Microstructural evolution of nanodiamond-reinforced aluminum matrix composites during the process of hot extrusion

Nanodiamond (ND) has been recently considered to be an excellent reinforcement for strengthening metal matrix composites. However, most of the previous studies focused on manufacturing process, final structure, and mechanical properties. Systematic exploration of the microstructural evolution, which is critical to understand the effect mechanism of ND particles, still lacks. Herein, we seek to understand the effect of ND particles on microstructural evolution via comparative investigation of microstructures in different test points on extrusion remnant specimens of pure aluminum, 0.5 wt% and 1.0 wt% ND-reinforced aluminum composites prepared by powder metallurgy and hot extrusion. Finite element simulations were used to analyze the relative stress–strain states and deformation modes in different test points. Electron backscatter diffraction and transmission electron microscopy studies reveal that the mean grain size of ND-reinforced aluminum composite declined rapidly after entering the extrusion deformation zone. Microstructures in simple shear, tensile pure shear, and compressive pure shear deformation modes were quite different. The dispersed ND particles effectively promoted grain refinement and improved dislocation driving force with the increase in plastic strain. The large localized high-content ND clusters were broken into small ones, and small ones acted as non-deformable particles to stimulate nucleation and recrystallization under high dislocation driving force. Test results show that the hardness of 0.5 wt% and 1.0 wt% ND-reinforced aluminum composites was 1.9 and 2.1 times that of pure aluminum, respectively. The 0.5 wt% ND-reinforced aluminum composites exhibited optimal comprehensive mechanical properties with a tensile strength of 205 MPa and elongation of 18%, which were 115% and 91% of pure aluminum, respectively.     

Synthesis of nanodiamond-reinforced aluminum metal composite powders and coatings using high-energy ball milling and cold spray

Nanodiamond-reinforced aluminum metal matrix composites (ND–Al MMC) powders were synthesized by means of high energy ball milling. We present a systematic study of the effect of various milling conditions on the structure and properties of the resulting MMC powders. The described method can be used to control important powder characteristics, including particle size and shape, Al crystal size and residual strain, and structural integrity and dispersion of the nanoparticle inclusions, a crucial requirement for subsequent powder consolidation. Raman spectroscopy was utilized for the first time to directly verify the structural integrity and the dispersion of ND in the Al matrix. For low ball-to-powder ratios (BPR), average particle size and size range of the ND–Al composite powders were found to decrease during milling, while the hardness increases. A BPR of 10:1, a milling time of 10 h, and a ND content of 10 wt.% were most effective in obtaining small powder particle sizes, small Al crystal sizes, and improved mechanical properties reaching a hardness of 3.46 GPa, a 210% increase over the pristine, untreated Al powder (1.10 GPa). Finally, we demonstrate that the as-produced composite powders are well-suited for low-temperature consolidation processing by fabricating the first cold-sprayed ND–Al MMC coating.     

Preparation of aluminum/silicon carbide metal matrix composites using centrifugal atomization

This paper describes the development of a new technique to produce metal matrix composites (MMCs) by injecting silicon carbide particles into molten aluminum just prior to centrifugal atomization. A centrifugal atomization apparatus has been constructed for this study. Silicon carbide particles are injected during atomization of 6061 aluminum alloy to form metal matrix composite powder. The prepared aluminum/silicon carbide powder contains 18 vol.% of SiC particles and 1.2 vol.% of voids. The particle grain size is almost independent from the particle size.     

Processing and characterisation of 2-D woven metal fibre-reinforced multilayer silica matrix composites using electrophoretic deposition and pressure filtration

A novel, cost-effective and rapid processing route including electrophoretic deposition (EPD) and pressure filtration (PF) has been developed for the fabrication of 2-D woven metallic fibre mat reinforced multilayer silica matrix composites. Commercially available silica sol containing ultrafine ceramic particles (15 nm) was used as the matrix whilst 2-D woven metal stainless steel 316L fibre mat was used as the metal reinforcement to produce a composite having 2-D isotropic properties. The colloidal silica sol was modified with boria and boehmite in order to produce a silica matrix which could be sintered at 900°C (the maximum use temperature for the particular fibre architecture employed), and with densification taking place before crystallisation. An in-situ electrophoretic deposition (EPD) cell capable of measuring the weight gain in real time during deposition was designed. This technique enabled the woven fibre inter/intra tow regions to be infiltrated with the ultrafine silica particles in a very short time (2 min). Green bodies made from electrophoretically deposited fibre mats were further consolidated using pressure filtration. The EPD parameters were optimised in terms of time, voltage and deposition thickness as well as deposit formation rate. Microstructural observation indicated that the composites produced were dense and of high microstructural homogeneity.     

短碳纤维增强铝基复合材料

通过化学镀再电镀的方法,在碳纤维表面镀上Cu镀层,制备C/Cu复合丝,并在硼酸的保护下,利用非真空条件下的液态机械搅拌法制备短碳纤维增强铝基复合材料,研究了碳纤维在复合材料中的分散程度,铜镀层存在状态及C/Al复合材料的拉伸性能.实验结果表明：在硼酸存在下,大大降低了铜的氧化程度,碳纤维分散均匀且没有损伤,少量硼酸的加入,对复合材料的力学性能没有影响,该复合材料的抗拉强度随碳纤维含量的增加而增加,其抗拉强度较基体材料提高50%以上,但塑性指标却明显下降.     

Long-fiber-reinforced thermoplastic matrix composites by slurry deposition

A process for producing long-fiber-reinforced thermoplastic matrix composites is described. This process, based on papermaking technology, consists of depositing a mixture of a polymeric powder and reinforcing fibers from an aqueous slurry. The degree of homogeneity of the mixture and the subsequent ability to handle the dried sheet have been significantly improved by the addition of less than 5% pulp fibers, based on solids concentration, to the slurry. The dried sheet is then consolidated into a composite sheet with a continuous matrix phase by the application of heat and then pressure. Tensile properties and the degree of reinforcement efficiency of composites produced by this process have been shown to be comparable to those produced by melt impregnation techniques.     

Microstructure and mechanical properties of TiB2-reinforced 7075 aluminum matrix composites fabricated by laser melting deposition

In this study, we adopt laser-melting deposition (LMD) technology to fabricate TiB₂/7075 aluminum matrix composites (AMCs), and we investigate in detail the effect of the TiB₂ content on the microstructure, nano-hardness, compressive properties, and wear performance. We prepare experimental samples by using a laser power of 800?W and a velocity of 0.01?m/s, and the results are evaluated. It was observed that the reinforcement particles dispersed irregularly throughout the Al matrix as the TiB₂ contents increased. The grain size of the fine-grain zone decreased appreciably by 31.9% from 8.41?µm (LMD sample without TiB₂ reinforcement) to 5.73?µm. Furthermore, the AMCs with 4?wt% reinforcement exhibited impressive mechanical properties, i.e., nanohardness of 1.939 Gpa, compressive strength of 734.8?MPa, and a wear rate of 1.889?×?10^?4 mm³/Nm. The wear resistance improved and the wear mechanism changed from adhesive wear to debris wear with the addition of TiB₂ reinforcement.     

Synthesis of nanostructured metal oxide by liquid-phase deposition

We synthesized hollow magnetite particles by liquid-phase deposition (LPD) using polystyrene (PS) particles as templates. We prepared β-FeOOH/PS composite particles by adding boric acid to an aqueous FeOOH/NH₄F·HF solution. PS particles were used as templates. Calcination of the composite particles under vacuum produced hollow magnetite (Fe₃O₄) particles that were readily attracted to a magnetic field.     

Controllable growth of aluminum nanorods using physical vapor deposition

This letter proposes and experimentally demonstrates that oxygen, through action as a surfactant, enables the growth of aluminum nanorods using physical vapor deposition. Based on the mechanism through which oxygen acts, the authors show that the diameter of aluminum nanorods can be controlled from 50 to 500 nm by varying the amount of oxygen present, through modulating the vacuum level, and by varying the substrate temperature. When grown under medium vacuum, the nanorods are in the form of an aluminum metal - aluminum oxide core-shell. The thickness of the oxide shell is ~2 nm as grown and is stable when maintained in ambient for 30 days or annealed in air at 475 K for 1 day. As annealing temperature is increased, the nanorod morphology remains stable while the ratio of oxide shell to metallic core increases, resulting in a fully aluminum oxide nanorod at 1,475 K.     

Synergistic strengthening effect of graphene-carbon nanotube hybrid structure in aluminum matrix composites

High-performance reinforcement and tailored architecture are currently explored to develop advanced metal matrix composites. In this work, aluminum (Al) matrix composite reinforced by hybrid carbon nanofillers was fabricated by a composite flake assembly process. It was found that for various carbon nanofiller volume fractions, a striking synergistic strengthening effect was achieved by employing graphene (reduced graphene oxide, RGO) and carbon nanotube (CNT) hybrid structure as reinforcement in the Al matrix. Particularly, a tensile strength of 415 MPa was achieved with the addition of 1.5 vol.% of RGO-CNT hybrid, which is significantly higher than those reinforced by individual CNT or RGO (326 and 331 MPa, respectively). The synergistic strengthening effect was attributed to the formation of a planar network of RGO and CNT, which improves the load transfer efficiency between the matrix and the reinforcement in composites. Our study highlights the importance of reinforcement architecture for enhancing the strengthening ability in composites, and provides an effective route to fully take the advantage of the superior properties of various reinforcements.     

Microstructures and thermal properties of aluminum matrix composites based on wood templates

Wood with its rational and magical inner structures was used as a template to fabricate Al/C and Al/(SiC + C) composites in this research. Porous carbon was first pyrolyzed from the wood template. The final composites were then obtained by injecting aluminum alloy and silicone resin into the porous carbon. The microstructures, thermal conductivity, and thermal expansions of these products were then analyzed. The results indicated that the structures of the composites are controlled by the natural structure of wood. Moreover, the composites exhibit a lower coefficient of thermal expansion than aluminum and a higher thermal conductivity than porous carbon.     

Electrical properties of composites of hard metal carbides in a polymer matrix

The electrical conductivity of composites containing hard metal carbide powder in a nonconducting polymer matrix has been studied. In composites with low and medium filler contents, the expansion of the nonconducting matrix with increasing temperature caused interruption of conducting paths and a rapid drop in conductivity (switching effect). In contrast, at high filler loadings (Φ_P > 50 vol%), a continuous and slight decrease in conductivity with temperaute inducates a specific composite structure with a dense particle arrangement and a great number of conducting contants, which change only little during heating.     

Synthesis of aluminum titanate using stabilizing additives

The advantages of joint preliminary grinding of the initial-material components, as compared to separate grinding, and its effect on the regularities of phase formation in the aluminum oxide — titanium oxide system are considered. Joint activation makes it possible to shorten the time expended on thermal synthesis of TiO₂ · Al₂O₃. The effect of stabilizing additives of magnesium and silicon oxides and talc on the kinetics of thermal synthesis of aluminum titanate is studied. It is proposed that talc in an amount of 7% be used as a stabilizing additive to prevent incongruent melting of TiO₂ · Al₂O₃ accompanied by formation of the initial components. Translated from Steklo i Keramika, No. 4, pp. 20 – 23, April, 1999.     

Characterisation of thermoplastic matrix composites using variable frequency microwave

Abstract

In most industrial microwave processing operations, the frequency of the microwave energy launched into the waveguide or cavity containing the sample is fixed. This brings with it inherent heating uniformity problems. This paper describes a new technique for microwave processing, known as variable frequency microwave (VFM) processing, which alleviates the problems brought about by fixed frequency microwave processing. In VFM processing, microwave energy over a range of frequencies is transmitted into the cavity in a short time, e.g. 20 μs. It is therefore necessary to determine the best frequency range for processing a material. The best range frequency for microwave processing of five different thermoplastic matrix composites using the VFM facilities has been determined. The optimum frequency band for microwave processing of these five materials was in the range 8–12 GHz. This data enables bonding of the materials using microwave energy under the most favourable conditions.     

金属基复合材料复合层的制备工艺及发展概况

金属基复合材料作为第三代复合材料,是21世纪复合材料的主要发展方向,其复合层的质量关系到该材料的组织性能是否满足使用要求.所以其复合层的制备工艺对复合材料的使用至关重要.本文概述了钢基复合材料先进的制备工艺及其发展概况,以期抛砖引玉,使该材料的制备工艺取得新的突破.     

Manufacturing of polymer/metal composites by fused deposition modeling process with polyethylene

In this study, production of metal/polymer composites using polyethylene as the matrix with various contents of metal powder was investigated. Fused deposition modeling (FDM) process is one of the most popular and conventional additive manufacturing methods to produce three-dimensional (3D) specimens from computer-aided design data with complex geometry and lower prices in comparison with the alternative methods. Given the advantages of this process, it seems inevitable for the development of new materials. Utilizing semicrystalline plastics impose challenges for producing parts due to printing issues such as distortion and warpage. In this experimental work, a compounding production line was implemented to produce composite filaments with 25, 50, and 75 wt % of copper powder suitable for the FDM process. After dealing with printing issues, flexural, electrical conductivity, and bulk density tests were done. The micrographs of the specimens were examined via scanning electron microscopy to reveal the distribution of the copper particles. It is believed that the metal/polymer filament could be used to print new 3D parts. The material could be utilized in electromagnetic structures for some specific applications, such as shielding, with new properties. Also, by solving printing problems for a semicrystalline polymer, it can be encouraging to examine printing process for other rarely used thermoplastics. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48717.     

Fabrication technologies for oxide–oxide ceramic matrix composites based on electrophoretic deposition

Electrophoretic deposition (EPD) was used to fabricate alumina matrix composites with high volume fraction of woven fibre mat (Nextel™ 720) reinforcement in a multilayer structure. Colloidal suspensions of Al₂O₃ nanoparticles in ethanol medium with addition of 4-hydrobezoic acid were used for EPD. Two different techniques were developed for fabrication of Al₂O₃ matrix/Nextel™ 720 fibre composites. The first method is a combination of standard EPD of single fibre mats with a subsequent lamination procedure to fabricate the multilayered composite. The second method involves the simultaneous infiltration of several (three or more) Nextel™ 720 fibre mats by EPD in a tailor-made cell. The composites exhibit a homogeneous matrix microstructure, characterised by a very high particle packing density and relatively low porosity after sintering at 1300 °C. The EPD cell allows production of relatively large bodies (10 cm diameter). By combination of the multilayer EPD infiltration and lamination processes developed here, thick ceramic matrix composite components (>10 mm thickness) can be fabricated, which opens the possibility of greater industrial application of the materials.     

增材制造连续碳纤维增强金属基复合材料性能

采用增材制造工艺方法进行具有高比强度、密度小等优良性能连续碳纤维增强金属基复合材料的直接制备。研究了连续碳纤维表面改性、路径搭接率、打印喷头温度、基板温度、打印速度等过程处理方法及工艺参数对所制备金属基复合材料抗拉强度的影响。研究结果表明,对连续碳纤维原材料实施表面改性处理,可以实现制备过程中熔融金属基体与连续碳纤维之间的良好浸润复合,以提高复合材料的抗拉强度;增大路径搭接率,可以有效提高增材制造复合材料内部纤维的体积占比,从而增大其抗拉强度;升高打印喷头温度、基板温度、打印速度,可以减小熔融金属表面张力,提高其流动性,并有利于沉积层间实现良好重熔,从而有效避免在已沉积层表面裂纹处和路径搭接区凹坑处形成气孔缺陷,进一步提升复合材料的抗拉强度。