ZL109铝合金及其复合材料干滑动磨损表面及亚表面的观察与分析

利用预制体挤压浸渗法分别制备了Al2O3或C短纤维单一增强以及两者混杂增强ZL109金属基复合材料，探讨了基体合金及其复合材料的干滑动摩擦磨损行为，并对其磨损表面及亚表面形貌进行了观察和分析。结果表明：C纤维在复合材料中起到一定的自润滑作用，Al2O3和C短纤维混杂增强复合材料的磨损率低于基体合金和单一纤维增强的复合材料。与基体相比，单一Al2O3增强复合材料从轻微磨损到急剧磨损的临界转变载荷明显提高，经C纤维混杂后，其临界载荷进一步提高。经磨损表面及亚表面的观察与分析表明：纤维增强对基体合金的磨损机制没有明显影响，在轻微磨损阶段，主要磨损机制为犁沟磨损和层离，亚表面分为3个区域：表层未脱落的剥离层、亚表面裂纹形成区以及未受影响区。发生严重磨损时，磨损机制转变为严重的粘着磨损，此时表层未脱落的剥离层遭到破坏。     

硅酸铝纤维增强铝基复合材料的抗拉强度及其影响因素

研究了基体合金化,硅酸铝纤维处理方法以及不同粘结剂对硅酸铝纤维增强的铝基复合材料室温强度的影响。结果表明：基体为ＺＬ１０９铝合金的复合材料的强度高于以其它铝合金为基体的铝基复合材料;用莫来石硅酸铝纤维增强的铝基复合材料的抗位强度高于用γ型三氧化二铝纤维增强的铝基复合材料;     

Compressive strength of continuous fiber reinforced aluminum matrix composites

Aluminum matrix composites can exhibit exceptionally high compressive strength (ε 4 GPa). The main failure mechanism has been identified to be plastic kinking, although an upper bound seems to be attained when the fibers reach their compressive strength. The experimental results are consistent with a plastic kinking model in strain hardening composites. The important parameters controlling the compressive strength are the composite shear modulus, the shear yield strength, the strain hardening rate and the maximum initial fiber misorientation. Interfaces can also play an important role; composites reinforced with weakly bonded fibers have a reduced compressive strength due to their low shear strength in the fiber direction. The results can be used to design composite systems with high compressive strengths; in practice this is done by selecting matrices with high yield strengths and fast hardening rates.     

The thermal plasma near-net-shape spray forming of Al composites

The vacuum-plasma-spraying technique presented in this article is suited to produce aluminum-matrix composites with a low coefficient of thermal expansion reinforced with fine ceramic particles, resulting in a uniform particle dispersion and bulk porosity of less than 1.5% in the as-sprayed condition. Plastic deformation of the plates followed by annealing resulted in significant increases in ultimate tensile strength, hardness, and elongation.     

Designing DRA composites for high creep strength

Metal-matrix composites with discontinuous reinforcement are attractive for high-temperature applications because of their creep strength. An additional benefit is the ease of fabrication through a number of processing routes. The magnitude of creep strengthening depends on the chemistry, size, and volume fraction of the reinforcement phase. By using a dislocation-creep-mechanism map, it is possible to predict the level of creep strengthening in discontinuously reinforced aluminum-matrix composites. Editor’s Note: All compositions are given in volume percent unless otherwise indicated. For more information, contact R.S. Mishra, Department of Metallurgical Engineering, University of Missouri, 1870 Miner Circle, Rolla, Missouri 65409; (573) 341-6361; fax (573) 341-6934; e-mail rsmishra@umr.edu.     

The damping performance of aluminum-based composites

Metal-matrix composites may offer better damping properties than unreinforced alloys. Because damping properties (and metal-matrix composites) are becoming important in airframe design, the damping capabilities of a number of aluminum-matrix composites were measured over a wide range of frequencies at low strain amplitudes, using a new laser vibrometer technique. Silicon carbide and alumina reinforcements resulted in a material with damping properties similar to that of unreinforced aluminum 6061-T6, but unidirectional and planar-random graphite continuous-fiber reinforcements increased the damping by 5 and 14 times, respectively. The increased damping of the continuous fiber composites is attributed to the absence of interfacial reaction resulting from the high-pressure infiltration method used for their manufacture.     

非连续增强铝硅合金复合材料的凝固组织与断口形貌

用扫描电子显微镜(SEM)观察和研究了氧化铝短纤维增强铝硅合金复合材料的凝固组织和断口形貌。结果表明，在复合材料中纤维分布均匀，氧化铝纤维可作为硅相非自发形核的衬底；氧化铝纤维与铝合金基体之间的界面对材料性能影响很大。改善制备工艺应从控制界面反应和细化组织入手。     

Application of alumina fiber reinforced plastics as a grinding material

This work deals with the evaluation of ceramic fiber reinforced plastics as a grinding or polishing material. The plastics were manufactured by mixing continuous alumina fiber of definite diameters and thermosetting resin as a bond material. Composites containing fibers of three different diameters ranging from 10 to 22 μm were used in the study. The performance of these composites was evaluated for surface finishing of hardened steel. Bars of the composite were pressed against the rotating workpiece material S55C on a lathe. Wear of the work and the composite and the surface finish of the work materials were investigated. The self-sharpening characteristic was confirmed and the chip removal process is explained. The most important factor affecting the rate of metal removal to tool wear loss is the average pressure. The fine surface is obtained with the fine fiber. The advantages of the alumina fiber reinforced plastics as a grinding tool are their toughness and flexural strength. They assure a practically fracture-free grinding operation. Resin matrix composites reinforced with ceramic fibers are proposed as efficient tool materials for small stock removal. Paper presented at the First International Conference of New Manufacturing Technology, Chiba, Japan, March 1990.     

液态浸渗后直接挤压铝基复合材料的力学性能

实验研究了采用液态浸渗后直接挤压工艺制备的氧化铝短纤维增强铝基复合材料（Al2O3Sf／Al）的力学性能。发现该方法制备的复合材料不仅具有很高的弹性模量和强度性能、材料中增强纤维的增强承载作用得到了充分发挥,而且延伸率能保持在相对较高水平。结果表明,该工艺是一条非常有效的制备金属基复合材料的新途径。     

Optimization to develop multiple response hardness and compressive strength of zirconia reinforced alumina by using RSM and GRA

In this work the effect of powder forming process parameters of zirconia reinforced alumina composites on micro hardness and compressive strength was studied. The weight percentages of zirconia added to alumina, compaction pressure and sintering temperature are the process parameters selected for this analysis. Using Box–Behnken technique in Response Surface Methodology (RSM), seventeen experimental runs are developed. The sintering temperature and weight percentage of zirconia added to alumina are found to influence the responses. The influencing parameters were identified by using analysis of variance and Grey Relational Analysis (GRA). The regression model for both micro hardness and compressive strength are developed. The increasing amount of zirconia added to alumina matrix is found to enhance the compressive strength of the composite and reduces the hardness of composite. Also, multi response optimization to obtain higher hardness and compressive strength are done using both RSM and GRA.     

颗粒含量对TiB2(p)/Fe复合材料显微组织和力学性能的影响

基于室温单轴拉伸、显微硬度、纳米压痕和扫描电镜观察等试验,表征和分析了TiB2颗粒增强铁基复合材料的宏观、微观力学行为。结果表明,随着高模量TiB2颗粒体积分数从15%增至25%,抗拉强度和弹性模量分别从531.0 MPa和215.5GPa提高到659.0MPa和247.0GPa,比刚度从28.8GPa·cm^-3·g^-1逐步增加至34.7GPa·cm^-3·g^-1,伸长率从22.0%降至7.9%;断裂机制由微孔聚集型韧性断裂转变为穿晶解理型脆性断裂,强化机制可能以细晶强化和位错增殖为主。     

Subcritical crack growth in CVI SiCf/SiC composites at elevated temperatures: effect of fiber creep rate

Subcritical crack-growth studies in SiC_f/SiC composites were conducted with composites reinforced with Hi-Nicalon fibers over a broad temperature range for comparison to earlier studies on materials reinforced with Nicalon-CG fibers. Composites with a 0/90 plain weave architecture and carbon interphase were tested in argon from 1173 to 1473 K. Crack growth data obtained in inert environments are consistent with a proposed fiber-creep-controlled crack-growth mechanism. Measured crack-growth activation energies and time–temperature exponents in argon agree with fiber creep-activation energies and nonlinear creep equations for both fiber types. Estimates of local strains during crack growth are in reasonable agreement with estimated fiber creep strains for the given times and temperatures. The increased creep resistance of Hi-Nicalon fibers is reflected in reduced crack-growth rates for composites containing those fibers.     

Effect of Pyrolysis Temperature on the Properties of Three-Dimensional Silica Fiber Reinforced Nitride Matrix Composites

Three-dimensional silica fiber reinforced nitride matrix composites (3D SiO_2f/nitride composites) were prepared through four cycles of vacuum infiltration of a hybrid precursor and pyrolysis under ammonia atmosphere. The effects of pyrolysis temperature on densification behavior, mechanical properties, and microstructures of the composites were investigated. With the increase of pyrolysis temperature from 800 to 1300 °C, the density of SiO_2f/nitride composites increased from 1.83 to 1.88 g/cm³, while the flexural strength decreased from 148 to 53 MPa, and the elastic modulus decreased from 41.5 to 25.1 GPa. The higher temperatures cause serious damage to silica fibers. The properties of silica fibers and the reinforcing mechanism determine the mechanical properties of the composites.     

硅酸铝短纤维增强AZ91复合材料的制备

以晶化的硅酸铝短纤维为增强体，以偏磷酸铝为粘结剂，把干法和湿法结合起来制做预制块，采用挤压浸渗工艺制备AZ91镁基复合材料，结合光学显微镜和扫描电镜进行铸造缺陷和显微组织分析。结果表明，中性的磷酸铝溶液是制备硅酸铝短纤维增强镁基复合材料（Al2O3-SiO2/AZ91）的最合适的预制块用粘结剂之一；采用复合挤压工艺可以有效防止或减轻金属基复合材料的组织缩松。     

Superplastic behavior of zirconia-reinforced alumina nanocomposites from powder alcoxide mixtures

Here we report the synthesis, microstructure and superplastic creep behavior of alumina-based composites reinforced with 5–20 wt% ZrO₂, prepared from high-purity alumina powders and zirconium alcoxide precursor mixtures. The composites reached 100% true strain at 1350 °C, deformed by stationary creep in the range of strain rates ~10⁻⁷ to 10⁻⁴ s⁻¹. The microstructure remained stable during creep; no evidence of grain growth, grain boundary opening or cracking were observed in deformed samples. We conclude from the analysis of creep parameters that creep takes place mainly by interface-reaction-accommodated grain boundary sliding, and that the mobility of alumina grain boundaries controls the creep rate. The observed behavior is explained by the role of alumina–zirconia interphases, stronger and with a faster relaxation kinetics than alumina interfaces, to achieve an effective grain boundary pinning. Zirconia particles (~0.2–0.4 μm) are homogeneously placed at alumina grain boundaries (~1–2 μm).     

Influence of mechanical milling on the SiC particulate size in an Al-SiC composite

Particle reinforced aluminum-matrix composites are particularly attractive for the automobile and air-craft industries, due to their light weight, high strength, and good wear resistance. In the present work, silicon carbide (SiC) particulates have been incorporated into a pure Al matrix with the help of mechanical milling in a planetary ball-mill. Composite powders were prepared using both raw as well as premilled SiC powders. The effect of milling time on the SiC particulate size was investigated. Systematic analysis of x-ray diffraction data revealed a reinforcement particle size of about 30 nm in a composite containing 50 vol.% SiC. It has been observed that the size reduction occurs at a faster rate when indirect milling is used.     

Strain-rate effects in high-purity alumina

Ultrahigh-strength alumina specimens made from disks produced by vacuum hot pressing high-purity alumina powders were subjected to uniaxial compressive loads at a range of strain rates. It was observed that the material exhibited a failure strength far superior to commercially available alumina. The failure strength was strongly strain-rate dependent and varied from 5.5 GPa at 10^-4 s^-1 to 8.3 GPa at 10³ s^-1. Microscopic studies on the fragments of the specimens deformed under uniaxial strain revealed extensive twinning and dislocation activity. Based on the experimental results and microscopic observations, the factors and mechanism responsible for the observed high compressive strength are discussed.     

氧化铝纤维对锌合金复合材料凝固组织的影响

利用挤压铸造制备了氧化铝纤维增强锌合金复合材料，研究了氧化铝纤维对锌合金复合材料凝固组织的影响。结果表明，在复合材料中，纤维与基体间存在致密界面层，合金元素通过适当的化学反应可改善纤维与基体的结合；在凝固过程中，氧化铝纤维可作为锌合金共晶体非自发形核的衬底，纤维／基体界面上的硅在共晶体的共生生长过程中起了领先相作用，导致复合材料的共晶转变由铝硅共晶转变和锌铝共晶转变两者组成     

Cf/SiC复合材料的氧化及抗氧化技术研究进展

连续碳纤维增强碳化硅陶瓷基复合材料（C_f/SiC）因其具有高比强、高比模、耐磨损、良好热稳定性以及耐高温等突出性能,成为航空、航天、高性能武器装备等高尖端领域极具潜力的热结构材料。但高温氧化是其工程应用上的弱点,会造成C_f/SiC复合材料性能的下降,直接影响到材料的使用寿命和安全性。分析C_f/SiC复合材料的氧化影响因素,从界面相、基体和表面涂层3个方面综述C_f/SiC复合材料高温抗氧化技术的研究进展,结果表明:不同的温度区间内C_f/SiC复合材料的氧化行为不同,而界面改性、涂层抗氧化和基体改性相结合是实现材料抗氧化的关键。     

CeO2在镀镍碳纤维增强铝合金基复合材料中的作用

以稀土氧化物CeO2为添加剂,研究CeO2对镀镍碳纤维增强铝合金基复合材料碳纤维的分布、气孔率以及力学性能的影响,利用扫描电镜分析和拉伸力学性能检测等探讨了CeO2在镀镍碳纤维增强铝合金基复合材料中的行为。结果表明:CeO2能够使碳纤维均匀分布在复合材料中,而不产生分层及团聚;而且能够降低复合材料的气孔率,使轧制态复合材料的抗拉强度、屈服强度分别提高23%和26%。