Metal-Matrix Composites

An aluminum alloy, i.e., aluminium-silicon alloy reinforced with particulates of titanium diboride (TiB₂) and in situ processed metal-matrix composites can safely be categorized to be an advanced material that has shown much promise for selection and use in the industries spanning structural, automotive, aerospace, and both performance-critical and non-performance-critical end products. This is essentially because of its high strength-to-weight [σ/ρ] ratio and good-to-excellent wear resistance characteristics. These composites tend to exhibit superior wear resistance coupled with good fatigue strength in comparison with the monolithic counterpart at both room temperature and at elevated temperatures. An exothermic reaction between the hexafluorotitanate (K₂TiF₆) salt, potassium borofluoride (KBF₄) salt, and molten aluminum-silicon (Al-Si) alloy results in the production of the TiB₂ particulates which is present as the reinforcing phase in the soft aluminum alloy metal matrix. Two volume fractions of the TiB₂ particulate reinforcement, i.e., 3 weight pct. and 6 weight pct. were considered for synthesizing test specimens of the composite material. The presence of both titanium and boron in the reinforcing TiB particlesB was confirmed using energy-dispersive X-ray analysis. Study of microstructure of the in situ processed composite specimens revealed a near-uniform distribution of the TiB₂ particulates in the aluminum alloy [Al-Si alloy] metal matrix. Mechanical properties and dry sliding wear behavior of the as-synthesized composite materials were studied using a pin-on-disk tribometer. The coefficient of friction (COF) and wear rate were studied with precision under various conditions. The intrinsic mechanisms governing wear and elemental analysis of the wear surfaces of the composite test specimens were established following examination in a scanning electron microscope.

The fabrication of aluminium matrix composites with lightweight nanoreinforcements has proven to be very attractive due to their superior properties. In the present study, Carbon Nanotubes (CNTs) and Graphene Nanoplatelets (GNPs) have been incorporated into an aluminium matrix using the Spark Plasma Sintering (SPS) process. Composite samples with varying amounts of CNTs and GNPs (0.1–0.5 wt.%) were prepared and the effect on the mechanical properties was investigated. The microstructural evolution and the yield strength of each sample were evaluated and compared with neat reference samples. It was established that the CNT reinforced nanocomposites exhibited a relatively higher yield strength than the GNP reinforced. An improvement by 13% and 18%, respectively, for additions of 0.5 wt.% CNTs was found. Based on the experimental results, the presence of a 2D planer geometry is modelled and discussed in view of its ability to enable a more efficient network at low wt.% of the fillers.

Aluminum-graphite (Al/Gr) metal matrix composites (MMC) have shown reduced friction, wear, and resistance to seizure. Triboinformatics or the data-driven approach is promising in predicting the tribological behavior of metal alloys and metal matrix composites (MMC). Five Machine Learning (ML) models: Artificial Neural Network (ANN), K-Nearest Neighbor (KNN), Support Vector Machine (SVM), Gradient Boosting Machine (GBM), and Random Forest (RF) have been applied to predict the coefficient of friction (COF) and wear rate of aluminum (Al) alloys and Al/Gr MMCs using material and tribological variables. The performance metrics indicate that the graphite incorporation as a solid lubricant makes the friction and wear behavior more consistent and predictable. Feature importance analysis shows that graphite content is the most significant variable in both wear rate and COF prediction of Al/Gr composites while tribological variables are found significant for aluminum alloys. Additionally, material hardness is found important in friction and wear prediction for both aluminum alloys and Al/Gr MMCs.

In today's technological and scientific era, new generation materials are intended to achieve the demands of several engineering industries. The researchers are now turning their attention towards new age composite materials from monolithic materials which can be attributed to the increased and exceptional capabilities of these materials. Aluminium-based hybrid metal matrix composites have a tremendous potential and can be used for many technical applications that can meet the growing need for enhanced properties such as better toughness, corrosion resistance, and high strength. Aluminium-based metal matrix composites are at the top of the list of composites for a variety of applications in automotive, aircraft, and marine industries owing to their high strength-to-weight ratio, better toughness, high wear resistance, and hardness. This literature review highlights the various aspects pertinent to hybrid reinforcement in composites where aluminium was employed as the integral matrix material. While different fabrication techniques and processing routes were also studied by means of mechanical characterization, property enhancements with further augmentation in mechanical and thermal properties resulting in lower wear rates, and better microstructures. The comparison between various reinforcements, such as nitrides, borides, carbides, oxides, etc. has been evaluated, aiming to climax the properties and obtain the best results for diverse technical applications. The aluminium-based hybrid metal matrix composites’ future capabilities and scope are also covered at the conclusion of this article.

Lightweight composite materials require a healthy combination of mechanical strength, wear resistance, and good damping capacity for purpose of selection and use in engine and structural parts of the industries spanning automobile and aerospace. In this short and succinct paper, the salient aspects of an aluminium alloy reinforced with particulates of titanium diboride (TiB₂) are presented and discussed. Salient aspects specific to measurement of damping capacity using experimental modal analysis are neatly presented. The tribological behaviour of the engineered aluminium alloy metal matrix composite and the role and contribution of different sliding variables are presented and adequately discussed through pin-on-disc tests. The damping capacity of the TiB₂ particulate-reinforced aluminium alloy revealed an observable improvement over the as-cast counterpart and comparable to grey cast iron. The intricacies specific to tribological behaviour of the engineered aluminium alloy composites is highlighted with respect to microscopic segregation of the particulate reinforcement (TiB₂) coupled with the role of test parameters. The fundamental strengthening and damping mechanism governing behaviour of the chosen composite is neatly detailed considering the conjoint and mutually interactive influences of reinforcement agglomeration, nature of loading, and interfacial bonding.

Additive manufacturing (AM) or 3D printing (3DP) is an approach to process parts directly from its computer-aided design (CAD) file. Additive manufacturing (AM) is changing the landscapes of current industrial practices. On-demand manufacturing using additive manufacturing (AM) technologies is a new trend that will significantly influence many industries and product design protocols. Since there is no need for part-specific tooling, different parts can be built using the same machine. We have worked on AM of metal matrix composites over the last two decades using the directed energy deposition (DED) and powder bed fusion (PBF) processes. Among others, we have manufactured parts with compositional and functional gradation using titanium (Ti) alloys, steels, Inconel 718, and tungsten for structural and biomedical applications. This presentation will focus on some of the key success stories from our research and current challenges in the field.

Developing human habitation on extraterrestrial sites such as Moon and Mars has been scientists’ dream for many years. Establishing such an outpost requires the development of in situ fabrication and characterization of various constructions and resources for reliable performance and developing repair methods and continued operation of components sent to the surface. The surface of Mars is covered with heterogeneous soil-like rock termed as regolith. The processability of this regolith into a strong yet stable structure needs to be addressed. To this end, additive manufacturing (AM) is considered as a promising approach to making such structures with improved properties. In this study, we have utilized the directed energy deposition (DED) technique to fabricate premixed Martian regolith (MR) and Ti6Al4V (Ti64). AM-processed samples were tested for hardness and microstructures to understand the processing–structure–property relationship. While the hardness profile shows an increase from 171.5 ± 1.5 HV_0.2 in the substrate to 924.7 ± 38 HV_0.2 in the pure deposition of Martian regolith, the microstructure reveals there are different crack and void zones in the 10 weight percent addition of Martian rock to the Ti64 base powder. Our results show promise for developing hard coating fabrication technologies on the Martian surface.

Metal matrix composites with fiber reinforcement elements have a high potential to improve properties such as mechanical strength and elastic behavior. Therefore, the development of fiber-reinforced aluminum alloys provides an opportunity for increased use in the automotive, aerospace, and aerospace fields. In this study, studies on the development of the interface properties required to make aluminum composite with reinforcing elements such as carbon fiber, metallic fiber, and glass fiber were compiled. In addition, the usage areas of the composites that can be produced and their effects on possible innovative technologies will be discussed.

Due to their high specific strength, aluminium-based metal matrix nanocomposites reinforced with ceramics are an attractive proposition for applications in the transport sector. High-Pressure Die Casting (HPDC) is a cost-effective manufacturing route for the mass production of aluminium castings exhibiting complex near-net-shape geometries. Through the application of high pressure and high cooling rates, improved distribution of the reinforcing particles compared to other casting methods can be attained. This is a result of the increased filling capacity of the composite melt and the resultant finer grain structure. In this study, an AlSi9Cu3 (LM24) commercial alloy was reinforced with SiC nanoparticles. The reinforcement was introduced using novel Al-nanoSiC alloys and processed using stir mixing, ultrasonic processing, and HPDC technologies to achieve enhanced mechanical properties. The results showed the good distribution of the loose SiC agglomerates, demonstrating a nearly 40% reduction in the Al grain size, from ~23.7 µm to ~14.8 µm, and indicating a ~15 MPa and ~18 MPa increment in the yield strength (YS) and the ultimate tensile strength (UTS), due to a combined effect of the grain refinement, CTE strengthening, and Orowan strengthening.

The microstructure and mechanical properties of aluminum-magnesium-boron and aluminum-magnesium-cadmium composites with boride and intermetallic particles have been investigated. In aluminum-magnesium alloys, the beta phase readily forms at grain boundaries, and is responsible for the failure of the structural components made of these alloys as a result of stress corrosion cracking. Here, we report the prevention of the beta phase formation within grains as well as at grain boundaries in aluminum-magnesium composites by alloying separately with small amount of boron and cadmium. Transmission electron microscopy, energy dispersive spectroscopy, and X-ray diffraction were used to characterize the boride phase, interfaces, intermetallic particles, and overall microstructure of aluminum matrix composites. It was revealed by transmission electron microscopy and X-ray diffraction that a boride compound, aluminum-magnesium di-boride, forms with the addition of boron in the aluminum matrix. Similarly, an intermetallic phase, cadmium-magnesium, forms in the aluminum -matrix with the addition of cadmium. In all these, the boride and intermetallic phases trap most of the magnesium and decrease the supersaturation level of magnesium in the matrix, which is a driving force for the formation of the beta phase_. This is a significant finding as it prevents the longstanding problem of sensitization in aluminum-magnesium alloys.

Globally, there has been a noticeable wave to gradually shift to green materials for the purpose of sustainable and climate-friendly development. The emergence of metal matrix composites contributed in a small way to this revolution. In this technical manuscript, the potential for metal matrix composites (MMCs) to aid in achieving sustainable and eco-friendly development goals is presented and briefly highlighted. The family of metal matrix composites is gaining increased attention among the scientific research community and industrial community for selection and use in applications due in essence to their advantages of being eco-friendly and sustainable coupled with an acceptable combination of physical properties and mechanical properties. The sustainable development goals can be made possible by applying the technology specific to metal matrix composites to both recyclable materials and materials having lightweight. This would result in replacing the existing material with metal matrix composite having fewer energy inputs for manufacturing while concurrently offering better characteristics. A short overview of the interest of the end-user in climate-friendly materials and related technologies is presented.

In this paper, microstructural development and properties (to include both physical and mechanical) of Zirconia Toughened Alumina (ZTA) composite reinforced with one volume percent of magnesium oxide (MgO)/multi-walled carbon nanotubes (MWCNTs) and processed using the technique of spark plasma sintering (SPS) are presently and adequately discussed. The role of processing parameters is both explained and appropriately highlighted through different sections of this manuscript. The average grain size, density, and microhardness were determined for the addition of magnesium oxide (MgO) reinforcement to the zirconia toughened alumina (ZTA) matrix. The highest fracture toughness was obtained for the addition of MWCNTs reinforcement to the zirconia toughened alumina (ZTA) matrix. Microhardness of the samples increased with the addition of magnesium oxide (MgO) reinforcement to the zirconia toughened alumina (ZTA) matrix, and the fracture toughness increased with the addition of MWCNTs to the zirconia toughened alumina (ZTA) matrix. The development of a material for use as a thermal barrier coating and also for its selection and use in dental-related applications is presented and briefly discussed.

This paper examines the turning process for an Al-4.5%Cu/TiB₂/3p MMC composite on an HMT lathe machine. An attempt has been made to explore the machining characteristics such as cutting force of the in situ MMC composite by varying the machining input parameters to include cutting speed, depth of cut, and feed rate. To have an enhanced understanding of the mechanism behind the turning operation, a three-dimensional finite element simulation model was developed for the estimation of cutting force by replicating the process of turning using the software code ANSYS 19.1. In this research study, the Johnson–Cook material and failure model was used for deformation of the constitutive material using finite element (FE) simulation modelling while considering the ductile nature of the Al-4.5%Cu/TiB₂/3p composite. In this study, several simulation models were developed with varying cutting parameters and finite element (FE) mesh size. The cutting forces were estimated by conducting both numerical simulation modelling and turning experiments of the chosen aluminum alloy metal matrix composite [Al-4.5%Cu/TiB₂/3p], and contrasts are drawn between the results obtained from using these two methods. The simulation models for the different cutting parameters and conditions exhibited near-similar chip morphology and cutting forces as was obtained through the turning operation. Further, as the mesh of the chip was refined, the cutting force was observed to be in good agreement with the experimental value.

Metal matrix composites (MMCs) have improved mechanical and thermal properties with applications in the automotive, aerospace, and tools industries among others. However, manufacturing MMCs is challenging and not cost-effective, resulting in limited utilization. Additive manufacturing techniques to form MMCs simplify the manufacturing process and therefore create opportunities for more widespread use of MMCs without compromising the optimum properties that can be reached. Among additive manufacturing techniques, binder jet additive manufacturing (BJAM) can further simplify the formation process of MMCs with tailorable mechanical and thermal properties mainly through reactive sintering and infiltration following the printing process. A concise review of MMCs and their fabrication techniques is presented, followed by presenting the current state of the utilization of BJAM in the fabrication of MMCs, and the opportunities and the challenges regarding the development of MMCs using BJAM.

Multifunctional palladium and palladium composite nanomaterials with tailored shapes and compositions are produced by solution chemistries. This includes (a) palladium nanocubes, (b) palladium nanocubes adorned on iron oxide nanospheres, (c) hollow palladium-silver nanospheres, (d) palladium nanospheres adorned on copper fiber, and (e) palladium nanostars adorned on copper fiber. Palladium nanocubes and palladium cubes adorned on iron oxide nanospheres are prepared in a one-step reduction approach in the presence of a structure-directing reagent, namely cetyltrimethylammonium bromide. Palladium-silver nanospheres are created through a simple galvanic replacement reaction by using silver spheres as a sacrificial template. Copper fibers are decorated with palladium nanostars and nanospheres in a one-step reduction process. The monometallic and bimetallic nanoparticles are stable and can be easily purified and retrieved by centrifugation and/or magnetic separation. A series of analytical tools were employed to elucidate nanomaterials’ physico-chemical properties, including scanning electron microscopy, energy-dispersive X-ray analysis, and ultraviolet–visible spectroscopy.

Functionally Gradient Materials (FGM) exhibit gradual transitions in the microstructure and/or the composition in a specific direction, the presence of which leads to variation in the functional performance within a part. The presence of gradual transitions in material composition in FGM can reduce or eliminate the deleterious stress concentrations and result in a wide gradation of physical and/or chemical properties within the material. Functionally graded metal–ceramic composites (FGMCC) are also getting the attention of researchers. Among the fabrication routes for FGMs such as chemical vapour deposition, physical vapour deposition, the sol–gel technique, plasma spraying, molten metal infiltration, self-propagating high-temperature synthesis, spray forming, and centrifugal casting, the ones based on solidification route are preferred for FGM because of their economics and capability to make large-size products. The present paper discusses and compares various solidification processing techniques such as centrifugal casting, sequential casting, selective infiltration and laser melting for the fabrication of functionally gradient metals and metallic composites.

This paper focuses on the role and significance of material development for simultaneous enhancement of electrical properties, thermal properties, and mechanical properties as economies shift towards reduced carbon emission with increased importance and emphasis being given to a “greener environment”, thereby emphasizing upon electrification as a potentially viable source of “clean” energy. In this manuscript, an effort is made to elaborate upon recent developments in the domain of copper nanocarbon composite materials for comparison with commercially pure copper with the prime objective of meeting the emerging demands of electrical devices. Carbon nanotubes and graphene have been some of the most widely studied materials due to a healthy combination of attractive physical properties and mechanical properties. The addition of these carbon allotropes to a copper matrix is anticipated to significantly enhance the electrical properties, thermal properties, and mechanical properties of the resultant copper nanocomposite. Further, integration of the constituent phases present is a non-trivial task that often results in detrimental effects and observably lower levels of enhancement than expected. This paper discusses the various methods of synthesis of the high-performing copper nanocarbon composites compiled in the published literature and attempts to consolidate the key findings in accordance with the process-structure–property framework. This is essential so that they can better fulfil their role and potential as next-generation materials for selection and use in power and electrical systems.

Recent progress in research and development of self-healing metal matrix composites (MMCs) by (a) embedding micro-balloons/capsules/tubes encapsulating a low-melting alloy as a healing agent into the matrix of a higher melting alloy, and by (b) reinforcing metal matrices with long, short, or nanosized NiTi and other Shape Memory Alloy (SMA) fibers is reviewed. Self-healing mechanisms, advantages, and disadvantages of different self-healing concepts in MMCs are discussed. Future challenges, knowledge gaps, and future research directions, including the need for autonomous and multicycle healing capability in MMCs are outlined.

Magnesium (Mg)-based materials have great potential to replace the existing aluminum alloys and steels used in applications spanning the industries of defense, aerospace, and automotive due in essence to their excellent specific strength [σ/ρ], damping characteristics, and impact resistance. In this research study, we design an ultralow density magnesium/glass microballoon (GMB) syntactic foam having a density of 1.47 g/cc using the technique of Disintegrated Melt Deposition (DMD). The resultant material offered a healthy combination of extraordinary properties outperforming the existing aluminium and iron syntactic foams in terms of a noticeable improvement in specific strength [σ/ρ]. Further, the wear resistance of magnesium under dry sliding conditions showed a significant enhancement (~2.5 times) following the addition of glass microballoon (GMB). Abrasion and oxidation were identified to be the dominant wear mechanisms post worn-surface analysis. Morphology of the worn specimen provided clean, clear, and convincing evidence for the occurrence of delamination wear, which has traditionally limited the competitive advantage of magnesium and its alloy counterparts for selection and use in safety–critical components in transportation vehicles. This can be effectively overcome by the development of the proposed syntactic foams, which provide a unique cushioning effect against the applied load.

Titanium and its alloys are known for their excellent biocompatibility and mechanical performance and are used widely in load-bearing implant applications. However, titanium is bioinert, i.e., it does not help in bone–tissue interactions, thus not aiding in expedited patient healing. The inorganic phase of the bone contains macro-nutrients in trace elements such as Mg²⁺, Si⁴⁺, which play a vital role in bone formation and remodeling. The addition of ceramics such as magnesium oxide (MgO) and silicon dioxide (SiO₂) in calcium phosphate coatings on titanium surfaces is widely popular. Magnesium is known to promote osteogenesis and silicon for angiogenesis. This study introduced 1 wt.% of MgO and SiO₂ in commercially pure titanium (CpTi) via additive manufacturing. Also, surface modification of titanium via TiO₂ nanotubes (TNTs) has proven to enhance osseointegration. We have tested the effects of MgO- and SiO₂-based CpTi compositions with TNT on osteoblast cells to evaluate the synergistic effect of ceramic addition and TNT on biocompatibility. It was observed that CpTi–TNT showed better osteoblast cellular proliferation and differentiation compared to CpTi–MgO–TNT and CpTi–SiO₂–TNT compositions. Post cell culture, good cellular coverage was observed on CpTi–TNT surfaces, whereas delamination of TNTs on MgOand SiO₂–TNT compositions was observed, indicating that TNTs were not stable on the ceramic-Ti surface.

Monitoring the level of contaminants in aquatic environment is critical for the protection of both human health and ecosystem function. Remediation and management of contaminated sites is often technically difficult and costly when there are large volumes of contaminated material. We developed a novel in situ detection and remediation capability able to acquire, display, and disseminate real-time pollution data. Specifically, we designed and created metal matrix hybrid composite comprised of (a) iron oxide (Fe₂O₃), (b) iron oxide–silica (Fe₂O₃/SiO₂), (c) iron oxide–silica–titania (Fe₂O₃/SiO₂/TiO₂), and (d) iron oxide–silica–titania–gold (Fe₂O₃/SiO₂/TiO₂/Au) nanoparticles that are effective, environmentally friendly and can be readily deployed at various contaminated sites for monitoring water polluted organic contaminants.

An efficient and rapid technique has been developed to enhance detection and extraction of organic dye contaminants from aqueous media using iron oxide-based nanomaterials. The technology is used to remotely remediate environments by scavenging and removing species from water sources at desired location. An electromagnetic field is selectively coupled to engineered iron oxide-based nano-antenna susceptor for nanoparticle’s regeneration and reuse. Specifically, the adsorption and removal of a model analyte, methylene blue dye (MB) identified here as ‘payload’, from a simulated contaminated water media is demonstrated. Remote manipulation of ‘payloads’ adsorbed on iron oxide-based materials is achieved through a non-contact and highly selective thermal process. Heat is selectively generated through susceptor nano-antennas, i.e. iron oxide-based nanomaterials when exposed to an electromagnetic field. The release of ‘payload’ from the iron oxide nanoparticles is due to localized temperature increase in the surrounding media upon exposure to the electromagnetic field. Heating is localized and occurs extremely fast, reducing the wasted thermal load on the environment. The susceptor nano-antennas can be activated remotely to generate localized heat on demand. Careful selection of the nano-antenna’s composition and surface chemistry permits manipulation and control of the adsorption and regeneration thermal process. Contaminant dye removal via adsorption onto sorbent media is faster, easier, and more economic and is, therefore, industrially preferred.

Each year, millions of tons of hazardous materials are shipped through tank cars on railroads. Accidents involving these tank cars can create punctures that release these hazardous materials into the surrounding area, resulting in potential fire and even explosions, human fatalities, and substantial damage to the environment. Despite all enhancements to mitigate the consequences of such accidents, there is still an immediate need for novel material with superior puncture and fire resistance with lower weight than the current carbon-steel in use, to improve the safety and efficacy of tank cars carrying hazardous materials (HAZMAT). Composite metal foam (CMF) is a novel class of light-weight material made of closely packed metallic hollow spheres with a surrounding metallic matrix. In this study, the latest developments on evaluating the performance of composite metal foam against extreme heat through both experimental and analytical approaches will be reported and compared to those properties of the base bulk steel materials in use.