碳纤维增强Al-4.5Cu复合材料的凝固组织、偏析及性能的研究

铸造金属基复合材料的凝固决定着材料的机械性能.本文中研究了凝固冷却速率对CF/Al-4.5Cu复合材料的显微组织、偏析及机械性能的影响.实验结果表明,挤压铸造CF/Al-4.5Cu复合材料凝固过程中,α-Al相首先在纤维间隙中开始形核,并逐渐向纤维表面生长,而共晶θ-Al₂Cu相依附CF表面形核并长大.随着凝固冷却速率的降低,θ相的形态从块状转变为颗粒状,析出量逐渐减少,Cu元素显微偏析逐渐降低,复合材料的抗弯强度逐渐提高.另外,CF/Al-4.5Cu复合材料由于其强的界面结合力,其断裂特征为脆性断裂,断口形貌表现为平切型.     

残余形变对莫来石短纤维/Al-4.5Cu复合材料及其基体合金时效析出行为的影响

用挤压铸造法制备莫来石(mullite)短纤维/Al-4.5Cu复合材料及其基体合金。用硬度测试(HB)、差示扫描量热仪(DSC)和透射电镜(TEM),研究固溶淬火后残余形变(0 %,12.5 %,25 %,34.4%)和纤维对复合材料及其基体合金时效析出行为的影响。结果表明:形变对Al-4.5Cu合金的时效析出过程具有十分明显的加速作用,随着形变度增加,时效加速作用进一步加强;莫来石短纤维对Al-4.5Cu合金的时效析出过程具有加速作用;纤维和形变同时存在时,复合材料的时效析出过程还会进一步加快。但是,形变或/和纤维抑制了Al-4.5Cu合金中GP区的形成。     

δ-Al2O3短纤维/铝合金复合材料的拉伸强度及断裂机理

用挤压铸造方法制备了"Saffil"短纤维增强的Al-5.5Mg、Al-5.5Zn基复合材料,纤维体积分数分别为10%、15%、20%。金相分析表明:纤维近似呈二维随机分布。在室温及300℃下测试了基体及MMCs的拉伸强度,并对断口进行了SEM分析。分析和讨论不同情况下的断裂机理及强度预测公式。     

氧化铝短纤维增强铝基复合材料的蠕变破坏行为

研究了挤压铸造Al₂O₃短纤维增强铝基复合材料在350℃恒应力条件下的蠕变行为。蠕变试验过程中采用中断实验的方法对复合材料的显微组织进行观察,发现复合材料在蠕变过程中纤维发生断裂,弱界面发生破坏以及基体合金在应力作用下发生变形。根据复合材料在蠕变三个阶段中显微组织的变化情况,对其宏观蠕变行为进行了分析,认为位错在复合材料中滑移和攀移控制整个蠕变过程,并提出了短纤维增强金属基复合材料的蠕变断裂机理,合理地解释了复合材料的蠕变过程。      

等轴晶移动条件下金属凝固温度场、流场及溶质分布数值模拟

本文利用作者提出的固相移动条件下金属凝固传热、传质及动量传输数学模型对砂型铸造 Al-4.5%Cu 合金铸锭凝固过程进行了数值模拟研究与试验验证。模拟冷却曲线及宏观偏析与试验结果基本相符。     

纤维长度对M／ZL109复合材料强度及可靠性的影响

对在相同的挤压工艺参数的条件下,用具有不同的长度分布及平均长度的莫来石短纤维与ＺＬ１０９复合得到复合材料,然后比较这些复合材料的抗拉强度及其分散度,考察和分析了纤维长度分布状况及平均长度对复合材料的强度及强度数据分散性的影响规律。     

Al_2O_3颗粒与 Al 合金固液界面的相互作用

本文采用定向凝固技术探讨了 Al_2O_3颗粒/Al-2.0Mg-4.5Cu 合金复合材料在凝固过程中颗粒与生长着的固液界面的相互作用,得出了胞晶或胞状树枝晶生长条件下颗粒的分布规律、机制以及 Al_2O_3颗粒在试样中的分布与氢、铈之间的联系。但未发现铈对颗粒主要沿晶界分布产生显著影响。     

Al_2O_3短纤维/M124F复合材料的凝固组织

采用挤压铸造法制备了Al2O3短纤维增强M124F铝合金复合材料,并研究了其拉伸强度、基体凝固组织和界面。结果表明:用挤压铸造法制备的复合材料组织致密,纤维分布均匀,抗拉强度与M124F相比明显提高;基体组织的α-Al枝晶和Si相明显细化。分析表明,纤维的加入具有双重增强作用:高强度陶瓷纤维的介入增强了基体材料的力学性能;在凝固过程中,Al2O3短纤维阻碍了α-Al枝晶的生长,同时可作为Si相非自发形核的衬底,细化了基体组织,提高了复合材料的力学性能。纤维与基体间未发现界面生成物MgAl2O4。     

Al2O3短纤维/Al-12Si复合材料启裂特征的TEM原位观察研究

利用挤压铸造法制备了Al₂O₃(15%)/Al-12Si复合材料,并采用透射电镜动态拉伸技术对复合材料的裂纹形成及微观断裂过程进行了原位观察,发现该复合材料的纤维/基体界面是破坏路径之一,并发现了纤维中裂纹形成及扩展至完全破坏的现象.     

短纤维增强铝铜二元合金复合材料凝固偏析的数值模拟

根据凝固过程中的守恒原理,建立了铝基复合材料凝固过程的数学模型.根据所建立的模型对氧化铝短纤维增强铝铜二元合金复合材料进行数值模拟,模拟结果表明:氧化铝短纤维周围有低熔点物质及溶质富集;随冷却速度增大,复合材料基体偏析加剧;随复合材料中纤维体积分数增大,基体中偏析减小.     

Effect of solidification on microstructures and mechanical properties of carbon nanotubes reinforced magnesium matrix composite

A novel approach was successfully developed to fabricate bulk carbon nanotubes (CNTs) reinforced Mg matrix composites. The distribution of CNTs in the composites depends on the solidification rate. When the solidification rate was low, CNTs were pushed ahead of the solidification front and will cluster along grain boundaries. When the solidification rate was high, CNTs were captured by the solidification front, so the CNTs remained inside the grain. Moreover, good interfacial bonding was achieved in the composite under high solidification rate. Meanwhile, compared with the matrix alloy, the ultimate tensile strength (UTS) and yield strength (YS) of the composite were significantly improved. The mechanical properties of the composite under higher solidification rate are better than composite under low solidification rate and the alloy. Moreover, most CNTs on the fracture surfaces were directly pulled out from the matrix. The Kelly–Tyson formula agreed well with the experimental tensile value in the composite under higher solidification rate, and the load-transfer efficiency is almost equal to 1.     

断裂方式对氧化铝基复合陶瓷耐磨性的影响

通过磨粒磨损试验测定了氧化铝 陶瓷、氧化铝/碳化硅复合陶瓷和氧化铝/莫来石复合陶瓷的耐磨性. 利用透射电子显微镜(TEM)观察了样品的微观结构, 采用扫描电子显微镜(SEM)分析了样品的断口形貌和磨损表面的剥落情况. 研究了断裂方式对磨损表面剥落和耐磨性的影响. 结果表明: 氧化铝陶瓷的磨损主要由断裂磨损机制控制, 氧化铝/碳化硅复合陶瓷的磨损主要由塑性磨损机制控制, 氧化铝/莫来石复合陶瓷受这两种磨损机制共同作用. 相对于氧化铝陶瓷, 氧化铝/碳化硅复合陶瓷和氧化铝/莫来石复合陶瓷的耐磨性提高2～4倍, 这主 要是由于其断裂方式转变为以穿晶断裂为主, 减少了磨损面的脆性剥落.     

C/Mullite/Si-C-N复合材料的组织结构及其弯曲行为研究

本研究制备出了以莫来石为界面层的炭纤维增强Si-C-N陶瓷基复合材料(C/Mullite/Si-C-N).使用三点弯曲法研究了复合材料在室温、1300℃和1600℃时的弯曲断裂行为,利用扫描电镜(SEM)和透射电镜(TEM)观察了复合材料的组织和弯曲断口形貌.结果表明:在室温和1300℃时,C/Mullite/Si-C...     

橡胶改性对硼纤维/环氧单向复合材料力学性能的影响

对环氧树脂进行液体丁腈橡胶改性, 并采用缠绕无纬布层压成型工艺制备了硼纤维/环氧单向复合材料。测试了环氧树脂液体丁腈橡胶改性前后硼纤维/环氧单向复合材料的力学性能, 研究了硼纤维/环氧单向复合材料的纵向拉伸破坏模式。结果表明, 基体中的10%液体丁腈橡胶使硼纤维/环氧单向复合材料的拉伸强度、 弯曲强度、 层间剪切强度和断裂延伸率分别提高了18.42%、 13.39%、 28.45%和43.40%, 但其拉伸和弯曲模量稍有下降。基体中含10%液体丁腈橡胶的硼纤维/环氧单向复合材料的纵向拉伸破坏模式为界面层的内聚破坏和脱黏破坏共存的混合破坏。      

Study on graphite fiber and Ti particle reinforced Al composite

Graphite fiber and Ti particle-reinforced aluminum matrix composite were produced by squeeze casting technology. A small amount of needle aluminum carbide at graphite fiber and Al interface was observed, and TiAl₃ intermetallic compound at Ti particle and Al interface was detected. Tensile strength and bending strength of the composite have been measured. The fracture surface of the composite after tensile and bending tests was observed; graphite fiber-reinforced Al was brittle fracture, whereas Ti particle-reinforced Al was ductile fracture. The corresponding fracture mechanism was discussed.     

In situ reacted TiB2-reinforced mullite

In situ formation of TiB₂ in mullite matrix through the reaction of TiO₂, boron and carbon has been studied. In hot-pressed and pressureless-sintered samples, in addition to TiB₂, TiC was also found to be dispersed phases in mullite matrix. However, in the case of pressurelesssintered samples, mullite/TiB₂ composite with 98% relative density can be obtained through a preheating step held at 1300 °C for longer than 3 h and then sintering at a temperature above 1600 °C. Hot-pressed composite containing 30 vol% TiB₂ gives a flexural strength of 427 MPa and a fracture toughness of 4.3 MPam^1/2. Pressureless-sintered composite containing 20 vol% TiB₂ gives a flexural strength of 384 MPa and a fracture toughness of 3.87 MPam^1/2.     

莫来石溶胶的制备及对钛酸铝粉体的包裹

以硝酸铝和正硅酸乙酯为主要原料制备稳定莫来石溶胶, 用浸渍包膜的工艺方法对钛酸铝(Al₂TiO₅, AT) 粉体进行包裹, 研究了溶胶性能及含量对钛酸铝粉体包裹效果及性能改善的影响。结果表明: 溶胶的浓度为0.18~0.30mol/L、 黏度在56~93mPa · s之间、 pH=3.0、 包膜厚为0.15~0.20μm时, 可得到包裹效果良好的莫来石-钛酸铝粉体, 制备出性能优良的莫来石-钛酸铝复合材料。复合材料的抗折强度为36~50MPa, 为钛酸铝材料强度的10~15倍, 复合材料的热膨胀系数为1.89~2.25×10-6/℃(室温至1000℃), 复合材料中的钛酸铝在1100℃/300h的热处理未发生分解。应用TG-DSC、 XRD、 SEM、 EPMA等对包膜前后莫来石粉体和复合材料粉体的热学行为、 形貌和成分进行研究, 探讨了性能与结构之间的关系。      

Preparation of Al2TiO5 from alkoxides and the effects of additives on its properties

Al2TiO5 was prepared by the sol-gel method from alkoxides and its mechanical and thermal properties measured. The prepared Al2TiO5 powder was very fine and had a narrow particle-size distribution. The addition of mullite and Al2O3 to the prepared Al2TiO5 inhibited the grain growth during sintering, resulting in a decrease of microcracking and an increase of fracture strength. Al2TiO5/mullite composite exhibited a higher fracture strength than Al2TiO5/alumina composite. The thermal expansion coefficient of Al2TiO5 increased with the addition of mullite and alumina, and also increased with temperature up to 1000°C; however, it decreased in the temperature range between 1000 and 1200°C during heating, due to decomposition of Al2TiO5. The addition of mullite inhibited the decomposition of Al2TiO5, but the addition of Al2O3 accelerated it. Al2TiO5 prepared from metal alkoxides was also more stable than that prepared from the commercial alumina and titania powders. This revised version was published online in November 2006 with corrections to the Cover Date.     

Zirconia-toughened hydroxyapatite ceramic obtained by wet sintering

A toughened hydroxyapatite (HA) ceramic has been obtained through the incorporation of magnesia partially stabilized zirconia (Mg-PSZ) under uniaxial pressing and sintering in wet oxygen at 1250 °C for 4 h. The powder X-ray diffraction (XRD) patterns and infrared spectra (FT-IR) show that HA is the only calcium phosphate phase present. The composite (MgPSZ-HA) has a density of 94% the theoretical value. The bending strength and the fracture toughness are around 50% higher for Mg-PSZ reinforced than for HA. The grain size and the fracture surface were studied by scanning electron microscopy (SEM). The influence of the Mg-PSZ particles on the fracture mechanism of the HA ceramic is discussed.