Low-Temperature Nitriding by Means of SMAT

The microstructure in the surface layer of iron and steel samples can be refined at the nanometer scale by means of a surface mechanical attrition treatment (SMAT) that generates repetitive severe plastic deformation to the surface layer.The subsequent nitriding kinetics of the as-treated samples with the nanostructured surface layer is greatly enhanced so that the nitriding temperatures can be reduce to 300 ～ 400℃ regions. This enhanced processing method demonstrates both the technological significance of nanomaterials in advancing the traditional processing techniques, and provides a new approach for selective surface reactions in solids. This article reviews the present state of the art in this field. The microstructure and properties of SMAT samples nitrided will be summarized. Further considerations of the development and applications of this new technique will also be presented.     

Hydrophilic property of SiO2-TiO2 overlayer films and TiO2／SiO2 mixing films

The photo-induced hydrophilicity of SiO2 overlayer on TiO2 films prepared by sol-gel method was investigated by means of soak angle measurement, XPS, UV-VIS and FTIR spectra. The results show that, compared with the TiO2 film without SiO2 overlayer, when the TiO2 film is thoroughly covered by SiO2 overlayer, the hydrophilicity and the sustained effect are enhanced. It is found that the significant growth of the OH- group occurs in the surface of SiO2 overlayer. The different mechanism of enhanced hydrophilicity between SiO2 overlayer on TiO2 films and TiO2/SiO2 mixing films was analyzed. The result suggests that the photo-generated electrons created in the interface between TiO2 and SiO2 tend to reduce the Ti(Ⅳ) cation to the Ti( Ⅲ ) state, and the photogenerated holes transmit through the SiO2 layer to uppermost surface efficiently. Once the holes go up to the surface， they tend to make the surface hydrophilic. The stable hydrophilicity of SiO2 overlayer which adsorbs more stable OH groups, enhances the sustained effect, i.e. the super-hydrophilic state can be maintained for a long time in dark place.     

Preparation and photocatalytic activity of composite films containing clustered TiO2 particles and mineral tourmaline powders

The novel composite films containing clustered TiO2 particles and fine tourmaline particles on the surface of copper webs were prepared by the sol-gel method. The microstructures of the composite films were investigated by scanning electron microscopy （SEM）, and the photocatalytic activity of the films was evaluated by photocatalytic degradation of methyl orange, respectively. The results indicate that tourmaline particles can obviously influence the microstructures of TiO2 films and enhance the photocatalytic activity due to their spontaneous permanent polarity and high radiotechnology of far infrared. During preparing the composite films, the clustered TiO2 particles with lots ofnano-sized ladder layers can grow on the surface of fine tourmaline particles, the thickness of ladder layer is 10 nm, and the average diameter ofnano-sized TiO2 particles is 15 nm.     

SAM AND XPS STUDIES ON SURFACE SEGREGATION OF SUBSTRATE ELEMENTS IN Au-Ni-KOVAR ALLOY SYSTEM

The surface segregation of substrate elements through the Au layer in the Au-Ni-Kovar sys- tem specimens heated at 250—350℃ for 0.5—1.5 h has been studied by SAM and XPS. Visual evidence of the mechanism for Ni and Co surface segregation of the complicated sys- tem has been given,i.e.Ni and Co penetrated the gold layer mainly by grain boundary diffu- sion and then covered the Au layer by surface diffusion.The strdy results of the chemical states of surface segregation elements not only indicate that oxygen adsorption and oxidation reaction are the driving force for the surface segregation of Ni and Co,but also show that the above segregation can result in water absorption on surfaces.     

Sol-gel derived HA/TiO2 double coatings on Ti scaffolds for orthopaedic applications

Hydroxyapatite/titania （HA/TiO2） double layers were coated onto Ti scaffolds throughout for orthopaedic applications by sol-gel method. Differential scanning calorimetry （DSC）, thermogravimetric analysis （TG） and X-ray diffractometry （XRD） were used for the characterisation of the phase transformations of the dried gels and coated surface structures. Scanning electron microscope （SEM） equipped with energy dispersive spectrometry （EDS） was used for the observation and evaluation of the morphology and phases of the surface layers and for the assessment of the in vitro tests. The in vitro assessments were performed by soaking the HA/TiO2 double coated samples into the simulated body fluid （SBF） for various periods. The TiO2 layer was coated by a dipping-coating method at a speed of 12 cm/min, followed by a heat treatment at 600 ℃ for 20 min. The HA layer was subsequently dipping-coated on the outer surface at the same speed and then heat-treated at difference temperatures. The results indicat that the HA phase begins to crystallize after a heat treatment at 560 ℃. The crystallinity increases obviously at 760 ℃. SEM observations find no delamination or crack at the interfaces of HA/TiO2 and TiO2/Ti. The HA/TiO2 coated Ti scaffolds displays excellent bone-like apatite forming ability when it is soaked into SBF. Ti scaffolds after HA/TiO2 double coatings can be anticipated as promising implant materials for orthopaedic applications     

Analysis of trace mercury in water by solid phase extraction using dithizone modified nanometer titanium dioxide and cold vapor atomic absorption spectrometry

A new method for analysis of trace mercury in water samples was developed, based on the combination of preconcentration/separation using dithizone-modified nanometer titanium dioxide (TiO2) as a solid phase extractant and determination by cold vapor atomic adsorption spectrometry (CVAAS). Dithizone was dissolved with alcohol and loaded on the surface of nano-sized TiO2 powders by stirring. The static adsorption behavior of Hg2 on the dithizone-modified nanoparticles was investigated in detail. It was found that excellent adsorption ratio for Hg2 could be obtained in the pH range of 7-8 with an oscillation time of 15 min, and a 5 mL of 3.5 mol·L-1 HCl solution could quantitatively elute Hg2 from nanometer TiO2 powder. Common coexisting ions caused no obvious influence on the determination of mercury. The mechanisms for the adsorption and desorption were discussed. The detection limit (3σ) for Hg2 was calculated to be 5 ng·L-1. The proposed method was applied to the determination of Hg2 in a mineral water sample and a Zhujiang River water sample. By the standard addition method, the average recoveries were found to be 94.4%-108.3% with RSD (n = 5) of 2.9%-3.5%.     

Selective adsorption of bacteria on sulfide minerals surface

The adsorption of bacteria on sulfide minerals surface was studied, and the selective adsorption mechanism of cells on the sulfide minerals was investigated by means of FTIR, UVS and XPS. The results show that the three strains of bacteria adsorbed more preferentially on pyrite than on other two sulfide minerals surface at neutral and alkaline pH conditions. FTIR and UVS of three strains of bacteria indicate that there are more functional groups on their surface, such as O---H, C=O, N--H, C--43, and the content of saccharide is more than that of protein. The state of every element on sulfide minerals surface was analyzed by XPS. The empty orbital number of electronic shell of metal ions on minerals surface is important in selective adsorption process, and some stable constants of metal coordinates can be used to explain the contribution of some groups in saccharide of cell wall to the selective adsorption.     

Plastic flow pattern and its effect in friction stir welding of A2024 and A1060

During the friction stir welding （FSW）, the property of the welding joint is highly affected by the plastic and viscous flow behavior of the softened material. The flow pattern of the welded material was examined through observing the microstructural distribution of friction stir welded joints between dissimilar 2024 and 1060 aluminum alloy. The experimental results show that the flow patterns of material at different locations in the weld are different and can be divided into four layers along the thickness direction： surface flow layer influenced by the shoulder of the tool, in which the material tends to flow as integrity; horizontal flow layer influenced by the surface flow layer, in which the material of surface flow layer enters and flows forwards under the advancing force of the tool; vertical flow layer （plastic flow area induced by stirring of the pin）, in which the flow pattern is complex and onion rings can often be observed; unstirred bottom layer because of the length of the pin being shorter than the thickness of the plates. The effeet of plastic flow on welding quality was further investigated. The study suggests that welding quantity is significantly influenced by the flow pattern and defects always appear in horizontally lamellar flow region because of the complex flow pattern.     

Microstructure and Mechanical Property of Ni Metal Treated by Surface Mechanical Attrition

A nanostructured surface layer can be formed in Ni metal treated by surface mechanical attrition (SMA). The microstructure was investigated by using optical microscope, X-ray diffractometer and transmission electron microscope,respectively. Mechanical property measurements indicate that the yield strength of the surface layer raises significantly while the tensile strength somewhat changes and the elongation percentage reduces severely compared with that of the inside layer. Meanwhile, yield-drop-like phenomenon occurs in the surface layer after SMA treatment. In order to compare the mechanical behavior of nanostructured materials with two phases, Fe-30Ni nanostructured alloy was also investigated.     

Degradation of benzene on Zr-doped TiO_2 photocatalysts with a bimodal pore size distribution

Zr-doped TiO2 was prepared from TiOSO4 and ZrOCO3 by a co-precipitation method using NH3H2O as the precipitation agent. The Zr-doped TiO2 was characterized by X-ray diffraction(XRD), low temperature N2adsorption–desorption measurement, and UV–Vis diffuse reflectance spectroscopy technology. Appropriate amounts of ZrO2 addition can greatly improve the TiO2 microstructure properties and its photocatalytic activities. In addition, polyethylene glycol(PEG) was used as a surfactant for templating the pore structure of samples. A bimodal pore structure can be controlled using PEG6000 and PEG20000 surfactants simultaneously during the preparation. The rate constant of benzene degradation over the Zr-doped TiO2 linearly decreases with the increase of photocatalytic reaction temperature and decreases in a polynomial relation with the benzene concentration.Moreover, it increases approximately linearly with the increase of the illumination intensity or area.     

Compound Ceramic Coatings on Ti-6AI-4V by Micro-Plasma Oxidation in NaAlO2 Solution

Micro-plasma oxidation (MPO) technique is a new technique by which compound ceramic coating can be grown in situ on AI, Ti, Mg and many other valve-metals. Compound ceramic coatings on Ti-6Al-4V alloy were prepared for different time by pulsed bi-polar MPO in NaAlO2 solution. The phase composition, morphology and the element distribution of the coatings were studied by XRD, SEM and JEOL SUPERPROBE 733 electric probe, respectively. Electrochemical Impedance Spectra (EIS) of the coatings were measured to study the structure character of the coatings. Through the proper EIS interpreting software, the “equivalent circuit“ of the coatings was established, and the fitting values of equivalent element were calculated. The coating is mainly composed of Al2TiO5, α-Al2O3 and futile TiO2. The content of Ti element in the coating is less than that of substrate; its distribution is relatively uniform, and Ti in the outer layer is less than that in the inner layer. The content of A1 in the coating is more than that of substrate, and its distribution is not even: Al in the middle part is more than that on both sides of the coating; And the EIS analysis has illustrated the double-layer structure of the coatings, and the outside layer is loosen and the inner layer compact; with the increase of the oxidizing time, the surface roughness of the coatings, and the porosity of the outer layer of the coating are increased while the compactness of the inner layer of the coatings are improved.     

Fabrication of curved micro structures on photoresist layer

A novel fabrication process for micro patterns with curvature was introduced. The curved structures were made by compensating rectangular micro structures with liquid photoresist layer. Because of the surface tension of the liquid in micro scale, various shapes of meniscus can be made on the micro channels. The micro channels were made on the silicon substrate in advance, and then the liquid layer was coated on the micro channels. From the nature of liquid behavior, the curved patterns with smooth surface are obtained, which cannot be made easily with the conventional mechanical machining, as well as with the microfabrication processes, such as wet and dry etching. With this principle, it is expected that the smooth and curved surfaces can be made by simple processes and the results can be applied widely, such as optical patterns.     

Study on improving properties of welded joints of 400 MPa ultra fine grained steel by mechanical surface hardening

The welded joints of 400 MPa ultra fine grained steel in manual arc welding were treated by mechanical surface hardening. Microstructure and mechanical properties of the treated joints were compared with those of the untreated joints, based on which, primary study on the process and principle of mechanical surface hardening was carried out. The results shows that： Grain size of HAZ increases greatly and mechanical properties of welded joint decrease obviously compared with those of base martial, but grain size in the surface layer of HAZ can be refined （the grain size is about 100 nm or so） and mechanical properties of welded joints can be improved greatly by mechanical surface hardening.     

Coating process of multi-material composite sand mold 3D printing

Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.     

Formation mechanism of pulse current anodized film on AZ91D Mg alloy

The kinetics of forming process of pulse current anodized film on AZ91D Mg alloy was studied by the voltage-time and thickness-time curves. The surface morphology, structure, elemental constitution and valences of the anodic films were analyzed by SEM, EDS, XPS and XRD respectively. The results show that the film-forming process can be divided into four stages. Formation of a dense layer before sparking is the first stage. Formation of a porous layer accompanied with slight sparking is the second stage. The third stage is characterized by fast growth of the porous layer accompanied with more intensive sparking. The fourth stage starts after the sparking process becomes even more vigorous and the pores become large.     

Study on the subsonic speed flame spraying coating of hydroxyapatite

A new method of preparation of biomaterial composite coating by the technique of subsonic thermal spraying was discussed in this paper. Ti6Al4V and pure Ti were chosen as substrate and sublayer material respectively and the working layer was sprayed with biomaterial hydroxyapatite (HAP), forming the composite coating. The experiments of heat shock and tensile strength showed that the bonding strength between coating and substrate is almost as same as that of specimen in which Ni/Al powder was adopted as sublayer. The phases of TiN, TiO2, and Ti2O3 were formed in the sublayer, which are free of toxic and have no side effects. The powder of working layer HAP was decomposed partly during spraying, but it can be solved by later treatment.     

Microstructure of Nitrided Aluminum Alloys Using an Electron-Beam-Excited-Plasma （EBEP）

Nitriding of surface of aluminum alloys was carried out with using an electron-beam-excited-plasma (EBEP) technique. The EBEP is sustained by electron impact ionization with energetic electron beam. Two kinds of substrates,aluminum alloys AA5052 and AA5083, were exposed to the down flow of EBEP source at 843 K for 45min. The specimens were characterized with respect to following properties: crystallographic structure (XRD), morphology (SEM) and the cross sectional microstructures of the nitrided layer was observed using a scanning electron microscopy (SEM). There are some Al2O3 particles on the surface of the nitrided AA5052 and AA5083. The AlN layers were formed on the substrates with the thickness of 4.5μm for AA5052 and 0.5μm for AA5083. A relatively uniform nitrided surface layer composed of AlN can be observed on the AA5052 substrate. The grains size near the interfaces between the substrate and AlN layer were smaller than that near the surface. On the surface of AlN layer, the concentration of nitrogen was high and in the middle of AlN layer it had a constant concentration like the aluminum and the concentration was decreased with approaching to the interface. On the surface of nitrided AA5083, a uniform AlN layer was not formed as the reason for the high nitriding temperature.     

Research on depositing Ni45 alloy on titanium alloy surface by electrospark deposition

Taking Ni45 bar as electrode, a strengthened layer of thickness up to 50 μm was built up on BT20 titanium alloy matrix by means of electrospark deposition. Results of phase analysis by using of X-ray diffraction confirmed that the deposition layer was composed mostly of three phases, NiTi, NiTi2 and Ti. The surface microhardness of the deposition layer was up to 910 HV0.05, about 2.7 times as high as that of the matrix. The hardness at the cross-section of the entire deposition layer showed a gradient distribution. The effects of capacitance and deposition time on thickness of deposition layer were also studied, and results showed that with relatively low capacity and short deposition time the deposition layer without cracks can be obtained.     

Solvothermal synthesis of nano-CeO_2 aggregates and its application as a high-efficient arsenic adsorbent

Aggregates of cerium dioxide nanoparticles(nano-CeO_2) were successfully prepared via a facile solvothermal process in this study. The crystallographic information and morphological information of nano-CeO_2 were systematically studied by X-ray diffraction(XRD),transmission electron microscopy(TEM), laser particle size analyzer(LA) and specific surface area and pore size analyzer during the solvothermal process. Among all the obtained samples, the 18-h solvothermal-prepared nano-CeO_2 aggregates show the best crystallinity and the largest specific surface area of 110.92 m~2·g~(-1). Owing to the high activity derived from the high specific surface area of the aggregates, the application as arsenic(As) adsorption was also studied. The adsorption efficiency of arsenic by nano-CeO_2 aggregates was established as the function of adsorbent dose, then pH value and at last adsorption time.The results indicate that the nano-CeO_2 aggregates show a high efficiency in removing arsenic from low As concentration solution, from which the nano-CeO_2 adsorbent could be easily separated. In addition, the adsorption kinetics is best fitted to pseudo-second-order model(R~2 = 0.99999).     

Interaction between alloying and hardening of cast iron surface

To improve wear resistance of surface will increase the service life of gray cast iron directly.This paper presents that gray cast iron surface coated with alloy powder is locally remelted by TIG arc of increase the wear resistance.The influences of arc current and scanning rate etc on surface properties are found.Under different conditions.the microstructure,hardness and wear resistance of remelted layer are analyzed and measured.The results indicate that the gray cast iron surface can be strengthened by TIG arc local remelting treathent.Especially,surface alloying hardening effect is best and surface properties are improved remarkably.