Thermal stability of Al/Al11 Ce3 and Al/Al11 La3 /Al3 Ni eutectics obtained by Bridgman growth

Abstract

The effects of extended treatment at 500°C on microstructure and microhardness of Al/Al₁₁ Ce₃ and Al/Al₁₁ La₃ /Al₃ Ni eutectics in Al–12·1Ce and Al–11·3La–5·4Ni (wt-%) alloys Bridgman solidified at 0·1 mm s^-1 are reported. Coarsening of Al/Al₁₁ Ce₃ occurs more rapidly in some eutectic cells than others such that areas coarsening at a lower rate still form 10% of the microstructure even after 3024 h. It was found that Al/Al₁₁ La₃ /Al₃ Ni showed accelerated coarsening at eutectic cell boundaries but association between Al₁₁ La₃ and Al₃ Ni still remained within cells and at cell boundaries even after 3024 h. Associated decreases in hardness for Al/Al₁₁ Ce₃ were similar to fibrous Al/Al₆ Fe of similar initial spacing subjected to the same heat treatment. The 30% higher initial hardness of Al/Al₁₁ La₃ /Al₃ Ni largely persisted even after 3024 h at 500°C.     

Ultrasonic spot welding of Al/Mg/Al tri-layered clad sheets

Solid-state ultrasonic spot welding (USW) was used to join Al/Mg/Al tri-layered clad sheets, aiming at exploring weldability and identifying failure mode in relation to the welding energy. It was observed that the application of a low welding energy of 100 J was able to achieve the optimal welding condition during USW at a very short welding time of 0.1 s for the tri-layered clad sheets. The optimal lap shear failure load obtained was equivalent to that of the as-received Al/Mg/Al tri-layered clad sheets. With increasing welding energy, the lap shear failure load initially increased and then decreased after reaching a maximum value. At a welding energy of 25 J, failure occurred in the mode of interfacial failure along the center Al/Al weld interface due to insufficient bonding. At a welding energy of 50 J, 75 J and 100 J, failure was also characterized by the interfacial failure mode, but it occurred along the Al/Mg clad interface rather than the center Al/Al weld interface, suggesting stronger bonding of the Al/Al weld interface than that of the Al/Mg clad interface. The overall weld strength of the Al/Mg/Al tri-layered clad sheets was thus governed by the Al/Mg clad interface strength. At a welding energy of 125 J and 150 J, thinning of weld nugget and extensive deformation at the edge of welding tip caused failure at the edge of nugget region, leading to a lower lap shear failure load.     

Impact of graphite particle on milling of Al/15Al2O3 and Al/15Al2O3/5Gr composites

ABSTRACT

Hybrid Metal Matrix Composites (MMCs) are a new class of composites, formed by a combination of the metal matrix and more than one type of reinforcement having different properties. Machining of MMCs is a difficult task because of its heterogeneity and abrasive nature of reinforcement, which results in excessive tool wear and inferior surface finish. This paper investigates experimentally the addition of graphite (Gr) on cutting force, surface roughness and tool wear while milling Al/15Al₂O₃ and Al/15Al₂O₃/5Gr composites at different cutting conditions using tungsten carbide (WC) and polycrystalline diamond (PCD) insert. The result reveals that feed has a major contribution on cutting force and tool wear, whereas the machined surface roughness was found to be more sensitive to speed for both composite materials. The incorporation of graphite reduces the coefficient of friction between the tool–workpiece interfaces, thereby reducing the cutting force and tool wear for hybrid composites. The surface morphology and worn tool are analyzed using scanning electron microscope (SEM). The surface damage due to machining extends up to 200 µm for Al/15Al₂O₃/5Gr composites, which is beyond 250 µm for Al/15Al₂O₃ composites.     

Al and Ti/Al contacts on n-GaN

Al(60 nm) and Ti(40 nm)/Al(160 nm) metal layers have been deposited by thermal evaporation onto n-GaN epitaxial layers grown by metal organic chemical vapour deposition (MOCVD) on a c-plane sapphire substrate. The samples have been annealed at 300, 400, 700 or 900 °C for 10 min in vacuum. The microstructural and electrical properties of the contacts have been investigated by electron microscopy, X-ray diffraction and by current-voltage measurements. As-deposited Al and Ti/Al contacts were rectifying with Schottky barrier heights below 0.35 eV and 0.38 eV, respectively. After heat treatment at 300 °C and 400 °C both contacts exhibited linear current-voltage characteristics. After annealing at 700 °C Al contacts became rectifying with a barrier height of 0.42 eV, while Ti/Al contacts remained nearly linear at the same temperature. The electrical characteristics and XRD analysis indicated that the upper metal in Ti/Al contact diffused in the Ti layer already during deposition. Cross-sectional transmission electron microscopy revealed that in the case of Ti/Al contacts, the continuity of the Ti layers ceased when annealing above 700 °C. X-ray diffractions showed, that a Ti₂N interface phase formed in Ti/Al contacts at 700 and 900 °C, and an AlN interface phase developed in the same contact at 900 °C.     

Accelerated aging of Al/Ge and Al/Si thin film couples

The sheet resistances of Al/Ge and Al/Si thin film couples which had been heated in air or vacuum were measured. The annealing temperatures were kept below those at which any liquid phase is present. We find that at relatively low annealing temperatures the resistance of vacuum-annealed samples is higher than that of air- annealed samples. However, the observed peak resistance is higher for air than for vacuum annealing. Assuming a direct correlation between the sheet resistances and the diffusion profiles of the heated samples, we used the vacuum annealing data to obtain an activation energy E_a of 0.46 eV for diffusion in the Al/Ge structure and 0.70 eV for diffusion in the Al/Si couple. The results are discussed with reference to the electrical stability of silicon surface barrier detectors using an amorphous semiconductor/metal couple as the back contact.     

Interface analysis in Al and Al alloys/Ni/carbon composites

Nature of fibre/matrix interfaces existing in Al/C composites were investigated depending on the presence of a nickel interlayer deposited on carbon fibres and on the composition of the aluminium matrix. Auger and electron microprobe analyses were used. The role of the nickel layer on the chemical evolution of the system after a 96 h heat treatment at 600°C is discussed. The presence of this nickel layer limits the diffusion of carbon into aluminium, and thereby, eliminates the formation of a carbide interphase, Al₃C₄, which is known to lower the mechanical properties of Al/C composites. The mechanisms differ according to the composition of the matrix. In the case of pure aluminium, an Al-Ni intermetallic is formed after thermal annealing. It does not react with the carbon fibre and so inhibits the growth of Al₃C₄. In the case of the alloyed matrix (AS7G0.6), the dissolution of the Ni sacrificial layer, after annealing, does not lead to the same Al-Ni intermetallic but a thin nickel layer remain in contact with the carbon fibre avoiding formation and growth of Al₃C₄ carbide. This difference of behaviour is tentatively ascribed to the presence of silicon that segregates at the fibre/matrix interface.     

Growth and physicochemical characterization of CuAlTe2 films obtained by reaction, induced by annealing, between Cu/Al/Te/Al/Cu... Al/Cu/Al/Te layers sequentially deposited

CuAlTe₂ thin films have been synthesized by annealing under an argon flow a multilayer structure of thin Cu, Al and Te layers sequentially deposited by evaporation under vacuum. The films have been characterized by X-ray diffraction, microprobe analysis, photoelectron spectroscopy and Raman scattering. At the end of the process, the XRD spectra demonstrate that textured CuAlTe₂ films have been obtained with preferential orientation of the crystallites along the (112) direction. The Raman patterns are in good accordance with the reference. The XPS spectra show that the binding energies of the elements are in good agreement with bonds of CuAlTe₂. Even after a decrease of the oxygen contamination by improvement of the depositing process the oxygen present in the films is found to be about 12 at %. This revised version was published online in September 2006 with corrections to the Cover Date.     

应用于FED Al/Ag/Al导电复合薄膜的研究

利用Ag的高温抗氧化能力,采用磁控溅射沉积Al/Ag/Al导电复合薄膜,并在480℃下进行热处理。扫描电子显微镜（SEM）和能谱分析（EDS）研究表明磁控溅射的Al/Ag/Al导电复合薄膜表面平整,热处理后表面Al膜生成致密的氧化层。溅射沉积和热处理过程中Ag和Al原子的相互扩散,最后形成富Ag的Ag-Al合金和Ag3Al化合物。Al/Ag/Al导电复合薄膜比Ag/Al复合薄膜的电阻率增大了一个数量级,导电复合薄膜热处理后导电性能更优,电阻率约为19.4×10-6Ω.cm。     

Development of Some Fundamental Research of SiC_W/Al Composites in HIT PartⅠ Microstructure and SiC/Al Interface of SiC_W/Al Composites

The microstructure of SiC whisker reinforced aluminium alloy (SiC_w/Al) composite is reviewed,andthe SiC-Al interface in SiC_w/Al composite is especially discussed,The main contents aremorphology of the aluminium matrix in SiC_w/Al composite;microstructures and defects of SiCwhiskers in SiC_w/Al composite and bonding mechanisms of the SiC-Al interface in SiC_w/Al com-posite.     

Mechanical properties of an Al/Mg/Al trilaminated composite fabricated by hot rolling

An Al/Mg/Al composite with a trilaminate structure was fabricated by hot rolling and its mechanical properties at quasi-static rates of strain were investigated. The bonding strength of the trilaminated composite is about 40 MPa, mainly attributing to the mechanical bond at the interfaces. The first layer failure strength of the laminated composite increases from 305 to 372 MPa when the relative thickness of aluminium alloy layer increases from 0.235 to 0.265. The tensile and bending properties of the laminates were calculated based on the Classical Laminate Theory (CLT). The calculations of first layer failure strength based on CLT agree with the experimental data in the error of 2.9–18%. Thus, the first layer failure strength of the Al/Mg/Al trilaminated composite fabricated by hot rolling can be calculated by CLT with the maximum stress criteria. The calculations also show that the tensile modulus, the tensile rigidity, the specific tensile rigidity and the first layer failure strength of the laminated composite increase almost linearly with the relative thickness of the aluminium alloy component. The bending rigidity of the laminated composite increases with the relative thickness of aluminium alloy, and approximates to a fixed value after the relative thickness over 0.3. The specific bending rigidity increases with the relative thickness of aluminium alloy and reaches a maximum value when the relative thickness is 0.25.     

AlNP/Al和TiB2P/Al复合材料摩擦磨损性能研究

研究了油润滑条件下两种不同铝基复合材料及其基体合金的摩擦磨损性能,分析了增强体对材料摩擦磨损性能的影响以及相应的磨损机理.结果表明:油润滑条件下,随着摩擦时间的延长,AlNP/Al复合材料的摩擦系数由小变大趋于稳定;而TiB2P/LY12复合材料的摩擦系数却是由大变小趋于稳定,这主要与其摩擦过程中形成凹坑产生润滑油膜有关.由于增强体强度的增加,50%(体积分数,下同)TiB2P/Al复合材料的摩擦系数低于50%AlNP/Al复合材料,且耐磨性优于50%AlNP/LY12复合材料.增强相的加入显著提高了材料的耐磨性,使得复合材料的抗粘着能力明显优于基体合金.     

Bonding strength of Al/Mg/Al alloy tri-metallic laminates fabricated by hot rolling

One of major drawbacks of magnesium alloy is its low corrosion resistance, which can be improved by using an aluminized coating. In this paper, 7075 Al/Mg-12Gd-3Y-0·5Zr/7075 Al laminated composites were produced by a hot roll bonding method. The rolling temperature was determined based on the flow stresses of Mg-12Gd-3Y-0·5Zr magnesium alloy and 7075 Al alloy at elevated temperature. The bonding strength of the laminate composites and their mechanism were studied. The effects of the reduction ratio (single pass), the rolling temperature, and the subsequent annealing on the bonding strength were also investigated. It was observed that the bonding strength increased rapidly with the reduction ratio and slightly with the rolling temperature. The bonding strength increases with the annealing time until the annealing time reaches 2 h and then decreases. The mechanical bond plays a major role in the bonding strength.     

Fabrication of Al/Al2O3 composites and FGM

Al/Al2O3 composites of different ratios were hot-press sintered at 575 similar to 640℃ under a pressure of 30 MPa for 2 h in a vacuum furnace. It was found that the relative density of the Al/Al2O3 composites could be increased evidently with the rise of sinter temperature. No reaction occurred between Al and Al2O3 at the sinter temperatures. Under 640℃-30 MPa-2 h experimental condition, Al/Al2O3 system FGM was successfully fabricated, and its density range changed quasi-continuously from 2.887x10(3) kg/m(3) to 3.1909x10(3) kg/m3 within the middle 1.0 mm thickness range.     

SiCp/Al-Si复合材料中SiC/Al界面处亚晶铝带的研究

通过利用ＴＥＭ研究ＳｉＣｐ／Ａｌ－Ｓｉ昨合材料发现,ＳｉＣ／Ａｌ界面结合紧密,在靠近ＳｉＣ界面的Ａｌａ基体中,有一层厚度小于１μｍ的“亚晶铝带”,它紧靠ＳｉＣ表面形成,与远离ＳｉＣ的Ａｌ基体有几度的位向差,这种“亚晶铝带”在ＳｉＣ／Ａｌ界面上普遍存在,其内有大量位错。     

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.     

A study of the failure mechanisms in Al/Al2O3 and Al/SiC composites through quantitative microscopy

The failure mechanisms in tension and fatigue of three Al alloys reinforced with ceramic particulates were studied by means of optical and scanning electron microscopy. Damage was concentrated in the reinforcements, which failed in a brittle fashion during deformation, leading to the specimen fracture when a critical fraction of broken particulates was reached in a given section of the specimen. This critical fraction was measured on polished longitudinal sections of broken specimens for each composite, temper, and loading condition, and was mainly dependent on the matrix alloy. It was also found that the reinforcement fracture probability was controlled by the particulate size and aspect ratio: large and elongated particulates oriented in the loading direction were more prone to fail than small, equiaxed ones. Finally, a significant fraction of the reinforcements in the cast materials was broken prior to testing. They were shattered during extrusion rather than fractured, and associated with clusters of particulates formed during solidification.     

SiC_p/Al-Si复合材料中SiC/Al界面处亚晶铝带的研究

通过利用 TEM研究 Si Cp/ Al- Si复合材料发现 :Si C/ Al界面结合紧密 ,在靠近 Si C界面的 Al基体中 ,有一层厚度小于 1μm的“亚晶铝带”,它紧靠 Si C表面形成 ,与远离 Si C的 Al基体有几度的位向差 ;这种“亚晶铝带”在 Si C/ Al界面上普遍存在 ,其内有大量位错。     

Investigation of annealing treatment on the interfacial properties of explosive-welded Al/Cu/Al multilayer

In this study, an Al/Cu/Al multilayer sheet was fabricated by explosive welding process and the effects of annealing temperature on the interfacial properties of explosively bonded Al/Cu bimetal have been investigated. For this purpose, hardness changes along the thickness of the samples have been measured, and the thickness and type of intermetallic compounds formed at the joining interface have been explored by means of optical microscopy (OM), scanning electron microscopy (SEM) and also energy dispersive spectroscopy (EDS). The obtained results indicate that, with the increase of the annealing temperature, the thickness of intermetallic compounds has increased and the amount of hardness along the thickness of the joining interface has diminished. In the annealed sample at 400 °C for 30 min, it was observed that intermetallic layers have formed at the interface of Al/Cu bimetals. These layers consist of the intermetallic compounds AlCu₃, Al₂Cu and AlCu, and their thickness gets to about 5 μm at some points. The examinations performed by the SEM, following the Vickers micro-hardness test, indicated the existence of a number of microcracks at the top and bottom interface of the sample annealed at 400 °C. This shows the formation of brittle intermetallic compounds at the joining interface, and also indicates the low ductility of these compounds.     

铝/氮化铝电子陶瓷基板的制备及性能的研究

在675～750℃、氮气气氛下,使用石墨模具压铸的方法将金属纯Al敷接在AlN电子陶瓷基板上,随后利用力学拉伸试验机测试了Al和AlN的结合强度,其界面抗拉强度>15.94MPa,然后使用金相显微镜、SEM等微观分析仪器研究其界面的微观结构,发现在Al/AlN界面没有任何新物质生成,金属铝晶粒直接在AlN陶瓷表面结晶长大.