Effects of Ga and In on the properties of cadmium-free Ag-Cu-Zn filler metal

Melting temperature, spreadability, mechanical properties and the microstructures of joints brazed with silver-base filler metals including different amounts of Ga and/or In were studied respectively in this paper, and the results show that the melting temperature of the silver-base filler metals is decreased, spreadability of the silver-base filler metals is improved, and the microstructures of silver-base filh, r metals are refined obviously with the addition of Ga and/or In. Using copper and brass plates as base metal and brazing with flame method, the mechanical properties of the lap-joint and butt joint were also examined and analyzed respectively, and the results indicate that the fracture position of two kinds of brazed joints occurred on the base metal, except for the lap-joint of brass, which shows better mechanical properties of the joints brazed with the silver- based filler metals including Ga. For the lap-joint of brass, the tensile strength gradually increased with the increase of Ga content, while the addition of In has little effect on mechanical properties. It is also found that the best comprehensive properties of cadmium-free Ag-Cu-Zn filler metals are obtained when Ga content is about 3.0 wt. % and In content is between 1.5 wt. % and 2. 0 wt. %.

Effects of Silane Coupling Agent on Microstructure and Mechanical Properties of EPDM/Carbonyl Iron Microwave Absorbing Patch

The effects of types and amounts of silane coupling agent on mechanical properties of vuleanized rubber microwave absorbing patch （VRMAP） were studied. The mechanisms of silane coupling agent＇s effects on mechanical properties of rubber microwave absorbing patch （ RMAP ） and microvave absorbing patch＇s （MAP＇s） mierostrueture were also discussed by using SEM and FT-IR. The experimental results show that the tensile strength of RMAP could be increased through adding the filler of carbonyl iron powder （CIP） modified by silane coupling agent. RMAP fiUed with CIP, which was treated by silane coupling agent KH550, possessed a high tensile strength of 11.5 MPa, which was 448% more than that of MAP whose filler wus not modified by any coupling agent. It was found that the optimal amount of KH550 was 1.0 phr to 100.0 phr carbonyl iron powder. The effects of different modifying techniques on RMAP＇s mechanical properties were also inrestigated. It is indieated that MAP whose filler is modified by the wet process has the highest tensile strength, but it is not the optimal modiifying technique due to complieated wet process. On the contrary, the dry process was very simple, and VRMAP possessed fairly high mechanical properties, therefore, it was the perfect modifying process.

High-speed butt welding of magnesium alloy using pulsed laser-arc hybrid heat source

Laser-arc hybrid welding at a speed of 6 000 mm/min is carried out on 2 mm thick magnesium alloy AZ61 plateand completely-penetrated butt joints are obtained, lnvestigations of the influence of parameters on weld formation show that Ihe addition of pulsed laser can effctively enhance tlle heat penetrability attd directivity nf the hybrid heat source. Measurements on microstructures and mechanical properties the joint indicate that grain in the.fhsion zone is refined and the grain size is sensitive to the arc current ; the fitsioa zone exhibits the highest hardaess; the tensile strength of the joint reaches 93% of base metal; there is the brittle fracture along the grain bozmdaries in the fusion zone. High-speed camera images exhibit that although the two adjacent laser pulses can not overlap, the recorery relaxation of the concentrated electric arc after laser intlse action can still maintain the continuous welding process.

Elaboration of AlSi10Mg casting alloys using directional solidification processing

The effects of pulling velocity on the solidification behavior and microstructural parameters of A1Sil0Mg alloys prepared in a Bridgman-type directional solidification furnace were investigated. The microstructure, particularly the secondary dendritic arm spacing （SDAS）, and the Brinell hardness （BH） of the solidified A1Sil0Mg alloys were characterized for samples with cylindrical shapes and differ- ent conicities （θ = 0°, 5°, and 10°）. Microstructural studies revealed an increased density of ct-A1 phase dendrites and a decreased interden- dritic distance with increasing pulling velocity. The dendrites were found to be preferentially oriented along the pulling direction for low pulling velocities. For larger pulling velocities, the dendrites grew first in the cooling direction but then broke as others nucleated and coars- ened. The HB values of the solidified samples increased as the pulling velocity increased. In regard to sample conicity, smaller dendrites were observed for an apex angle of θ = 5°, resulting in the largest HB value. This result was interpreted in terms of the favorable orientation of the dendrite along the pulling direction.

Fabrication of non-superconducting and superconducting joints of Ag/Bi-2223 tapes by diffusion bonding

Diffusion bonding of multifilamentary Ag/Bi-2223 （ Bi2 Sr2 Ca2 Cu3Ox ） superconducting tapes has been performed successfally. Three types of joints, namely, with sih,er interlayer （type Ⅰ）, bonded directly （type Ⅱ）, with Bi-2212 （BizSr2Ca1 Cu2Ox ） powder interlayer or with Bi-2223 powder interlayer （type Ⅲ） were researched, respectively. The critical currents（ Ic ） of these joints were measured ond microstructures of the joints were evaluated by scanning electron microscope （SEM）. The result shows that type Ⅰ is non-superconducting joint with very low resistance, and type Ⅱ joint and type Ⅲ （with Bi-2212 or Bi-2223 ） joints are both of superconducting property. By comparing, type Ⅱ joint possesses most exceUent superconductivity, type Ⅲ joint with Bi-2223 powder interlayer takes the second place, and type ,任家烈 joint with Bi-2212 powder interlayer is least.

Fine-Grained Bulk NiTi Shape Memory Alloy Fabricated by Rapid Solidifcation Process and Its Mechanical Properties and Damping Performance

A near-equiatomic NiTi shape memory alloy was fabricated by rapid solidification process through vacuum arc melting followed by vacuum suction casting in water-cooled thick copper mold. The rapidly solidified （or suction cast） NiTi alloy shows much finer grains and homogenous microstructure, in particular a uniform distribution of various fine precipitates, compared to the conventional cast one. The resultant alloy also exhibits the homogenous Ni distribution in the matrix of the alloy, allowing the martensitic transformation to take place throughout the NiTi alloy matrix simultaneously and resulting in sharper transformation peaks compared to the conventional cast alloy. Moreover, the suction cast NiTJ alloy shows a significant improvement over the conventional cast one, in terms of possessing higher deformation recovery rates and displaying the increased compressive strength and damping capacity by 4% and 20%, respectively.

Microstructure Transformation Behaviour of 610 MPa HSLA Steel Plate for 150000 m^3 Oil Storage Tank Construction

Static and dynamic continuous cooling transformations （CCT） of 610 MPa HSLA steel plate for 150000 m^3 oil storage tank construction were measured by using an MMS200 thermomechanical simulation system. It was found that with the increase in cooling rate, the proeutectoid ferrite, pearlite, granular bainite, and lath bainite appeared in the transformed microstructure. Compared with those of static CCT, the transformation points of acicular ferrite, granular bainite, and lath bainite in the dynamic CCT curve were shifted to the left, resulting in an increased acicular ferrite and bainite transformation area.

Carbon-coated Li_4Ti_5O_(12) Anode Materials Synthesized Using H_2TiO_3 as Ti Source

Two low-cost synthesis routes have been developed to fabricate carbon-coated Li4Ti5O12 by using H2TiO3 instead of anatase TiO2 as Ti source through solid-state reaction process. One route is a direct solid mixture of H2TiO3, Li2CO3 and pitch followed by high-temperature solid-state reaction. The other includes mixture of H2TiO3 and Li2CO3 with pitch dissolved in furanidine under vacuum and the same solid-state reaction procedure is followed after the mixture is totally dried. Microstructural investigations indicate that H2TiO3 exhibits secondary aggregates morphology with primary particle sizes of 10-20 nm. Carbon-coating layers with thickness of 2-3 nm have been observed on Li4Ti5O12 synthesized by the two routes. Cyclic performance, rate capability and electrochemical impedance spectrum of the two Li4Ti5O12/C composites have been performed, which indicate that Li4Ti5O12/C obtained by furanidine-assisted mixture exhibits better electrochemical performance than Li4Ti5O12/C synthesized by direct solid mixture. The possible reasons have been discussed. The low-cost synthesis routes of Li4Ti5O12/C using H2TiO3 as Ti source are expected to be more competitive than the traditional one for practical applications.

Influence of Gating System,Sand Grain Size,and Mould Coating on Microstructure and Mechanical Properties of Thin-Wall Ductile Iron

Two gating systems namely stepped and tapered runners were used to cast strip samples with different thicknesses by CO2/silicate process using sand grain sizes of AFS 151 and 171. To assess the effect of mould coating on the properties of thin wall ductile iron, half of the moulds were coated whilst the rest were not coated. Molten metal with the carbon equivalent of 4.29% was prepared and poured at 1 450 ℃. Microstructure of the specimens was analyzed by optical and scanning electron microscopes. Count, area fraction, roundness and diameter of the graphite nodules of the samples were measured by image analyzer. Brinell hardness and tensile tests of all the samples were also conducted. The results show that by using stepped runner gating system with uncoated and coarse sand mould, roundness and count of the graphite nodules decrease whereas diameter and area fraction increase. Although fine sand and coated mould cause longer distance of molten metal travel, hardness and strength of the samples decrease.

Corrosion mechanism research and microstructure analysis of Baosteel No.3 blast furnace hearth

Baosteel No.3 blast furnace hearth was divided into tuyere area,taphole area,taphole upper side wall and taphole lower side wall according to different working situations.Through chemical composition analysis,scanning electron microscopy,X-ray diffraction,energy dispersive spectrometry and other means,chemical composition and microstructure of different parts of hearth carbon brick were analyzed and markedly different corrosion mechanisms of these areas were found.Zn element in form of ZnO mainly deposited on the hot side of carbon brick.There was no obvious evidence that Zn permeates into carbon bricks and erodes them.Except for taphole area,K,Na,and Fe contents from hot side to cold side gradually rise and fall,resulting in the decrease of apparent porosity,the increase of density and the higher thermal conductivity compared with those of new carbon brick.The higher content of Fe in carbon brick leads to more serious erosion because Fe has greatly changed the physical properties of carbon brick.In the taphole area,the contents of Si and Al present obvious concentration gradient because of the mechanical souring of molten iron and slag.The SiO;and Al;O;particles that have different expansion factors with carbon brick damaged the carbon substrate because of temperature fluctuation.The graphitized carbon found on H4 where is the most serious corrosion site means that the carbon brick ever directly contacts with molten iron.

Characterizing the Structure Evolution of Tertiary Scale during Simulated Coiling by EBSD

An oxide scale formed at 900 ℃ for 60 s in dry air was subjected to the simulated coiling processed with different coiling temperatures. The phase transformation behavior, especially the orientation distribution of the oxide scale, was analyzed using electron backseattered diffraction （EBSD） technique. When cooling from the coiling tem- perature of 650 ℃, the scale consists of FeaO4 layer, FeO layer and FeaO4 seam. The FeaO4 precipitates are ob served in the FeO grains of the scale formed with the coiling temperature of 550 and 450 ℃. With the cofling temperature of 350 ℃, the decomposition of FeO is suppressed due to the low temperature. The Fe3O4 grains, which are decomposed from FeO, has the same orientation as the parent FeO grains. Moreover, the FeO grains, of which the growth direction is parallel to 〈001〉, is easier to decompose into Fe3O4 than the grains with other orientations.

Facile Synthesis of Bimetallic Au@Pd Nanoparticles with Core-shell Structures on Graphene Nanosheets

In this paper, we report a simple one-step thermal reducing method for synthesis of bimetallic Au@Pd nanoparticles with core-shell structures on the graphene surface. This new type of Au@Pd-G composites is characterized by transmission electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. It is found that Au@Pd nanoparticles with an average diameter of 11 nm are well dispersed on the graphene surface, and the Au core quantity as well as the Pd shell thickness can be quantitatively controlled by loading different amounts of metallic precursors, and the involved core-shell structure formation mechanism is also discussed. The ternary Pt/Au@Pd-G composites can also be synthetized by the subsequent Pt doping. The catalytic performance of Au@Pd-G composites toward methanol electro-oxidation in acidic media is investigated. The results show that Au@Pd-G composites exhibit higher catalytic activity, better stability and stronger tolerance to CO poisoning than Pd-G and Au-G counterparts.

MICROSTRUCTURE FEATURES IN Bi-Ca-Sr-Cu-O SUPERCONDUCTOR

Three compositions of Bi-Ca-Sr-Cu-O superconducting ceramics have been studied and characterized by X-ray energy dispersive spectroscopy (EDS) and high-resolution electron microscopy (HREM).In addition to the basic lattice structure A1 with unit-cell of a=5.41 A, b=5.44 A and c=30.8 A, other 3 kinds of perovskite-related structure A0, A3, A4 have been found.Furthermore, a prominent structural phenomenon, the intergrowth between A1 and other perovskite-related structures (A0, A2 and A4) have been found. Some difficulties in isolating pure 120 K phase may be caused by the intergrowth.

Study of Nano-crystalline Silicon Films

By using strong hydrogen dilution of silane in PECVD system and controlling the deposition parameters strictly, we have prepared a-Si:H and nc-Si:H as well as μc-Si:H films respectively. The structural characters of nc-Si: H films detected by means of HREM, Raman and X-ray diffraction spectra are identified as coinciding with the known definition of nanometer solids. The unique electrical and optical properties of nc-Si:H films are considered as the consequence of its novel structures.

Effect of Finishing Rolling Temperature on Microstructure and Mechanical Properties of Microalloyed TRIP Steels

Different samples of TRIP （transformation induced plasticity） steel obtained by two different hot rolling schedules are investigated by using a SEM （scanning electron microscope）. The microstructure is characterized by using an OM （optical microscope） for phase distribution and by EBSD （electron backscatter diffraction） for texture and phase mapping. ODF （orientation distribution function） graphs are used to investigate the effect of recrystallization behavior of the hot-deformed austenite on phase transformation during the controlled cooling process. The mechanical behavior is interpreted in terms of the strength of both hard and soft phases, in combination with the quantity, loca- tion and transformation kinetics of the mechanically induced martensite （TRIP effect）. The results show that more austenite grains exist in the steels obtained at finishing rolling temperature （FRT） of 750 ℃, which inherited the de- formation structure after the hot-rolling process. The instantaneous n value （ni） of those steels is kept high during a large range of strain before failure, while the tensile strength and total elongation of the steels with respect to the dif- ferent finishing rolling temperatures do not show any significant differences.

Influence of Processing Parameters on Microstructural Evolution and Tensile Properties for 7075 Al Alloy Prepared by an ECAP-Based SIMA Process

A modified strain-induced melt activation（SIMA）process consisting of homogenization,equal-channel angular pressing（ECAP）and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 aluminum alloy with superior thixotropic behaviors.The effects of both the homogenization and the number of ECAP passes,as well as the isothermal temperatures on the microstructural evolution,were investigated.The results indicate that ideal microstructure wherein fine and globular solid grains surrounded by uniform liquid films can be achieved through ECAP deformation-recrystallization mechanism.Increasing the number of ECAP passes accelerates the recrystallization of strained grains,thus reducing the average grain size and improving the grain sphericity.Moreover,higher holding temperatures and prolonged soaking time can improve the growth of the solid grains.Two main coarsening mechanisms,viz.coalescence and Ostwald ripening,contribute to the growth of the solid grains simultaneously and independently.The tensile strength of the 7075 alloys after four-pass ECAP-based SIMA and T6 heat treatment is relatively lower than the as-received billet,while the elongation of SIMA processed samples is much higher than that of as-received ones.Increasing the number of ECAP passes improves the tensile strength for alloys with and without T6 treatment due to the fine grain strengthening mechanism.