界面SiO2层对SiC/Al电子封装材料热膨胀系数的影响

用无压浸渗的方法制备了高体积分数的SiC/Al复合材料.通过改变SiC预制样品的烧结工艺来改变SiC和Al的界面状况,分析了SiC表面SiO2层的变化对SiC/Al复合材料的热膨胀系数的影响.用无压浸渗的方法可得到常温下热膨胀系数为(5.68～7.12)×10-6/K的SiC/Al复合材料.颗粒大小一定时,复合材料的热膨胀系数随着SiO2界面层的厚度增加而减小.当界面SiO2层厚度从45 nm增加到2100 nm时,常温下热膨胀系数从7.12×10-6/K减小到5.68×10-6/K.     

反应熔渗法制备C/C-SiC复合材料及其反应机理和动力学的研究进展

对反应熔渗法制备C/C-SiC复合材料过程中Si的渗入行为以及Si/C的反应机理和动力学进行了综合评述.分析了高温下Si的密度、粘度、表面张力及Si/C润湿角对渗入能力的影响.概括了Washburn公式及其改进模型在液Si渗入行为方面的研究进展,给出了渗入时间、SiC生成速率与渗入高度之间的关系.对控制Si/C反应的溶解-沉淀机理和扩散机理进行了阐述,总结分析得出：不同阶段Si/C反应发生的区域不同,因而控制反应的机理也不同.最终的SiC相是由不同反应机理共同作用形成的.     

颗粒增强ZA27室基复合材料的界面

通过对复合材料的界面研究发现，在SiCp／ZA27复合材料中SiC颗粒不能作为初生α相的形核衬底，金属化合物CuZn4依附于SiC颗粒形核、长大。而在Al2O3p／ZA27复合材料中，Al2O3颗粒和Al液有良好的浸润性,使α相优先在颗粒周围形核。SiCp／ZA27及Al2O3p／ZA27复合材料界面处无反应物或反应层，且Al2O3p／ZA27复合材料的界面结合强度优于SiCp／ZA27复合材料。     

无压自浸渗法制备SiCp/Al复合材料的概况

概述了无压自浸渗法制备SiCp/Al复合材料的理论及现状,介绍了利用无压自浸渗法制备SiCp/Al复合材料最佳工艺条件,并就过程中工艺参数对浸渗和材料性能的影响进行了分析。     

Lanxide~(TM)法制备SICp/AI复合材料

LanxideTM技术是制备铝基复合材料的一种新方法,适于制备低孔隙率的 MMC。本文对利用该技术制备 SiCp/Al复合材料进行了综述,阐述了 Al对 SiCp的润湿、渗透及界面反应等问题,并介绍了增强 SiCp/Al的润湿、渗透及控制界面反应的方法。     

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.     

镁含量对无压浸渗SiC/Al复合材料性能的影响EI北大核心CSCD

以SiC粉及铝合金(3%Mg(质量分数)、5%Mg、7%Mg、10%Mg)为主要原料,采用无压浸渗工艺制备得到了SiC/Al复合材料。表征了SiC/Al复合材料的物相组成、显微结构、力学性能及热导率,研究了合金中Mg含量对SiC/Al复合材料结构组成、力学及热学性能的影响。结果表明:制备得到的SiC/Al复合材料主晶相均为SiC与Al。适量Mg的引入有助于改善铝合金与SiC颗粒间的浸渗性能,能有效促进SiC/Al复合材料的界面反应。其中引入5%Mg样品的显微结构较为致密,综合性能较优,其气孔率为0.13%,体积密度为2.94 g/cm3,抗弯强度为(366.36±14.37)MPa,断裂韧性为(9.2±0.27)MPa·m1/2,热导率为178.81 W/(m·K)。     

镁含量对无压浸渗SiC/Al复合材料性能的影响

以SiC粉及铝合金(3%Mg(质量分数)、5%Mg、7%Mg、10%Mg)为主要原料,采用无压浸渗工艺制备得到了SiC/Al复合材料。表征了SiC/Al复合材料的物相组成、显微结构、力学性能及热导率,研究了合金中Mg含量对SiC/Al复合材料结构组成、力学及热学性能的影响。结果表明:制备得到的SiC/Al复合材料主晶相均为SiC与Al。适量Mg的引入有助于改善铝合金与SiC颗粒间的浸渗性能,能有效促进SiC/Al复合材料的界面反应。其中引入5%Mg样品的显微结构较为致密,综合性能较优,其气孔率为0.13%,体积密度为2.94 g/cm~3,抗弯强度为(366.36±14.37) MPa,断裂韧性为(9.2±0.27) MPa·m~(1/2),热导率为178.81 W/(m·K)。     

表面渗铝氧化处理后8407钢的抗熔损性能

将表面经冷喷涂铝处理的8407钢样在550℃下扩散处理4h,并在2.5A/dm~2电流密度下常温硬质阳极氧化处理60min,使试样表面形成Fe_3O_4·Al_2O_3氧化膜.采用失重法评价了静置和旋转条件下,表面渗铝氧化处理和未处理试样在620℃的ADC12铝液中的熔损性能.利用光学显微镜观察熔损后试样横截面组织,利用SEM观察分析了表面未处理试样熔损后铁-铝界面组织和局部成分,探讨了8407钢的熔损机理及氧化膜抗熔损机理.结果表明,8407模具钢经渗铝氧化处理后形成的氧化膜隔绝了钢基体与铝液的直接接触,降低了钢与熔融铝液间的润湿性能,提高了钢的静态和动态熔损抗力,且动态熔损抗力提高得更显著.     

Zr-Si合金熔渗改性C/C复合材料的微观结构及耐高温氧化机理研究

采用Zr-Si合金在较低温度下熔渗制备了不同密度的C/C-ZrC复合材料,研究了不同密度C/C多孔体的熔渗行为以及不同密度复合材料的相组成和微观形貌,并且在1 500℃下对其静态氧化行为进行了研究。结果表明:中等密度多孔体熔渗较为理想,气孔率仅为4.78%。随着原材料密度的增加,C/C-ZrC复合材料密度增量相应下降。物相分析显示,C/C-ZrC复合材料由C,ZrC,Zr和Zr_2Si组成,未发现SiC相的存在。微观结构解析表明,反应生成的ZrC陶瓷相主要集中在网胎层,合金除与C基体反应生成ZrC层外,在熔体内部也有部分ZrC析出。论文从界面反应以及元素扩散的角度探讨了熔渗机理。C/C-ZrC复合材料在1 500℃静态氧化后的产物主要包括单斜相ZrO_2和非晶态SiO_2,未能形成致密氧化膜,改性后的样品失重率随着熔渗增重增大而减小。     

Processing and impact behavior of Al/SiCp composites fabricated by the pressureless melt infiltration method

In the current investigation, pressureless melt infiltration was applied to fabricate the Al/SiC composites based on the SiC porous preforms. The process was conducted by introducing the aluminum melt into the SiC preforms at 950 °C under the nitrogen atmosphere, without the aid of pressure. To explore development of melt infiltration, initial preforms were produced with variable SiC fractions (40, 50, and 60 vol.%) using three different SiC powders with the mean particle size of 20, 50, and 90 μm. While the infiltration of aluminum melt into the preforms with 40 vol.% initial SiC volume fraction (SiC particle size of 90 μm) resulted to the composites with final density of 0.94 theoretical density (TD), this value drops down to ～0.9 TD for the composites produced by preforms with the SiC (90 μm) volume fraction of 60 vol.%. On the other hand, composites fabricated by 50 μm SiC powder (SiC volume fraction of 40 vol.%) demonstrated the final density of ～0.91 TD. The impact resistance tests performed on the composites demonstrated an enhancement in the value of impact energy with an increase of SiC powder particle size. Results, additionally, revealed a significant superiority of impact energy for the composites fabricated by a combined melt infiltration and sintering (MIS) procedure compared to those produced by infiltration at 950 and 1350 °C.     

Effect of Heating Rates on the Synthesis of Al2O3–SiC Composites by the Self-Propagating High-Temperature Synthesis (SHS) Technique

Various aspects of in situ formation of Al₂O₃–SiC composites by the self-propagating high-temperature synthesis (SHS) technique have been investigated using thermal analyses (TG/DTA) of a powder mixture (4Al, 3SiO₂, 3C) and pellets in an argon atmosphere at different heating rates. Both the reaction initiation and peak temperatures are found to increase with the heating rates. At lower heating rates, the powder samples do not reveal any exothermic peak possibly because of poor reactivity and sluggish exothermic reaction. The appearance of exothermic peaks in the DTA plots after melting of aluminum indicates reduction of silica by liquid aluminum. Conversion of aluminum is found to decrease marginally with an increase in heating rates. The apparent activation energy of the process compares well with the interdiffusion activation energy of silicon and oxygen, indicating that oxygen diffusion in Si formed at the reaction front may be the rate-controlling factor for this SHS process. From SEM studies it appears that the formation of SiC whiskers is through liquid-phase mass transfer.     

The effect of processing conditions on the microstructure and impact behavior of melt infiltrated Al/SiCp composites

In the current research, pressureless melt infiltration (PMI) was applied to study the effect of different processing conditions on the final properties of Al/SiC composites, fabricated through the infiltration of aluminum melt into SiC particulates porous preforms. Charpy impact test was used to explore the impact behavior of the Al/SiC composites, obtained from variable processing conditions. Conducting the process at a higher infiltration temperature (1350 °C) increased the final relative density of composites up to the value of 0.97 of theoretical density (TD). The application of a post sintering procedure in nitrogen atmosphere after the completion of infiltration resulted in a slight increase (∼1) in the final density of composites compared to the only infiltrated ones. Instead, the final density of argon sintered composites has undergone a 0.41% reduction. This can be originated from the occurrence of chemical reactions in the N₂ atmosphere resulting in the formation of consequent phases, contrary to the argon neutral gas. Results concerning with the impact resistance demonstrated a remarkable superiority for the impact energy of the composites subjected to the combined infiltration and sintering (MIS) procedure compared to the infiltrated ones. While such an observation was found to be identical through sintering in both atmospheres, the appearance of brittle phases formed through sintering procedure in nitrogen gave rise to higher impact energy for the argon sintered composites.     

Finite element analysis and experimental investigation of ultrasonic testing of internal defects in SiCp/Al composites

Revealing the interactions of sound waves with both SiC particles and internal defects is crucial for facilitating the detectability of internal defect features in SiCp/Al by using ultrasonic testing (UT). In the present work, we demonstrate the feasibility of UT of internal flat-bottom holes with diameters ranging from 0.2 mm to 2 mm in SiCp/Al composites through the combination of finite element (FE) simulations and experiments. Specially, a 2D FE model of UT of SiCp/Al with consistent geometrical features of SiC particles with experimental one is established, the accuracy of which is validated by theoretical and experimental characterizations of P-wave velocity and ultrasonic attenuation coefficient of SiCp/Al. Subsequently, the propagation behavior of sound waves in the SiCp/Al specimen with pre-existing defects under UT, in particular the impact of defect boundary on the scattering behavior of sound waves, is revealed in detail by FE simulations and also validated by corresponding experiments. Furthermore, the UT limit of detectable size of the internal defects is revealed jointly by FE simulations and experiments, based on which a correlation map between defect size and echo signal amplitude is established. Current study provides theoretical and practical guidance for the UT of internal defects in SiCp/Al composites.     

Material deformation and removal mechanism of SiCp/Al composites in ultrasonic vibration assisted scratch test

The material removal process of SiCp/Al composites is a result of synergetic deformation and interaction among Al matrix, SiC particles and interface. The non-homogeneity of microscopic mechanical properties due to the inherent polyphase heterogeneity of SiCp/Al composites will directly affect the removal mechanism and surface integrity in the machining process. This paper aims to gain further insight of the material deformation and removal mechanism of SiCp/Al composites in ultrasonic vibration assisted machining process. The elastic modulus and hardness of SiCp/Al composites were determined through the indentation test by loading on Al matrix and SiC particles, respectively. Due to the interaction effects of the three phases during the deformation process, when the indenter is on a single phase, the influence of the other phases cannot be neglected and is reflected in the P-h curves. Scratch force, friction coefficient and material removal behavior were investigated in traditional scratch (TS) and ultrasonic vibration assisted scratch (US) tests. In most cases, with the assistance of ultrasonic vibration, scratch force and friction coefficient in US process are smaller than those in TS process, and the reduction of them is modeled and analyzed. The material removal behavior of SiCp/Al composites is similar to metal at the macroscale, and a high material removal rate is achieved in US process. SiC particles tend to maintain the structural integrity rather than be fractured or pulled out in US process. The scratched surface in TS process is damaged to a greater degree than that subjected to US process.     

Preparation of SiC/SiC composites with high toughness by reaction of the SiCP+C double-cladding layer with liquid silicon

SiC/SiC composites prepared by liquid silicon infiltration (LSI) have the advantages of high densification, matrix cracking stress and ultimate tensile strength, but the toughness is usually insufficient. Relieving the residual microstress in fiber and interphase, dissipating crack propagation energy, and improving the crystallization degree of interphase can effectively increase the toughness of the composites. In this work, a special SiC particles and C (SiC_P +C) double-cladding layer is designed and prepared via the infiltration of SiC_P slurry and chemical vapor infiltration (CVI) of C in the porous SiC/SiC composites prepared by CVI. After LSI, the SiC generated by the reaction of C with molten Si combines with the SiC_P to form a layered structure matrix, which can effectually relieve residual microstress in fiber and interphase and dissipate crack propagation energy. The crystallization degree of BN interphase is increased under the effects of C-Si reaction exotherm. The as-received SiC/SiC composites possess a density of 2.64 g/cm³ and a porosity of 6.1%. The flexural strength of the SiC/SiC composites with layered structure matrix and highly crystalline BN interphase is 577 MPa, and the fracture toughness reaches up to 37 MPa·m^1/2. The microstructure and properties of four groups of SiC/SiC composites prepared by different processes are also investigated and compared to demonstrate the effectiveness of the SiC_P +C double-cladding layer design, which offers a strategy for developing the SiC/SiC composites with high performance.     

半固态搅拌制SiC颗粒增强镁基复合材料过程的数值模拟

采用商用的计算流体动力学(CFD)计算软件Fluent对SiC颗粒增强镁基复合材料搅拌过程进行动态模拟,研究了不同搅拌速度、搅拌时间及温度对于SiCp/AZ91(SiC颗粒增强镁合金AZ91)组织的影响。研究结果表明,搅拌时间和搅拌速度对于SiCp/AZ91材料成品质量有显著的影响,搅拌速度的增加有助于SiC颗粒的分散,但速度过快导致液面起伏较大,大量气体进入镁液中,最终使成品中气孔较多。而在搅拌时间方面,当时间较短时,SiC颗粒未充分与合金液混合,因此出现大片SiC颗粒团聚现象。随着搅拌时间的延长,团聚的颗粒逐渐向镁合金液中均匀分散,当搅拌时间为15 min时,SiC固相颗粒与镁合金液所组成的混合相最为均匀,此时继续延长搅拌时间,其固相颗粒的宏观均匀性并未发生进一步变化。根据模拟和试验的结果得出最佳的搅拌时间为15 min,搅拌速度为300 r/min。     

基体改性对SiC/SiC复合材料高温抗氧化性能的影响

采用先驱体浸渍-裂解工艺结合三种基体改性方式制备了SiC/SiC复合材料,通过形貌分析和力学性能测试,分析了基体改性对Si C/SiC复合材料高温抗氧化性能的影响。研究表明,经1200℃静态空气氧化100h后,三种基体改性的复合材料弯曲强度几乎没有下降,氧化200h后,弯曲强度保留率均可达到80%;氧化300h后,复合材料内部结构没有氧化现象,表面区域界面层的氧化程度降低。改性基体中的B元素氧化生成液相封填SiC涂层表面,延缓了SiC涂层的氧化进程,并阻止氧化介质进入复合材料内部,保护纤维和界面层,从而使SiC/SiC复合材料的长时静态高温抗氧化性能明显提高。     

Compressive strength and wear properties of SiC/Al6061 composites reinforced with high contents of SiC fabricated by pressure-assisted infiltration

Pressure-assisted infiltration was used to synthesize SiC/Al 6061 composites containing high weight percentages of SiC. A combination of PEG and glass water was used to fabricate SiC preforms and the effect of the presence of glass water on the microstructure and mechanical properties of the preforms was evaluated by performing compression tests on the preforms. Also, the compressive strength and the hardness of the SiC/Al composites were investigated. The results revealed that the glass water improved the compressive strength of the preforms by about five times. The microstructural characterization of the composites showed that the penetration of the aluminum melt into the preforms was completed and almost no porosity could be seen in the microstructures of the composites. Moreover, the composite containing 75 wt% SiC exhibited the highest compressive strength as well as the maximum hardness. The results of the wear tests showed that increasing the SiC content reduces the wear rate so that the Al-75 wt% SiC composite has a lower wear rate and a lower coefficient of friction than those of Al-67 wt% SiC composite. This indicated higher wear resistance in these composites than the Al alloy due to the formation of a tribological layer on the surface of the composites.     

Cellular Molybdenum Silicide/Silicon Carbide Composites from Stems of Maize

Biomimicking of woods has been conducted extensively in the past. In this work, the unique microstructural feature of maize stems has been explored. These stems appear to be promising precursor materials for producing fiber-reinforced composites with unique anisotropic properties. A unique melt infiltration technique has been adopted to mineralize this structure into ceramic composites. The cellular morphology of the precursor stem was retained in the final composite. SiC–Si and MoSi₂–SiC cellular composites were obtained by infiltration with Si and Si–MoSi₂–Al mixture, respectively. It has been found that a small (2 wt%) addition of aluminum in the infiltrating mixture can help in attaining a homogeneous distribution of MoSi₂ in the SiC cellular matrix.