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The nano-SiCp/ZA38 composites reinforced by nano SiC particles were fabricated by stirring assisted ultrasonic vibration. To establish the influence of the fusant temperature, stirring speed, and ultrasonic power on the mechanical and tribological properties of the cast nano-SiCp/ZA38 composite material, orthogonal experiments in four different fusant temperatures, stirring speed, and ultrasonic power were conducted. The synergistic effects of the thermalforce-acoustic field aroused by melting, stirring, and ultrasonic vibration were investigated. It was observed that the wear rate decreased with the dimension of the primary dendrite arm spacing. The wear rate of fabricated composite material decreased to a minimum value of 0.0042 mm s-1 when melting at 730AC, stirring with a speed of 300 rpm and ultrasonic vibration with a power of 850W. The hardness reached 163.9 HV, and the compression strength reached 803MPa. It was concluded that the acoustic field works prominently in improving the mechanical properties of the nano-SiCp/ZA38 composite, while the thermal and acoustic fields play a major part in the friction and wear properties. Thus, the force field gets converted into an assistant field. In addition, the simultaneously or solely increased thermal-force-acoustic field does not ensure a considerable enhancement in the mechanical and tribological properties of the nano-SiCp/ZA38 composite. [ABSTRACT FROM AUTHOR]

In the present experimental research, the compo-casting process was employed to fabricate Zn-35Al-1.2Mg-0.2Sr composite alloy reinforced with nano-SiC(p) + micro-Gr(p) particles and the water-cooling control system casting was applied to realize the effects of different chilling conditions on the as-synthesized material. Also, dry sliding wear experiments were performed to study the wear behavior of Zn-35Al-1.2Mg-0.2Sr composite alloy. Moreover, the effects of nano-SiC(p) +micro-Gr(p) addition on wear behavior of the as-prepared composite at different wear temperatures were analyzed. It was noticed that the abrasive resistance of Zn-35Al- -1.2Mg-0.2Sr composite alloy was dependent on the percentage and the dendritic arm spacing of the wearable Al-rich a-phase as well as on the distribution of nano-SiC(p) + micro-Gr(p) particles. With the increase in cooling rate during casting, the dendritic arm spacing of the a-phase decreased apparently. Further, with the increase in wear temperature, the percentage of the wearable Al-rich a-phase, especially for the specimen cooled under a full cooling mode, started to increase significantly. The specimen cooled under a full cooling mode manifested excellent high-temperature abrasive resistance. Furthermore, the tensile strength of the ascast composite increased with the increase in cooling rate during casting, and it could be attributed to the refined microstructures and the distribution of nano-SiC(p) + micro-Gr(p) particles. [ABSTRACT FROM AUTHOR]

In this study, medium-carbon steel was subjected to warm deformation experiments on a Gleeble 3500 thermosimulator machine at temperatures of 550°C and 650°C and strain rates of 0.001 s-1 to 1 s-1. The warm deformation behavior of martensite and the effects of strain rate on the microstructure of ultrafine grained medium-carbon steel were investigated. The precipitation behavior of Fe3C during deformation was analyzed and the results showed that recrystallization occurred at a low strain rate. The average ultrafine ferrite grains of 500 ± 58 nm were fabricated at 550°C and a strain rate of 0.001 s-1. In addition, the size of Fe3C particles in the ferrite grains did not show any apparent change, while that of the Fe3C particles at the grain boundaries was mainly affected by the deformation temperature. The size of Fe3C particles increased with the increasing deformation temperature, while the strain rate had no significant effect on Fe3C particles. Moreover, the grain size of recrystallized ferrite decreased with an increase in the strain rate. The effects of the strain rate on the grain size of recrystallized ferrite depended on the deformation temperature and the strain rate had a prominent effect on the grain size at 550°C deformation temperature. Finally, the deformation resistance apparently decreased at 550°C and strain rate of 1 s-1 due to the maximum adiabatic heating in the material. [ABSTRACT FROM AUTHOR]

The growth of austenite grains and the dissolution of carbonitrides under heating of a structural steel microalloyed with niobium and titanium are studied. The microstructure of the steel is investigated with the help of light and transmission electron microscopes. The content of elements in precipitated particles is determined using an energy dispersive spectrometer. The kinetic equation of grain growth is derived and the critical temperature above which the carbonitrides stop to hinder grain growth is determined. Recommendations are given on the temperature modes of hot rolling. [ABSTRACT FROM AUTHOR]

Abstract: The study described here is in sequel to our studies on the mechanics of microscale deformation in thermoplastic materials where a perspective of deformation processes occurring over different strain–strain rate regimes was obtained. The specific aim here is to enhance our fundamental understanding from microscale to nanoscale deformation in polymeric material systems containing dispersion of nanoparticles, considering the growing use of polymeric materials as functional materials. A Berkovich nanoindenter was used to induce surface damage using a load of 0.5–1mN and scratch velocity of 1μm/s. The secondary objective is to investigate the commonality in surface deformation behavior between nano- and microscale deformation to reinforce the underlying fundamental principles governing surface deformation. Combining electron microscopy with nanoscale surface deformation experiments enabled us to extend the understanding of microscale deformation to nanoscale deformation. In the intercalated polypropylene-nanoclay system, the susceptibility to surface deformation was significantly reduced because of the shift of von Mises stress from the surface to the sub-surface region, with consequent reduction in the maximum tensile stress induced by the nanoindenter. This conclusion was consistent with electron microscopy observations and theoretical analysis. [Copyright &y& Elsevier]

Abstract: In recent years, the focus of our research has been to obtain insights on microscale deformation mechanisms in thermoplastic materials reinforced with micrometer-sized particles. A perspective of deformation processes occurring over different strain–strain rate regimes was obtained [Dasari, A., Misra, R.D.K., 2004. Acta Mater. 52, 1683; Nathani, H., Dasari, A., Misra, R.D.K., 2004. Acta Mater. 52, 3217; Surampudi, N.L., Pesacreta, T.C., Misra, R.D.K., 2007. Mater. Sci. Eng. A 456, 218]. The objective here is to advance our basic understanding to nanoscale deformation in polymeric systems containing dispersion of nanoparticles, considering the growing use of polymeric materials as functional materials. A Berkovich nanoindenter was used to induce surface damage using a load of 0.5–1mN and scratch velocity of 1μm/s. An accompanying objective is to investigate the commonality in surface deformation behavior between nano- and microscale deformation to reinforce the underlying fundamental principles governing surface deformation. An understanding of mechanics of surface deformation is accomplished via electron microscopy analysis of scratch damage at and beneath the surface in conjunction with physical and mechanical properties. The electron microscopy analysis suggests that the understanding of microscale surface deformation can be extended to nanoscale surface deformation. In the intercalated high density polyethylene–nanoclay system, the susceptibility to scratch deformation is significantly reduced because of the shift of von Mises stress from the surface to the sub-surface region, with consequent reduction in the maximum tensile stress induced by the scratch. This conclusion is derived from electron microscopy and supported by the theoretical analysis. To the best of our understanding this is the first electron microscopy study that combines micro- and nanoscale deformation response during scratching of polymer nanocomposites in terms of processes that occur at and beneath the surface. [Copyright &y& Elsevier]

Abstract: We describe here phase evolution and structural changes that are induced when high density polyethylene (HDPE) containing dispersion of nano-calcium carbonate is isothermally crystallized in the pressure range of 0.1–100MPa. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat HDPE and HDPE containing nano-calcium carbonate under similar experimental conditions. X-ray diffraction studies point toward the evolution of monoclinic phase at high crystallization pressure together with the commonly observed orthorhombic phase of HDPE. Furthermore, the nucleation of monoclinic phase is promoted by nanoparticles even at low crystallization pressure. The equilibrium melting point is insignificantly influenced on the addition of nanoparticle, such that the crystallization pressure has no obvious effect. The strong thermodynamic interaction between nano-calcium carbonate and HDPE is supported by the shift in glass transition temperature and changes in the modification of absorption bands of HDPE in Fourier transform infrared (FTIR) spectrum. Furthermore, the reinforcement of HDPE with nano-calcium carbonate increases impact strength and alters the micromechanism from crazing-tearing in polyethylene to fibrillated fracture in polymer nanocomposite, such that the fibrillation increases with crystallization pressure. [ABSTRACT FROM AUTHOR]

Abstract: Significant differences in the microstructure occur when the polypropylene matrix dispersed with 4wt.% and 8wt.% nanoclay. In neat polypropylene, α-crystals nucleate in the low to moderate crystallization pressure range of (∼0.1–60MPa), while γ-phase nucleates at crystallization pressure of ∼60–200MPa. In contrast to neat polypropylene, the presence of nanoclay in the polymer matrix, promotes the formation of γ-phase at ambient crystallization pressure of 0.1MPa. Nanoclay and pressure-induced crystallization governs phase evolution and microstructure of polypropylene and is associated with change in the thermodynamic and physical properties such as equilibrium melting point and glass transition temperature. This change in equilibrium melting point and glass transition temperature points toward thermodynamic interaction between polymer-nanoparticle and nanoparticle interface-driven microstructural evolution. The dependence of equilibrium melting point on crystallization pressure and spherulite size on undercooling delineates two distinct regimes which are ascribed to dominant α- and γ-phases of polypropylene. However, the effect of nanoparticles is less dramatic when nanoclay content is increased from 4wt.% to 8wt.% implying that the effect maximizes at ∼4wt.% nanoclay. [ABSTRACT FROM AUTHOR]

Abstract: We describe here the relationship between fracture resistance and microstructural changes that are induced when polymers containing dispersion of nanoparticles are isothermally crystallized at elevated pressures. To identify the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between polyethylene and polyethylene containing dispersion of nanoclay under similar experimental conditions. At high crystallization pressure, besides commonly observed orthorhombic phase, monoclinic phase is also observed. The nucleation of monoclinic phase is promoted by nanoclay even at low crystallization pressure, implying that both pressure and nanoclay have an influence on phase evolution. The addition of nanoclay to polyethylene retains adequately high impact strength and the micromechanism of deformation is altered from a combination of craze and drawing of fibrils in polyethylene to microvoid coalescence–fibrillation in polyethylene with dispersion of nanoclay. The monoclinic phase has no obvious influence on fracture resistance. [Copyright &y& Elsevier]

Scanning electron microscopy was used to observe the microstructures of a cork wood. It showed that the wood consists of countless rectangular and honeycomb wood cells. The wall of each wood cell connects with adjacent wood cells at the middle of the cell wall. More careful observation showed that the walls of the wood cells are a kind of fibre reinforced biocomposite consisting of crystalline cellulose fibre layers and hydrocarbonated polymer matrix. The crystalline cellulose fibres in different fibre layers possess different directions, which compose a kind of fibre helicoidal microstructure. In the microstructure, the helicoidal angle is very large. The maximum pullout force of the fibre helicoidal microstructure, which is closely related to the fracture toughness of the wood, was theoretically and experimentally investigated and compared with that of the fibre parallel microstructure. It showed that the maximum pullout force of the fibre helicoidal microstructure is markedly greater than that of the fibre parallel microstructure and that the larger the helicoidal angle, the more the maximum pullout force will increase compared with that of the parallel microstructure. [ABSTRACT FROM AUTHOR]

Bone possesses excellent mechanical properties, which are closely related to its favorable microstructures optimized by nature through millions of years. In this work, a scanning electron microscope (SEM) was used to observe the microstructures of a shankbone. It showed that the bone is a kind of bioceramic composite consisting of hydroxyapatite layers and collagen protein matrix. The hydroxyapatite layers are further composed of long and thin hydroxyapatite sheets. The hydroxyapatite sheets in different hydroxyapatite layers distribute along different orientations, which composes a kind of intersectant microstructure. The maximum pullout force of the intersectant microstructure was investigated and compared with that of 0° microstructure with their representative models. The result indicated that the maximum pullout force of the intersectant microstructure is markedly larger than that of the 0° microstructure, which was experimentally verified. [ABSTRACT FROM AUTHOR]

Abstract: We describe here phase and morphological changes that are induced when polyethylene-containing dispersion of nanoclay is isothermally crystallized in the pressure range of 0.1–150MPa. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat polyethylene and polyethylene containing dispersion of nanoclay under similar experimental conditions. X-ray diffraction studies support the evidence of monoclinic phase at high crystallization pressure in addition to commonly observed orthorhombic phase of polyethylene. The nucleation of monoclinic phase is encouraged by nanoclay even at low crystallization pressures. Furthermore, orientation effects were observed in the nanocomposite system. The equilibrium melting point is insignificantly influenced on the addition of nanoclay and weakly refines the structure, such that the crystallization pressure has no obvious effect. The weak thermodynamic interaction between nanoclay and polyethylene compared to polypropylene–nanoclay system is supported by the small shift in glass transition temperature and no changes in the modification of absorption bands of polyethylene in Fourier transform infrared spectrum. [Copyright &y& Elsevier]

Abstract: We examine here the mechanical behavior and the micromechanism of fracture in impact tested neat and nanoclay-reinforced thermoplastic olefins, both of which have been processed under similar conditions. The reinforcement of thermoplastic olefins with nanoclay increases modulus and yields strength of the resulting nanocomposite and retains impact strength. The enhancement of modulus and yield strength is related to the reinforcement effect of nanoclay, while the retention of impact strength on reinforcement is attributed to the strong interaction between clay and polymer matrix. Both neat and clay-reinforced thermoplastic olefins are characterized by plastic deformation processes that involve ductile ploughing, fibrillation and voiding. [Copyright &y& Elsevier]

Abstract: The reinforcement of polyethylene and polypropylene with 4wt.% nanoclay exhibits a striking variation in impact toughness behavior in the temperature range of −40 to +70°C under identical processing conditions. The reinforcement of polypropylene with nanoclay increases the impact strength, while polyethylene experiences a decrease in the impact strength. To explain this dissimilar and contrasting behavior, we discuss here the possibility of clay–polymer interaction based on conclusions derived from differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FTIR). The observations suggest the possibility of a strong polypropylene–clay interaction, whereas the polyethylene–clay interaction is weak. The strong interaction in polypropylene–clay system is responsible for significant change in physical and mechanical properties. [Copyright &y& Elsevier]

Abstract: The mechanical response of calcium carbonate-reinforced high density polyethylene nanocomposite is investigated and the behavior compared with the unreinforced polyethylene processed under similar conditions. The reinforcement of high density polyethylene with nanocalcium carbonate retains adequately high strength in the temperature range of −40 to +20°C. The positive influence of reinforcement on the impact strength is reflected in the fracture characteristics and is attributed predominantly to the nucleating effect of calcium carbonate in decreasing the spherulite size. The achievement of high impact strength is accompanied by increase in modulus and no loss in yield strength. The reinforcement of neat high density polyethylene (HDPE) with nanocalcium carbonate alters the deformation micromechanism from crazing–tearing in HDPE to fibrillated fracture in polymer nanocomposite. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The mechanical response of clay–reinforced polyethylene nanocomposite is investigated and the behavior compared with the un-reinforced polyethylene under identical conditions of processing. The micromechanism of plastic deformation during impact loading of neat polyethylene and clay–reinforced polyethylene nanocomposite are studied with scanning electron microscopy (SEM). The impact strength of composites is linked to structural studies by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) and SEM observations. The addition of clay to polyethylene retains adequately high-impact strength in the investigated temperature range of −40 to +70°C. The micromechanism of deformation is altered from a combination of craze and drawing of fibrils in neat polyethylene to microvoid coalescence-fibrillated process in the nanocomposite. The aspects related to micromechanism of deformation are discussed. [Copyright &y& Elsevier]

Abstract: A Graceful Fig shell’ microstructures are observed with a scanning electronic microscope (SEM). It shows that the shell is a kind of natural hierarchical bioceramic composite. The shell is composed of parallel aragonite-layers and each aragonite layer consists of thin aragonite sheets. Furthermore, each thin aragonite sheet is composed of lesser nano-aragonite fibers. It is also found that the aragonite fibers in arbitrary two adjacent aragonite-layers compose a kind of intersectional microstructure. The maximum pullout energy of the intersectional microstructure is investigated and compared to that of conventional parallel microstructure. It shows that the maximum pullout energy of the intersectional microstructure is markedly larger than that of the parallel microstructure. The larger the intersectional angle of the intersectional microstructure is, the more the maximum pullout energy of the intersectional microstructure will increase, compared to that of the parallel microstructure, which is experimentally validated. [ABSTRACT FROM AUTHOR]

Abstract: Scanning electron microscope (SEM) observation shows that a shank bone is a kind of bioceramic composite consisting of inorganic hydroxyapatite and organic collagen protein. The hydroxyapatite possesses laminated microstructure and the each hydroxyapatite layer is composed of numerous long and thin hydroxyapatite sheets. The hydroxyapatite sheets in an arbitrary hydroxyapatite layer make an almost fixed angle with the hydroxyapatite sheets in their adjacent hydroxyapatite layers which compose a kind of particular screwy microstructure. The maximum pullout energy of the screwy microstructure, which is closely related to the fracture toughness of the bone, is theoretically investigated and compared with that of the parallel microstructure of the sheets. It shows that the maximum pullout energy of the screwy microstructure is markedly larger than that of the parallel microstructure, which is experimentally verified. [Copyright &y& Elsevier]

Abstract: The objective of the study described here is to investigate the determining influence of impact modifier on the microstructure and physico-chemical and mechanical properties of polypropylene crystallized at elevated pressures. The impact modified polypropylene referred as thermoplastic olefin (TPO) is characterized by a small spherulite size in the range of ∼1–8μm and the effect is retained when nanoclay is introduced into TPO. The impact strength of TPO and TPO–nanoclay system though similar, but is significantly higher than the polypropylene system, a behavior attributed to refinement of spherulite size. The study demonstrates that the nanoclay in TPO retains the impact strength of TPO and controls the dispersion of elastomer. [Copyright &y& Elsevier]

Zr 50-x/2 Co 50-x/2 Al x (x = 0, 4, 7) alloys fabricated by water-cooled copper mold casting yields excellent mechanical properties like high strength and large plasticity. Al can reduce the stacking fault energy and simultaneously improve strength and yield strength of the alloys. With increasing Al content, the effect of grain refinement strengthening, solid solution strengthening and second phase precipitation strengthening are enhanced to a certain extent. The good plasticity of these alloys primarily originates from the dislocation entanglement at the end of dislocation pileup and the transformation-induced plasticity associated with B2-to-B33 deformation-induced martensitic transformation. Zr 46.5 Co 46.5 Al 7 alloy shows the highest ultimate compressive strength of 1787 MPa, and the largest ultimate failure strain of more than 25%. • Al element can effectively increase the strength of Zr 50- x /2 Co 50- x /2 Al x (x = 0, 4, 7) alloy. • The good plasticity mainly originates from dislocation entanglement and TRIP. • Comprehensive mechanical properties originate from the synergy of various strengthening mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Insect cuticle is a kind of natural biocomposite. There are many eximious microstructures in the cuticle which come through biologic evolution over many centuries and endow the cuticle with excellent mechanical properties. In this work, the microstructures of a Tumblebug cuticle are observed through a scanning electronic microscope (SEM). Several kinds of different fiber distributions and fiber shapes are found at the different locations of the cuticle, which may provide beneficial information to the design of high-performance synthetic composites. The maximum pullout energy of a kind of particular dendritic fibers found in the cuticle is investigated and compared with that of conventional straight fibers based on their pullout models. It indicates that the maximum pullout energy of the dendritic fiber is markedly larger than that of the conventional straight fiber, and that the more the branches of the dendritic fiber is, the more the maximum pullout energy of the dendritic fiber will increase compared to that of the conventional straight fiber, which is experimentally validated. [ABSTRACT FROM AUTHOR]