连续SiC纤维增强钛基复合材料横向强度分析

连续SiC纤维增强钛基复合材料(SiCf/Ti)具有良好的综合性能,但其横向性能低于钛合金基体,为了准确地预测SiCf/Ti复合材料的横向强度,提出一种基于界面脱粘强度的计算模型。采用SiCf/Ti复合材料十字拉伸试件来测试复合材料的纤维/基体界面脱粘强度,并分析了热处理工艺对界面脱粘强度影响规律,以及不同纤维之间界面脱粘强度的差别。复合材料横向拉伸试件采用箔-纤维-箔方法制备,每个试件的纤维层数为10层,纤维百分数为30%左右。在不同温度条件下测试复合材料的横向拉伸强度,拉伸温度分别为室温、300,400,550℃,通过对比实验结果和模型预测结果,模型预测的结果与实验结果的误差不超过5%。     

原位还原法制备Al/Al2O3复合材料的力学性质及反应动力学

以石英为先驱体,以液态铝为还原剂,在1073～1523 K的温度范围内对原位生成铝/氧化铝复合材料进行了研究,对获得的复合材料的物理和机械性能做了测定,并对材料显微结构进行了观测和分析.在1473K制备的铝/氧化铝复合材料密度为2.95g/cm3,最大弹性模量为130 GPa,最大三点抗弯强度为580 MPa,最大拉伸强度为268 MPa,洛氏硬度为86.产物铝/氧化铝复合材料的形状与作为先驱体的二氧化硅的形状几乎一致.讨论了反应过程的动力学.     

稻草上段短切物/淀粉环保复合材料的制备及性能研究

开发基于农作物秸秆的复合材料是提高农副产品附加值,变废为宝,节约资源,保护环境的重要途径.采用热压方法制备了稻草上段短切物/淀粉复合材料,研究了淀粉用量、热压温度、热压时间对复合材料拉伸性能及硬度的影响.当淀粉用量为40%,热压温度为120℃,热压时间为8min时,复合材料的拉伸强度可达到2.05MPa.     

SiCf/TC11复合材料拉伸行为研究

采用磁控溅射先驱丝法和热等静压工艺制备SiC_f/TC11复合材料，研究了SiC_f/TC11复合材料室温和500℃拉伸性能及断裂机制。结果表明，SiC_f/TC11复合材料室温和500℃抗拉强度分别为1 530 MPa和1 553 MPa，明显高于基体TC11钛合金，与TC11钛合金相比，抗拉强度分别提升了～57%和～133%，纤维增强效果显著。通过观察SiC_f/TC11复合材料室温、500℃拉伸断口和纵剖面断裂特征，指出了室温和500℃拉伸断裂机制主要包括反应层多次断裂、纤维一次断裂、纤维多次断裂、纤维-基体界面脱粘、纤维拔出、W芯-SiC界面脱粘、基体断裂、包套断裂等，揭示了SiC_f/TC11复合材料室温和500℃拉伸载荷下多组元失效断裂过程。     

热挤压对铝基复合材料力学性能的影响

利用金相显微镜、扫描电镜和万能拉伸试验机等手段考察了粒度为50～80 μm的Si颗粒增强Al-Si复合材料在热挤压前后的显微组织及室温拉伸性能.结果表明以17.31的挤压比热挤压后复合材料组织的均匀性得到了明显改善;复合材料挤压材的抗拉强度、屈服强度和延伸率较压渗材普遍提高;热挤压没有改变复合材料的断裂机制,由于挤压后颗粒分布均匀等原因,使复合材料的塑性得到改善.     

热压工艺对碳纤维增强铜基复合材料力学性能的影响

研究了热压工艺对碳纤维增强铜基复合材料力学行为的影响。结果表明:随热压温度的提高,CF/Cu复合材料的拉伸强度增大,显微硬度提高;热压温度超过800℃后,材料的强度和显微硬度随热压温度的升高而降低。对复合材料显微组织的研究表明,随热压温度的提高,材料的显微组织更加均匀。SEM断口分析表明:CF/Cu复合材料的断裂以纤维拔出为主要方式。     

固溶温度及SiC含量对粉末冶金SiC/Al-Mg基复合材料组织与性能的影响

以SiC颗粒为增强体,Al-Mg-Cu-Fe-Sn合金作为基体合金,采用真空热压再热挤压的方法制备SiC/Al-Mg基复合材料,然后进行固溶和时效热处理,通过扫描电镜观察热压与挤压态材料的形貌,测试时效态材料的维氏硬度、拉伸性能,并进行电化学腐蚀实验,研究固溶温度及SiC颗粒含量(体积分数,下同)对该复合材料的显微组织与性能的影响。结果表明:随SiC颗粒含量增加,SiC/Al-Mg其复合材料的抗拉强度明显提高,材料在拉伸过程中的Serration现象减弱,10%SiC/Al-Mg基复合材料的屈服强度从基体合金的57 MPa提高到246 MPa,而伸长率从23.5%降低到6.0%。随固溶处理温度从400℃升高到570℃,材料的硬度先升高后降低,在固溶温度为500℃时,10%SiC/Al-Mg基复合材料的硬度HV达到92。粉末冶金SiC/Al-Mg基复合材料的腐蚀行为除了受SiC含量影响外,还与固溶温度有关。     

苎麻纤维增强聚乳酸复合材料性能研究

通过密炼?注塑成型工艺制备了不同苎麻纤维含量的聚乳酸基复合材料,研究了纤维含量对复合材料性能的影响规律,并揭示了纤维增强机理。研究表明,苎麻纤维的添加提高了复合材料的耐热性能,尤其是当纤维质量分数为40%时,复合材料的热变形温度提高了10.5%。此外,苎麻纤维均匀地分散在基体中,由于纤维与聚乳酸的界面强度较弱,断面上有大量的纤维拔出和纤维孔洞;差示扫描量热仪测试表明高含量的纤维限制了聚乳酸分子链的运动,促进复合材料形成更加致密完善的晶核;同时,流变行为也表明苎麻纤维含量的增加有助于提高复合材料的黏弹响应和复合黏度;最后,苎麻纤维的加入提高了复合材料的拉伸和弯曲强度,且随纤维含量的增加而增大。与聚乳酸相比,当纤维质量分数为40%时复合材料的拉伸和弯曲强度分别提高了30%和21.9%。      

TiC粒子增强钛基复合材料的显微组织与性能研究

探讨了添加粒子的形态对熔铸法制备的TiC粒子增强钛基复合材料力学性能与显微组织的影响。研究采用的TiC粒子增强的钛基复合材料是用预处理熔炼法 (PTMP)工艺制备的。将二次真空自耗电弧熔炼的铸锭用常规方法锻造成Φ13mm左右的棒材 ,在其上切取拉伸试样和蠕变试样 ,在 80 0～ 10 5 0℃温度范围内热处理 1h ,空冷。测试复合材料的室温和高温拉伸以及蠕变性能。研究结果表明 ,TiC粒子在基体分布均匀 ,添加尺寸为 5 μm以下的球形或近似球形TiC粒子时 ,粒子增强的钛基复合材料的综合性能优异 ,具有良好的热强性与室温塑性匹配 ,直至 65 0℃ ,复合材料仍具有良好的综合机械性能     

(WO_3p+ABOw)/Al混杂复合材料制备与力学性能

采用湿成型法成功制备了比重差别大的WO3颗粒(WO3p)和硼酸铝晶须(ABOw)混杂预制块,用挤压铸造法制备混杂铝基复合材料。混杂复合材料中含(原子分数)5%WO3p和20%ABOw,不同大小的WO3p尺寸分别为18和3μm。采用扫描电镜(SEM)和万能拉伸试验机对制备的混杂复合材料试样进行微观组织观察和拉伸性能测试。复合材料组织观察表明,WO3p和ABOw在基体中随机、均匀地分布,在高倍照片中可以观察到大尺寸WO3p存在裂纹,铝液不能渗入到裂纹中。力学性能研究结果表明,尺寸较小的颗粒增强的复合材料具有高的抗拉强度和断裂延伸率;含大尺寸WO3p的混杂复合材料的抗拉强度、屈服强度和断裂延伸率分别为266.8,197.3 MPa和1.16%,含小尺寸WO3p的混杂复合材料的抗拉强度、屈服强度和延伸率分别为290.3,180.5 MPa和1.37%。复合材料拉伸断口形貌观察表明,两种不同WO3p尺寸的混杂复合材料断裂机制有所不同,大颗粒增强复合材料中大颗粒发生断裂,裂纹穿过颗粒扩展,晶须与界面脱粘;小颗粒增强复合材料中小颗粒与基体界面脱粘以及晶须与界面脱粘,但晶须脱粘数量明显减少,晶须拔出数量增多。     

Effect of lithium on the mechanical properties and microstructure of sic whisker reinforced aluminum alloys

Aluminum-silicon carbide whisker composites containing nominally 3 to 5 pct Li in the matrix alloys have been fabricated and tested. Tensile and compression tests have been conducted at room temperature, and compression creep tests have been conducted at elevated temperatures. Lithium additions were found to increase the strengthening effect of silicon carbide whiskers at room and elevated temperatures. Lithium also reduced the density of the composites and increased the elastic modulus. Transmission electron microscopy showed no obvious chemical reaction between the whiskers and the aluminum-lithium alloy matrix.     

原位自生钛基复合材料的研究进展

原位自生钛基复合材料以其高比强度和高比模量引起了人们的广泛关注,尤其是如何提高其高温性能成为近年来钛基复合材料研究的热点.该文详细综述了原位自生钛基复合材料的各种制备方法、增强体与钛基体的选择、各种增强体的反应体系以及原位自生钛基复合材料的组织结构与力学性能,指出了原位自生钛基复合材料今后的发展方向.     

炭/炭刹车盘的复合抗氧化涂层探讨

在C/C刹车盘的非摩擦面上涂层是氧化防护的一种有效方法,对涂层配方进行DTA分析,确定了涂层的固化温度,对经磷酸和氧氯化磷处理过的样品的起始氧化温度进行了测试,对不同复合抗氧化剂处理过的样品的抗氧化、抗热震性能进行了试验,采用SEM,TGA,EDAX对涂层及涂层与基体之间的界面结构、涂层的成分等进行了观察和分析,表面预浸磷酸后浸TEOS(正硅酸乙酯)再涂层有最佳且稳定的抗氧化效果。     

Experimental Comparison of the Effects of Nanometric and Micrometric Particulates on the Tensile Properties and Fracture Behavior of Al Composites at Room and Elevated Temperatures

This article studies the influence of nanometric (n-SiC_p) and micrometric-scale SiC particulates (μ-SiC_p) on the tensile properties of the Al 7075 alloy. The unreinforced Al and its composites were synthesized using the powder metallurgy (P/M) route and were tested uniaxially in tension at both room and elevated temperatures. Aging behavior was studied to observe any effect of the reinforcement on the aging kinetics and hardness of the composites. X-ray diffraction was performed to determine the crystal structures of the raw materials and any reaction phase formed in the composites. The n-SiC_p were not dispersed uniformly in the Al matrix and clustered mainly at the grain boundaries. The stiffness of the composites increased and the ductility decreased with an increase in the volume fraction of the n-SiC_p. The n-SiC_p proved to be a better reinforcement than the traditional μ-SiC_p in terms of imparting higher ductility to the composite. Fractography and microscopy using optical, scanning electron, and transmission electron microscopes were performed for failure and microstructural analysis of all the materials. At room temperature, the fracture altered from ductile in the unreinforced Al to brittle in the composites. At an elevated temperature, the fracture mechanism transformed from brittle to ductile rupture in the composites.     

Fracture at elevated temperatures in a particle reinforced composite

The tensile fracture behavior of a cast and extruded 2014 aluminum alloy metal matrix composite (MMC) reinforced with 10, 15, and 20 vol.% aluminum oxide particles was investigated as a function of temperature between 100 and 300°C and hold time, and compared with the unreinforced alloy. In addition, the effect of aging condition was investigated in a 15 vol.% composite tested at 200°C. At lower temperature the composites have higher yield strength and UTS than the unreinforced material, and both decrease with increasing temperature. At higher temperatures all the materials have similar strength levels. The elongation is lower in the composites, decreasing with increasing level of reinforcement and increasing with increasing temperature, except at the highest temperature where all the composites are about the same. The microstructural damage in the composites also varies with temperature: particle fracture dominates at lower temperatures and interparticle voiding is the main damage feature at elevated temperatures. The time at temperature, and hence the degree of overaging, has little effect on the observed trends in the composite, in contrast with the unreinforced material where the density of voids decreases with increasing hold times. The transition temperature where the major damage changes from particle cracking to interparticle voiding increases with volume fraction and particle size, and decreases with overaging. The cracked particle density and void density both increase with strain, and the highest rate of increase occurs in the overaged material. In general, the tendency for particle cracking is reduced and for interparticle voiding is increased by any factor which permits accomodation of strain by the matrix, such as lower volume fraction of particles, small particle size, nonclustered particle distribution, and matrix softening from underaging or overaging.     

The effect of thermal exposure on the mechanical properties of aluminum-graphite composites

The mechanical properties of aluminum-graphite composites were measured at room temperature in the as-received condition, after elevated temperature exposure and after thermal cycling. The composites were fabricated by solid-state diffusion bonding of liquid-phase Al-infiltrated Thornel 50 fibers. The results showed that the maximum longitudinal tensile strength of the as-received material was 80,000 psi (552 MN/m²), which corresponds well with the rule of mixture value. The composite strength was observed to vary widely, depending on the extent of wetting of the fibers by the aluminum. The strength of the composites in the transverse direction was generally very low, due to poor interfacial bonding. Aluminum carbide (A1₄C₃) formed at the surface of the fibers at temperatures greater than 500‡C (773 K). Development of the carbide was shown to be diffusion-controlled and was dependent on the time and temperature used. It was shown that the tensile strength was virtually unaffected by heat-treatment up to 500‡C (773 K); beyond that temperature a drastic degradation of tensile strength occurred. The degradation could be correlated with the extent of carbide development at the interface. Thermal cycling of the composites below 500‡C (773 K) resulted in an observable degradation of the composite strength. Scanning electron microscopy of fractured surfaces indicated that the relatively weak interface governs the mode of failure in tension.     

Effect of Volume Fraction of Particle on Wear Resistance of Al2O3／Steel Composites at Elevated Temperature

Inpreviouswork,heat resistingsteelwithlow carboncontentandhighoxidationresistanceatele vatedtemperaturewastakenasthematrixmaterial. AndAl2O3ceramicparticleswereutilizedasrein forcedphasefortheirgreatstabilityandhighrigidi tyatelevatedtemperature.Inorde…     

The effect of thermal exposure on the mechanical properties of aluminum-graphite composites

The mechanical properties of aluminum-graphite composites were measured at room temperature in the as-received condition, after elevated temperature exposure and after thermal cycling. The composites were fabricated by solid-state diffusion bonding of liquid-phase Al-infiltrated Thornel 50 fibers. The results showed that the maximum longitudinal tensile strength of the as-received material was 80,000 psi (552 MN/m²), which corresponds well with the rule of mixture value. The composite strength was observed to vary widely, depending on the extent of wetting of the fibers by the aluminum. The strength of the composites in the transverse direction was generally very low, due to poor interfacial bonding. Aluminum carbide (A1₄C₃) formed at the surface of the fibers at temperatures greater than 500?C (773 K). Development of the carbide was shown to be diffusion-controlled and was dependent on the time and temperature used. It was shown that the tensile strength was virtually unaffected by heat-treatment up to 500?C (773 K); beyond that temperature a drastic degradation of tensile strength occurred. The degradation could be correlated with the extent of carbide development at the interface. Thermal cycling of the composites below 500?C (773 K) resulted in an observable degradation of the composite strength. Scanning electron microscopy of fractured surfaces indicated that the relatively weak interface governs the mode of failure in tension.     

Thermal cycling-induced deformation of fibrous composites with particular reference to the tungsten-copper system

Dimensional stability of fibrous composites under conditions of elevated temperature cycling has been examined with reference to the familiar model system, tungsten wirereinforced copper. Preferential growth of the matrix in the direction parallel to the reinforcing fibers, the amount of which increased with the number of cycles, was observed in specimens subjected to hundreds of repctitive thermal cycles in the temperature range between 0.35 and 0.8 of the matrix homologous temperature. The amount of growth per unit length after a given number of cycles was found to increase with increasing the holding time at the upper cycling temperature; it was also dependent on such composite variables as the fiber length, fiber diameter, and fiber volume fraction. This observation strongly suggests that interface sliding plays an important role in elevated temperature deformation of this class of material. On the basis of a model which assumes a viscous nature of the phase boundaries, the phenomenon observed is theoretically explained in terms of interfacial sliding-induced relaxation of the internal stress built up in the composite due to differential thermal expansion of the composite constituents. Formerly Graduate Student.