Effect of Ultrasonic Output Power on Refining the Crystal Structures of Ingots and Its Experimental Simulation

In this study, a series of tests were conducted by using aluminum-based alloy to determine the formation of grain refining structure based on the ultrasonic vibration (UV). Furthermore, the simulation test and effect of ultrasonic output power were studied using ammonium chloride. Finally, the mechanism of grain refinement was investigated. The results show that: (1) By applying the UV to aluminum-base alloy, the grain refining rate of ingots tended to increase with the increase of the output value of UV. (2) It was confirmed that time from after the pour to the beginning of crystallization as well as cloudiness tended to decrease with increasing the ultrasonic power value of UV. Moreover, it can be seen from each cooling curve that a uniform temperature gradient existed in the melt as the power of UV increased, that made the melt strongly stirred. (3) It was also considered that the grain refining effect of ingots, which was observed from the simulation tests, resulted from nucleation action and stirring division action by applying the UV.

Numerical Simulation on Temperature and Microstructure during Quenching Process of Large-sized AISI P20 Steel Die Blocks

In this paper, a model of coupled thermal and phase transformation is described. The temperature and microstructure during the quenching process for large-sized AISI P20 steel die blocks have been simulated using the finite element method (FEM). The optimum quenching technology of large-sized AISI P20 steel die blocks has been proposed based on the simulation results, which not only can effectively avoid quenching cracks and obtain deeper hardened depth, but also can improve the microstructure and properties of the large-sized die blocks.

Effect of Thermal Treatment on the Grain Growth of Nanostructured YSZ Thermal Barrier Coating Prepared by Air Plasma Spraying

A nanostructured thermal barrier coating is prepared by air plasma spraying using the 8wt% Y_2O_3 partially stabilized zirconia nano-powder with an average grain size of 40 nm. The microstructure and phase composition of feedstock nano-powder and coating are investigated using SEM, TEM and XRD. It is found that the as-sprayed zirconia coating has an average grain size of 67 nm and mainly consistes of metastable tetragonal phase, together with some monoclinic phase and tetragonal phase. Thermal treatment results show that the grains of the nanostructured coating grow slightly below 900℃, whereas over 1000℃ the gains grow rapidly and monoclinic phase noticeably appeares.

Fabrication of an in-situ nanoAl_2O_3/Cu composite with high strength and high electric conductivity

A heat-resistant dispersion-strengthening nano-Al_2O_3/Cu composite with highstrength and high electric conductivity was fabricated in a multiplex medium. The internaloxidation product, microstructures and properties of the composite, and the process flow weresystematically studied. It is confirmed that this new technique simplifies the process and improvesthe properties of the composite. X-ray analysis indicates that the alumina particles formed duringinternal oxidation consist of a large mount of gamma-Al_2O_3 and a certain amount of theta-Al_2O_3and alpha-Al_2O_3. TEM observation shows that the obtained gamma-Al_2O_3 nano-particles areuniformly distributed in the copper grains; their mean size and space between particles are 7 runand 30 nm, respectively. The main properties of the composite with 50 percent cold deformation areas follows: the electric conductivity is 51 MS/m (87 percent IACS), sigma_b = 628 MPa, and thehardness is HRB86. After annealing at 1273 K, all or most of the above properties remain, and themicrostructures are still dependent on elongated fiber-form grains.

A Macroscopic Model for the Portevin-Le Chatelier Effect

The Portevin-Le Chatelier (PLC) effect means serrated yielding or jerky flow phenomenon in some alloys. In this paper a macroscopic model is developed to investigate the PLC effect with the emphasis on mechanical response of the structure evolution on microscopic scale. In addition to the normal work hardening effect, the model takes account of the thermal activation of dislocation moving with the aid of stress and the collective interactions between mobile dislocations and solute atoms due to dynamic strain ageing (DSA). It can satisfy the negative strain rate sensitivity of flow stress, which is believed to be one of the most special features associated with the PLC effect. The heterogeneous nature of the deformed material is also considered by introducing a nonuniform spatial distribution of some model parameters. The serrated yielding and localized deformation behavior can be successfully reproduced via numerical simulation based on this model.

Preparation of Terbium Sesquisulfide and Holmium Sesquisulfide by Sulfurization of Their Oxide Powders Using CS_2 Gas

The formation behaviors of terbium sesquisulfide(Tb_2S_3)and holmium sesquisulfide(Ho_2S_3)synthesized via the sulfurization of their oxide powders using CS_2 gas in the range of temperature 673 to 1323 K were investigated. In the sulfurization of Tb_4O_7 powder, Tb_2O_3 and Tb_2O_2S were formed in the initial stage of reaction, and α-Tb_2S_3 was finally formed at higher temperature. For long sulfurization time of 8 h, single-phase α-Tb_2S_3 could be synthesized at 1323 K. In the sulfurization of Ho_2O_3 powder using CS_2 gas, only Ho_2O_2S was formed as an intermediate product. At a sulfurization temperature above 873 K, Ho_2O_2S was formed in the initial stage of reaction, and single-phase δ-Ho_2S_3 was formed at 1323 K for 8 h instead of Ho_2O_2S. Furthermore, the influence of the addition of carbon black to the sulfurization of Ho_2O_3 powder using CS_2 gas was investigated, and the result implied that the reactions were accelerated slightly by the addition of carbon black.

Co^3+-modified Surface of LiMn2O4 Spinel for its Improvement of Electrochemical Properties

Cobalt was used to modify the surface of spinel LiMn2O4 by a solution technique to produce Co3+-modified surface material (COMSM). Cobalt was only doped into the surface of LiMn2O4 spinel. XPS(X-ray photoelectron spectroscopy) analysis confirms the valence state of Co3+. COMSM has stable spinel structure and can prevent active materials from the corrosion of electrolyte. The ICP(inductively coupled plasma) determination of the spinel dissolution in electrolyte showed the content of Mn dissolved from COMSM was smaller than that from the pure spinel. AC impedance patterns show that the charge-transfer resistance (Ret) for COMSM is smaller than that for pure spinel. The particles of COMSM are bigger in size than those of pure spinel according to the micrographs of SEM(scanning electron microscopy). The determinations of the electrochemical characterization show that COMSM has both good cycling performance and high initial capacity of 124.1 mA/h at an average capacity loss of 0.19 mAh/g per cycle.

Sol-gel Preparation and Preliminary in vitro Evaluation of Fluorapatite/Hydroxyapatite Solid Solution Films

Fluorapatite/hydroxyapatite solid solution has better biological properties than other apatites, especially used as films or coatings. In this work, sol-gel preparation and in vitro behavior of fluorapatite/hydroxyapatite solid solution films on titanium alloy were investigated. Ca(NO3)2·4H2O and PO(OH)K(OEt)3-x. were selected as precursors, and hexafluorophosphoric acid (HPF6) was used as a fluorine containing reagent. The Ca and P precursors were mixed with HPF6 to keep the Ca/P molar ratio 1.67. The mixtures refluxed for 12 h were used as dipping sols for the preparation of the films. The phase of the films obtained at 600℃ was apatite. The F contents in the films increased with the concentrations of HPF6 in the dipping sols. The solid solution films were shown to have better stability than hydroxyapatite films, and a reasonably good bioactivity in the in vitro evaluation.

GALVANIC CORROSION AND PROTECTION OF GECM/LY12CZ COUPLES UNDER DIFFERENT ATMOSPHERIC EXPOSURE CONDITIONS

Galvanic, compatibility between graphite epoxy composite materials (GECM) and LY12CZ aluminum alloy was evaluated in different atmospheric corrosion environments and by laboratory electrochemical measurements. Open circuit potential electrochemical measurements showed a relatively large potential difference about 1 volt between the GECM and LY12CZ aluminum alloy, and this difference provided the driving force for galvanic corrosion of the LY12CZ aluminum alloy as an anode. Having been exposed for 1, 3 or 5 years in Beijing, Tuandao and Wanning station, GECM/LY12CZ couples showed significant losses of strength and elongation. Protective coatings and non-conductive barriers breaking the galvanic corrosion circuit were evaluated under the same atmospheric corrosive conditions. Epoxy primer paint, glass cloth barriers and LY12CZ anodizing were effective in galvanic corrosion control for GECM/LY12CZ couples.

Precipitation behavior of B2-like particles in Fe-Cu binary alloy

The precipitation behavior in Fe-Cu binary allow was investigated undertransmission electron microscope (TEM) during aging at 650 deg C for the time range of 100 s to 300h. In addition to the zones with higher copper content and epsilon-Cu were observed, a metastablephase with B2-like structure was found in the early stage of the precipitation process, which isquite different from the equilibrium copper phase shown in the Fe-Cu binary phase diagram and hasperfect coherent relationship to the alpha-Fe matrix. The appearance of B2-like structure is veryimportant concerning the mechanism of aging strengthening effect and mechanical properties ofcorresponding engineering steels and alloys containing copper.

Preparation of Single Crystalline V_6O_(13) Nanobelts

Ultralong beltlike nanostructures was successfully synthesized for V6O13 crystal by ahydrothermal route. The products are characterized by means of X-ray powder diffraction,transmission electron microscopy and high-resolution transmission electron microscopy. Theexperimental results give the evidence that the V6O13 nanobelts are pure, structurally uniform andsingle crystalline, with typical widths of 50 to 300 nm and lengths of up to a few millimeters.

Behavior of Aramid Fiber/Ultrahigh Molecular Weight Polyethylene Fiber Hybrid Composites under Charpy Impact and Ballistic Impact

The aramid fiber礥HMWPE (ultrahigh molecular weight polyethylene) fiber hybrid composites (AF礑F) were ma-nufactured. By Charpy impact, the low velocity impact behavior of AF礑F composite was studied. And the high velocity impact behavior under ballistic impact was also investigated. The influence of hybrid ratio on the performances of low and high velocity impact was analyzed, and hybrid structures with good impact properties under low velocity impact and high velocity were optimized. For Charpy impact, the maximal impact load increased with the accretion of the AF layers for AF礑F hybrid composites. The total impact power was reduced with the decrease of DF layers and the delamination can result in the increase of total impact power. For ballistic impact, the DF ballistic performance was better than that of the AF and the hybrid ratio had a crucial influence. The failure morphology of AF礑F hybrid composite under Charpy impact and ballistic impact was analyzed. The AF礑F hybrid composites in suitable hybrid ratio could attain better performance than AF or DF composites.

INTRAGRANULAR FERRITE FORMED IN ASSOCIATION WITH INCLUSIONS IN A VANADIUM MICROALLOYED STEEL

Intragranular ferrite was formed at inclusions in a vanadium microalloyed steel with excess amount of sulfur. The chemical composition of inclusions in the steel was analyzed by SEM-EDS. The inclusions were mainly composed of MnS and aluminum oxides. The precipitation of MnS at aluminum oxides might result in Mn depletion, which, in turn, pro- motes the formation of intragranular ferrite. Optical and SEM observations and three- dimensional (3D) reconstruction demonstrated that intragranular ferrite was formed at inclusions. The morphology of intragranular ferrite changed with undercooling. At higher temperatures intragranular ferrite was nearly equiaxed whereas it was plate-like or lath-like at lower temperatures.

Hydrogen storage properties of Mg-doped Ti_(1.2)Fe alloys synthesized by mechanical alloying

Hydrogen storage properties and phase components of Mg doped TiFe alloys, that were prepared by Ti, Fe and Mg metal powders using a mechanical alloying technique, were studied. XRD analyses show that the main phase of all the Mg doped Ti 1.2 Fe alloys is the TiFe phase. Some TiFe 2 phase and α Ti phase exist as secondary phases and Mg is dispersed in the alloy matrix. 3% Mg doped and 5% Mg doped Ti 1.2 Fe alloy samples can be fully activated within three hydriding/dehydriding cycles at room temperature and the hydrogen storage capacities of the alloys can reach 222 mL/g and 198 mL/g, respectively. Both two samples exhibit only one plateau region in their P C T curves with a low hydrogen absorption/desorption pressure hysteresis. The effect and mechanism of Mg addition as well as overstoichiometric Ti on the activation properties and hydrogen storage capacities of the alloys was also discussed.

CRYSTAL STRUCTURE AND MORPHOLOGY OF NASCENT SAMPLES OF SYMMETRIC AROMATIC POLYESTERS——Ⅰ.POLY(P-PHENYLENE TEREPHTHALATE)

The morphology and crytal structure of poly(p-phenylene terephthalate) (PPT), prepared by confined thin filmmelt (CTFMP) and solution (CTFSP) and bulk solution polymerization, were characterized by transmission electronmicroscopy, electron dimaction and molecular modeling. The unit cell is monoclinic (P2_1/a space group) with parameters a =7.89, b = 5.49, c = 12.65 A, α=γ= 90°, β=100.33°, density = 1.48 g/cm^3, the a, b and β values differing slightly from thosereported previously in the literature. A degree of variation in relative intensities of hk0 reflections in, apparently, untilted[001] ED patterns was observed from a given sample, suggesting some variation in molecular packing. ED evidence wasfound for a second phase, with [001] appearing the same as for phase Ⅱ of the related poly(p-oxybenzoate) (PpOBA)polymer. CTFMP crystals polymerized above 220℃ (up to 370℃) and CTFSP crystals polymerized at 300℃ consisted oflamellae 100-200 A thick.

EFFECT OF CERIUM ION IMPLANTATION ON THE AQUEOUS CORROSION BEHAVIOR OF ZIRCONIUM

In order to study the influence of cerium ion implantation on the aqueous corrosion behavior of zirconium, specimens were implanted by cerium ions with a dosage range from 1×1016 to 1×1017 ions/cm2 at about 150℃, using MEVVA source at an acceler ative voltage of 40kV. The valence of the surface layer was analyzed by X-ray photo- electron spectroscopy (XPS); Three-sweep potentiodynamic polarization measurement was employed to value the aqueous corrosion resistance of zirconium in a 0.5mol/L H2SO4 solution. It was found that a remarkable decline in the aqueous corrosion behavior of zirconium implanted with cerium ions compared with that of the as-received zirconium. Finally, the mechanism of the corrosion resistance decline of the cerium-implanted zirconium is discussed.

Development of grain boundary allotriomorphic ferrite/granular bainite duplex steel

A new hot-rolled low alloy high strength steel with grain boundaryallotriomorphic ferrite/granular bainite duplex microstructure has been developed through novelmicrostructure and alloying designs without any noble metal elements such as nickel and molybdenum.Its as-rolled microstructure and mechanical properties, fatigue crack propagation behavior comparedwith single granular bainitic steel as well as continuous cooling transformation, were investigatedin detail. The measured result of CCT (continuous cooling transformation) curve shows that suchduplex microstructure can be easily obtained within a wide air-cooling rate range. More importantly,this duplex microstructure has much better combination of toughness and strength than the singlegranular bainite microstructure. It is found that the grain boundary allotriomorphic ferrite in thisduplex microstructure can blunt the microcrack tip, cause fatigue crack propagation route branchingand curving, and thus it increases the resistance to fatigue crack propagation, improves steeltoughness. The mechanical properties of the above commercial duplex steel plates have achieved orexceeded 870 MPa ultimate tensile strength, 570 MPa yield strength, 18 percent elongation and 34 JCharpy V-notch impact energy at -40 deg C, showing good development potential.

Separation of the Martensite in TiNi Fiber Reinforced Aluminum Matrix Composite

The reverse martensitic transformation of TiNi shape memory alloy fibers embedded in a pure aluminum matrix was studied in this paper. Results showed that the phase composition of the TiNi alloy fibers prior to prestraining at the room temperature had a significant influence on the differential scanning calorimetry (DSC) results of the composites. By a comparison to the high temperature X-ray diffraction (XRD) results, it was confirmed that the martensite was divided into two groups: the self-accommodating martensite (SAM) and the preferentially oriented martensite (POM). The evolving process of the separation of martensite was discussed.

Hydrothermal Synthesis and Structure of a Novel 1-D Mn(II) Compound with Carboxlyto and Imidazole Ligands

A novel manganiferous polymeric complex [(imid)2(ta)Mn0.5]n (imid = imidazole, ta = terephthalato) was synthesized by the hydrothermal reaction of MnO2, terephthalic acid, imidazole, and H2O. Structure analysis indicates that the compound crystallizes in the triclinic system, space group P1, with a = 8.1500(16), b = 8.5100(17), c = 9.0500(18) ?, α = 72.77(3), β = 65.50(3), γ = 77.22(3)o, V = 542.02(19) ?3, Z = 2, Dc = 1.505 g/cm3, F(000) = 253, Mr = 245.69, μ(MoKα) = 0.655 mm-1, R = 0.0733 and wR = 0.1703 for 1673 observed reflections (I > 2σ(I)). The compound is characteristic of a zigzag chain-like framework built up of ta bridge and (Imid)4Mn group. The 1-D frameworks are held together by H-bonds between the dangling N–H donors from imid and O acceptors from ta.

MORPHOLOGY EVOLUTION IN PTFE AS A FUNCTION OF MELT TIME AND TEMPERATURE——Ⅰ.HIGH MOLECULAR WEIGHT SINGLE-AND MULTI-MOLECULE FOLDED CHAIN SINGLE CRYSTALS AND BAND STRUCTURES

The effect of sintering dispersed dispersion and nano-emulsion particles of high molecular weightpolytetrafluoroethylene(PTFE)on a substrate as a function of“melt”time and temperature is described.Folded chain singlecrystals parallel to the substrate and as ribbons on-edge(with double striations),as well as bands,are produced for longersintering times;particle merger and diffusion of individual molecules,crystallizing as folded chain,single(or few)molecule,single crystals when“trapped”on the substrate by cooling occur for shorter sintering times.It is suggested the observedstructures develop with sintering time,in a mesomorphic melt.The structure of the nascent particles is also discussed.