Cu含量对CNTs/Al-Cu复合材料显微组织和压缩力学性能的影响（英文）

通过热压烧结和热轧制备碳纳米管(CNTs)增强的Al-Cu基复合材料,系统研究Cu含量对Al与CNTs的界面反应、含Cu沉淀物的析出行为及相应复合材料力学性能的影响。研究表明,提高Cu含量不仅能使复合材料制备过程中含Cu析出相的数量和尺寸增加,而且能促进CNTs与Al基体之间的界面反应,加剧CNTs转化为Al₄C₃。由于含有1%Cu(质量分数)的复合材料保持CNTs的原始结构,因此,它在所有复合材料中具有最高的强度、弹性模量和硬度。此外,增加Cu含量还能改变影响复合材料强度的主要强化机制。     

Al2O3晶须与石墨烯纳米片共增强铜基复合材料的显微结构及界面行为(英文)

研究Al₂O₃晶须和石墨烯纳米片共增强铜基复合材料的力学性能和显微结构。采用机械合金化、真空热压烧结和热等静压工艺制备不同石墨烯含量的铜基复合材料。含0.5%石墨烯(质量分数)的铜基复合材料(GNP-0.5)具有良好的Cu/C和Cu/Al₂O₃界面结合性能;复合材料的硬度和抗压强度随石墨烯含量的增加呈现先增加到一个临界值后减小的趋势。研究结果表明,石墨烯和Al₂O₃晶须在铜基复合材料中最主要的强化机制是能量耗散和载荷传递以及石墨烯导致的晶粒细化。石墨烯与Al₂O₃晶须的双相混杂增强效应在于：当Al₂O₃/Cu界面存在微裂纹并沿着界面扩展时,嵌于铜基复合材料中的石墨烯会阻碍裂纹扩展路径,从而强化Al₂O₃晶须在铜基复合材料中的增强作用。     

Synthesis and Characterization of Air-Sintered Al2O3-Bronze Composites

Powder blends of Al₂O₃ and a Cu-Sn-Pb bronze (0-20% bronze) were cold compacted and air-sintered at 1473-1773 K. The Al₂O₃-bronze composites exhibited networks of metal microchannels, some porosity, and diffusion of Pb in Al₂O₃ and of Al and O in bronze. The hardness of un-doped Al₂O₃ increased linearly with temperature, from 455 Knoop microhardness (HK) at 1473 K to 2010 HK at 1773 K, but the hardness of the Al₂O₃/bronze composite exhibited a sluggish, nonlinear dependence on temperature, with a peak hardness of 1150 HK at 1673 K. Air sintering may be viable to synthesize Al₂O₃/bronze composites with low bronze contents     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Content on Electrical Breakdown Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Cu Composite

Al₂O₃/Cu composites were prepared by external addition of Al₂O₃, and the effect of Al₂O₃ content on microstructure, density, hardness, electrical conductivity and vacuum electrical breakdown properties was studied. The results show that with increasing Al₂O₃ addition, the density of Al₂O₃/Cu composite significantly decreases, the hardness sharply increases and then slowly decreases, but the electrical conductivity invariably decreases. The vacuum breakdown test shows that with increasing Al₂O₃ addition, the breakdown strength first sharply increases and then decreases when the Al₂O₃ content exceeds 1.2 wt.%; the chopping current always exhibits a decreasing trend and the arc life first increases and then decreases. According to the morphology of arc erosion and analysis, the arc erosion resistance increases and then decreases sharply. In the range of experiments, the optimal arc erosion resistance of Al₂O₃/Cu composite can be obtained with the addition of 1.2 wt.% Al₂O₃.     

Effect of Heat Treatment on the Microstructure and Wear Properties of Al–Zn–Mg–Cu/In-Situ Al–9Si–SiCp/Pure Al Composite by Powder Metallurgy

This study examined the effects of heat treatment on the microstructure and wear properties of Al–Zn–Mg–Cu/in-situ Al–9Si–SiCp/pure Al composites. Pure Al powder was used to increase densification but it resulted in heterogeneous precipitation as well as differences in hardness among the grains. Heat treatment was conducted to solve this problem. The heat treatment process consisted of three stages: solution treatment, quenching, and aging treatment. After the solution treatment, the main dissolved phases were η′(Mg₄Zn₇), η(MgZn₂), and Al₂Cu phase. An aging treatment was conducted over the temperature range, 100–240 °C, for various times. The GP zone and η′(Mg₄Zn₇) phase precipitated at a low aging temperature of 100–160 °C, whereas the η(MgZn₂) phase precipitated at a high aging temperature of 200–240 °C. The hardness of the sample aged at 100–160 °C was higher than that aged at 200–240 °C. The wear test was conducted under various linear speeds with a load of 100 N. The aged composite showed a lower wear rate than that of the as-sintered composite under all conditions. As the linear speed was increased to 1.0 m/s, the predominant wear behavior changed from abrasive to adhesive wear in all composites.     

Al2O3/Mo composite and its tribological behavior against AISI201 stainless steel at elevated temperatures

Al₂O₃-reinforced molybdenum (Mo) composites were successfully prepared by powder metallurgy to improve the wear resistance of Mo components at high temperature. The reinforced Al₂O₃ particles are uniformly distributed in the Mo matrix; thus, the Al₂O₃/Mo composite is harder than monolithic Mo. The friction coefficients of both monolithic Mo and the Al₂O₃/Mo composite decrease by 37% and 42%, respectively, at 700 °C compared with those at room temperature (self-lubricating phenomenon). This phenomenon is attributed to the formation of very soft MoO₃ and FeMoO₄ metal oxides on the friction surface at high temperature. The Al₂O₃/Mo composite has better wear resistance than monolithic Mo at both room temperature and at 700 °C. The notable resistance of the composite particularly at 700 °C can be attributed to its increased hardness and the soft tribofilm forming on the worn surface.     

Phase and Microstructure Evolution and Toughening Mechanism of a Hierarchical Architectured Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating under High Temperature

In recent years, numerous techniques have been developed to mimic nacre-like hierarchical architectures in order to improve the damage tolerance of materials. We present herein a simple strategy to fabricate such a hierarchical architectured Al₂O₃–Y₂O₃ composite coating via atmospheric plasma spraying. The evolution of the phase and microstructure of the Al₂O₃–Y₂O₃ composite coating were characterized under conditions of high-temperature exposure in air at 800-1350 °C. The hardness and porosity of several typical coatings were determined. In situ formation of dense hierarchical architectured Al₂O₃–YAG composite coating with improved hardness was achieved after heat treatment at 1350 °C. Compared with Al₂O₃ coating, elevated toughness was found for the hierarchical architectured Al₂O₃–YAG composite coating, which can be ascribed to the distribution of YAG phase that contributed to crack termination and deflection, and microbridging. After thermal aging treatment at 1350 °C, the hierarchical architectured Al₂O₃–YAG composite coating was quite stable after 100 h of thermal exposure. Furthermore, the Al₂O₃–Y₂O₃ composite coating exhibited superior sintering resistance compared with the Al₂O₃ coating.     

Effects of Al2O3 content on densification,microstructure, mechanical properties and oxidation resistance of TaC-Al2O3 composites

TaC-Al₂O₃ composites were prepared by hot pressing. Influence of Al₂O₃ content ranging from 10 to 40 vol. % on densification, phase composition, microstructure, mechanical properties and oxidation behavior of the TaC-Al₂O₃ composites was investigated. With 30 and 40 vol. % Al₂O₃ addition a closed porosity was achieved. The Al₂O₃ particles were uniformly distributed among TaC grains retarding grain growth and resulting in refined microstructures with grains below 2 μm in size. The most densified composite with 40 vol. % Al₂O₃ addition exhibited good mechanical properties with a Vickers’ hardness of 17.8 GPa, a flexural strength of 485 MPa and a fracture toughness of 5.4 MPa·m^1/2. After holding at 700°C for 3 h in air, the dense 30 and 40 vol. % Al₂O₃ compositions showed hardly noticeable and mainly surface oxidation, whereas less densified TaC-Al₂O₃ composites with 10 and 20 vol. % Al₂O₃ content and with open porosity were disintegrated to powders.     

Effect of Milling Time on Electrical Breakdown Behavior of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Cu Composite

In order to clarify the relationship between the microstructure and the arc erosion behavior of metal-matrix composite, Al₂O₃/Cu composites with different distributions of Al₂O₃ particles were prepared by high energy ball milling and powder metallurgy. The effect of milling time on microstructure, properties, and arc erosion behavior of Al₂O₃/Cu composite was investigated. The results show that the distribution of Al₂O₃ particles improves significantly with increase of milling time, but Al₂O₃ particles will be aggregated if milling time is too long. The optimal milling time is 24 h in the range of experiments. A uniform distribution of Al₂O₃ particles in copper matrix can improve the hardness, electrical conductivity, average breakdown strength, chopping level, and arc life. With improvement in the distribution of Al₂O₃ particles, the erosion area becomes larger, and the erosion pits become shallower and are dispersed more uniformly.     

The mechanical milling of Al/TiO2 composite powders

The processing of Al/TiO₂ composite powders produced by high-energy mechanical milling leads to production of a range of valuable, titanium-based materials. They include Ti(Al,O)/Al₂O₃ and Ti_xAl_y(O)/Al₂O₃ composite powders, bulk composites and Ti₃Al/TiAl alloy powders, and corresponding bulk materials. The strength of the Ti(Al,O)/Al₂O₃ and Ti_xAl_y(O)/Al₂O₃ composites is moderate, but their high-temperature oxidation resistance is exceptionally high, making the titanium-based composite powders favorable feedstock materials for protective coatings. The hardness of the Ti(Al,O)/Al₂O₃ and Ti₃Al(O)/Al₂O₃ composites is also very high (10–16 GPa). For more information, contact D.L. Zhang, University of Waikato, Waikato Centre for Advanced Materials, Department of Materials and Process Engineering, Private Bag 3105, Hamilton, New Zealand; 011-64-7-838-4783; fax 011-64-7-838-4835; e-mail d.zhang@waikato.ac.nz.     

Synthesis and characterization of Al2O3–TiC nano-composite by spark plasma sintering

Al₂O₃–10TiC composite was synthesized by high energy ball milling followed by spark plasma sintering (SPS) process. Microstructure of the sintered composite samples reveals homogeneous distribution of the TiC particles in Al₂O₃ matrix. Effect of sintering temperature on the microstructure and mechanical properties was studied. The sample sintered at 1500 °C shows a measured density of 99.97% of their theoretical density and hardness of 1892 Hv with very high scratch resistance. These results demonstrate that powder metallurgy combined with spark plasma sintering is a suitable method for the production of Al₂O₃–10TiC composites.     

Fabrication of A356 composite reinforced with micro and nano Al2O3 particles by a developed compocasting method and study of its properties

Aluminum/alumina composites are used in automotive and aerospace industries due to their low density and good mechanical strength. In this study, compocasting was used to fabricate aluminum-matrix composite reinforced with micro and nano-alumina particles. Different weight fractions of micro (3, 5 and 7.5 wt.%) and nano (1, 2, 3 and 4 wt.%) alumina particles were injected by argon gas into the semi-solid state A356 aluminum alloy and stirred by a mechanical stirrer with different speeds of 200, 300 and 450 rpm. The microstructure of the composite samples was investigated by Optical and Scanning Electron Microscopy. Also, density and hardness variation of micro and nano composites were measured. The microstructure study results revealed that application of compocasting process led to a transformation of a dendritic to a nondendritic structure of the matrix alloy. The SEM micrographs revealed that Al₂O₃ nano particles were surrounded by silicon eutectic and inclined to move toward inter-dendritic regions. They were dispersed uniformly in the matrix when 1, 2 and 3 wt.% nano Al₂O₃ or 3 and 5 wt.% micro Al₂O₃ was added, while, further increase in Al₂O₃ (4 wt.% nano Al₂O₃ and 7.5 wt.% micro Al₂O₃) led to agglomeration. The density measurements showed that the amount of porosity in the composites increased with increasing weight fraction and speed of stirring and decreasing particle size. The hardness results indicated that the hardness of the composites increased with decreasing size and increasing weight fraction of particles.     

Wear characteristics of Al−Si−Mg−(Cu)/Al2O3 composites fabricated by thermit reaction

Al₂O₃ particles could be formed by a thermit reaction in an Al-12Si-4Mg-1.5Cu/Al₂O₃ composite due to thein-situ reaction between Al-12Si-4Mg-(1.5Cu) molten metal and SiO₂ particles in preform, which took place at 1173 K for 24 hours, resulting in the decomposition of SiO₂ particles and the formation of Al₂O₃ particles simultaneously. The mechanically mixed layers (MMLs) consisting of α-Fe and Fe oxides existed on the subsurface layers beneath the worn surface in composites or mother alloys, which improved the wear resistance. The characteristics of wear resistance and hardening of an Al-12Si-4Mg-1.5Cu/Al₂O₃ composite are superior to those of the Al-12Si-4Mg/Al₂O₃ composite and Al-12Si-4Mg-1.5Cu alloy.     

NiAl–Al2O3 composites produced by pulse plasma sintering with the participation of the SHS reaction

The paper presents the results of examinations of the NiAl–Al₂O₃ sinters (13, 38 and 55 vol% of Al₂O₃) produced from a mixture of nickel, aluminum and alumina powders in a single technological process, using the pulse plasma sintering (PPS) method. By subjecting the elemental powders to a PPS process for 900 s, we obtained NiAl–Al₂O₃ composites of a hardness ranging from 480 HV10 (13% Al₂O₃) to 680 HV10 (55% Al₂O₃). The fracture toughness of the sintered materials depended on the amount of the dispersed Al₂O₃ phase. When examined with a Vickers indenter under a load of 10 kg, the composite containing 13% of Al₂O₃ showed no cracking. In the composites with 38% Al₂O₃ and 55% Al₂O₃ contents, the value of K_IC was 9.1 and 8.2 MPam^1/2, respectively.     

Formation of nanostructured eutectic network in α-Al2O3 reinforced Al–Cu alloy matrix composite

We report the fabrication and characterization of an Al–Cu alloy matrix composite, which is reinforced by α-Al₂O₃ particles and nanometer-sized (nm-sized) lamellar eutectic. The composite was fabricated by sintering and rapid quenching of an Al–20wt.%CuO sample. We had performed differential thermal analysis on the sample, and found that the reaction between Al and CuO took place between 580 and 700 °C. Results from scanning and transmission electron microscopies indicated that amorphous Al₂O₃ was initially formed in the reaction. It was then crystallized and transformed to the more stable α-Al₂O₃ particles at higher temperature. When the sintered sample was cooled down from 1000 °C, the two-phase Al(Cu)–Al₂Cu eutectic was formed. The size and the distribution of the eutectic network strongly depended on the rate of cooling. The final sintered product contains α-Al₂O₃ particles and Al(Cu)–Al₂Cu eutectic, which are embedded in the Al(Cu) matrix. In comparison, the eutectic network in the oil-quenched sample is distributed more evenly and is finer in size, with lamellar spacing as small as 200–300 nm, than that of the furnace-cooled sample. The Vickers hardness value of the oil-quenched sample has an average of 123, which is 50% higher than that of the furnace-cooled sample.     

Wetting phenomena of Al–Cu alloys on sapphire below 800 °C

Using a modified dispensed drop method, a decrease in contact angle on sapphire from pure aluminum to low-copper-containing Al alloys (7–12 wt.%) was found; with higher copper additions θ transitions to the non-wetting regime. Atomic force microscopy on long-term samples showed a significantly increased surface roughness beneath the drop. Using high-resolution transmission electron microscopy, the reaction product at the interface was identified as CuAl₂O₄ for Al–7Cu and Al₂O₃ for an Al–99.99 drop. X-ray photoelectron spectroscopy further confirmed the formation of CuAl₂O₄ under CuAl₂ drops. Spinel formation is caused by reaction of the alloy with residual oxygen in the furnace that is transported along the interface as modeled by thermodynamic simulations. The formation of CuAl₂O₄ causes the reduced σ_sl and hence the improved wettability of sapphire by low-copper-containing alloys compared to pure aluminum. The main reason for the increase in θ with higher copper contents is the increasing σ_lv of the alloy.     

Preparation and characterization of Mo/Al2O3 composites

In order to improve the performance of molybdenum, the Mo/Al₂O₃ composites were prepared by using a hydrothermal method for the synthesis of the precursor powders and subsequent powder metallurgical processing. The morphologies of the composite powders and the microstructures and properties of the composites were investigated. Compared with the pure Mo powder, the grains of composite powders are smaller because of the existence of the fine Al₂O₃ particles. The results from the sintered composites show that the fine Al₂O₃ particles are evenly distributed in the Mo matrix and well bonded with the Mo matrix. With increasing Al₂O₃ content, all the values of the micro-hardness, compressive strength and flow stress at 0.08 strain are increased. The strengthening effect is more remarkable at elevated temperatures. At room temperature, the compressive strength and the flow stress at 0.08 strain of the composite with 40 vol.% Al₂O₃ are 1.67 and 2.01 times greater than those of pure molybdenum, respectively, while the values are up to 2.02 and 2.52 at 1100 °C.     

Mechanical Properties and Thermal Shock Resistance of Al2O3-TiC-Co Composites

Ductile cobalt was introduced into Al₂O₃-TiC (AT) composites by using a chemical deposition method to improve toughness and resistance to thermal shock. The mixture of Co-coated Al₂O₃ and TiC powders was hot-pressed into an Al₂O₃-TiC-Co (ATC) composite. The flexure strength and fracture toughness of the ATC composites have been improved considerably, compared with AT and Al₂O₃. The fracture surface of ATC shows a large proportion of transgranular cracks with some intergranular type, unlike the intergranular fracture modes of AT and Al₂O₃. The thermal shock properties of the composites were evaluated by water quenching technique and compared with the traditional AT and Al₂O₃. The composites containing only 3.96 vol.% cobalt exhibited higher critical temperature difference and retained flexure strength. The SEM examination of the fracture surfaces of the ATC composites after single thermal cycle showed that voids increased in number and size, and most isolated voids coalesced with increasing temperature difference, which caused the density and strength to decrease. The ATC composite is less sensitive to repeated thermal shock than the AT composite.     

Non-isothermal aging behavior of in-situ AA2024−Al3NiCu composite

The effect of non-isothermal aging treatment on microstructure and mechanical properties of in-situ AA2024?Al₃NiCu composite fabricated by the stir casting process was examined. The Al₃NiCu intermetallic was created by adding 3 wt.% nickel powder during stir casting and homogenization treatment at 500 °C for 24 h after casting. The microstructural results obtained using optical and scanning electron microscope indicate that, after non-isothermal aging treatment, the S-Al₂CuMg precipitates become finer, forming a poor zone of this precipitate in the area between the dendrites. Also, adding nickel during stir casting reduces the precipitation rate and the contribution of S-Al₂CuMg precipitates in strengthening composite during non-isothermal aging. The maximum hardness, ultimate tensile strength, and toughness achieved in the 3 wt.% nickel-containing sample after non-isothermal aging at 250 °C are (121.30±4.21) HV, (221.67±8.31) MPa, and (1.67±0.08) MJ/m³, respectively. The maximum hardness and ultimate tensile strength of AA2024?Al₃NiCu composite are decreased by 6% and 4%, respectively, compared to those of nickel-free AA2024 aluminum alloy.     

Effect of thermal-cooling cycle treatment on thermal expansion behavior of particulate reinforced aluminum matrix composites

Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology.Microstructures and effect of thermal-cooling cycle treatment(TCCT) on the thermal expansion behaviors of three composites were investigated.The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly.Inflections at about 300 °C are observed in coefficient of thermal expansion(CTE) versus temperature curves of two SiCp/Al composites,and this characteristic is not affected by TCCT.The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles.However,no inflection is observed in Al2O3p/Al composite,while TCCT has effect on CTE of Al2O3p/Al composite.These results should be due to different relaxation behavior of internal stress in three composites.