Design and development of novel cost effective casting route for production of metal matrix composites (MMCs)

The production of metal matrix composites (MMCs) has been a great challenge for research fraternity. A number of modified and hybrid techniques has been designed and developed by the researchers to tackle the fundamental issues related to production of MMCs. The fundamental issues are: uniform distribution of reinforcement, wettability of reinforcement with the matrix, porosity etc. In the present research experimental investigation, a novel technique has been designed and developed for the production of MMCs using stir casting route. The stir casting route consists of melt-stir-squeeze-bottom pouring to yield MMCs. Simulation of the experimental setup has been performed to optimize the stirring parameters such as blade angle, rotational speed and duration of stirring. The microstructure investigation has been performed to ensure the uniform distribution and bonding of reinforcement with the matrix.     

金属基复合材料强度的影响因素

过去30年里金属基复合材料虽然得到了广泛的研究与发展，但其性能一致性差的问题制约了其应用，因此复合材料的性能设计受到了普遍的关注。强度是材料在工程应用上重要的衡量指标，对强度影响因素的研究对复合材料的性能设计至关重要。本文着重分析了复合材料中基体合金化，增强体，基体与增强体的相容性，界面，工艺等因素对强度的影响。     

Al-Mg系自生纤维增强铝基复合材料组织与性能

为解决金属基复合材料中外加增强体与基体间异质界面对材料性能带来的不利影响，提出一种基于粉末冶金技术的原位复合新工艺，并制备出自生金属间化合物纤维增强铝基复合材料。研究结果表明，原位生成的金属间化合物纤维均匀分布在基体中，并平行于材料制备时的挤出方向；原位复合材料的增强效果明显，屈服强度比外加复合材料和基体分别高出28％和95．7％，断裂强度则相应提高了20．6％和88．5％；原位复合材料的强化机制主要是基体和增强体间界面结合良好，既能发挥基体的塑韧性，又能有效发挥自生增强体的强度优势，材料的断裂机制为自生纤维脆性断裂和劈裂。本研究同时表明，此方法工艺简单，成本低廉，且效率高，容易实现产业化。     

Progress in Metal Matrix Composites

Abstract

Metal matrix composites are produced by several contrasting manufacturing techniques and in many different shapes and forms. Solid state processing routes are generally favoured for putative aerospace applications, whereas liquid metal routes appear more promising for automobile applications. Both groups of production routes can accommodate reinforcements of continuous fibre, short fibre, particulate and hybrid fibre-particulate types and the reinforcement phase can be distributed uniformly throughout the composite structure or, using preform technology, in selected regions of the casting.

The greatest problem arising during manufacture and during post-production thermal processing of MMCs is that of chemical instability of the constituent phases. Thermodynamic incompatibilities restrict the use of certain manufacturing routes for specific composite couples and limit the working environment of others. Commercial aspects of MMC production, either directly to near net shape or by subsequent machining, indicate high cost penalties for specific limited gains.

The mechanical properties of MMCs are inevitably a compromise between the properties of the matrix and reinforcement phases. In particular, ductility and toughness are frequently sacrificed for higher modulus. Measures to improve toughness whilst maintaining stiffness are being explored. Wear properties of MMCs are extremely good; machinability, on the other hand, can be poor.     

Mechanical spectroscopy of thermal stress relaxation at metal–ceramic interfaces in Aluminium-based composites

The micromechanisms of thermal stress relaxation in aluminum-based metal-matrix composites (MMCs) have been investigated by mechanical loss and dynamic shear modulus measurements during thermal cycling between 100 and 500 K. A transient mechanical loss maximum, which is absent in the monolithic material, appears during cooling. This damping maximum is strongly dependent on the measurement parameters: oscillation frequency, oscillation amplitude and cooling rate. In addition, it increases with the volumetric reinforcement content and decreases if the matrix strength is improved. The shear modulus evolution during thermal cycling shows that no detectable interfacial debonding occurs. Compared with alloyed MMCs, Al4N-based MMCs show the highest damping maximum simultaneously with a plateau in the elastic shear modulus. The mechanical loss maximum is attributed to dislocation generation and motion near the interfaces, resulting from the differential thermal contraction of matrix and reinforcement. A new model is proposed which describes this specific mechanical behavior of MMCs in terms of the development of microplastic zones in the matrix near the metal–ceramic interfaces.     

The stability of interfaces in high-temperature metal-matrix composites

The interface between the matrix and the reinforcement is an area of great importance in the design of viable high-temperature metal-matrix composites (MMCs). Thorough understanding of the phenomena taking place at the interface is necessary to ensure reliable performance, but the thermodynamic data that would help to predict interfacial reactions are lacking for many systems. However, given certain knowledge, interfaces can be classified according to their stability, providing a tool for composites designers and an impetus for further fundamental work. This article describes the classification system and provides examples of interfacial behavior in a titanium-based material.     

Cutting forces and TEM analysis of the generated surface during machining metal matrix composites

Cutting of metal matrix composites (MMCs) has been considerably difficult due to the extremely abrasive nature of the reinforcements that causes rapid tool wear and high machining cost. An investigation was carried out to clearly understand the role played by the ductile matrix on the machining performance based on the estimation of line defects generated as a result of cutting. The microstructural studies were conducted using transmission electron microscopy (TEM) on the machined surface to reveal the deformation pattern of the work hardening matrix and its correlation with the forces generated during turning MMCs. Cracking and debonding of the reinforcement particles are the significant damage modes that directly affect the tool performance. It was found that the particle size and volume fraction affect the extent of deformation in the generated surface. Also the machining forces are correlated to the plastic deformation characteristics of the matrix material. This investigation provided valuable information on the deformation behaviour of particulate reinforced composites that can improve the performance and accuracy of machining MMCs.     

Mechanical properties and fracture of Al–15 vol.-%B4C based metal matrix composites

The present work was performed on three aluminium metal matrix composites (MMCs) containing 15 vol.-%B₄C particles. The matrix in two of these materials is pure aluminium, whereas the matrix of the third material was an experimental 6063 aluminium alloy. All composites were homogenised at elevated temperatures for 48 h before being quenched in warm water. The quenched samples were aged in the range of 25–400°C for 10 h, at each temperature. Hardness and tensile tests performed on the aged MMCs show that the presence of Zr (with or without Ti) resulted in a noticeable hardening due to the precipitation of a Zr rich phase. Maximum strengthening was obtained from the 6063 based MMC due to the precipitation of Mg₂Si phase particles. The present technique used to produce the MMCs examined proved capable of manufacturing composites with a uniform distribution of B₄C in the matrix with a strong degree of matrix/particle bonding. When the MMC samples were deformed to failure, the B₄C was fractured transgranularly without debonding from the matrix. The addition of Zr and Ti resulted in the formation of protective layers around the B₄C particles that were retained after fracture; these protective layers were not affected by the B₄C particle size (0·15–20 μm). Stacking faults were commonly observed in fractured Al 6063/B₄C/15p samples. The precipitation of zirconium–titanium compounds during aging contributed to the composite strength.     

高阻尼AA6061/SiCp/石墨复合材料的制备与性能

介绍采用粉末冶金法制备ＡＡ６０６１／ＳｉＣｐ／石墨混杂金属基复合材料的工艺过程,并对复合材料的力学和阻尼性能进行了初步探讨。粉末冶金法制备的ＡＡ６０６１／ＳｉＣｐ／石墨混杂金属基复合材料中增强增阻颗粒分布均匀,其体积分数可精确控制,加之制备温度低,可避免有害的界面反应。ＳｉＣ颗粒作为增强剂能够增加复合材料的刚度和强度,而石墨颗粒为增阻剂可以提高复合材料的阻尼特性。试验结果表明,能够应用粉末冶金法制     

金属基复合材料相界面区力学性能显微力学探针分析

雾化喷射沉积成型２０１４铝合金＋１５％ＳｉＣｐ和１８Ｎｉ马氏体时效钢＋１０％（Ａｌ２Ｏ３）ｐ金属基复合材料表现出加速时效行为。采用显微力学探针技术研究了复合材料的时效行为，发现在增强颗粒附近存在明显的弹性模量和硬度的梯度分布１，是热错配应力造成的位错密度分布引起的析出相梯度分布的结果。     

Prediction of effect of volume fraction, compact pressure and milling time on properties of Al-Al2O3 MMCs using neural networks

An artificial neural network (ANN) model was developed to predict the effect of volume fraction, compact pressure and milling time on green density, sintered density and hardness of Al-Al₂O₃ metal matrix composites (MMCs). Al-Al₂O₃ powder mixtures with various reinforcement volume fractions of 5, 10, 15% Al₂O₃ and milling times (0 h to 7 h) were prepared by mechanical milling process and composite powders were compacted at various pressure (300, 500 and 700 MPa). The three input parameters in the proposed ANN were the volume fraction, compact pressure and duration of the milling process. Green density, sintered density and hardness of the composites were the outputs obtained from the proposed ANN. As a result of this study the ANN was found to be successful for predicting the green density, sintered density and hardness of Al-Al₂O₃ MMCs. The mean absolute percentage error for the predicted values didn’t exceed 5.53%. This model can be used for predicting Al-Al₂O₃ MMCs properties produced with different reinforcement volume fractions, compact pressures and milling times.     

Review of recent trends in friction stir welding process of aluminum alloys and aluminum metal matrix composites

Welding is a vital component of several industries such as automotive, aerospace, robotics, and construction. Without welding, these industries utilize aluminum alloys for the manufacturing of many components or systems. However, fusion welding of aluminum alloys is challenging due to several factors, including the presence of non-heat-treatable alloys, porosity, solidification, and liquation of cracks. Many manufacturers adopt conventional in-air friction stir welding (FSW) to weld metallic alloys and dissimilar materials. Many researchers reported the drawbacks of this traditional in-air FSW technique in welding metallic and polymeric materials in general and aluminum alloys and aluminum matrix composites in specific. A number of FSW techniques were developed recently, such as underwater friction stir welding (UFSW), vibrational friction-stir welding (VFSW), and others, for welding of aluminum alloy joints to overcome the issues of welding using conventional FSW. Therefore, the main objective of this review is to summarize the recent trends in FSW process of aluminum alloys and aluminum metal matrix composites (Al MMCs). Also, it discusses the effect of welding parameters of the traditional and state-of-the-art developed FSW techniques on the welding quality and strength of aluminum alloys and Al MMCs. Comparison among the techniques and advantages and limitations of each are considered. The review suggests that VFSW is a viable option for welding aluminum joints due to its energy efficiency, economic cost, and versatile modifications that can be employed based on the application. This review also illustrated that significantly less attention has been paid to FSW of Al-MMCs and considerable attention is demanded to produce qualified joint.     

Metal-matrix composites in ground transportation

Metal-matrix composites (MMCs) are used in a variety of automotive and other ground transp ortation applications. This article provides a brief overview of the major applications of MMCs in ground transportation. The main attractive features of MMCs are: high strength-to-weight ratio, enhanced mechanical and thermal properties over conventional materials, improved fatigue and creep characteristics, better wear resistance, and general tailorability of properties. Because the transportation industry is extremely cost-sensitive, reducing the manufacturing costs of MMC components will aid in the use of MMCs.     

Tribological Behavior of Aluminum Alloy AlSi10Mg-TiB<Subscript>2</Subscript> Composites Produced by Direct Metal Laser Sintering (DMLS)

Direct metal laser sintering (DMLS) is an additive manufacturing technique for the production of parts with complex geometry and it is especially appropriate for structural applications in aircraft and automotive industries. Aluminum-based metal matrix composites (MMCs) are promising materials for these applications because they are lightweight, ductile, and have a good strength-to-weight ratio This paper presents an investigation of microstructure, hardness, and tribological properties of AlSi10Mg alloy and AlSi10Mg alloy/TiB₂ composites prepared by DMLS. MMCs were realized with two different compositions: 10% wt. of microsize TiB₂, 1% wt. of nanosize TiB₂. Wear tests were performed using a pin-on-disk apparatus on the prepared samples. Performances of AlSi10Mg samples manufactured by DMLS were also compared with the results obtained on AlSi10Mg alloy samples made by casting. It was found that the composites displayed a lower coefficient of friction (COF), but in the case of microsize TiB₂ reinforcement the wear rate was higher than with nanosize reinforcements and aluminum alloy without reinforcement. AlSi10Mg obtained by DMLS showed a higher COF than AlSi10Mg obtained by casting, but the wear rate was higher in the latter case.     

Effect of Heat Input on Mechanical and Metallurgical Properties of Friction Stir Welded AA6061-10% SiCp MMCs

Metal matrix composites (MMCs) reinforced with SiC particles combine the matrix properties with those of the ceramic reinforcement, leading to higher stiffness and superior thermal stability with respect to the corresponding unreinforced alloys. However, their wide application as structural material needs proper development of a suitable joining process. In this investigation, an attempt was made to study the effect of heat input on the evolution of microstructure in weld region of friction stir welded AA6061-10% SiCp MMCs. The tensile properties of the joints were evaluated and they are related with microstructure and heat input of the process. The microstructure characterization of the weld zone shows evidence of a substantial grain refinement of the aluminum matrix and fracturing of reinforcement particles due to dynamic recrystallization induced by the plastic deformation and frictional heating during welding.     

Microstructure,mechanical and corrosion properties of electron-beam-melted and plasma-transferred arc-welded WC_P/NiBSi metal matrix composites

As one of the new additive manufacturing processes,electron beam melting(EBM)has seen its promising potential in the fabrication of metal matrix composites(MMCs)components with complex geometries.In this work,WC_P/NiBSi MMCs were fabricated by EBM and plasma-transferred arc welding(PTAW)for a comparative study.The microstructures of both samples were examined using a scanning electron microscope(SEM)equipped with an electron backscattered diffraction(EBSD)detector.The macrohardness was tested using a Rockwell hardness method(Type C),while the microhardness was measured using different loadings(0.5-1.0 N)based on different phases.The anti-abrasion performance was tested as per the ASTM G105 standard.The corrosion behavior of the MMCs was also assessed by potentiodynamic polarization.The results indicate that the EBM bulk and the PTAW cladding MMCs exhibit different microstructures due to the different local solidification conditions.This is believed to lead to the varied mechanical properties and corrosion resistance of the MMCs,and the possible mechanisms were also discussed.     

Metal matrix composites for fabricating tooling

The objective of this work is to investigate the fabrication, microstructures and, properties of metal matrix composites (MMCs) net-shaped using a four-step hybrid manufacturing method. The manufacturing method consisted of soft tooling fabrication, slurry casting, debinding-sintering followed by metal infiltration. Firstly, silicone rubber molds were fabricated. Subsequently, WC-Co pellets and stainless steel powders were mixed with polymer-based binders and cast into these rubber molds. After solidification, the parts were removed from the rubber molds, and placed in a furnace for debinding and sintering. Finally, sintered parts were infiltrated with bronze and the ensuing microstructures and properties were evaluated. The dimensional changes and mechanical properties of these MMCs as a function of amount of infiltrant were also examined. The results showed that the wear resistance of the MMC parts was comparable to M2 and D2 steels. Demonstrations of the process for net-shaping MMCs were conducted by fabricating wear-resistant tooling. The implications for fabricating MMCs by directly 3D printing rubber molds soft tooling are presented.     

Emerging technologies for the in-situ production of MMCs

Among the numerous methods of producing discontinuously reinforced metal-matrix composites, technologies allowing insitu production of the reinforcing phase offer significant advantages from a technical and economic standpoint. The in-situ formation of a ceramic second phase provides greater control of the size and level of reinforcement, yielding better tailorability of the composite properties. As an example, significantly finer ceramic particulates are possible, which minimizes toughness degradation that is traditionally associated with composites containing relatively large particles. Several emerging, innovative technologies in this area are under development. As with any new technology there are technical challenges, but it is believed that these processes have unique capabilities and, thus, they present cost-effective production processes for metal-matrix composites.     

铝基复合材料在交通运输工具中的应用

铝基复合材料在汽车中的应用日益增多。杜拉坎是一种用常规铸锭冶金法生产的以氧化铝粒子增强的铝合金基复合材料,已在国外一些汽车中批量应用。     

Effects of particle arrangement and particle damage on the mechanical response of metal matrix nanocomposites: A numerical analysis

The spatial distribution of reinforcement particles has a significant effect on the mechanical response and damage evolution of metal matrix composites (MMCs). It is observed that particle clustering leads to higher flow stress, earlier particle damage, as well as lower overall failure strain. In recent years, experimental studies have shown that reducing the size of particles to the nanoscale dramatically increases the mechanical strength of MMCs even at low particle volume fractions. However, the effects of particle distribution and particle damage on the mechanical response of these metal matrix nanocomposites, which may be different from that observed in normal MMCs, has not been widely explored. In this paper, these effects are investigated numerically using plane strain discrete dislocation simulations. The results show that non-clustered random and highly clustered particle arrangements result in the highest and lowest flow stress, respectively. The effect of particle fracture on the overall response of the nanocomposite is also more significant for non-clustered random and mildly clustered particle arrangements, in which particle damage begins earlier and the fraction of damaged particles is higher, compared to regular rectangular and highly clustered arrangements.