SiC颗粒增强铝合金基梯度复合材料弯曲力学性能及其评价

采用三点弯曲法,对SiC颗粒增强铝合金基梯度复合材料的弯曲力学性能进行了研究,提出了梯度复合材料抗弯强度比R₁和R₂两个新的力学性能评价指标。结果表明:金属基梯度复合材料(MMGC)的弯曲力学性能与其基本组分力学性能的关系不符合ROM法则,材料的抗弯强度和最大挠度强烈地受到SiC颗粒梯度分布方式与弯曲方向的影响;当基体处于受拉侧,高SiC含量组分处于受压侧时,MMGC能充分发挥其性能优势;MMGC在受梯度应力作用下的力学性能优势和其方向性特征受到材料状态、材料宏观不均匀性和微观连续性等因素的影响;MMGC的抗弯强度比R₁反映了这类材料的性能优势,而抗弯强度比R₂则反映了材料的方向性能特征。     

SiCP/AZ80镁基复合材料的界面与断口特征

本文用SEM,TEM研究了SiC颗粒增强AZ80镁合金复合材料的界面结构和断口形貌。结果表明,SiC颗粒与镁合金界面结合紧密,没有发生界面化学反应,但在界面处可以观察到Mg₁₇Al₁₂共晶相在SiC表面形核生长。对复合材料断口观察表明,SiC颗粒与镁合金界面之间的粘结强度大于基体的撕裂强度,SiC颗粒的聚集、团聚是导致复合材料断裂的主要原因,且复合材料的断裂形式趋向脆性断裂。     

层状Ti3SiC2陶瓷的组织结构及力学性能

利用热压烧结TiH₂,Si和C粉获得了致密度大于98%的层状Ti₃SiC₂陶瓷。利用压痕法,在不同的载荷下测定了材料的维氏硬度, 发现其硬度值随载荷的增加而降低,在最大载荷30kg时,硬度值为4GPa。压痕对角线没有发现径向裂纹的出现。 这归因于多重能量吸收机制——颗粒的层裂、裂纹的扩展、颗粒的变形等。利用三点弯曲法和单边切口梁法测定了材料的强度和韧性分别为270MPa和6.8MPa·m1/2。Ti₃SiC₂材料的断口表现出明显的层状性质,大颗粒易于发生层裂和穿晶断裂,小颗粒易被拔出。当裂纹沿平行于Ti₃SiC₂基面的方向扩展造成颗粒的层裂,当裂纹沿垂直于基面的方向扩展时,裂纹穿过颗粒的同时,在颗粒内部发生偏转,使裂纹的扩展路径增加。裂纹的扩展路径类似人们根据仿生结构设计的层状复合材料。裂纹在颗粒内的多次偏转、裂纹钉扎以及颗粒的层裂和拔出等是材料韧性提高的主要原因。此外,在室温下得到的荷载-位移曲线,说明Ti₃SiC₂材料不象其它陶瓷材料的脆性断裂,而是具有金属一样的塑性。     

自生复合Al11La3/Al共晶材料的轴向拉伸性能及其断裂机制

本文研究了自生复合Al₁₁La₃/Al共晶材料从室温到673K时的轴向拉伸性能和轴向拉伸断裂机制.结果表明:在G=700K/cm、R=11.1μm/s的定向凝固条件下,该材料轴向拉伸性能在室温时为260MPa、在673K时为265MPa.对拉伸过程的动态观察和断口形貌的分析表明:自生复合Al₁₁La₃/Al共晶材料在室温到673K温度范围内,其轴向拉伸断裂机制相同:纤维相Al₁₁La₃的断裂是整个共晶体断裂的控制机制:其轴向拉伸的断裂模型为:弹性变形、裂纹萌生、界面脱粘、搭桥过程、宏观断裂.     

三维整体编织物增强陶瓷基复合材料的制备工艺及性能表征

本文研究了以连续碳纤维(C_f)三维整体编织物(3D-B)为增强体,以聚碳硅烷(PCS)裂解转化成碳化硅(SiC)为基体的陶瓷基复合材料(CMC)的制备工艺,探讨了不同工艺方法对复合材料微观和宏观性能的影响,并提出进一步改善制各工艺,提高复合材料性能的途径。研究结果表明,采用聚碳硅烷/二乙烯基苯(PCS/DVB)体系浸渍经交联固化后可以大大缩短裂解时间,致密化效率较聚碳硅烷/二甲苯溶液(PCS/Xylene)体系有着显著提高。对于3D-B C_f/SiC CMC用PCS/DVB体系浸渍经7个浸渍裂解周期后试样密度为1.65g/cm3,弯曲强度达326MPa,断裂韧性K_IC为13.72MPa·m1/2;用PCS/Xylene体系浸渍的试样密度为1.54g/cm3,弯曲强度为243MPa,断裂韧性K_IC为8.19MPa·m1/2。研究中利用扫描电镜观察了弯曲试样的断口以分析材料破坏时纤维的断裂、拨出形貌。     

SiCP混杂对C/Al浸渍成型复合材料性能的影响

碳纤维经混杂SiC_P后用压力浸渍成型方法制备成C/Al复合材料,分析混杂的SiC_P对C/Al复合材料力学性能的影响。测试了制备成的复合材料性能,并用SEM对复合材料断面组织与断口形态进行分析。结果表明,混杂的SiC_P可以分隔纤维,有利浸渍,使纤维分布均匀从而提高了复合材料的性能,而用sol-gel方法涂复SiC层并混杂SiC_P可获得最佳的性能。     

SiC颗粒尺寸对喷射共沉积7075 Al/SiCp挤压及轧制的组织和性能的影响

研究了喷射共沉积方法制备的7075 Al / SiCp复合材料挤压及轧制过程中SiC颗粒的分布.通过拉伸实验、微观组织的金相及拉伸断口SEM观察分析了SiCp颗粒尺寸对材料组织和性能的影响.实验表明,SiCp在挤压过程中沿厚度方向形成分层分布,SiCp的尺寸及粒度分布对于聚集有较大的影响;轧制过程对挤压时形成的SiCp分层分布有一定的减弱作用,但改善程度和SiCp的尺寸有关;SiCp颗粒尺寸对复合材料的力学性能及断裂机制有很大的影响.     

PP/PET原位成纤复合材料的增强效应

用挤出-拉伸-注塑法制得了PP/PET原位成纤增强复合材料,以不拉伸的普通共混材料作对照,研究了PET质量含量(C_m)对PET成纤性和材料拉伸强度(σ_t)及模量(E)的影响及其作用机制。结果表明,C_m由0增至20%时,PET纤维数量增多,纤维直径及其分散性以C_m=15%为界先减少后增大;材料的σ_t、E在C_m=15%时有最大值,分别比纯PP提高约20%和70%。熔体拉伸时分散相液滴的聚结-形变成纤对PET相形态随C_m的变化起关键作用,分散相对基体增强效应与两相界面缺陷效应的相互竞争,纤维对基体增刚作用受纤维数量和细度的双重控制,分别是决定材料σ_t~C_m、E~C_m关系的支配因素。     

环氧玻璃钢层合板冲击破坏及其断口微观特征的研究

S-GF/Ep648复合材料层合板[0₉°/θ]_s冲击抗力试验的结果表明其冲击抗力值与铺层角θ无关,只受浸水时间的影响;而另一种铺层形式[+θ₈/-θ₈]的复合材料层合板,在落重冲击试验中却发现:在相同的冲击能量下,θ越大,分层破坏越严重,损伤区面积也越大。利用SEM-505扫描电子显微镜对发生穿透性断裂、层间分层断裂或仅出现冲击损伤等破坏形式的断口表面进行了观察和分析,讨论了影响该复合材料冲击断裂和冲击损伤性能的因素。     

Y2O3表面改性Al2O3P增强6061Al复合材料组织与性能

采用液相包裹法对Al₂O₃微粉进行稀土Y₂O₃表面改性,用挤压铸造法制备表面经稀土Y₂O₃改性的Al₂O_3P/6061Al复合材料,并对复合材料的显微组织及拉伸性能进行分析和研究。结果表明:表面经稀土Y₂O₃改性的Al₂O₃微粉能均匀的分布于基体中,界面润湿性得以改善,复合材料组织更加均匀。TEM观察表明:改性粉体在制备复合材料前后表面存在颗粒状包裹层。对其表面进行EDAX分析,结果显示含有Y,Al和O元素。粉体XRD图谱中有Y₂O₃衍射峰的存在。拉伸性能测试表明:改性粉体对Al合金增强效果明显增加,抗拉强度提高29.8％,屈服强度提高38.4％,延伸率提高10.3％。对拉伸断口进行SEM分析,改性后复合材料断口韧窝更加均匀、丰满,材料表现出良好的塑性。     

Effects of particle size and distribution on the mechanical properties of SiC reinforced Al-Cu alloy composites

This paper studied the combined effects of particle size and distribution on the mechanical properties of the SiC particle reinforced Al-Cu alloy composites. It has been shown that small ratio between matrix/reinforcement particle sizes resulted in more uniform distribution of the SiC particles in the matrix. The SiC particles distributed more uniformly in the matrix with increasing in mixing time. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength and elongation. Yield strength and ultimate tensile strength of the composite reinforced by 4.7 μm sized SiC particles are higher than those of composite reinforced by 77 μm sized SiC particles, while the elongation shows opposite trend with yield strength and ultimate tensile strength. Fracture surface observations showed that the dominant fracture mechanism of the composites with small SiC particle size (4.7 μm) is ductile fracture of the matrix, accompanied by the “pull-out” of the particles from the matrix, while the dominant fracture mechanism of the composites with large SiC particle size (77 μm) is ductile fracture of the matrix, accompanied by the SiC particle fracture.     

原位反应热压烧结SiC/MoSi_2复合材料的力学性能研究

采用原位反应热压烧结工艺成功制备了不同SiC体积分数的SjC/MoSi2复合材料,研究了SiC/MoSi2复合材料的室温抗弯强度、断裂韧性随SiC体积分数变化的规律,分析了SiC/MoSi2复合材料的强韧化机理.结果表明,SiC的加入显著提高了MoSi2基复合材料的室温力学性能,SiC/MoSi2复合材料的抗弯强度和断裂韧性均优于纯MoSi2,并且随着SiC体积分数的增加而增大;SiC/MoSi2复合材料的强化机制主要是弥散强化和细晶强化,韧化机制主要是微裂纹增韧.     

High mechanical performance SiC/SiC composites by NITE process with tailoring of appropriate fabrication temperature to fiber volume fraction

Unidirectional SiC/SiC composites are prepared by nano-powder infiltration and transient eutectic-phase (NITE) process, using pyrolytic carbon (PyC)-coated Tyranno-SA SiC fibers as reinforcement and SiC nano-powder with sintering additives for matrix formation. The effects of two kinds of fiber volume fraction incorporating fabrication temperature were characterized on densification, microstructure and mechanical properties. Densification of the composites with low fiber volume fraction (appropriately 30 vol%) was developed even at lower fabrication temperature of 1800 °C, and then saturated at 3rd stage of matrix densification corresponding to classic liquid phase sintering. Hence, densification of the composites with high volume fraction (above 50 vol%) became restricted because the many fibers retarded the infiltration of SiC nano-powder at lower fabrication temperature of 1800 °C. When fabrication temperature increased by 1900 °C, densification of the composites was effectively enhanced in the intra-fiber-bundles and simultaneously the interaction between PyC interface and matrix was strengthened. SEM observation on the fracture surface revealed that fiber pull-out length was accordingly changed with fabrication temperature as well as fiber volume fraction, which dominated tensile fracture behaviors. Through NITE process, SiC/SiC composites with two fracture types were successfully developed by tailoring of appropriate fabrication temperature to fiber volume fraction as follows: (1) high ductility type and (2) high strength type.     

SiCp/MoSi2原位反应高温热压复合工艺的研究

运用乙醇湿法混合和氩气保护原位反应高温热压方法制备了不同配比的SiCp/MoSi2复合材料,研究了原位生成的SiC颗粒对MoSi2基体材料显微结构和室温力学性能的影响.结果表明:原位反应高温热压制备SiCp/MoSi2的工艺是可行的,反应生成的适量SiC颗粒细化了基体晶粒,改善了其力学性能;与该工艺下制备的纯MoSi2相比,含40vol%SiCp的SiCp/MoSi2复合材料室温抗弯强度提高了260%,含50vol%SiCp的SiCp/MoSi2复合材料室温断裂韧性提高了50%;该种工艺的强化机制为细晶强化和弥散强化,韧化机制为细晶韧化.     

A Numerical Modeling of Failure Mechanism for SiC Particle Reinforced Metal-Metrix Composites

The present work is to investigate the failure mechanisms in the deformation of silicon carbide (SiC) particle reinforced aluminum Metal Matrix Composites (MMCs). To better deal with crack growth, a new numerical approach: the MLPG-Eshelby Method is used. This approach is based on the meshless local weak-forms of the Noether/Eshelby Energy Conservation Laws and it achieves a faster convergent rate and is of good accuracy. In addition, it is much easier for this method to allow material to separate in the material fracture processes, comparing to the conventional popular FEM based method. Based on a statistical method and physical observations, the hard SiC particles are distributed randomly over the cubic space of the matrix. Four failure mechanisms are found to be critical to the accurate prediction of the mechanical properties of MMCs: a) the failure inside the matrix; b) the failure between the interface of aluminum matrix and the SiC particles; c) the fracture of the SiC particles; and d) the separation of two neighboring SiC particles. Plastic work is used as a failure criterion. It is found that the current approach can accurately predict the mechanical behavior of MMCs, including Young's moduls, stress strain curve, tensile strength, and limit strain. When the SiC volume fraction is low, the interface failure is more important; while for the case of high SiC volume fraction, all the four failure mechanisms work together to affect the mechanical property for the composite structure.     

Thermal properties of diamond/SiC/Al composites with high volume fractions

The diamond/SiC/Al composites with high volume fractions and a large ratio of diamond to SiC particle size (7.8:1) were fabricated by gas pressure infiltration. The results show that the fine SiC particles occupy efficiently the interstitial positions around coarse diamond particles; the main fracture mechanism of the composite is matrix ductile fracture, and diamond brittle fracture was observed which confirms a high interfacial bonding strength; the diamond/SiC/Al composites with 80% and 66.7% volume fraction of diamond in the reinforcement have the higher volume fraction in the reinforcement and lower coefficient of thermal expansion compared to the diamond/Al composite. Turner and Kerner models are not in good agreement with the experimental data for the composites based on reinforcement with two phases different in shape and component. When the effect of the coating layer considered, differential effective medium (DEM) model is confirmed a reliable model in designing a composite with a given thermal conductivity based on reinforcement with two phases different in size.     

SiC w/BAS复合材料的显微结构及力学性能的研究

本文采用热压烧结法制备出致密的SiCw增强BAS玻璃陶瓷基复合材料．结果表明,BAS基体晶化后获得以钡长石为主晶相和莫来石为次晶相的复相BAS玻璃陶瓷．晶须的加入对BAS基体有显著的强韧化效果,加入30vol％SiCw可使材料的室温抗弯强度和断裂韧性分别由基体的156MPa和1．40MPa·m1/2提高到356MPa和4．06MPa·m1/2．TEM观察结果表明,晶须／基体界面结合良好,无界面反应物和非晶层的存在．断口形貌和压痕裂纹扩展路径的SEM观察结果表明,复合材料的主要增韧机制为裂纹偏转、晶须的拔出和桥接．     

高温等静压烧结碳化硅基复相陶瓷的强化与增韧

本文通过Si₃N₄、TiC及SiC晶须补强SiC基复相陶瓷的高温等静压烧结,研究了复相陶瓷的显微结构与力学性能,探讨了晶须及第二相颗粒对复相陶瓷的强化与增韧机理．结果表明,不同的补强颗粒及晶须在基体中的作用也不同,Si₃N₄的引入将在基体与第二相颗粒之间产生径向压应力,阻碍裂纹的扩展,TiC的引入将在基体与第二相颗粒之间产生径向张应力,诱导裂纹的偏转;SiC晶须的引入也将产生阻碍裂纹扩展的机制,从而达到SiC基复相陶瓷强化与增韧,改善其力学性能．     

SiCw/BAS复合材料的显微结构及力学性能的研究

本文采用热压烧结法制备出致密的SiC_w增强BAS玻璃陶瓷基复合材料．结果表明,BAS基体晶化后获得以钡长石为主晶相和莫来石为次晶相的复相BAS玻璃陶瓷．晶须的加入对BAS基体有显著的强韧化效果,加入30vol％SiC_w可使材料的室温抗弯强度和断裂韧性分别由基体的156MPa和1．40MPa·m^1/2提高到356MPa和4．06MPa·m^1/2．TEM观察结果表明,晶须／基体界面结合良好,无界面反应物和非晶层的存在．断口形貌和压痕裂纹扩展路径的SEM观察结果表明,复合材料的主要增韧机制为裂纹偏转、晶须的拔出和桥接．