制为裂纹偏转与晶片拔出.     

光固化3D打印SiC：粉体氧化处理提升浆料UV固化性能

为了进行碳化硅(SiC)的光固化3D打印,本文提出采用表面氧化处理提升SiC浆料的光固化性能。采用扫描电子显微镜、X射线衍射仪、X射线光电子能谱等研究了SiC颗粒的氧化过程以及氧化温度与保温时间对氧化过程的影响;采用动态流变仪、紫外分光光度计、数字千分尺等研究了浆料的流变性能和光固化性能。结果表明：经表面氧化处理后的SiC颗粒紫外反射率有显著的提高,最高为48.11%,为未氧化SiC颗粒的1.8倍;配制的浆料光固化性能有明显的改善,曝光5 s时固化厚度最高为76μm,为未氧化的3.6倍。随着氧化温度的上升以及保温时间的延长,氧化层厚度持续增长,最高达到144.8 nm。考虑到过度氧化不利于后续SiC陶瓷的烧结成型,最终选择使用1100℃保温3.0 h的氧化SiC粉末,并以1%(质量分数)的KOS163为SiC浆料的分散剂,制备了固含量为45%(体积分数)的SiC浆料,成功实现了SiC陶瓷坯体的光固化3D打印。     

三维网络SiC多孔陶瓷增强铝基复合材料的制备

以中间相沥青添加质量分数为50%的Si粉制备的炭泡沫预制体为坯体,在高温感应烧结炉中结合反应烧结工艺制备了SiC多孔陶瓷预制体.利用挤压铸造工艺制备了SiC多孔陶瓷增强铝基复合材料.采用扫描电子显微镜(SEM)观察了SiC多孔陶瓷骨架及复合材料的微观形貌和界面结构,通过X射线衍射分析仪(XRD)对多孔陶瓷预制体物相组成进行了分析.利用阿基米德排水法,测试了多孔陶瓷的孔隙率和复合材料的密度.结果表明:添加Si的质量分数为50%的炭泡沫预制体反应烧结后获得的SiC多孔陶瓷具有三维连续通孔结构,孔筋致密并且具有较高的开口孔隙率.通过挤压铸造工艺制备的SiC多孔陶瓷增强铝基复合材料界面结合良好,无明显缺陷.     

高温过滤支撑体用SiC基多孔陶瓷的制备与表征

通过以平均粒径300 μm的SiC为骨架材料,特定配比的高岭土、长石和二氧化硅的混合物为粘结剂,制备了可用于高温过滤膜管支撑体的SiC基多孔陶瓷.将粘结剂在1300 ℃烧结并保温1 h,X射线衍射(XRD)分析表明粘结剂中主要为石英相和玻璃相.多孔陶瓷的气孔率随着粘结剂含量从3%增加到15%(质量分数,下同)先升高后降低,其抗弯强度随着粘结剂含量的增加而增加.在粘结剂含量为10%时,多孔陶瓷的气孔率和抗弯强度都取得了较高的值,分别是34.3%和36.6 MPa.压汞法测得其平均孔径为24 μm,孔径分布较窄.用X射线能谱(EDS)测得不同SiC颗粒粘结处的粘结剂的元素组成,并与粘结剂设计组成对比,结果显示粘结剂各组分在多孔陶瓷中分布较均匀.利用扫描电子显微镜(SEM)观察了多孔陶瓷试样条断面的形貌.研究表明此多孔陶瓷可用作高温煤气过滤管的支撑体材料.     

High-Temperature Nanoindentation of SiC/SiC Composites

JOM - The results of high-temperature nanoindentation testing on both a control and a neutron-irradiated silicon carbide matrix silicon carbide fiber composite sample are presented. The mechanical...     

Elevated-temperature effects of oxygen on SiC/SiC composites

High-temperature exposures of SiC/SiC composites to oxidizing environments can lead to substantial changes in mechanical behavior. In the work reported here, results from flexure and crack growth experiments are used to demonstrate such effects. Flexure tests of graphite-coated Nicalon-reinforced SiC previously oxidized in air at 950°C revealed that degradation of fracture resistance began after very short exposure times (less than 1 h) and could be described in terms of distinct oxidation effects on strength and fiber pullout. Crack velocities were determined as a function of applied stress intensity and time for varying O₂ levels. It was observed that crack velocities increased at 1,100°C in the presence of oxygen, which also shifted the onset of stage III (power law) growth to lower values of applied stress intensity. The crack growth observations were described using a two-dimensional micro-mechanical model developed to simulate cracks bridged by continuous fibers. Fiber creep relaxation predicted the correct crack velocity and time-dependence in argon, but other mechanisms, such as interface removal, are required to explain the data in Ar + O₂     

Flexural strength distribution of 3D SiC/SiC composite

Flexural strength of a four-step, three-dimensional (3D) braiding SiC/SiC composite was tested at room temperature. The strength distribution was studied based on Weibull distribution and Normal distribution as well as examined by the Kolmogorov test. The results indicated that the flexural failure behavior of the composite was rather brittle with a small displacement. And the statistical strength distribution of the 3D SiC/SiC composite was in agreement with two-parameter Weibull distribution of the Weibull modulus,m=8.1545 and normal distribution. And the predicated mean flexural strength of the 3D SiC/SiC composite by the two-parameter Weibull distribution was consistent with the tested value.     

Interfacial characterization of a slurry-cast melt-infiltrated SiC/SiC ceramic-matrix composite

An SiC-particulate, silicon-metal melt-infiltration-matrix composite reinforced with SiC fibers is being developed for combustor applications under the High Speed Civil Transport (HSCT) Enabling Propulsion Material (EPM) Program. A major part of this effort has dealt with the characterization and optimization of the boron nitride (BN) based fiber/matrix interface. BN was chosen as the primary interfacial material due to its inherently weak structure and thus good crack-deflecting ability, ease of deposition by chemical vapor infiltration (CVI) into woven fiber preforms, and relatively good environmental stability. Topics discussed in this paper include an overview of the differences in composite microstructure between the EPM SiC/SiC material and a more conventional CVI SiC/SiC composite material, the microstructure/property relationships for the EPM SiC/SiC composite with two different types of SiC fiber (High-Nicalon and Sylramic^™), and the effect of moist, high-temperature environments on the stability of the BN interface.     

Preparation and oxidation protection of CVD SiC/a-BC/SiC coatings for 3D C/SiC composites

An amorphous boron carbide (a-BC) coating was prepared by LPCVD process from BCl₃-CH₄-H₂-Ar system. XPS result showed that the boron concentration was 15.0 at.%, and carbon was 82.0 at.%. One third of boron was distributed to a bonding with carbon and 37.0 at.% was dissolved in graphite lattice. A multiple-layered structure of CVD SiC/a-BC/SiC was coated on 3D C/SiC composites. Oxidation tests were conducted at 700, 1000, and 1200 °C in 14 vol.% H₂O/8 vol.% O₂/78 vol.% Ar atmosphere up to 100 h. The 3D C/SiC composites with the modified coating system had a good oxidation resistance. This resulted in the high strength retained ratio of the composites even after the oxidation.     

Active Oxidation of SiC

Silicon carbide (SiC) forms a protective condensed-phase oxide (SiO₂) in passive oxidation and a volatile sub-oxide (SiO(g)) in active oxidation. The transition between these two modes of oxidation and the rates of active oxidation are critical issues. A literature review indicates that impurity effects, the difference between active-to-passive and passive-to-active transitions, and the effect of total pressure on these transitions remain unexplored for SiC. Measurements were made in a thermogravimetric apparatus (TGA) by changing oxygen potentials either by blending O₂/Ar mixtures or changing total pressures in a pure oxygen gas stream to the point where a transition occurs. Specimens were examined with standard optical and electron-optical techniques. Active-to-passive and passive-to-active transitions were measured and found to be similar for SiC, which is in contrast to pure Si. The similarity in SiC is attributed to SiC/SiO₂ interfacial reactions producing the necessary conditions for passive scale formation (active-to-passive) or passive scale breakdown (passive-to-active). Comparable results were obtained in both the O₂/Ar and reduced total O₂ pressure cases for SiC.     

SiC颗粒增强Al-Fe-V-Si复合材料的SiC/Al界面形貌

采用喷射沉积工艺制备SiCp/Al-Fe-V-Si复合材料,并通过热压和热轧工艺对沉积坯进行致密化;通过高分辨电镜观察其SiC/Al界面形貌,并对比热暴露后的界面形貌。结果表明:复合材料主要存在两种SiC/Al界面,一种是厚度为3nm左右的晶态Si界面层,且在界面附近的基体中生成细小的Al4C3相;另一种是厚度为5nm的非晶态SiO2界面层,部分溶解的SiC颗粒向附近Al基体中注入游离态的Si,在界面附近形成Si的浓度梯度;两种界面都具有良好的润湿性,界面结合强度高;经640℃热暴露10h后,SiC/Al界面处生成的粗大Al4C3脆性相降低界面结合强度,从而降低复合材料的力学性能。     

SiC泡沫陶瓷/SiCp混杂增强Al基复合材料的性能

以SiC泡沫陶瓷和SiC颗粒(7、15、20 μm)为混合增强体,用挤压铸造法制备出SiC泡沫陶瓷/SiCp混杂增强Al基复合材料,研究了SiCp颗粒尺寸对复合材料压缩强度和弯曲性能的影响,以及金属基体的韧性对复合材料压缩行为的影响.结果表明,随着SiC颗粒尺寸的增大,复合材料的压缩强度和弯曲强度降低,最大挠度减小,这是因为随着SiC颗粒尺寸的增大,颗粒间距随之增大,SiC颗粒的强度降低,使SiC颗粒的增强效果减弱.随着基体韧性的提高,复合材料的塑性变形明显增大,但压缩强度和模量降低.     

Effect of SiC particle size on flexural strength of porous self-bonded SiC ceramics

Porous self-bonded silicon carbide (SBSC) ceramics were fabricated from SiC powders with various particle sizes (0.7 μm, 25 μm, 50 μm, 65 μm), plus Si, C and boron (as a sintering additive). The effects of submicron (0.7 μm) SiC particle incorporation into the SBSC and the SiC particle size (25 μm, 50 μm, 65 μm) on the flexural strength and porosity of the ceramics were investigated as a function of sintering temperature. Incorporating 0.7 μm SiC particles into the ceramic material containing 25 μm SiC particles increased the flexural strength by 3 times, from 11.7 MPa up to 35.5 MPa after sintering at 1800 °C. Simultaneously, the porosity was reduced by ∼5 %. Furthermore, the flexural strength of ceramic with 25 μm SiC particles was superior to that with 65 μm SiC particles. Generally, the flexural strength of the SBSC increased as, both, a function of submicron SiC particle incorporation along with relatively small micron-sized particles (25 μm) in the microstructure of the ceramic plus increased sintering temperature.