Fatigue damage development in Al2O3/Al composite

Fatigue damage development in two aluminium matrix (Al7SiO.6Mg and Al5Si-3Cu1Mg) composites reinforced with discontinuous Al₂O₃ fibres has been monitored by means of acoustic emission (AE). The AE signals (RMS) recorded during the tests clearly exhibit three distinct stages which correspond to crack initiation, dominant crack formation and stable propagation. Generally speaking, the cracks initiated at a high load level form close together and a dominant crack forms easily. By contrast, at a low load, initiated cracks are widely separated and the formation of a dominant crack is difficult. If there are large defects in the composite, the first stage is absent, even at low load. In the first stage, little change in microstructure and modulus of the composite is observed; in the second, fibre fracture, interface debonding and matrix cracking occur and there are often sinusoidal cracks in the matrix; in the last stage, the principal characteristic is stable propagation of the dominant crack. The degradation of the elastic modulus of the composite in the last two stages is small.     

Ni3Al合金热/机械疲劳裂纹扩展行为研究

对ＩＣ１０定向凝固高温合金进行了４５０￣９９０℃热／机械疲劳裂纹扩展行为的试验研究。分别研究了相位角、保持时间、温度、频率对ＩＣ１０合金裂纹扩展行为的影响,并建立了热／机械疲劳裂纹扩展速率预测模型。研究发现：温度的升高和频率的降低均会加速裂纹扩展;同相位热／机械疲劳裂纹扩展速率大于反相位热／机械疲劳裂纹扩展速率,而且它们两者介于最大温度和最小温度的等温度裂纹扩展速率之间;载荷保持加速裂纹扩展。     

Al2O3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

1.IntroductionTo improve the mechanical properties and relieve mis-matches between the filler metals and base materials,the particulates of superalloys,ceramic or carbon fiberswere added into the conventional brazing filler metal toform composite filler material.The method has beenused in aero-engine component repairing[1,2],fine castcomponent joining[3],wide clearance butt jointing[4],ce-ramic brazing[5,6]and electronic package[7].However,the method was used mostly in metal brazing.The mi-cro…     

Al2O3含量对Al2O3/W复合材料合成的影响

以铝热法为基础制备了A12O3/W复合材料，探讨了A12O3含量对复合材料合成的影响。研究表明：主要物相为α-A12O3、金属W。刚玉含量小于0．3时，温度影响不显著，大于0．3时，温度影响显著，有大量碳化物生成，且WC/W2C相对含量随A12O3含量增加及煅烧温度的提高而增加。当刚玉含量为0．5mol时，有正交晶钨酸铝生成。随刚玉含量变化，金属钨分布从连续分布向弥散分布变化。连续分布的金属钨因被氧化铝包裹因此难以碳化，而弥散分布的金属钨则易于被碳化。     

Processing and Heat Treatment Effects on an Al2O3/Ni3Al Composite

Various processing routes may be used to fabricate Ni₃Al matrix composites. In the present study, vacuum hot pressing and hot extrusion were used to fabricate an Al₂O₃ Composite particulate-reinforced Ni3Al composite. Relatively low extrusion temperatures promoted gamma-phase formation as did extended high temperature anneals. The room-temperature bend strength was found to increase as the gamma-phase content increased. Furthermore, the composite creep rate was affected by the. processing parameters and their effect on the amount of gamma/pgamma-prime interface. The matrix and particulates did not exhibit any reaction after normal processing. However, a minor reaction was noted after annealing near 1000°C, while extensive reaction resulting in Ni-Al spinel formation occurred above 1200°C in air     

ITO/Al2O3复合透明导电膜的制备及光电性能

采用磁控溅射技术 ,在预先沉积有金属Al膜的玻璃衬底上制备了ITO薄膜。通过高温热处理 ,获得了透射率高、导电性能好的ITO/Al2 O3 复合透明导电膜。研究了不同Al薄膜厚度下ITO薄膜的晶体结构及其光、电性能 ,结果表明 ,当预沉积Al层厚度为 4 0nm左右时 ,ITO的结晶质量得到提高 ,取向性能变好 ,电阻降低 ,而且在 4 0 0 - 80 0nm范围内具有很高的可见光透过率。实验表明 ,通过改变预沉积Al膜的厚度 ,可以改变ITO薄膜最大透过率对应的波长 ,实现ITO预器件工作波长的匹配     

挤压SiCw／LD2复合材料的疲劳裂纹扩展

本文测量了挤压19％(Vol)SiCw/LD2复合材料疲劳裂纹扩展的门槛值ΔK_(th)和扩展速率da/dN。并在扫描电镜下观察了疲劳断口形貌。结果表明,复合材料在门槛值附近和中速扩展区的疲劳裂纹扩展抗力高于基体材料LD2合金。复合材料纵向试样于170℃时效后的疲劳裂纹扩展抗力高于150℃时效,疲劳裂纹扩展扩展过程包括不在一个面内的微裂纹长大和联接这些微裂纹的(Ⅰ+Ⅱ)复合型裂纹的扩展。与裂纹相垂直的晶须有效地阻碍了微裂纹的长大。     

Al2 O3/Al 复合涂层对贫铀的保护性能研究

为探讨Al2O3/Al复合涂层在贫铀表面保护中应用的可行性,采用盐雾腐蚀试验和磨损试验方法,结合SEM/EDS和XRD表征,分析了贫铀表面Al2O3/Al复合涂层的保护性能.结果表明,贫铀表面反应磁控溅射Al2O3/Al涂层没有明显的腐蚀特征,而等离子喷涂Al2O3/Al涂层发生了严重的腐蚀剥落现象.Al2O3/Al涂层表现为磨粒磨损行为,抗磨损性好.作为对比样的贫铀表面Al涂层则表现为粘着磨损行为,抗磨损性差.讨论了贫铀表面涂层的腐蚀和磨损行为.     

原位合成TiB2/Al2O3复相陶瓷显微组织的研究

采用自蔓延燃烧合成法在室温下的空气中制备出了TiB2/Al2O3复相陶瓷,通过X射线衍射(XRD)和扫描电镜(SEM)分析表明:大部分TiB2的形貌为规则的块状,晶粒细小,平均尺寸为几个μm,但也出现了TiB2枝晶和棒状晶。而Al2O3的颗粒较大(10~40μm左右),形状不规则,Al2O3的断口呈层片状,Al2O3和TiB2出现聚集现象。     

气压烧结Al2O3/TiCN复合材料的研究

运用气压烧结工艺克服了热压工艺的局限性,制备了Al2O3/TiCN复合材料,考察了材料在不同温度烧结时的致密化行为及其力学性能,结果表明气压烧结制备的Al2O3-30wt%TiCN陶瓷复合材料,相对密度达到99.5%,抗折强度为772MPa,硬度为19.6GPa,断裂韧性高达5.82MPa/m2.     

Investigation on Wear-resistant Properties of Al2O3/SiC Nano Composite Ceramics in Fused Zinc

Al2O3/SiC nano composite ceramics can replace wear-resistant and heat-resistant alloys used in preparing the arm-bush that is the key parts in the equipment of galvanizing steel strip. Conventional alloy for arm-bush could only operate 4 similar to7 days, and the ceramic Arm-bush can operate more than 100 days continuously tested in the same equipment and its service life has increased 15 times more than that of alloy. According to the results of microstructure analysis, one of the most important cause that the composite ceramics possess excellent wear-resistant properties in the fused zinc is that nano SiC particles have existed within fine grains of Al2O3.     

GH4169合金焊接接头高温疲劳裂纹扩展性能试验研究

对GH4169合金焊接接头在650℃下的疲劳裂纹扩展性能进行了测试和分析.结果表明,疲劳裂纹扩展速率、初始裂纹尺寸、裂纹容限和温度对焊接接头的疲劳裂纹扩展寿命都有影响.母材及焊缝的疲劳裂纹扩展速率和裂纹容限均有较大的差异.     

Investigation of Fatigue Growth Behavior of an Inclined Crack in Aluminum Alloy Plate

In the present paper, fatigue tensile tests are carried out on a servo-hydraulic fatigue testing machine to study the whole propagation process of the inclined crack. And the scanning electron microscope is employed to observe the micromorphology of the fracture surface to further probe the crack growth rate from a microscopic point of view. Meanwhile, the finite element method has also been applied to predict the crack propagation trajectory and the fatigue life of the sample with two finite element analysis codes. The fatigue tensile tests indicate the inclined crack propagates along the direction perpendicular to the external loading and the crack growth rate increases continuously based on the micromorphology of the fracture surface. The numerical analysis results reveal the variation of the stress distribution at the crack tip as well as the crack trajectory at different extension steps. Moreover, the stress intensity factor values are discussed in detail. And the computed results, the inclined crack propagation path and fatigue life of the sample, agree well with the experimental ones, which provide certain referential significance for the prediction of the inclined crack propagation in thin plate.     

原位Al2O3/Al-Cu复合材料的制备与组织研究

采用原位反应近液相线铸造方法制备含有3.6%(质量分数)原位Al2O3颗粒的Al-6.8Cu基复合材料,在基体合金的固液两相区选择580,590,600℃和610℃进行二次加热保温实验,淬火固定其半固态组织。通过光学显微镜及透射电镜观察合金的组织结构,研究Al2O3原位颗粒对材料组织的影响。结果表明:原位Al2O3颗粒对Al-6.8Cu合金的铸态组织具有一定的细化作用,但没有明显的球化作用。在半固态二次加热过程中原位Al2O3颗粒对晶粒长大行为具有抑制作用和球化作用,与基体合金相比,在相同的二次加热条件下晶粒尺寸减小20~40μm。     

Al2O3/SiO2／MgO复合纳米添加剂的抗磨减摩性能

采用超声机械法制备纳米Al2O3、SiO2、MgO等颗粒，并对其进行化学修饰，使其稳定地分散在基础油中，获得自修复纳米润滑添加剂。通过四球试验与止推圈试验考察摩擦学性能。试验结果表明：自修复纳米润滑添加剂具有良好的分散稳定性、抗磨减摩性和自修复性。     

CuAl_2O_3复合材料中Al_2O_3的长大动力学分析

通过分析铜铝颗粒表面铝与氧的反应,计算铜铝合金中铝的沉淀析出量、铝在铜基体中的扩散速率以及Al2O3颗粒大小,研究了喷射沉积内氧化法制备CuAl2O3复合材料中Al2O3的长大动力学行为。结果表明,在反应合成制备过程中,氧化铝颗粒长大动力学行为满足抛物线规律;铜铝合金表面铝与氧的反应是一种铝扩散控制型反应,该氧化铝颗粒的长大与铝在铜铝合金中的含量、扩散速率和所处位置(晶内、晶界)有关。计算得到的Al2O3颗粒大小与实际获得的氧化铝颗粒大小相吻合。     

自蔓延高温合成Al2O3-TiC/Fe-Al复合材料的研究

以天然钛铁矿为主要原料,采用SHS技术,通过铝热、碳热还原法合成了Al2O3-TiC/Fe-Al 金属间化合物/陶瓷基复合材料.研究了SHS合成过程中制坯压力、预热时间、稀释剂和碳源对SHS合成过程的影响.研究结果表明:制坯压力在40MPa时,燃烧温度与燃烧波速率出现最大值;随着预热时间的延长,燃烧温度和燃烧波速率都增加,产物中TiC和Al2O3晶体的晶格间距增大,合成更为完全,产物中只包含有TiC相、Al2O3相、Fe-Al相和α-Fe固溶相;稀释剂会降低燃烧温度和燃烧波速率,同时使产物的密度降低,且不利于合成产物的形成;与炭黑相比用石墨做碳源时,燃烧温度、燃烧波速率以及产物的密度都高,反映了碳源结构差异对燃烧合成的影响.     

Fatigue and R-curve behavior of an Al2O3-10vol%Cr3C2 composite

The static and dynamic fatigue properties of an Al₂O₃-10 composite were studied. The R-Curve behavior was determined using the indentation strength in bending (ISB) technique. Results indicated that both alumina and the Al₂O₃-Cr₃C₂ composite exhibit time-dependent slow crack growth under static fatigue test conditions. In addition, the resistance for slow crack growth in the Al₂O₃-Cr₃C₂ composite is higher than that in monolithic alumina. The toughness of alumina was substantially increased and R-curve behavior became evident after the incorporation of Cr₃C₂ particles.     

Development and Characterization of Al2O3 Dispersed Al/Mg/Cu/Ti Matrix Composite

The effect of dispersion with different weight fractions of Al2O3 particles in metallic matrices （AI/Mg/Ti/Cu） fabricated by powder metallurgy was investigated. In the case of 15 wt% Al2O3 reinforced composites, peak hardness was attained which subsequently decreased with increasing the content of Al2O3. A correlation between the microhardness and nanomechanical properties at submicron scale was examined for all the composites. Specific strength and specific modulus were measured in order to figure out the performance of the composites.