Tensile Strength and Electrical Conductivity of Carbon Nanotube Reinforced Aluminum Matrix Composites Fabricated by Powder Metallurgy Combined with Friction Stir Processing

A route combining powder metallurgy and subsequent friction stir processing was utilized to fabricate carbon nanotube(CNT) reinforced Al(CNT/AI) and 6061 Al(CNT/6061AI) composites.Microstructural observations indicated that CNTs were uniformly dispersed in the matrix in both CNT/AI and CNT/6061 AI composites.Mg and Si elements tended to segregate at CNT—Al interfaces in the CNT/6061 AI composite during artificial aging treatment.The tensile properties of both the Al and 6061 Al were increased by CNT incorporation.The electrical conductivity of CNT/AI was decreased by CNT addition,while CNT/6061 AI exhibited an increase in electrical conductivity due to the Mg and Si segregation.     

Humidity Effect on Transport Properties of Titanium Dioxide Nanoparticles

Rutile TiO2 nanoparticles were synthesized using co-precipitation method with an average diameter of 30 nm TiO2 nanoparticle device was then fabricated on glass substrate.Aluminum electrodes were defined using photolithography and vacuum evaporation.A suspension of TiO2 nanoparticles was prepared in isopropanol using ultrasonic agitation.The nanoparticles were deposited between the electrodes.The device was tested by AC electrical measurements at 40%-90%relative humidity（RH）.The impedance of the TiO2nanoparticles decreases by about 80 times with the increase in RH from 40%to 90%at 100 Hz.The response time and the recovery time were 4 s and 5 s,respectively between 40%and 90%RH.At 100 Hz,the sensitivity of the aluminum electrode TiO2 nanoparticle device in the range of 40%—90%RH was17 MΩ/%RH.Complex modulus analysis also confirms the increase in DC conductivity of TiO2 nanoparticles as RH increases.     

Thermal and Oxygen Barrier Properties of Chitosan Bionanocomposites by Reinforcement of Calcium Carbonate Nanopowder

Chitosan and calcium carbonate nanopowder（chitosan/CaCO3） bionanocomposites were prepared by solution method.Interaction between chitosan and CaCO3 was studied by Fourier transform infrared spectroscopy（FTIR）.Structure and surface morphology of chitosan/CaCO3 bionanocomposites were investigated by X-ray diffraction（XRD） and field emission scanning electron microscopy（FESEM）,respectively.The energy dispersive X-ray spectroscopy（EDS） of chitosan/CaCO3 bionanocomposites was studied in order to establish the elements of composition.Thermal stability of prepared bionanocomposites was studied by thermogravimetric analysis（TGA） and a substantial increase of thermal stability of virgin chitosan was noticed due to incorporation of CaCO3 nanopowder.The oxygen permeability was reduced by three times as compared to the raw chitosan due to the dispersion of nano CaCO3 filler.Biodegradability and resistance towards dilute acid and alkali of the prepared bionanocomposite were investigated.The bionanocomposite having gas barrier and thermal stable property may be suitable for packaging and biomedical applications.     

Effects of Y on the Microstructure,Mechanical and Bio-corrosion Properties of Mg-Zn-Ca Bulk Metallic Glass

The micro-alloying effects of Y on the microstructure, mechanical properties, and bio-corrosion behavior of Mg69-xZn27Ca4Yx（x= 0, 1, 2 at.%） alloys were investigated through X-ray diffraction, compressive tests,electrochemical treatments, and immersion tests. The Mg69Zn27Ca4 alloy was found to be absolutely amorphous, and its glass-forming ability decreased with the addition of Y. The Mg68Zn27Ca4Y1 alloy exhibited an ultrahigh compressive strength above 1010 MPa as well as high capacity for plastic strain above 3.1%.Electrochemical and immersion tests revealed that these Y-doped MgeZ neC a alloys had good bio-corrosion resistance in simulated body fluid（SBF） at 37℃. The results of the cytotoxicity test showed high cell viabilities for these alloys, which means good bio-compatibility.     

Comparison of Mechanical Properties of Acid and UV Ozone Treated Nanodiamond Epoxy Nanocomposites

Nanodiamond（ND） powder was successfully activated by wet chemical method and by exposure of UV/O3 in a chamber followed by mixing in triethylenetetramine（TETA） solution.The reinforcement role of activated ND in the mechanical properties of epoxy matrix was studied.Both treatments,i.e.acid and UV/O3 provide ND surface with chemical functionalities for adhesion with epoxy resin.Fourier transform infrared spectroscopy was utilized to confirm the attachment of surface groups to the ND particles.The low content of acid and UV/O3 activated ND was dispersed ultrasonically in the epoxy matrix separately to make nanocomposites.The mechanical properties of the nanocomposites were investigated under three point bending.The strong interactions among activated ND particles and the epoxy resin provide efficient load transfer interfaces,which enhances the mechanical properties of the composites.It was found that the flexural strength,modulus,and toughness of 0.1 wt%ND loaded nanocomposites have been enhanced up to 85%,57%,and 39%,respectively for UV/O3 treated ND powder.It is also found that the optimum ND concentration to achieve maximum reinforcement is 0.1 wt%while higher concentrations lead to decrease in mechanical properties.The significant improvement of the mechanical properties of the ND/epoxy nanocomposites is attributed to the good dispersion of the functionalized ND in epoxy matrix.     

Large-sized CuZr-based Bulk Metallic Glass Composite with Enhanced Mechanical Properties

A large-sized CuZr-based bulk metallic glass （BMG） composite with enhanced mechanical properties is prepared successfully. With the addition of Ta to CuZr-based alloys, the critical composite size changes and the microstructure diversifies. The composite with 0.5 at,% Ta addition has the largest critical size with the microstructure of single CuZr（B2） phase uniformly dispersing in amorphous matrix. This composite exhibits good mechanicat properties, i.e., large compressive plasticity and work-hardening ability, which should be attributed to the uniformly distributed CuZr（B2） phase. The increased critical size of CuZr-based BMG composite can be explained by the fact that proper Ta addition can suppress the precipitation of crystalline phases other than B2 CuZr phase during solidification. This study may be helpful for the fabrication of large- sized BMG composites with excellent mechanical properties.     

High Temperature Thermoelectric Properties of Dy-doped CaMnO3 Ceramics

Dy-doped CaMnO3 ceramics have been synthesized by co-precipitation method combined with the solid-state reaction.Phase composition and microstructure analysis indicate that high density and pure CaMnO3 phase can be achieved.The electric conductivity can be enhanced by Dy doping,and result in a slight increase of the thermal conductivity.The highest dimensionless figure of merit ZT of 0.15 has been obtained at 973 K for x = 0.02 sample,which is about 4 times larger than that of the pure CaMnO3,which indicate that CaMnO3can be a promising candidate for n-type thermoelectric material at high temperature.     

Waterborne Epoxy Nanocoatings Modified by Nanoemulsions and Nanoparticles

Electrically conductive coatings are required for static charge dissipation in power ground network. In the present investigation electrically conductive nanocoatings were prepared by the incorporation of graphite, nano-SiO2 concentrate, acrylic nanoemulsion and fluorocarbon emulsion onto the waterborne epoxy polymer. The nanosize distribution of nano-SiO2 concentrate and nanoemulsion was characterized with laser diffraction analyzer and scanning electron microscopy （SEM）. From the results of SEM image, the graphite particles were well distributed in conductive coating. The corrosion resistance and thermal stability of nanocoatings were comparatively studied by SEM and thermogravimetry （TG）. The corrosion-inhibiting properties of the conductive nanocoatings were investigated by salt immersion test. The measurements of contact angle, bonding strength and heat-freeze charge demonstrated that 1.5-2.0 wt% nanoparticles improve the resistance to pollution, adherence and resistance to heat-freeze charge of conductive nanocoatings. The measured results of surface electric resistance of nanocoatings demonstrated that a small amount of nano- SiO2 particles could enhance the conductivity in the corrosive environment.     

Dynamic Mechanical Relaxation in Bulk Metallic Glasses： A Review

Metallic glasses have aroused considerable interest in the past decades because they exhibit fascinating properties. First, this article briefly outlines the mechanical, thermal properties and application of the metallic glasses. In addition, we focus on the dynamic mechanical relaxation behaviors, i.e. main （α） and secondary （β） relaxations, in metallic glasses. The mechanical relaxation behaviors are connected to the mechanical properties and physical properties in glassy materials. The main relaxation in glassy materials is related to the glass transition phenomenon and viscous flow. On the other hand, the β relaxation is linked to many fundamental issues in metallic glasses. In these materials relaxation processes are directly related to the plastic deformation mechanism. The mechanical relaxations, particularly, the β relaxation provides an excellent opportunity to design metallic glasses with desired physical and mechanical properties. We demonstrate the universal characteristics of main relaxation in metallic glasses. The phenomenological models and the physical theories are introduced to describe the main relaxation in metallic glasses. In parallel, we show the dependence of the α. and β relaxations on the thermal treatments in metallic glasses. Finally, we analyze the correlation between the atomic mobility and the thermo-mechanical treatments in metallic glasses. On the one hand, the atomic mobility in metallic glasses is reduced by physical aging or crystallization. On the other hand, the atomic mobility in metallic glass is enhanced by deformation （i.e. compression and cold rolling）. Importantly, to analyze the atomic mobility in amorphous materials, a physical theory is introduced. This model invokes the concept of quasi-point defects, which correspond to the density fluctuations in the glassy materials.     

Effect of Hot Isostatic Pressing Conditions and Cooling Rate on Microstructure and Properties of Ti-6Al-4V Alloy from Atomized Powder

The effects of temperature and pressure on density, microstructure and mechanical properties of powder compacts during hot isostatic pressing（HIPping） were investigated. Optimized HIPping parameters of temperature range from 900 to 940℃, pressure over 100 MPa and holding time of 3 h, were obtained. Tensile properties after different heat treatments show that both the geometry of samples and cooling rate have a significant influence on mechanical properties. Finite element method was used to predict the temperature field distribution during HIPped sample cooling, and the experimental results are in agreement with simulation prediction. The interaction of HIPping parameters was analyzed based on the response surface methodology（RSM） in this study.     

Microstructure Evolution and Tensile Properties of Ti3Al/Ni-based Superalloy Welded Joint

In the present work,the dissimilar joining of a Ti_3AI-based alloy to a Ni-based superalloy was attempted by gas tungsten arc(GTA) welding technology.Sound joints were successfully achieved by using a Cu—Ni alloy as filler material.According to X-ray energy dispersive spectroscopy and X-ray diffraction analysis results three transitional layers at the weld/Ti_3AI interface were verified as follows:Ti_2AINb phase dissolved with Cu and Ni;AI(Cu,Ni)_2Ti,(Cu,Ni)_2Ti and(Nb,Ti) solid solution;Cu-rich phase and a complex multi-element phase.The In718/weld interface is characterized by solid solutions of Ni,Cu,Cr,Fe and Nb.The average tensile strength of the as-welded joints at room temperature is 1 63 MPa,and after a post—weld heat treatment it is increased slightly to 177 MPa.The fracture occurred at the surfacial layer of the joined Ti_3AI base alloy,indicating that the Ti_2AINb layer dissolved with Cu and Ni is the weak link of the Ti_3AI/ln71 8 joint.     

Proportional Limit Stress and Residual Thermal Stress of 3D SiC/SiC Composite

Proportional limit stress （PLS） and residual thermal stresses （RTS） of 3D SiC/SiC composite were investigated. PLS was obtained by four different methods from the monotonic stress-strain response curve to get a convincing value. RTS in the SiC matrix was quantified by solving the geometric intersection point of the regression lines of hysteresis loops from the periodical loading-unloading-reloading cycle test curve. Classical ACK model and analytical formulas were used to analytically calculate the PLS and RTS of 3D SiC/ SiC composite. Good agreement between the experimental results and the analytical calculation was observed. And relationship between the PLS and the RTS of 3D SiC/SiC was discussed.     

Improving the Economic Values of the Recycled Plastics Using Nanotechnology Associated Studies

Recycled polystyrene （PS） cups were chopped up and separately incorporated with multiwall carbon nanotubes （MWCNTs） and NiZn ferrite （Ni0.6Zn0.4Fe2O4） nanoparticles prior to electrospinning under different conditions. These nanoscale inclusions were initially dispersed well in dimethylformamide （DMF）, and then known amounts of the recycled PS pieces were added to the dispersions prior to 30 min of sonication followed by 4 h of high-speed agitation at 750 r/min. The thermal, dielectric, surface hydrophobic, and magnetic properties of the resultant nanocomposite fibers were determined by thermal comparative, capacitance bridge, vibrating sample magnetometer （VSM）, and goniometer techniques, respectively. Test results confirmed that the physical properties of recycled nanofibers were significantly increased as a function of the inclusion concentrations, which may be because of their excellent properties. The consumption of polymeric products as well as their waste materials has dramatically grown worldwide. Although plastic recycling, reprocessing, and reusing rates are growing, the physical properties and economic value of recycled plastics are significantly low. Consequently, this work provides a detailed explanation of how to improve recycled plastics, making them into highly valued new nanoproducts for various industrial applications, including filtration, textile, transportation, construction, and energy.     

Effect of Post Cryorolling Treatments on Microstructural and Mechanical Behaviour of Ultrafine Grained Al-Mg-Si Alloy

To investigate the effect of post cryorolling treatments on simultaneous enhancement in strength and ductility of ultrafine grained material （UFG）, AI 6061 alloy was subjected to cryorolling followed by warm rolling （CR ＋ WR） and compared with cryorolling followed by short annealing （CR ＋ SA） at the same temperature. Transmission electron microscopy （TEM） was used to characterize the microstructural features of the processed material. The mechanical properties were investigated through Vickers hardness testing and tensile testing at room temperature. TEM, X-ray diffraction （XRD） and differential scanning calorimetry （DSC） were used to investigate the precipitation evolution in UFG material. Results indicated that the alloy subjected to CR ＋ WR has shown improved mechanical properties （114 HV, ultimate tensile strength （UTS）： 350 MPa） as compared to that in the case of CR ＋ SA （105 HV, UTS： 285 MPa）. The size of the precipitates observed in CR ＋ WR sample after peak ageing treatment is finer than that of peak aged CR ＋ SA sample. The UTS of peak aged CR ＋ WR sample （UTS： 390 MPa） was found to be higher than that of peak aged CR ＋ SA sample （UTS： 355 MPa）, without decrease in ductility.     

Microstructure and Properties of 3.5 vol.% TiBw/Ti6Al4V Composite Tubes Fabricated by Hot-hydrostatic Extrusion

Tubes of 3.5 vol,% TiB whiskers reinforced Ti6Al4V matrix composites （TiBw/Ti6Al4V） were successfully fabricated by a two-step hot-hydrostatic extrusion process： （3 extrusion at 1100 ℃ and subsequent near-β extrusion at 950℃. The dimensions of tubes were about 7 mm in diameter and 2 mm in thickness. A refined basket-weave structure in Ti6Al4V matrix was achieved at ambient temperature after the extrusion process. Besides, the original network structure formed by TiB whiskers synthesized was broken, while the TiB whiskers were preferentially aligned in the extruding direction. Meanwhile, a fibrous texture was evolved finally, resulting from partial dynamic recrystallization during the β extrusion and the involvement of α phase during the near-β extrusion. The tensile and compressive tests results showed that both the strength and ductility of the tubes were significantly improved. In particular, the tubes exhibited good mechanical properties at elevated temperatures.     

Tungsten Doped Indium Oxide Thin Films Deposited at Room Temperature by Radio Frequency Magnetron Sputtering

Tungsten doped indium oxide(IWO) thin films were deposited on glass substrate at room temperature by radio frequency reactive magnetron sputtering.Chemical states analysis was carried out,indicating that valence states of element W in the films were W~(4+) and W~(6+).The effects of sputtering power and film thickness on the surface morphology,optical and electrical properties of IWO thin films were investigated.The IWO thin films had high transmittance in near infrared(NIR) spectral range.The resistivity,carrier mobility and carrier concentration owned their respective optimum values as sputtering power and thickness changed.The asdeposited IWO film with the minimum resistivity of 3.23 × 10~(-4) Ω cm was obtained at a sputtering power of50 W,with carrier mobility of 27.1 cm~2 V~(-1) s~(-1),carrier concentration of 7.15 × 10~(20) cm~(-3),average transmittance about 80%in visible region and above 75%in NIR region.It may meet the application requirement of high conductivity and transparency in NIR wavelength region.     

Type Inversion and Certain Physical Properties of Spray Pyrolysed SnO::A1Films for Novel Transparent Electronics Applications

Aluminium doped tin oxide films have been deposited onto glass substrates by using a simplified and low cost spray pyrolysis technique.The Al doping level varies between 0 and 30 at.%in the step of 5 at.%.The resistivity(ρ) is the minimum(0.38 Ω cm) for 20 at.%of Al doping.The possible mechanism behind the phenomenal zig-zag variation in resistivity with respect to Al doping is discussed in detail.The nature of conductivity changes from n-type to p-type when the Al doping level is 10 at.%.The results show that20 at.%is the optimum doping level for good quality p-type SnO_2:AI films suitable for transparent electronic devices.     

A Comparative in vitro Study on Biomedical Zr-2.5X(X=Nb,Sn) Alloys

Nb and Sn are major alloying elements in Zr alloys.In this study,the microstructure,mechanical properties,corrosion behavior,cytocompatibility and magnetic resonance imaging(MRI) compatibility of Zr-2.5X(X = Nb,Sn) alloys for biomedical application are comparatively investigated.It is found that Zr—2.5Nb alloy has a duplex structure of α and β phase and Zr—2.5Sn alloy is composed of 7.phase.Both separate addition of Nb and Sn can strengthen Zr but Nb is more effective in strengthening Zr than Sn.The studied Zr—2.5X(X = Nb,Sn) alloys show improved corrosion resistance compared to pure Zr as indicted by the decreased corrosion current density.The alloying addition of Nb enhances the pitting resistance of Zr,whereas the addition of Sn decreases the pitting resistance of Zr.The extracts of Zr—2.5X alloys produce no significant deleterious effect on fibroblast cells(L-929) and osteoblast-like cells(MG 63),indicating good in vitro cytocompatibility.The Zr—2.5X(X = Nb,Sn) alloys show decreased magnetic susceptibility compared to pure Zr and their magnetic susceptibility is far lower than that of pure Ti and Ti—6AI—4V alloy.Based on these facts,Zr-2.5Nb alloy is more suitable for implant material than Zr-2.5Sn alloy.Sn is not suitable as individual alloying addition for Zr because Sn addition decreases the pitting resistance in physiological solution.     

La Doping Effect on the Dielectric Property of Barium Strontium Titanate Glass – Ceramics

Ferroelectric barium strontium titanate(BST) glasse ceramics doped with different content of La2O3 were prepared via the melt-quenching technique followed by controlled crystallization. The microstructures of crystallized samples were examined by X-ray diffraction and scanning electron microscopy. Dielectric properties were also investigated. The aliovalent substitution of Ba by La induced dispersion of semiconducting BaxSr1-x TiO3 crystallites sealed in a glassy silicate matrix, which increased the εr and loss tangent values of the BST glasse ceramic. The experimental results indicate that aliovalent substitution is an effective method to process glasse ceramics with better dielectric properties.     

Dielectric Relaxation and Conductivity of Ba(Mg1/3Ta2/3)O3and Ba(Zn1/3Ta2/3)O3

The frequency dependent dielectric properties of barium magnesium tantalate(BMT),Ba(Mg_(1/3)Ta(2/3))O_3 and barium zinc tantalate(BZT),Ba(Zn_(1/3)Ta_(2/3))O_3 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy.BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm,respectively.The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides.The relaxation in the samples is polydispersive in nature.The temperature dependence of dc conductivity,the most probable relaxation frequency(ω_m) obtained from tanδ vs logw plots and ω_m obtained from imaginary parts of the complex electrical modulus vs logw plots follow the Arrhenius behavior.According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV,respectively.Thus the results indicate that samples are semiconducting in nature.The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms.Both these formalisms show qualitative similarities in relaxation time.Our study points that for complex perovskite oxides with general formula A(B'B")O_3,the dielectric properties significantly depend on the atomic radii of both A and B type cations.BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts.They may find several technological applications such as in capacitors,resonators and filters owing to their high dielectric constant and low loss tangent.