Effects of copper and Al2O3 particles on characteristics of Cu–Al2O3 composites

High-energy milling was used for production of Cu–Al₂O₃ composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al₂O₃ powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al₂O₃ particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al₂O₃ particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al₂O₃ particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al₂O₃ composites.     

The effect of solution temperature on the microstructure and tensile properties of Al–15%Mg2Si composite

The effect of different solution temperatures has been investigated on the microstructure and tensile properties of in situ Al–Mg₂Si composite specimens were subjected to solutionizing at different temperatures of 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C and 580 °C for holding time of 4 h followed by quenching. The microstructural studies of the polished and etched samples by scanning electron microscopy (SEM) in the solution condition indicated that the increase in the temperature changes the morphology of both the primary and secondary Mg₂Si phases. Solutionizing led to the dissolution of the Mg₂Si particles and changed their morphology. Tensile test results indicated that ultimate tensile strength (UTS) gradually decreased upon solutionizing from 300 to 550 °C while further increase in the temperature followed by a sharp decrease in UTS up to 580 °C solutionizing temperature. It was found that the elongation has become three times greater in comparison to the as-cast state. Elongation results showed an increase up to 500 °C and then reduced temperatures of 550 and 580 °C. Fractographic analysis revealed a cellular nature for the fracture surface. On the cellular fracture surface, the features of both brittle and ductile fracture were present simultaneously. As a result of solution treatment the potential sites for stress concentration and crack initiation areas were reduced due to softening of the sharp corners and break up of eutectic network respectively, while increase in the number of fine dimples rendered the nature of fracture to ductile and also increased elongation.     

Electro-codeposition of Al2O3-Y2O3 composite thin film coatings and their high-temperature oxidation resistance on γ-TiAl alloy

In this paper, electro-codeposition based on electrophoretic deposition and electrolytic deposition was developed to prepare Al₂O₃-Y₂O₃ composite thin film coatings on a γ-TiAl based alloy. Scanning electron microscope observations showed that the Al₂O₃-Y₂O₃ composite coatings were very compact and consisted of uniform nano-particles after microwave sintering. Cyclic oxidation at 900 °C indicated that the Al₂O₃-Y₂O₃ composite thin film coatings improved the oxidation and scale spallation resistance of the γ-TiAl alloy significantly. The superior oxidation and spallation resistance of the coatings were attributed to the suppression of outward diffusion of Ti and Al and inward diffusion of O, the promoted selective oxidation of Al in the γ-TiAl alloy, and the improved adhesion of oxide scale induced by the Al₂O₃-Y₂O₃ composite thin film coatings.     

The effect of rare earth CeO2 on microstructure and properties of in situ TiC/Al–Si composite

In this work, CeO₂ is investigated as an additive for in situ preparation of TiC/Al–Si composite using exothermal dispersion (XD)+casting technology. Experimental results show that CeO₂ at high temperature exhibits the same function as Ce, which is a kind of good modificator. When 0.5 wt.% CeO₂ additive is added, the microstructure of eutectic silicon is significantly changed (the size is greatly reduced). Meanwhile, the amount of TiC particles is increased and the size is reduced. Compared with the composite without added CeO₂, the hardness value (HB) value, tensile strength and tensile elongation are greatly increased. However, under dry sliding friction test, weight loss of the composite is not significantly changed.     

Formation of Al3Ti/Mg composite by powder metallurgy of Mg–Al–Ti system

Abstract

An in situ titanium trialuminide (Al₃Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al₃Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al₃Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.     

Corrosion behaviour of sediment electro-codeposited Ni–Al2O3 composite coatings

Ni–Al₂O₃ composite coatings were produced by the sediment electro-codeposition (SECD) technique at various particle loadings and current densities. The submicron Al₂O₃ particles were found to distribute uniformly in the coating, and 12–18 vol.% particles can be incorporated in the coating depending on deposition current density and particle loading in the plating bath. Electrochemical corrosion testing was conducted in 0.9 wt.% NaCl solution. The results show that the incorporation of Al₂O₃ particles in the coating did not affect the general corrosion behaviour of the Ni coating. However, at higher anodic potentials approaching the breakdown potential and with prolonged polarization, the composite coatings showed deteriorated corrosion resistance in terms of increased anodic current density, reduced pitting potential and quicker breakdown of the passive film. The detrimental effects of Al₂O₃ particle incorporation could be explained by the existence of numerous boundaries between the particles and the matrix, which would serve as active sites for anodic dissolution and micro-pit formation.     

Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al₂O₃–5B₂O₃) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε _r ), quality factor (Q × f) and temperature coefficient of resonant frequency (τ _f ) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B₂O₃ and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm³) as compared with pure alumina powders recycled from Al dross (3·55g/cm³ sintered at 1700 °C).     

Preparation,magnetization, and microstructure of ionic ferrofluids based on γ-Fe2O3/Ni2O3 composite nanoparticles

Ionic ferrofluids based on γ-Fe₂O₃/Ni₂O₃ composite nanoparticles are a polydispersed system prepared by the Massart method. The magnetization and optical relaxation behaviors of these ferrofluids show that, in addition to the ring-free micelle aggregates, there are also chainlike aggregates in the ferrofluids. The chainlike aggregation is attributed to so-called “depletion force” in the polydispersed ferrofluids because magnetic interaction between the ferrofluid particles is so weak that these particles cannot form the aggregates just by the magnetic interaction. For the γ-Fe₂O₃/Ni₂O₃ ionic ferrofluids, the “depletion force” stimulates the larger ferrofluid particles, forming short chains in the absence of a magnetic field and their macroscopic properties, e.g., magnetization and optical relaxation, all result from the short chains. Ferrofluids having chainlike aggregates alone could have excellent magneto-optical effects.     

Hardness and wear resistance improvement of surface composite layer on Ti–6Al–4V substrate fabricated by powder sintering

A wear resistant surface composite layer on Ti–6Al–4V substrate was fabricated using powder sintering method. The surface composite layer consisted of Ti–6Al–4V matrix and different fractions of TiN particles as reinforcement phase. The surface layer and the substrate were directly bonded together while the powders were cold formed and then sintered at an elevated temperature. The two layers showed good metallurgical bond. In this study, 5%, 10% and 15% TiN weight fractions were adopted to fabricate the surface composite layer. Effects of TiN addition on the microstructure, hardness and wear resistance were investigated. It was found that the wear resistance of the surface composite layer was improved due to the addition of TiN compared to that of pure Ti–6Al–4V.     

多孔Al2O3f/Al2O3复合材料研究进展

作为20世纪90年代兴起的一类连续陶瓷纤维增强陶瓷基复合材料,连续氧化铝纤维增韧氧化铝(Al₂O_3f/Al₂O₃)复合材料已经发展为与C_f/SiC、SiC_f/SiC等非氧化物复合材料并列的陶瓷基复合材料。以多孔基体实现基体裂纹偏转成为Al₂O_3f/Al₂O₃复合材料主要的增韧设计方法,形成的多孔Al₂O_3f/Al₂O₃复合材料具有优异的抗氧化性能和高温力学性能,可在高温富氧、富含水汽的中等载荷工况中长时服役,是未来重要的热结构材料。经过近30年的发展,多孔Al₂O_3f/Al₂O₃复合材料已被应用于航空发动机、燃气轮机等热端部件。本文综述了多孔Al₂O_3f...     

Tribological properties of Al6061–Al2O3 nanocomposite prepared by milling and hot pressing

Tribological properties of bulk Al6061–Al₂O₃ nanocomposite prepared by mechanical milling and hot pressing were investigated. Al6061 chips were milled for 30 h to achieve a homogenous nanostructured powder. A 3 vol.% Al₂O₃ nanoparticles (∼30 nm) were added to the Al6061 after 15 and 30 h from the beginning of milling. The milling times with Al₂O₃ in these two samples were then 15 h and 30 min, respectively. Additionally, 3 vol.% Al₂O₃ (1 μm and 60 μm) was added to the Al6061 after 15 h of milling; where, the micron size Al₂O₃ in these two samples, was milled 15 h with the matrix. Hot pressing of milled samples was executed at 400 °C under 128 MPa pressure in a uniaxial die. The hot pressed samples were characterized by micro-hardness test, bulk density measurements, pin on disc wear test, and finally scanning electron microscopy observations. Fifteen hour-milled nanocomposite with nanoscale Al₂O₃, showed improvement in wear resistance and bulk density compared with that of 30 min-milled nanocomposites due to better dispersion of Al₂O₃ nanoparticles, improved surface quality of nanocomposite particles before pressing and more grain refinement of Al matrix. Moreover, increasing the reinforcement size increased the wear rate because of reduction in relative density, hardness and inter-particle spacing.     

Effect of Nb?+?Ti coating on the wetting behavior, interfacial microstructure, and mechanical properties of Al/Al2O3 joints

The subject of the work was to study the effect of Nb + Ti thin film deposited by PVD method on alumina substrates on the wetting behavior, bond strength properties, and structure of interface in the Al/Al₂O₃ joints. Applying the sessile drop method, the wetting behavior of molten Al (99,999%) on coated alumina substrates was studied in the temperature range between 953 and 1373 K under a vacuum of 0.2 mPa for 30 min of contact. The sessile drop samples were used to examine the interface structure, shear strength, and interfacial fracture toughness under the concentrated load. The introduction of the thin Nb + Ti film layer of 900 nm thickness: (1) greatly improves the wettability of alumina by molten Al at above 1223 K and the shear strength of Al/Al₂O₃ joints produced at 1223 K, (2) has positive effect on structure transformation in the interface and leads to fabrication of reliable metal–ceramic joints. Microstructural investigations of the interface indicated that the precipitates of Nb and Ti-rich intermetallic phases were formed at the Al/Al₂O₃ interface, which influenced strengthening of these joints. Hence a conclusion can be drawn that the interface structure influences the durability increase in Al/Al₂O₃ joints.     

Low-Magnetoresistance RuO2–Al2O3 Thin-Film Thermometer and its Application

Thermometers consisting of RuO₂–Al₂O₃ composite thin films were prepared by RF sputtering. It was found that different electrode-patterning techniques have dissimilar effects on the magnetoresistance (MR) and the temperature coefficient of resistance (TCR). In general, the thermometers with electrodes fabricated by photo-resist lithography exhibit superior performance compared to those with electrodes prepared using a metal mask. By adjusting the relative compositions of RuO₂ and Al₂O₃, the thermometers can be applied to a wide temperature range from 60 mK to 500 K. In a pulsed magnetic field up to 55 T, the MR at 4.2 K of a typical thermometer for the temperature range from 1.4 K to 300 K increases linearly with magnetic field to a maximum of ~15 %, corresponding to a temperature deviation of ~−4 %. As frequency increases from dc to 1.9 MHz, the MR decreases from  −13 % to ~ − 0.5 % at T = 1.3 K and H = 55 T. By integrating the thermometer with a heater on a sapphire chip, a micro-calorimeter can be developed and successfully used to measure the heat capacity of small mg-sized sample. The RuO₂–Al₂O₃ composite film can also be employed as an infrared bolometer operated at room temperature.     

Al2O3颗粒对Al2O3p/Al复合材料时效析出的影响

本文通过采用硬度测量,差热分析及透射电镜综合研究了Al₂O₃p/6061复合材料在时效过程中的析出变化。结果表明,在Al₂O₃p/6061时效过程中,峰时效的主要强化相是β'相,并且以160℃,8小时时效的效果为最佳。     

The effect of strontium on the microstructure and wear properties of A356–10%B4C cast composites

This study was undertaken to investigate the effect of strontium (0.5%) as a modifier on the microstructure and dry sliding wear behavior of A356–10%B₄C particulate metal matrix composite (PMMC). The composite ingots were made by stir casting process. In this work, composite were characterized by scanning electron microscope equipped with energy dispersive spectrometer (EDS), and dry sliding wear experiment were performed in a pin-on-disc wear tester against a DIN 100Cr6 steel disc at speed of 0.5 ms⁻¹ and normal loads of 20, 40 and 60 N. The obtained results showed that 0.5%Sr was needed to modify of silicon eutectic in A356–10%B₄C cast composite. Also, the wear results showed that the addition of strontium to MMCs can lead to reduction of wear rate through strong bonding (between B₄C and matrix) and silicon particle modification. Formation of compact transfer layer has been identified on the entire surface of the pins at the applied load of 60 N. It is suggested that the transfer layer which was formed under an applied load of 60 N can act as a protective layer and helps to reduce wear rate.     

Synthesis and characterisation of nanostructured Al–Al3V and Al–(Al3V–Al2O3) composites by powder metallurgy

In this study, the formation and characterisation of Aluminium (Al)-based composites by mechanical alloying and hot extrusion were investigated. Initially, the vanadium trialuminide (Al₃V) particles with nanosized structure were successfully produced by mechanical alloying and heat treatment. Al₃V–Al₂O₃ reinforcement was synthesised by mechanochemical reduction during milling of V₂O₅ and Al powder mixture. In order to produce composite powders, reinforcement powders were added to pure Al powders and milled for 5?h. The composite powders were consolidated in an extrusion process. The results showed that nanostructured Al-10?wt-% Al₃V and Al-10?wt-% (Al₃V–Al₂O₃) composites have tensile strengths of 209 and 226?MPa, respectively, at room temperature. In addition, mechanical properties did not drop drastically at temperatures of up to 300°C.     

Effect of boronizing and shot peening in ferrous based FeCu–Graphite powder metallurgy material on wear,microstructure and mechanical properties

Ferrous based materials manufactured by powder metallurgy (P/M) method are widely used in industry. These materials are very important because they do not require machining, have self-lubricated properties as journal bearing material, find applications in medical industry. In this study, powder metal parts were manufactured from ferrous based FeCu–Graphite composites by P/M method. Wear and mechanical test samples were manufactured and boronizing and boronizing + shot peening was applied to samples. Wear properties of these parts were investigated by wearing at 17 N load and 50 rpm on pin-on-disc wear test rig under dry conditions. Moreover, mechanical properties of powder parts were investigated in detail.     

Reaction products and their solidification process of the plasma sprayed Fe2O3–Al composite powders

Fe₂O₃–Al composite powders were deposited onto steel substrate by plasma spraying. The reaction products of the Fe₂O₃–Al composite powders in the plasma flame and their solidification process were investigated. The results showed that the reaction products of the Fe₂O₃–Al composite powders in the plasma flame were Fe–Al–O ceramic melt and Fe melt. Fe was not always formed in the reaction products of each composite particle, and the formation of Fe was dependent on the composition distribution and the reaction kinetics process of each composite particle. The composition inhomogeneity, discontinuity and porousness of the composite particles resulted in the difference of the reaction kinetics of each composite particle and the composition difference of the droplets. Hercynite solid solution, Fe, Al₂O₃ and FeAl phases were formed by non-equilibrium solidification of the Fe–Al–O ceramic melt. For the smaller size droplet, when it spread on the substrate, the spreading droplet was quickly chilled to form equiaxed grains with size of 100–200 nm. Nano-sized or submicron equiaxed grains, nano-sized columnar grains and cellular structure were formed in the larger spreading droplet. Fe rich hercynite solid solution nucleated and grew preferentially and then Al rich hercynite solid solution grew, which form composition segregation in the columnar grains. The main phases in the composite coating were hercynite solid solution.     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

片状Al2O3对Al2O3/FEP复合材料热导率的影响

通过混炼工艺制备了片状Al₂O₃填充聚全氟乙丙烯(FEP)复合材料,以颗粒状Al₂O₃为对比样品,研究了片状Al₂O₃形状和尺寸对 FEP基复合材料热导率的影响,利用SEM观察了FEP基复合材料的微观形貌。结果表明：在低填充量下,Al₂O₃颗粒在FEP基体中呈“海岛”状分布,没有形成连续的导热网链,但其热导率明显提高;复合材料拉伸强度与断裂伸长率随Al₂O₃含量的增加而减小;低填充量时复合材料热导率的提高主要来自Al₂O₃的微细片状结构,这种微细片状结构一方面提高了有效导热路径,另一方面增加了颗粒与基体之间接触面积,因此有利于热导率的提高。