Microstructure and Tribological Behavior of Self-lubricating （Si：N）-DLC/MAO Coatings on AZS0 Magnesium Substrate

The combined micro arc oxidation （MAO） and a hybrid beam deposition process was used to deposit duplex （Si：N）-DLC/MAO coatings on AZ80 magnesium alloy. The microstructure and composition of the duplex coatings were analyzed by Raman spectroscopy, X-ray photoelectron spectroscope （XPS）, scanning electron microscope （SEM） and atomic force microscopy （AFM）. Tribological behaviors of the coatings were studied by ball-on-disk friction test. It was found that the ID/IG ratio of the （Si：N）-DLC （diamond-like carbon） top films increases with decreasing C2H2/N2 ratio. The （Si：N）-DLC top film with SigN4 was formed on the MAO coated sample as the C2H2/N2 ratio was 10sccm：5sccm, which showed an increasing critical load compared with the pure DLC directly deposited on the Mg alloy substrate. As a result, the （Si：N）-DLC/MAO coating exhibited an advanced wear protection for the substrate.     

Effect of Thermal Annealing on the Physical Properties of Zn1-xCuxSe Thin Films Deposited by Close Spaced Sublimation Technique

Thin films of Zn1-xCuxSe （x= 0.00, 0.05, 0.10, 0.15, 0.20） were grown on glass substrates by closed space sublimation technique. The deposited films were annealed at 200 ~C and 400 ~C in air for 1 h. The annealed samples have been investigated through Rutherford backscattering spectroscopy （RBS）, X-ray diffraction （XRD）, spectroscopic ellipsometer, spectrophotometer and Raman spectroscopy. Through RBS, the composition of the films was calculated and compared with the initial concentration. Structural characteriza- tion including crystal structure, crystal orientation, lattice parameter, grain size, strain and dislocation density were carried out using XRD data. From XRD spectra it was revealed that the as-deposited and annealed films were polycrystalline in nature with zinc-blende structure. However, the crystallinity and the grain size were improved with the increase of annealing temperature. According to Raman spectroscopy, it was observed that as deposited and annealed samples have the same characteristic vibrational modes of ZnSe at low and high frequency optical phonon modes while another mode was observed for 400 ℃ annealed samples at 745 cm-1. Spectroscopic ellipsometer has been used to found annealing effect on the optical properties of ZnSe. The band gap energy has been determined using transmission spectra. It was found that the band gap energy of the film increased with the increase of annealing temperature.     

Interfacial Microstructure and Properties of a Vacuum Hot Roll-bonded Titanium-Stainless Steel Clad Plate with a Niobium Interlayer

Vacuum hot roll bonding （VHRB） was used to bond pure titanium （Ti） plate to a 304 stainless steel （SS） plate with a niobium （Nb） interlayer, with the aim of producing a high-quality Ti-SS clad plate. The roll-bonding process was performed at different temperatures in the range of 850-1000℃, followed by characterization of microstructure and mechanical properties. The study demonstrates that the interfaces are free from cracks and discontinuities, and interdiffusion between the stainless steel and the titanium is effectively prevented by inserting a layer of pure Nb foil. No intermetallic reaction layer occurred at the Nb-Ti interface at any of the investigated temperatures. An intermetallic FeNb phase was formed at the Nb-SS interface when bonding was performed at 950 ℃ and above. The presence of the FeNb layer was confirmed by x-ray diffraction. The maximum shear strength of -396 MPa was obtained when bonding is carried out at 900 ℃. However, the formation of the FeNb layer at roll bonding temperature greater than 900 ℃ led to decrease in shear strength. Ductile fracture occurred through the Ti-Nb interface for roll-bonded temperatures of up to 900 ℃. On the other hand, at temperature of 950℃ and above, failure occurred through the Nb-SS interface, with brittle fracture characteristics.     

Effect of Austempering Route on Microstructural Characterization of Nanobainitic Steel

A low-temperature nanobainitic steel was obtained through one-step and two-step austempering.The effect of austempering temperature,time,and route on bainitic lath width,volume fraction of retained austenite,carbon concentration in retained austenite,and nanohardness of bainitic lath and retained austenite was studied.Results showed that the transformation kinetics was slowed down and the bainitic lath was refined as the austempering temperature decreased from300 to 250 ℃ Both coarser and finer bainitic laths were obtained with the two-step austempering,which was consistent with the lath size at 300 and 250 ℃ austempering,respectively.X-ray diffraction analysis showed that both volume fraction of retained austenite and its carbon concentration decreased with the decrease of austempering temperature for the one-step austempering,and especially the carbon concentration is obviously increased when the two-step austempering is adopted.The nanohardness of the bainitic lath in the sample after two-step austempering treated lies between that of the samples after 300 and 250 ℃ austempering treated.The product of tensile strength and total elongation of the two-step austempered sample is the highest,which increases monotonously with the product of retained austenite fraction and its carbon concentration.Higher strength-ductility balance may be resulted by the fine bainitic lath,high volume fraction,and high stability of retained austenite in the sample after two-step austempered.     

Efects of Molybdenum Concentration and Valence State on the Structural and Magnetic Properties of BaFe11.6MoxZn0.4-xO19 Hexaferrites

Barium hexaferrites BaFe11.6Mox Zn0.4-x O19(x=0.1,0.2,0.4)were prepared by precipitation of the precursors using wet chemical mixture method and then sintering the dried powders at 1100℃ .The properties of the prepared samples were investigated using X-ray difraction(XRD),scanning electron microscopy(SEM),vibrating sample magnetometer,and Mssbauer spectroscopy.XRD patterns revealed that all prepared samples had BaFe12O19hexaferrite structure as a majority phase.SEM images demonstated that the samples consisted mainly of hexagonal platelet-like grains with diameters ranging from 100 to 500 nm.Mssbauer spectra revealed that Zn2+ions occupy 4f1 sites leading to the splitting of the 12k component.However Mo6+ions occupy 2b sites while Mo4+ prefer 4f1 and 12k sites.For the sample with x=0.4,Mo6+and Mo4+ ions were found to have preference for 2b and 12k sites,respectively,and to induce the development of Fe2+ions in the hexaferrite,leading to noticeable changes in the magnetic properties of the system.The observed magnetic properties were found to be consistent with the preferential site occupation of metal ions,and the hyperfine fields derived from Mssbauer spectra of these samples.     

A Comparative Study on the Corrosion Behaviour of Hard Anodic Coatings on AA 6061 Obtained Using DC and Pulsed DC Power Sources

The corrosion behaviour of the hard anodic coatings prepared by three different methods viz., conventional hard anodizing （C-HA）, pulse hard anodizing （P-HA） and low voltage room temperature pulse hard anodizing （LVP- HA） on AA 6061 was compared using electrochemical impedance spectroscopy （EIS） and linear polarisation. Scanning electron microscope （SEM） was used to study the surface morphology before and after corrosion. EIS data revealed that no significant difference in corrosion resistance was observed among three types. Rp, Icorr and Ecorr were found to be highly stable over the exposure period up to 72 h which confirms the excellent corrosion resistance. The studies indicate that the corrosion resistance of LVP-HA and P-HA, which are processed at lower voltage and at relatively higher temperatures, are comparable to that of C-HA which is processed at sub-zero temperatures and high operating voltages. The corrosion resistance of all coatings was found to be improved after hydrothermal sealing.     

In-situ Observation of Crack Growth and Domain Switching Around Vickers Indentation on BaTiO3 Single Crystal Under Sustained Electric Field

The crack propagation and domain switching process around the indentation on the surface of barium titanate single crystal under the external electric field was investigated by atomic force microscope and polarized light microscope. The evolutions of domain switching and crack propagation were in-situ observed when a 90°a- c domain wall moved across the indentation which was driven by external electric field. The results show that the incompatible strain induced by domain switching in the residual stress zone around the indentation is the driving force of the anisotropic crack propagation. The crack propagation results in the changes of the fine domain stripes around the crack tip.     

The Influence of Ultrasonic Frequency on the Properties of Ni-Co Coatings Prepared by Ultrasound-assisted Electrodeposition

In this paper, Ni-Co coatings were electrodeposited onto carbon steel substrates with the aid of ultrasonic agitation. The coatings were analyzed by energy dispersive X-ray analysis （EDX）, X-ray diffraction analysis （XRD） and scanning electron microscopy （SEM）. The effects of the ultrasonic frequency on the roughness, hardness and corrosion resistance of the Ni-Co coatings were also investigated. The results indicated that the increase of the ultrasonic frequency from 20 to 120 kHz reduced the Ni content and the grain size of Ni-Co coatings. Moreover, the phase structure of the electrodeposited coatings was influenced by the ultrasonic frequency. Under 55 kHz ultrasonic agitation, the Ni-Co coating was single fcc phase and showed the finest roughness and the strongest corrosion resistance in 5 wt.% NaCl solution at the ambient temperature. Under ultrasonic agitation with frequency of 90 kHz, the coating was a mixture of fcc and hcp structure and showed the maximal hardness of about 420 HV. Therefore, ultrasonic agitation helped decrease the roughness, and enhance hardness and corrosion resistance of Ni-Co coatings.     

Influence of Strain Rate on Tensile Characteristics of SUS304 Metastable Austenitic Stainless Steel

The microstructure characteristics and plastic deformation behavior of SUS304 metastable austenitic stainless steel sheets have been investigated during tensile process at different strain rates at room temperature. The yield stress continuously increases with strain rates due to low fraction of martensite transformed from austenite at 0.2% plastic stain. While the ultimate tensile stress （UTS） and elongation gradually decreases and then slightly increases with increase in strain rate from 0.0005 s-1 to 0.i s-1, which is attributed to the variation of the martensite fraction that is affected seriously by adiabatic heating. A higher temperature increase in the tensile specimens restricts the martensitic transformation at high strain rate. The strain rate of 0.1 s-1 is considered as a transition deformation rate from quasi-static state to plastic forming, where the transformed martensitic content is very small in a higher strain rate range. Anomalous stress peaks in the later half stage of deformation occur at a very low strain rate （i.e., 0.0005 s-1） result from X-shaped strain localization repeatedly sweeping over the specimen. With increasing strain rates, the variation of dimple number density follows similar trend as that of UTS and ductility because martensite fraction mostly influences void nucleation and growth.     

Self-Assembled Silane Film and Silver Nanoparticles Coating on Magnesium Alloys for Corrosion Resistance and Antibacterial Applications

Contamination resulting from microbial adhesion on magnesium alloys is very common in many applications. Self-assembly technology was employed to prepare an antibacterial composite coating by fixing silver nanoparticles （AgNPs） onto the surface of magnesium alloys. The AgNPs were immobilized on the surface of 3-aminopropyltrimethoxysilane （APTMS）-modified magnesium alloy AZ31 （APTMS/Mg） through electrosta- tic inter-attraction between partially protonated amino groups and negatively charged citrate-capped AgNPs, resulting in the AgNPs attached APTMS/Mg （AgNPs/APTMS/Mg） substrate. The prepared Ag colloid and functionalized AZ31 alloy were characterized by ultraviolet-visible （UV-vis） spectroscopy, Fourier transform infrared （FTIR） spectroscopy, scanning electron microscopy （SEM）, and electrochemical methods. Finally, the bactericidal activity of AgNPs/APTMS/Mg substrate against Escherichia coli was assessed by the inhibition zone. The results demonstrated that Si-O-Si covalent bonds existed on the substrate with the formation of inorganic Si-O-Mg bonds. AgNPs were immobilized and well-dispersed, forming a uniform submonolayer on the silane film in two dimensions. The AgNPs/APTMS-pretreated AZ31 alloys exhibited better corrosion resistance and excellent antibacterial performance.     

Hot deformation behavior and microstructure evolution of as-cast AZ91D magnesium alloy without pre-homogenization treatment

The deformation behavior and the microstruc-ture evolution of as-cast AZ91D magnesium alloy without pre-homogenization treatment were systematically inves-tigated. The flow stress behavior was studied by com-pression tests in strain rate range of 0.001-1.000 s^-1 and deformation temperature range of 220-380 ℃ with a maximum deformation strain of 60 %. The dependence of flow stress on deformation temperature and strain rate was described by hyperbolic sine constitutive equation. Through regression analysis, the average apparent activa- tion energy and coefficient of strain rate sensitivity were estimated to be 181.98 kJ.mol^-1 and 0.14, respectively. The results also reveal that the variation of peak stress depends on strain rate and deformation temperature. Microstructure observation shows that, at temperatures higher than 300 ℃ and strain rates lower than 0.01 s^-1, DRX developed extensively at the grain boundaries and in the core of coarse grains, resulting in a more homogeneous microstructure. Furthermore, the effects of strain, defor-mation temperature, strain rate, and eutectic β phase on the microstructure evolution of as-cast AZ91D magnesium alloy were discussed.     

Electrochemical potassium ion sensor based on DNA G-quadruplex conformation and gold nanoparticle amplification

A simple, rapid, highly sensitive electrochem-ical sensor for potassium ion （K^＋） based on the confor-mationai change of DNA sequence containing guanine-rich segments is presented. In the presence of K^＋, guanine-rich DNA sequence folds to G-quadruplex structure, allowing a ferrocene tag to transfer electrons to the electrode. Gold nanoparticles （AuNPs）, which are self-assembled on the surface of a bare gold electrode by using 4-aminothio-phenol as a medium, offer a big surface area to immobilize a large number of aptamers and improve the sensitivity of the sensor. The square-wave voltammetry peak current increases with K^＋ concentration. The plots of peak current against K^＋ concentration and the logarithm of K^＋ con- centration are linear over the range from 0.1 to 1.0 mmol·L^-1 and from 1 to 30 mmol·L^-1, respectively. A lower detection limit of 0.1 mmol·L^-1 K^＋ is obtained for AuNPs-modified sensor, which greatly surpasses that （100 mmol·L^-1） of the sensor without AuNPs modification by three orders of magnitude. Thus, the sensor with AuNPs amplification is expected to open new opportunities for highly sensitive detection of other biomolecules in the future.     

Mechanical and Electrical Properties of the. Ternary Ag-Sb-Zn System

This paper presents comparative review of experimental and thermodynamic assessment of ternary Ag-Sb-Zn system.Isothermal section of the Ag-Sb-Zn system at 300 ℃ has been calculated by CALPHAD method using thermodynamic parameters from literature.Microstructural analysis of a number of alloys was carried out by scanning electron microscopy and optical microscopy,whereas chemical composition of observed phases was analyzed using energydispersive X-ray spectroscopy.Hardness of selected alloys from four vertical sections was determined using Brinell hardness test and additionally by micro Vickers hardness test.Electrical conductivity of a number of alloys in the ternary Ag-Sb-Zn system was experimentally determined.Good overall agreement between experimental and calculated values was obtained.     

Efects of Die Corner Radius and Temperature on the Formability of AA7075-T6 Alloy

This study focused on the formability of aluminium alloy（7075-T6） sheets through hydroforming route. Formability of these sheets was tested using a warm forming setup at three diferent temperatures and four diferent die corner radii. Forming limit diagrams（FLD） were generated by measuring the grids of the sheet formed. The results show that the forming limit of AA7075-T6 can be significantly improved when the blank was heated to 140–250℃. It was also observed that as the temperature increases above 140℃, dome height began to decrease. Also the results indicated that both the die corner radius and temperature have a significant efect on the stress-strain curve and warm forming of AA7075-T6 sheets. Thus, with the temperature increased from room temperature（RT） to 140℃, the flow stress decreased and the strain increased, hence, the formability is enhanced. However, further increase in temperature causes decreases the flow stress and strain. Similar changes of the flow curve were seen in die corner radius. Decreasing the die corner radius decreases the flow stress and increase the strain. Moreover, an equation was obtained by establishing correlations between the experimental parameters and their results. In this way, it became possible to make predictions.     

Influence of Temperature on in Nanocrystalline Materials： the Inverse Hall-Petch Effect Phase Field Crystal Simulation

The influence of temperature on the inverse Hall-Petch effect in nanocrystalline(NC) materials is investigated using phase field crystal simulation method.Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature.The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect.At elevated temperature,grain rotation and grain boundary(GB) migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect.However,at low temperature,both grain rotation and GB migration occur with great difficulty,instead,the dislocations nucleated from the cusp of serrated GBs become active.The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect.Furthermore,it is found that since small grain size is favorable for GB migration,the degree of weakening decreases with decreasing average grain size at low temperature.     

Fatigue of 0.55C-1.72Si Steel with Tempered Martensitic and Carbide-Free Bainitic Microstructures

High-Si spring steel was heat treated in three different ways:Quenching and tempering at 460 ℃ to obtain a tempered martensite microstructure,and austempering at 300 and 350 ℃,respectively,to obtain two different carbide-free bainitic microstructures.In the steel austempered at 350 ℃,both the bainite lath thickness and retained austenite content were higher than those of the steel austempered at 300 ℃.Rotating-bending fatigue tests were done in order to evaluate the effect of each heat treatment on the high-cycle fatigue behavior of the steel.When the austempering temperature was300 ℃,the endurance limit was increased by 25%despite a 5%reduction in tensile strength when compared with that of the quenched and tempered steel.The relationship between endurance limit[R_(fat)t(50%)]and ultimate tensile strength(R_m)was higher for the austempered samples in comparison with that of the quenched and tempered material.Therefore,it is believed that the presence of retained austenite affects the relationship between endurance limit and tensile strength.     

Luminescent properties of a new Nd3+-doped complex with two different carboxylic acids and pyridine derivative

A new Nd3+-doped organic complex featuring two different perfluorinated carboxylic acids as the first ligand and pyridine derivative 2-amino-3-chloro-5-(trifluoromethyl)pyridine as the second ligand was designed and synthesized.Successful coordination between the ligands and central rare earth ions was confirmed by Fourier transform infrared spectroscopy(FT-IR)spectra,1H nuclear magnetic resonance(1H NMR)spectra,and UV spectra,and the synthesized complex is inferred to be eight-coordinate structure.Solution of the complex dissolved in DMSO-d6 was prepared and then its fluorescence spectrum,UV–Vis–NIR absorption spectrum,and fluorescence decay curve were tested.The fluorescent lifetime is about 7 ls.Based on the above experimental research,Judd–Ofelt analysis was carried out,and the results indicate that appropriate coordination environment around Nd3?in this solution results in a high fluorescent quantum efficiency 2%and a large stimulated emission cross-section about 3.2 9 10-20cm2at 1,064 nm.     

Synthesis of Flower-Like Nanoparticles of Anatase Titania by Microwave Solvo-Hydrothermal Method

Anatase titania nanoparticles with an average size of about 14 nm were synthesized by microwave solvothermal method from TiCI4 and ethanol as a precursor and solvent respectively. The shapes of as prepared samples were modified by microwave hydrothermal treatment in strongly alkaline medium at 100℃ for 2 h, the agglomerate particles can be converted to the nanorods then to flower-like sphere. The structure, morphology and optical properties of as-prepared powders were investigated by X-ray diffraction, scanning electron microscopy and UV- vis absorption spectroscopy, the quality of the samples was examined by IR absorption spectroscopy and room temperature photoluminescence （PL）. The results showed that the synthesized Ti02 revealed the formation of the nanorods and the flower-like shape of titania after post treatment in 5 mol/L and 10 mol/L NaOH solution, respectively. IR absorption spectra showed that the as-prepared TiO2 nanocrystals were highly pure and strongly surface hydrated, The photoluminescence measurement showed that five main emission peaks appeared in UV, violet, blue and green regions.     

Influence of Temperature on the Protectiveness and Morphological Characteristics of Calcareous Deposits Polarized by Galvanostatic Mode

The influence of temperature on calcareous deposits formed under galvanostatic polarization mode was studied.The deposition was monitored by electrochemical impedance spectrum,and a supplementary loop in Nyquist diagram at high frequency was found to be an indicator of deposits precipitation with sufficient protection at above 20 ℃.An exponential increase of protectiveness with temperature was observed,which was quantified by linear polarization resistance technique.Observation by scanning electron microscope and X-ray diffraction analyses demonstrated that the critical temperature of calcium carbonate crystal form transition ranged from 15 to 20 ℃.Calcite formed below 15 ℃,while aragonite precipitated at above 20 ℃.     

Crystal Structure from bcc to 9R in Evolution of the Cu-rich Reactor Pressure Vessel Nano Precipitates Model Steel

The crystal structure evolution of the Cu-rich nano precipitates from bcc to 9R during thermal aging was studied in nuclear reactor pressure vessel （RPV） model steels. The specimens, contained higher copper and nickel contents than commercially available one, were heated at 890 ~C for 0.5 h and then water quenched followed by tempering at 0（50 ~C for I0 h and aging at 400 ~C for 1000 h. It was observed that bcc and 9R orthogonal structure, as well as 9R orthogonal and 9R monoclinic structure, coexist in a single Cu-rich nano precipitate. Further analyses pointed out that Cu-rich nano precipitates of bcc structure were not stable, it may preferentially transform to 9R orthogonal structure and then to 9R monoclinic structure. This results showed that the crystal structure evolution of the Cu-rich nano precipitates was complex.