电磁搅拌自生表面复合材料的组织与性能

根据电磁搅拌时定向凝固形成分离共晶的原理，制备了内表面的Ａｌ３Ｎｉ金属间合物、上表面为少量Ａｌ３Ｎｉ与亚共晶组织，而基体为亚共晶组织的自生表面复合材料管状试样，分析了复合层的组织形貌、结合强度、耐腐蚀性能，讨论了分离偏聚物的形成机理。     

仿生设计的Al2O3／纤维增强树脂层状复合材料

把贝壳珍珠层的韧化机制和结构机理应用于陶瓷基复合材料的仿生设计中，制备出Ａｌ２Ｏ３／环氧树脂及Ａｌ２Ｏ３／芳纶纤维增强环氧树脂叠层仿珍珠层复合材料。三点弯曲试验表明，与单相Ａｌ２Ｏ３相比，Ａｌ２Ｏ３／环氧树复合材料的断裂功提高２５％，而Ａｌ２Ｏ３／芳纶纤维增强环氧树脂的断裂功提高８０倍Ａｌ２Ｏ３／环氧树脂复合材料的断裂形貌与珍珠层相似，裂缝曲折扩展；而Ａｌ２Ｏ３／芳纶纤维增强环氧树脂复合材料除具有     

涂层对TI纤维与Ti／TiAl复合材料性能影响的研究

研究了涂层对Ｔｉ纤维及Ｔｉ纤维强化γ－ＴｉＡｌ金属间化合物基复合材料性能的影响。研究结果表明，运用物理气相沉积法（ＰＶＤ）在Ｔｉ纤维表面涂覆Ｙ２Ｏ３制得Ｔｉ／ＴｉＡｌ复合材料，不仅改善了γ－ＴｉＡｌ及其复合材料的力学性能，而且使纤维与基体间的界面反应层厚度减小，涂覆Ｙ２Ｏ３较Ａｌ２Ｏ３有较高的稳定性，这对深入研究涂层对复合材料合成及性能的影响有着重要的意义。     

颗粒包覆对Al_2O_3/青铜复合材料界面结合模式及性能的影响

采用化学镀的方法在Ａｌ２Ｏ３颗粒表面包覆镍或铜，研究了颗粒包覆对Ａｌ２Ｏ３／青铜复合材料界面结合模式及性能的影响。ＸＲＤ结果表明，包镍后，复合材料的界面有化学反应发生，生成Ｎｉ２Ａｌ３相，复合材料的界面结合强度因此而增加；包铜后，复合材料的界面无化学反应发生，但因机械锁合作用加强，也使复合材料的界面结合加强。颗粒包覆使复合材料的界面结合模式改善。研究表明，Ａｌ２Ｏ３颗粒表面包覆镍或铜对复合材料的致密度和力学性能（硬度、拉伸强度和耐磨性）有较大的影响     

Al2O3基板直接敷铜法的敷接机理研究

本文采用直接敷铜工艺,１０７０℃流动氮气氛下保温３ｈ制得当了强度达１１．５ｋｇ／ｃｍ＾２的直接铜ＡＩ２Ｏ３基板。介面产物ＣｕＡＩＯ２的形成是获得较高结合强度的关键,敷接温度下,在界面上产生了能很好润湿ＡＩ２Ｏ３表面的Ｃｕ〖Ｏ〗共晶液体,并反应生连续的ＣｕＡｌＯ２层降温时,共晶液体从Ｃｕ侧开始固化并淀析出ＣｕＯ２颗９粒,当固化前沿与ＣｕＡｌＯ２层相遇时,液相参与的界面反应停止,冷却至室温,即可获得Ｃ     

直接敷铜Al2O3陶瓷基板的界面产物研究

直接敷铜Ａｌ２Ｏ３基板已被广泛应用于大功率场合。本文通过Ｃｕ箔表面预氧化生成Ｃｕ２Ｏ的方法引入氧,１０７０℃在Ｃｕ箔和Ａｌ２Ｏ３基板界面上所产生的Ｃｕ－Ｃｕ２Ｏ共晶液体促进了二者的牢固结合,流动氮气氛下保温１ｈ,观察到了明显的界面产物层。ＳＥＭ和ＸＲＤ的分析表明,界面产物相为ＣｕＡｌＯ２。     

Al2O3／铜合金复合材料的磨损特性研究

研究了冷压烧结Ａｌ２Ｏ３／铜合金复合材料在摩擦条件下的磨损特性。采用化学镀的方法在一些Ａｌ２Ｏ３颗粒表面包覆铜镍，获得了具有不同界面结合强度的Ａｌ２Ｏ３／铜合金复合材料，进而研究了界面结合强度对该复合材料耐磨性的影响。本文还探讨了颗粒大小及体积分数对其耐磨性的影响。     

颗粒包覆对Al2O3／青铜复合材料界面结构模式及性能的影响

采用化学镀的方法Ａｌ２Ｏ３颗粒表面包覆镍或铜，研究了颗粒包覆对Ａｌ２Ｏ３／青铜复合材料界面结合模式及性能的影响。ＸＲＤ结果表明，包镍后，复合材料的界面有化学反应，生成Ｎｉ２Ａｌ３相，复合材料的界面结合强度因此而增加；包铜后，复合材料的界面无化学反应发生，但因机械锁合作用加强，也使复合材料的界面结构加强。     

Al—Al2O3—玻璃复合材料的制备与性能

采用无压烧结工艺，制备了Ａｌ－Ａｌ２Ｏ３－玻璃复合材料。研究了Ａｌ－玻璃，Ａｌ２Ｏ３－玻璃的润湿性。发现玻璃能促进Ａｌ与Ａｌ２Ｏ３结合；Ａｌ－Ａｌ２ｏ３－玻璃复合材料具有良好的强度和耐磨损性能。     

反应自生Al_3Ni－Al_2O_3－Al复合材料

通过热力学计算，选择Ｎｉ_２Ｏ_３粉末作原材料，采用反应挤压铸造方法实现了Ａｌ与Ｎｉ２Ｏ３直接压铸反应合成Ａｌ３Ｎｉ－Ａｌ２Ｏ３－Ａｌ原位复合材料。研究了压铸工艺参数和预制块中纯Ａｌ粉的含量对反应合成复合材料过程的影响，并对反应机理做了较深入的分析。结果表明，Ｎｉ２Ｏ３与Ａｌ的反应是为高放热反应，反应是爆发式的，通过调整预制块中Ａｌ粉的体积分数控制了反应的剧烈程度，并能获得不同组成和基体含量的复合材料。对反应机理的分析表明，在Ａｌ足量的情况下，Ｎｉ２Ｏ３与Ａｌ反应合成复合材料分为两个过程，一是反应过程，即Ｎｉ２Ｏ３＋Ａｌ→Ａｌ２Ｏ３＋［Ｎｉ］；二是凝固过程，即反应后多余的Ａｌ与反应生成的［Ｎｉ］在随后冷却中的凝固过程，最终形成Ａｌ３Ｎｉ＋α－Ａｌ２Ｏ３＋Ａｌ复合材料。     

激光双面区熔Al2O3/Y3Al5O12共晶自生复合陶瓷的制备与表征

采用激光区熔凝固技术制备大尺寸Al2O3/Y3Al5O12(YAG)共晶自生复合陶瓷,考察双面区熔条件下大尺寸氧化物共晶陶瓷的熔化及凝固成形规律,采用扫描电镜、能谱和X射线衍射对其凝固组织特征进行了表征和分析.研究结果表明:在优化的凝固工艺下,激光双面区熔增加了熔凝层的厚度,获得了熔凝层厚度8.2 mm,长度65.0 mm,致密度达98.5%±1%的Al2O3/YAG共晶陶瓷;共晶熔凝层厚度随激光扫描速率的减小而增加,随激光功率的增大而增大,并且致密度随着激光功率的增大呈现先增大后减小的趋势;双面区熔后的Al2O3/YAG共晶陶瓷微观组织由均一分布、相互交织的Al2O3和YAG共晶相组成,共晶层片间距较小(1.0~3.5μm),且与凝固速度满足Jackson-Hunt公式;共晶间距随扫描速率的增大逐渐减小;双面区熔界面处共晶组织生长具有连续性,界面结合良好;共晶陶瓷的Vickers硬度为(18.6±1.0)GPa.     

The Creep and Thermal Stability Characteristics of a Unidirectionally Solidified Al2O3/YAG Eutectic Composite

Compressive creep characteristics at 1773, 1873, and 1973 K, oxidation resistance over 1000 h at a temperature of 1973 K in ambient air, and the thermal stability characteristics at 1973 K in ambient air of a unidirectionally solidified Al2O3/YAG eutectic composite were evaluated. At a test temperature of 1873 K and a strain rate of 10–4/s, the compressive creep strength of a eutectic composite manufactured by the unidirectional solidification method is approximately 13 times higher than that of a sintered composite with the same chemical composition. The insite eutectic composite also showed greater thermal stability, with no change in mass after an exposure of 1000 hours at 1973 K in ambient air. The superior high-temperature characteristics are closely related to such factors as (1) the in-situ eutectic composite having a microstructure, in which single crystal Al2O3 and single crystal YAG are three-dimensionally and continuously connected and finely entangled without grain boundaries and (2) no amorphous phase is formed at the interface between the Al2O3 and the YAG phases.     

基于高温熔凝法Al_2O_3/ZrO_2/YAG共晶陶瓷显微组织演变规律

作为超高温结构材料,共晶氧化物陶瓷的力学性能和显微组织密切相关。采用高温熔凝法制备Al_2O_3/ZrO_2/YAG共晶陶瓷体,研究熔体温度和结晶种子对凝固组织影响规律,运用经典形核机制和Jackson-Hunt共晶生长模型探讨了凝固组织的演变机理。研究表明,随着熔体温度升高(1750~2000℃),凝固体物相组成从α-Al_2O_3,c-ZrO_2和YAG转变为α-Al_2O_3,c-ZrO_2和亚稳相YAP。凝固组织依次经历:非共晶Al_2O_3/ZrO_2/YAG、不规则共晶Al_2O_3/ZrO_2/YAG、纳米纤维状共晶Al_2O_3/ZrO_2/YAG和复杂粗大的亚稳复合陶瓷Al_2O_3/ZrO_2/YAP。分析表明,凝固组织的演变源于异质晶核点不断钝化导致形核过冷度和凝固路径改变,所以合理选择熔体温度和结晶种子是共晶组织调控的关键。     

熔渗温度对Si/Al复合材料组织及性能的影响

采用无压熔渗法制备Si/Al复合材料,研究了熔渗温度对所制备Si/Al复合材料Si相形貌的影响,对Si相间基体合金的凝固组织进行了分析,测试了Si/Al复合材料热膨胀系数、热导率及抗弯强度。结果表明,在相同熔渗时间下,随着熔渗温度升高,所制备Si/Al复合材料中Si相从颗粒状到形成网络状。Si相间的Al-Si基体合金中不再是典型的初生相和共晶组织,而是出现了类似离异共晶的结晶现象,即初晶Si和共晶Si是在原存的Si相上结晶长大。XRD分析显示在所制备复合材料中只有Si相和Al相。随着熔渗温度升高复合材料热膨胀系数、热导率以及抗弯强度均出现下降。     

Phase growth patterns for Al_2O_3/GdAlO_3 eutectics over wide ranges of compositions and solidification rates

Phase selection and growth characteristics of directionally solidified Al₂O₃/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled zone.Through the obse rvation of the quenched solid-liquid interface,the competitive growth of primary faceted Al₂O₃phase,prima ry non-faceted GAP phase and Al₂O₃/GAP eutectic with diffe rent morphologies is detected.Microstructure transitions from wholly eutectic to primary Al₂O₃(GAP)dendrite plus eutectic and then to wholly eutectic are found in Al₂O₃-2 O mol%Gd₂O₃hypoeutectic(Al₂O₃-26 mol%Gd₂O₃hypereutectic)ceramics with the increase of solidification rate.The dendrite growth of faceted Al₂O₃and non-faceted GAP phases are well predicted by KGT model,which have introduced appro p riate dimensionless supersaturationΩto characterize the anisotropic growth of dendrites.Based on the maximum interface temperature criterion,the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al₂O₃/GAP eutectic ceramics is in good agreement with the experimental results.Besides,the influence of microstructure with these different morphologies on the flexural strength of Al₂O₃/GAP eutectic ceramics is studied.     

氧化物/氧化物自生复合陶瓷的生长机理与微观结构的研究进展

基于国外定向凝固氧化物／氧化物自生复合陶瓷的晶体生长动力学行为研究,阐述了其动力学机制,分析动力学因素对微观结构的影响,探讨了晶体生长动力学行为与微观结构之间的关系;同时结合以重力、超重力下燃烧合成、快速凝固技术所制备的新型高强韧Al2O3／YSZ自生复合陶瓷,探讨了自生复合陶瓷在快速凝固条件下的晶体生长动力学行为。结合定向凝固与快速凝固两种晶体生长机制,得出过冷度、凝固界面前沿的温度梯度是影响晶体生长方式的重要因素,且受二者控制的晶体生长速率则决定材料的微观结构与形态。     

High-temperature strength and thermal stability of a unidirectionally solidified Al2O3/YAG eutectic composite

A unidirectional solidification method was investigated to manufacture Al2O3/YAG eutectic composites with high-temperature resistance that would make them usable at very high temperatures. We were successful in manufacturing a single-crystal Al2O3/single-crystal YAG eutectic composite with a dimension of 40 mm in diameter and 70 mm in length containing no colonies or pores. This composite also displayed excellent high-temperature strength characteristics. The flexural strength was in the range 350400 MPa from room temperature up to 2073 K (just below its melting point of about 2100 K) with no apparent temperature dependence. During tensile tests above 1923 K, the eutectic composite showed evidence of plastic deformation occurring by dislocation motion, and a yield phenomenon similar to many metals was observed. In addition, the microstructure of the composite was extremely stable: after 1000 h of heat treatment at 1973 K in an air atmosphere there was no growth. The above superior high-temperature characteristics are caused by such factors as the eutectic composite having a single-crystal Al2O3/single-crystal YAG structure, the formation of a compatible interface with no amorphous phase and thermal stability, and the combined effect of a YAG phase with superior high-temperature characteristics. © 1998 Chapman & Hall     

Phase formation sequence of high-temperature Zn–4Al–3Mg solder

Eutectic Zn–4Al–3Mg alloy is one of the potential candidates as high-temperature lead-free solders. The phase formation sequence of eutectic Zn–4Al–3Mg alloy under different solidification conditions were investigated in this work. The results show that the microstructure is strongly affected by the difference of solidification conditions. The microstructure of the furnace-cooled eutectic Zn–4Al–3Mg alloy with a lamellar eutectic structure is composed of (α-Al + η-Zn)_eutectoid, Mg₂Zn₁₁ and η-Zn three phases, while the metastable MgZn₂ phase acts as primary phase during the rapid solidification of the air-cooled and water-cooled alloy specimens, and it evolves into the Mg₂Zn₁₁ phase later through a peritectic reaction ( $ {\text{MgZn}}_{ 2} + {\text{L}} \to {\text{Mg}}_{ 2} {\text{Zn}}_{ 1 1} $ ). Actually, the final solidified microstructure exhibited a feature of the primary MgZn₂ phase surrounded by the Mg₂Zn₁₁ phase due to the incompleteness of the peritectic transformation. Compared with the air-cooled eutectic Zn–4Al–3Mg alloy specimen, the water-cooled eutectic Zn–4Al–3Mg alloy microstructure displayed a dendritic structure resulting from more rapid cooling rate. Furthermore, the difference between the microhardness in the eutectic Zn–4Al–3Mg alloy under various solidification conditions was mainly attributed to the high-hardness phases concluding Mg₂Zn₁₁ and MgZn₂.