Microstructure and Strength of Al2O3/Al2O3 Joints Bonded with ZnO-Al2O3-B2O3-SiO2 Glass-Ceramic

ZnO-Al2O3-B2O3-SiO2 （ZABS） glass powder was used as interlayer to join alumina ceramics. The effect of joining temperature on the microstructure and strength of joints was investigated. The results showed that the ZABS glass can react with alumina substrate to form a layer of ZnAl2O4 at Al2O3/glass interface. Bending test exhibited that low joining temperature （1150℃） led to low joint strength due to the formation of pores in the interlayer, originated by high viscosity of the glass. High joining temperature （1250 ℃） also resulted in low joint strength, because of large CTE （coefficient of thermal expansion） mismatch between amorphous interlayer and alumina substrate. Therefore, only when the joining temperature was appropriate （1200℃）, defect-free interface and high joint strength can be obtained. The optimum joint strength reached 285 MPa, which was the same as the base material strength.     

Microstructure and mechanical properties of Al2O3-Cr2O3-ZrO2 composites

Al₂O₃ is a popular ceramic and has been used widely in many applications and studied in many aspects. On the other hand, zirconia-toughened alumina (ZTA) is a desirable material for engineering ceramics because of its high hardness, high wear resistance and high toughness. In the present research, Al₂O₃-Cr₂O₃-ZrO₂ composites were produced by hot-pressing in order to harden the Al₂O₃ matrix in ZTA. Its microstructure and mechanical properties were studied by SEM, ESCA, XRD, Vickers hardness and bending strength test. It was found that addition of ZrO₂ inhibited the grain growth of Al₂O₃-Cr₂O₃ and the grain growth of ZrO₂ proceeded with increasing amounts of ZrO₂ in the Al₂O₃-Cr₂O₃-Zr₂ composite. The formation of solid solution Al₂O₃-Cr₂O₃ was also confirmed by XRD, and monoclinic ZrO₂ increased on addition of Cr₂O₃. Maximum hardness was at Al₂O₃-10wt% Cr₂O₃ with 10 vol% ZrO₂ and a stress-induced transformation was confirmed on the fracture surface of the specimen after the bending test.     

Microstructure of the Al2O3/Al2O3 Joint Brazed with Cu-Zn-Ti Filler Metal

Microstructure and interface reactions of Al2O3 joints brazed by Cu-Zn-Ti alloy were studied by using SEM, EDS and XRD. The effects of brazing temperature and Ti content on interfacial reactions and microstructure were investigated, and the action of adding Zn into brazing alloy was also studied. TiO, Ti3Al and CuTi were formed at the interface of ceramics and the filler metal, while CuTi, Cu3Ti and alpha -Cu were found in the brazing. The thickness of the reaction layer increased with increasing of brazing temperature, under the same brazing process, the thickness increased with the Ti content.     

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。     

Effect of Microstructure on the Mirror-Like Surface Quality of FCC and BCC Metals

The microstructure of machined metals changes near the tool-affected zone. This paper presents some new results concerning mirror-like surface cutting of aluminum, copper and tungsten. The microstructure of aluminum and copper represents polycrystalline mild metals with face centered cubic (FCC) crystal structure. Examination of a mirror-like surface by optical microscopy, scanning electron microscopy (SEM), electron backscattered diffraction and atomic force microscopy revealed that grain boundaries and twin boundaries were present, which separates two domains for different crystal orientation. The Young's modulus that depends on orientation can change considerably on these boundaries and, consequently, the value of elastic deformation of the layer under the machined surface. This effect modified the roughness. Ultraprecision machining of tungsten, which is a body centered cubic (BCC) metal, proved useless using diamond and/or boron-nitride tools. Since tungsten is a very brittle metal at room temperature, its ductile to brittle transition temperature is much higher. Therefore, in contrast to normal cutting, the material that is incapable of plastic deformation will cause brittle fracture of the chip and bad surface quality.     

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。     

Fe/Al2O3陶瓷梯度涂层的微观结构与性能

采用喷涂法和溶胶-凝胶法相结合的工艺,以FeAlNi混合粉体为过渡层材料在钢基体表面制备了Fe/Al2O3梯度涂层,并对其微观结构与性能进行分析.结果表明:当烧结温度为1220℃时,梯度涂层与钢基体的界面结合强度达到25.3MPa,涂层主要由α-Al2O3,AlFeO3和NiFe2O4等物相组成.Fe/Al2O3梯度涂层与钢基体的结合主要通过吸附与扩散化合两种方式共同起作用.涂层中没有明显的孔洞和平整的界面,且有树枝状组织生成,涂层与钢基体实现良好的结合,这表明涂层成分的梯度化设计能够有效地缓和界面处的应力集中,改善涂层与钢基体的界面结合状态,提高涂层材料的使用性能.     

Microstructure and mechanical properties of TiCAl2O3 coatings

The microstructure, phase distribution and hardness of TiCAl₂O₃ two-phase coatings prepared by high rate physical vapor deposition have been studied as functions of deposition temperature and feed composition. Structural analysis using X-ray diffraction shows that the coatings consist of α-Al₂O₃ and TiC (cubic) phases. Transmission and scanning electron microscopy have been used to study the distribution of the two phases in the coatings. The growth morphology is fine grained at low temperatures and becomes a dense columnar type at high temperatures of deposition. The microhardness shows a corresponding increase with deposition temperature. Details of the relationship between the microstructure, composition and hardness of the coatings are reported.     

Plasma spraying of Al2O3 and Al2O3Y2O3

A microstructural study has been carried out of plasma-sprayed Al₂O₃ and mixed and sintered Al₂O₃Y₂O₃. In order to ascertain the degree of metastability achieved by plasma spraying, these results are compared with a similar experiment utilizing a CO₂ laser for melting and the hammer-and-anvil technique for quenching of the same materials. X-ray diffraction methods were used to determine the obtained phases and crystal structures. In addition, transmission electron microscopy was used to confirm the phases present and to study their morpology. The porosity was studied with both mercury intrusion porosimetry and small angle neutron scattering. The addition of Y₂O₃ is shown to decrease the porosity from 15% to 7.5%. Adhesion is likewise related to the addition of Y₂O₃ and it is seen that adhesion of the mixture is measurably improved over that of pure Al₂O₃. The implication of these results is discussed.     

Al2O3/BaZrO3双陶瓷界面微观组织演化及机理

以Al₂O₃为背层(硅溶胶为粘结剂), 电熔BaZrO₃作为面层材料(钇溶胶为粘结剂), 1550℃烧结后制成50 mm×25 mm×5 mm的Al₂O₃/BaZrO₃双陶瓷试样。通过光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和EDS等手段观察了BaZrO₃层和Al₂O₃/BaZrO₃界面的显微结构, 研究了BaZrO₃与Al₂O₃的界面反应。结果表明, 面层由BaZrO₃基体和分布其上的大小10 μm左右的Y稳定的ZrO₂晶粒组成; Al₂O₃/BaZrO₃界面发生反应形成厚约300 μm的过渡层, 界面反应生成物有BaOAl₂O₃、ZrO₂和BaO·Al₂O₃·2SiO₂。界面从单纯的BaZrO₃/Al₂O₃双陶瓷结构演变为BaZrO₃、ZrO₂、BaO·Al₂O₃、BaO·Al₂O₃·2SiO₂和Al₂O₃等多种物相组成的复杂结构。反应过程中Al元素基本不迁移扩散, BaZrO₃中Ba元素向Al₂O₃所在的位置扩散形成BaO·Al₂O₃, 残留物形成一层条状ZrO₂, 而BaO·Al₂O₃·2SiO₂围绕着EC95(Al₂O₃+5%SiO₂)粉体颗粒周围生成。     

Microstructure and mechanical properties of glass-infiltrated Al2O3/ZrO2 nanocomposites

This work was to investigate the effect of zirconia nanoparticles content on microstructure and mechanical properties of glass-infiltrated alumina/zirconia composites (AZGs). A series of slip-cast zirconia-toughened alumina (ZTA) compacts containing 10, 20, 30 wt% nano-zirconia, respectively, were partially sintered at 1,250°C for 2 h, then infiltrated with lanthanum borosilicate glass of lower thermal expansion at 1,180°C for 4 h. A porosity ranging from 21 to 25% mainly with submicron pore size was demonstrated in the partially-sintered ZTAs. Homogeneous distribution and micro-crystallization of intergranular glass phase was showed in the AZGs. The mechanical strength and fracture toughness of AZGs increased with zirconia content, the maximum (633.5 ± 41.7, 6.7 ± 0.6 MPa m^0.5) were obtained in 30 wt% zirconia group, which were significantly higher than those in 10 wt% zirconia group (P < 0.05). The improved mechanical performance of AZGs containing 30 wt% zirconia was attributed to their larger zirconia content as well as thinner intergranular glass film.     

等离子喷涂纳米Al2O3/TiO2复合陶瓷涂层的显微组织与性能

采用液相喷雾造粒方法将纳米级Al2O3/TiO2团聚成微米级颗粒,制备了适用于等离子喷涂的陶瓷复合粉体,并利用等离子喷涂技术成功的制备出了含有纳米结构的陶瓷涂层.利用X射线衍射、扫描电镜、透射电镜和显微硬度计等设备对涂层的微观结构和性能做了初步的检测.结果表明,涂层中含有适当比例的未熔或半熔的纳米颗粒,涂层的硬度、韧性和耐磨性等性能与普通涂层相比都有了较大提高.     

Microstructure of Al2O3-ZrO2 nanocomposites prepared by combustion process

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Deformation Behaviour and Microstructure of a 20% Al2O3 Reinforced 6061 Al Composite

Deformation and microstructural behaviours of a 20% (volumepercent) particle reinforced 6061 Al matrix composite have been studied bytorsion from 25 to 540°C with strain rates of 0.1, 1 and5 s^-1. The logarithmic stress versus reciprocal temperaturerelationship exhibits two slopes indicating different deformationmechanisms. The 20% Al₂O₃/6061 Alcomposite shows a greater hardening behaviour than those of the 10% Al₂O₃/6061 Al composite and of the monolithic alloy. Above 250°C, TEM investigations reveal muchsmaller subgrain size and higher volume of non-cellular substructures, aswell as dynamic recrystallization nuclei in the 20% Al₂O₃/6061 Al composite in comparison to those of the10% Al₂O₃/6061 Al composite and matrixalloy the same test condition. The torsion fracture surface was studied andcompared to the three point bending failure specimens.     

Ni-纳米Al2O3复合镀层结构和耐磨性能研究

采用复合电镀技术通过向电镀溶液中加入平均粒度为90nm的Al2O3粉,在Ni基材上制备了Ni-纳米Al2O3复合镀层,应用扫描电镜(SEM)、X射线衍射(EDAX)及透射电镜(TEM)等手段对复合镀层的表面形貌和结构进行了表征,并通过试验考察了镀层的磨损性能.结果表明,纳米Al2O3颗粒均匀分布在Ni纳米晶中;纳米Al2O3颗粒的加入不仅细化了基体Ni的晶粒尺寸,而且还具有弥散强化作用,从而提高了Ni-Al2O3纳米复合镀层的硬度和耐磨性能.     

Surface,grain-boundary and interfacial energies in Al2O3 and Al2O3-Sn,Al2O3-Co systems

Using the multiphase equilibrium method for the measurement of contact angles, the surface and grain-boundary energies of polycrystalline Al₂O₃ in the temperature range of 1473 to 1923 K were determined. Linear temperature functions were obtained by extrapolation for both quantities between absolute zero and the melting point of Al₂O₃. The temperature dependence of the surface and grain boundary energies can be expressed as $$\gamma _{{\rm A}l_2 O_3 } = 2.559 - 0.784 \times 10^{ - 3} T(J m^{ - 2} )$$ and $$\gamma _{{\rm A}l_2 O_3 - Al_2 O_3 = } 1.913 - 0.611 \times 10^{ - 3} T(J m^{ - 2} )$$ respectively. The interfacial energies of Al₂O₃ in contact with the molten metals tin and cobalt revealed a linear dependence on temperature.     

纳米Al2O3强化铜基ODS 20的组织与性能

研究了铜基ODS的组织与性能。结果表明,采用内氧化方法生产的铜基ODS 20,在纯铜基体上原位生成弥散、10nm左右的-γAl2O3微粒。该材料导电率约90%IACS,比纯铜导电率约降低10%。加工状态的室温强度可达到610MPa,在1173K保温1.5h,硬度达到室温硬度的86%,表明软化温度高于1173 K。经1273K+1.5h退火,晶粒平均直径小于1μm,Al2O3微粒不发生熔解、聚集、长大等现象。