Fabrication and mechanical properties of metal matrix composite with homogeneously dispersed ceramic particles

Titanium carbide (TiC) particles were coated with nickel (Ni) to increase their compatibility with a metal matrix, leading to an improvement in the dispersibility of TiC particles in the molten matrix. TiC particles were dispersed into a basic aqueous solution of pH 12, and then nickel nitrate (Ni(NO₃)₂), as a Ni precursor, was added to the TiC suspension. The interaction between the TiC particles and the Ni precursor is driven by the attractive force between the Ni cations and the TiC particles with negative charge. An inoculant (ferrosilicon), which has been used in the foundry industry to improve crystal growth of graphite, was used as a core particle. The Ni-treated TiC particles were coated onto the surface of the inoculant using an inorganic binder converted into its glass phase by sol–gel reactions. The reinforcement particles prepared through the dual-coating process were then injected into the molten matrix based on iron at 1500 °C. The crystal phase of the graphite is more finely and shortly grown in the reinforced metal matrix than in that without the reinforcement particles. This means that the reinforcement particles are homogeneously and uniformly dispersed into the matrix without any aggregation of particles, implying that the mechanical properties of the reinforced matrix would be greater than those of a non-reinforced matrix. Consequently, metal matrix composites with reasonable properties can be fabricated successfully using the reinforcement particles prepared by the dual-coating process.     

Wear behavior of metal matrix nanocomposites

Metal matrix nanocomposites (MMNCs), a unique class of metallic materials having superior mechanical, chemical, thermal or tribological properties, are commonly used in critical applications Those light-weight aluminum and magnesium alloys usually working in harsh wear conditions are susceptible to surface attacks. Although a lot of investigations have already been performed on those conventional composites reinforced by micro-particles, the wear behavior of the nanocomposites has not yet been fully understood. The surface properties associated with MMNCs are presented in this paper focusing mostly on manufacturing & processing routes, nano-particles as well as the dominant wear mechanisms. Studying wear behavior of MMNCs shows that no quantitative comparison of different existing studies is available as it is aimed to be done in the present review. To this end, wear reports have been categorized and discussed wherein the following results has been obtained: (i) it is found that ceramics reinforced composites usually exhibit a relatively better wear resistance behavior compared to those filled by carbon-based nanomaterials, (ii) hybrid MMNCs with two or more reinforcement types are promising materials to improve the surface resistance, particularly when the combination of ceramic and carbon-based particles are employed, (iii) solid-state processes like powder metallurgy usually provide superior wear resistance as compared to those liquid processing methods like casting, (iv) the use of smaller reinforcement size may almost always result in superior response, (v) abrasion is the most governing wear mechanism amongst the abrasion, adhesion and delamination mechanisms being frequently observed in MMNCs. A comprehensive review is made with particular attention on the composites reinforced by nano-sized reinforcing agents in order to evaluate the current research activities, discuss the pitfalls and provide a roadmap for future endeavors. It is believed that still countless research opportunities exist in order to fill the existing voids and fulfill the challenges with MMNCs.     

Effect of exfoliation and dispersion on the yield behavior of melt‐compounded polyethylene–montmorillonite nanocomposites

The yield behavior of melt‐mixed nanocomposites containing 5 wt % organically modified montmorillonite in matrices of a linear low‐density polyethylene (LLDPE) or a modified polyethylene was studied as a function of the temperature and strain rate. In the melt‐mixed LLDPE nanocomposite, the montmorillonite showed a slight increase in the clay spacing, which suggested that the clay was at best intercalated. Transmission electron microscopy (TEM) images showed that the dispersion in this nanocomposite was poor. The use of the modified polyethylene promoted exfoliation of the clay tactoids in the nanocomposite, as assessed by X‐ray diffraction and TEM. In both nanocomposites, the yield mechanisms were insensitive to the addition of the organoclay, even though modest increases in the modulus were produced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3044–3049, 2006     

Fabrication of ZrO2/rGO nanocomposites by flash sintering under AC electric fields

Ceramic matrix nanocomposites containing graphene possess superior mechanical properties. However, these nanocomposites are very difficult to be prepared using the conventional methods due to severe grain growth and simultaneous degradation of the graphene at high sintering temperatures and long dwell time. Herein, the dense ZrO₂/rGO (reduced graphene oxide) nanocomposites are successfully fabricated by flash sintering of the green compacts consisting of ZrO₂ nanoparticles and graphene oxide (GO) at 893–951℃ in merely 5 seconds under the alternating current (AC) electric fields of 130–150 V cm⁻¹. The GO can be in situ thermal reduced during the flash sintering. The as-prepared ZrO₂/rGO nanocomposites exhibit excellent mechanical properties. This study presents a green and simple approach to fabricate the dense ceramic matrix nanocomposites reinforced with graphene at low temperatures in a short time.     

Compounding of nanocomposites by thermokinetic mixing

Nanocomposites have been prepared by melt mixing poly(propylene) (PP) and different levels of a premixed montmorillonite‐organoclay masterbatch (PP/clay concentrate). Melt mixing was achieved using a Gelimat, a high‐speed thermokinetic mixer. The Gelimat system is designed to handle difficult compounding and dispersion applications and can achieve mixing, heating, and compounding of products within a minute. Therefore, the thermal history of the compounded polymer is short, which limits degradation. The structure and properties of the nanocomposites prepared with a Gelimat were compared to ones prepared with a twin‐screw extruder. The structure and properties of PP/clay nanocomposites were compared by TEM, X‐ray diffraction, mechanical testing, and rheological analysis. Results indicate that a better dispersion of the clay can be achieved by thermokinetic mixing when compared to extrusion, resulting in better mechanical properties. Calculations, based on simplifying assumptions, showed that the shear rates generated in a Gelimat are at least one order higher than those generally generated in an extruder. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1557–1563, 2005     

Crystallization behavior of syndiotactic polystyrene nanocomposites for melt‐ and cold‐crystallizations

Analyses of the effects of montmorillonite (clay) on the crystallinity and crystallization behavior of syndiotactic polystyrene (s‐PS) were investigated by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The dispersibility of the clay in s‐PS nanocomposites was studied by X‐ray and transmission electron microscopy (TEM). The clay was dispersed into the s‐PS matrix by melt blending on a scale of 1–2 nm or few tenths–100 nm, depending on the surfactant treatment. On adding clay, the crystallization behavior of the s‐PS tends to convert into the β‐crystal from the α‐crystal after being cold‐crystallized because the clay plays a vital role in facilitating the formation of the thermodynamically favored β‐form crystal when the s‐PS is cold‐ or melt‐crystallized. This phenomenon leads to a change in a conventional mechanism of molecular packing for the s‐PS. Evidently, the clay significantly affects the crystallinity and crystallization behavior of the s‐PS. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2492–2501, 2002     

Effects of nanoparticle treatment on the crystallization behavior and mechanical properties of polypropylene/calcium carbonate nanocomposites

Effects of nanoparticle surface treatment on the crystallization behavior and mechanical properties of polypropylene (PP)/CaCO₃ nanocomposites were investigated by using differential scanning calorimetry (DSC), polarized optical microscope (POM), X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results demonstrated that the interfacial interaction formed between PP and nanoparticles significantly influenced the thermal and mechanical properties of nanocomposites. It was found that CaCO₃ nanoparticles modified by a single aluminate coupling agent (CA‐1) could improve the onset crystallization temperature more effectively than that modified by a compound surface‐treating agent (CA‐2) could. However, there is no significant difference in total rate of crystallization for the two PP/CaCO₃ nanocomposites (PPC‐1 and PPC‐2), which contained CA‐1 and CA‐2, respectively. In contrast, CA‐2 modified nanoparticles could cause smaller spherulites and induce much more β‐phase crystal in nanocomposites than that of CA‐1 modified nanoparticles. This may be explained by a synergistic effect of aluminate coupling agent and stearic acid in CA‐2, which also resulted in an improved toughness for PPC‐2. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 3480–3488, 2006     

Impact fracture behavior of clay-reinforced polypropylene nanocomposites

The micromechanism of plastic deformation during impact loading of polypropylene-clay nanocomposites is examined and compared with the unreinforced polypropylene under identical conditions of processing to underscore the determining role of clay. The addition of clay to polypropylene increases the impact strength in the temperature range of 0 to +70 °C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques provided an understanding of the micromechanism of plastic deformation in terms of the response of the polymer matrix, nucleating capability of the reinforcement, crystal structure, percentage crystallinity, lamellae thickness, and particle-matrix interface. The enhancement of toughness on reinforcement of polypropylene with nanoclay is associated with change in the primary mechanism of plastic deformation from crazing and vein-type in neat polypropylene to microvoid-coalescence-fibrillation process in the nanocomposite.     

Effect of matrix features on polypropylene layered silicate nanocomposites

The aim of this study was to examine the effect of the polypropylene based resin on the properties of organoclay-PP nanocomposites prepared by melt compounding using a twin screw extruder.The characterization of the obtained materials was performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), melt flow rate (MFR) and mechanical tests.The study has shown the effect of the polymer matrix molecular weight on the possibility of producing by melt compounding nanocomposites based on PP homopolymers or heterophasic PP-PE copolymers and an organically modified montmorillonite, in presence of maleic anhydride-modified polypropylene (PP-g-MAH).An increase of mechanical properties was achieved both for homopolymers and heterophasic copolymers. However the reinforcing effect of clay dispersed in heterophasic copolymers was not as high as found for the homopolymers.     

Non‐isothermal crystallization behavior of PLA/acetylated cellulose nanocrystal/silica nanocomposites

Poly(lactide) (PLA)/acetylated cellulose nanocrystals (ACN)/silica nanocomposites were prepared by solution casting. Surface modification of cellulose nanocrystal (CNC) was performed to prepare the ACN. The ACN and silica were expected to act as a mechanical reinforcement of PLA and a nucleation agent, respectively, to increase the crystallization rate. Introduction of acetyl groups on the surface of the cellulose nanocrystals was confirmed by Fourier transform infrared spectroscopy. A combined Avrami ? Ozawa analysis described the non‐isothermal crystallization effectively. The activation energy for the crystallization was calculated from the Kissinger and the Takhor equations. Spherulite growth behavior was observed by polarizing optical microscope and spherulite growth rate, the number of spherulite versus crystallization time have investigated. The development of PLA crystals and the thermal stability had a tendency to improve with increasing silica content. Increased tensile strength was observed due to the reinforcement effect of ACN and the morphology of the nanocomposites was investigated. © 2015 Society of Chemical Industry     

Fracture behavior of thermoplastic polyolefin/clay nanocomposites

A thermoplastic polyolefin (TPO) containing 70 wt % styrene–ethylene–butadiene‐styrene‐g‐maleic anhydride and 30 wt % polypropylene and its nanocomposites reinforced with 0.3–1.5 wt % organoclay were prepared by melt mixing followed by injection molding. The mechanical and fracture behaviors of the TPO/clay nanocomposites were investigated. The essential work of fracture (EWF) approach was used to evaluate the tensile fracture behavior of the nanocomposites toughened with elastomer. Tensile tests showed that the stiffness and tensile strength of TPO was enhanced by the addition of low loading levels of organically modified montmorillonite. EWF measurements revealed that the fracture toughness of the TPO/clay nanocomposites increased with increasing clay content. The organoclay toughened the TPO matrix of the nanocomposites effectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological behavior of new melt compounded copolyamide nanocomposites

In this paper the rheological behavior of new polyamide-based nanocomposites produced by melt compounding using three different silicate loadings and screw speeds was investigated. The thermoplastic matrices selected were a polyamide 6 and its statistical copolymer having partially aromatic structure, whereas the clay was a commercial organo-modified montmorillonite. Hybrid systems were prepared by means of a laboratory-scale twin screw extruder and were submitted to rheological and structural investigations. The rheological experiments (dynamic frequency sweep, steady rate sweep and stress relaxation tests) were performed to evaluate the effect of both system composition (kind of matrix and clay content) and extrusion rate on the flow behavior of the nanocomposites. Rheology, that is highly sensitive to the nanoscale structure of the materials, put out a pseudo-solid like flow behavior at long times in the hybrids with silicate content higher than 6 wt% and produced with high extrusion rate; this response was related to the formation of an extended structural network across the polymer matrix due to strong polymer-silicate interactions that slow the relaxation times of the macromolecules. Corresponding to this behavior, TEM micrographs have shown a quite uniform dispersion of clay particles on micron-scale and a fair level of silicate exfoliation on nanoscale with a macroscopic preferential orientation of the layers in samples. The rheological measurements also reveal that this flow response is more marked for nanocomposites based on the copolyamide matrix, suggesting that this resin may have a higher silicate affinity respect to polyamide 6 homopolymer.     

Preparation and characterization of PET/silica nanocomposites

Poly(ethylene terephthalate) (PET)/silica nanocomposites were fabricated by direct polymerizing PET monomer dispersed with organic modified silica nanoparticles. The characteristics and properties of these nanocomposites were investigated by the transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis, respectively. The results show that (1) the nanoparticles have been well dispersed in the polymer matrix; (2) the addition of nanoparticles can speed up the crystallization and melting point; and (3) the addition has no significant effect on the synthesis process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1229–1232, 2004     

Crystallization behavior of nylon 11/montmorillonite nanocomposites under annealing

Exfoliated nylon 11/montmorillonite (MMT) nanocomposites were prepared via in situ polymerization by the dispersion of organically modified MMT in 11‐aminoundecanoic acid monomer. The polymorphic behavior of the nylon 11/MMT nanocomposites was investigated with X‐ray diffraction, transmission electron microscopy, and Fourier transform infrared with attenuated total reflectance. MMT induced and stabilized the δ‐crystalline form of nylon 11. The crystal structure of nylon 11 was transformed from a hexagonal δ‐form structure to a triclinic α‐form structure during the annealing process. Meanwhile, the hydrogen bonds in the nanocomposites also exhibited some differences from neat nylon 11 after annealing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5483–5489, 2006     

Network model for the viscoelastic behavior of polymer nanocomposites

A theoretical network model reproducing some significant features of the viscoelastic behavior of unentangled polymer melts reinforced with well dispersed non-agglomerated nanoparticles is presented. Nanocomposites with low filler volume fraction (∼10%) and strong polymer-filler interactions are considered. The model is calibrated based on results obtained from discrete simulations of the equilibrium molecular structure of the material. This analysis provides the statistics of the network of chains connecting fillers, of dangling strands having one end adsorbed onto fillers, and that of the population of loops surrounding each nanoparticle. The network kinetics depends on the attachment-detachment dynamics of grafted chains of various types and is modeled by using a set of convection equations for the probability distribution functions. The overall viscoelastic response depends strongly on the lifetime of the polymer-filler junctions. The largest reinforcement is observed at low strain rates and low frequency oscillations. A solid like behavior is predicted for systems in which the polymer molecules interact strongly with the nanoparticles, effect which is associated with the behavior of the network of bridging segments.     

SBS／蒙脱土纳米复合材料的流变行为

用毛细管流变仪测定并研究了热塑性丁苯三嵌段共聚物（SBS）／蒙脱土纳米复合材料的熔体的稳态剪切流变行为，研究结果表明：温度和压力一定的条件下，加入一定量的改性蒙脱土可以降低熔体的粘度；在较低的剪切速率下，即出现剪切变稀现象；在高剪切速率下，粘度对剪切速率的敏感性是降低的，改性蒙脱土加入量对熔体的剪切粘度影响较小，主要是由基体材料所决定的；随温度的升高熔体粘度对剪切速率的敏感性是降低的。采用转矩流变仪对材料的加工性能进行研究，发现复合材料的加工性能基本上保持了纯SBS的加工性能。     

HDPE‐ash nanocomposites

Ash‐based polymer composites are assuming increasing importance because of the pollutant potential, fine particle size, and low price of ash. Fly ash and rice husk ash are two prominent ash materials on which some investigations have already been done for potential use in polymer composites. This article highlights the results of a study on the use of wood ash in HDPE. Wood ash is mainly a mixture of various metallic compounds and some silica. Here, the characterization of wood ash has been done with the help of XRD, ICPAES, light scattering based particle size analysis, FTIR, and SEM. The results show that wood ash particle size has an average value of 293 nm, much lower than other categories of ash. When blended with HDPE in the presence of a compatibilizer, wood ash gives rise to vastly improved mechanical properties over that of the base polymer. The results prove that wood ash is a valuable reinforcing material for HDPE and the environmental pollution due to wood ash can be solved in a most profitable way by this technique. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

In-plane thermal expansion behavior of dense ceramic matrix composites containing SiBC matrix

In order to reveal the effect of matrix cracks resulted from thermal residual stresses (TRS) on the thermal expansion behavior of ceramic matrix composites, SiBC matrix was introduced into C_f/SiC and SiC_f/SiC by liquid silicon infiltration. The TRS in both two composites were enlarged with incorporating SiBC matrix which has higher coefficients of thermal expansion (CTEs) than SiC matrix. Due to the relatively high TRS, matrix cracks and fiber/matrix (f/m) debonding exist in C_f/SiC-SiBC, which would provide the space for the expansion of matrix with higher CTEs. For SiC_f/SiC, no matrix cracking and f/m debonding took place due to the close CTEs between fiber and matrix. Accordingly, with the incorporation of SiBC matrix, the in-plane CTE of C_f/SiC between room temperature to 1100 °C decreases from 3.65 × 10⁻⁶ to 3.19 × 10⁻⁶ K^-1, while the in-plane CTE of SiC_f/SiC between room temperature to 1100 °C increases slightly from 4.97 × 10⁻⁶ to 5.03 × 10⁻⁶ K^-1.     

Novel preparation of poly(propylene)–layered silicate nanocomposites

We used a novel approach to prepare poly(propylene)–clay nanocomposite starting from pristine montmorillonite and reactive compatibilizer hexadecyl trimethyl ammonium bromide. The nanocomposite structure was revealed by X‐ray diffraction and high‐resolution electronic microscopy. The thermal properties of the nanocomposite were investigated by thermogravimetric analysis. An increase of thermal stability was observed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2586–2588, 2003     

Interaction of dendronized polymeric nanocomposites with isomeric cyclohexanediols

Dendronized poly(diethylaminoethyl methacrylamide) (PEAM) was studied in blends containing isomeric cyclic dialcohols. Monomers and polymers were characterized by spectroscopic measurements. The phase behaviors of blends of PEAM with 1,2‐, 1,3‐ and 1,4‐cyclohexanediols (1,2‐CHD, 1,3‐CHD and 1,4‐CHD, respectively) were established. Transparent films of the blends exhibited a single glass‐transition temperature (T_g). Thermogravimetric analysis (TGA) revealed the temperature at which the polymer releases the small molecules. UV‐vis spectra of 1,3‐CHD and 1,4‐CHD derivatives showed an isosbestic point that indicated the association of the alcohols. FT‐IR measurements showed shifts in several absorption bands. The results were analyzed in terms of the side‐chain structure and the interactions involved. AFM measurements revealed differences between the polymer and the blends. Compatibilization of blends of PEAM/CHDs occurred via the formation of hydrogen bonds, although hydrophobic interactions could not be disregarded. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42267.