Microstructure Evolution and Thermal Stability of Cu-15Cr in-situ Composites

The Cu-15Cr in-situ fiber-reinforced composites sheets were prepared by cold drawing combined with cold rolling process. The evolution process of Cr fibers was studied, and when cold rolling reduction ε = 95%, the morphology of Cr fiber at different annealing temperature and the thermal stability of Cu-15Cr alloy were studied. Microstructure was also studied by scanning electron microscopy(SEM). Meanwhile, the tensile strength of the alloy was tested by means of a precision universal tester, and the resistance value of the alloy was determined by using a digital micro-Euclidean instrument. The experimental results show that, with the increase of deformation, Cr dendrites evolve into homogeneous and parallelly arranged Cr fibers, and the cross-section of Cr fibers undergoes a "V" shape transition to "一" shape. In addition, spheroidization of the Cr fibers occurs on edges and extends to the center as annealing temperature rises. Moreover, the Cr fibers remains stable when the annealing temperature is below 550 ℃. Furthermore, the tensile strength of Cu-15Cr alloy decreases gradually as the annealing temperature increases, while the electrical conductivity maximizes when annealing at 550 ℃. Our study also shows that Cu-15Cr alloy has obtained a better comprehensive performance with tensile strength of 656 MPa and electrical conductivity of 82%IACS after annealing at 450 ℃.     

Fabrication and formation mechanism of NbCx—C three—dimensional netted fibers

Micrometer NbCx-C three-dimensional netted fibers were synthesized by the carbothermal method under 0.1 MPa of N2 ambient atmosphere at a relatively low temperature,Raw materials were commercial powders of Nb2O5(99.95%),reactive carbon (99.99%),NaCl(99.95%) and sucrose(99.94%).The relationship of the fabrication processing with the composition,crystal structure and morphology of fibers was investigated.The formation mechanism was also proposed and discussed.     

Microstructure and properties of W-15Cu alloys prepared by mechanical alloying and spark plasma sintering process

W-15Cu composite powders prepared by mechanical alloying （MA） of raw powders were consolidated by spark plasma sintering （SPS） process at temperature ranged 1 230-1 300 ℃ for 10 min and under a pressure of 30 MPa. By using high energy milling, particles containing very fine tungsten grains embedded in copper, called composite particles, could be produced. The W grains were homogeneously dispersed in copper phase, which was very important to obtain W-Cu alloy with high mechanical properties, fine and homogeneous microstructure. The microstructure and properties of W-15Cu alloys prepared by SPS processes at different temperature were researched. The results show that W-15Cu alloys consolidated by SPS can reach 99.6 % relative density, and transverse rupture strength （TRS） is 1 400.9 MPa, Rockwell C hardness （HRC） is 45.2, the thermal conductivity is 196 W/m-K at room temperature, the average grain size is less than 2 μm, and W-15Cu alloy with excellent properties, homogeneous and fine microstructure is obtained.     

Preparation of BN／SiO2 ceramics by PIP method

The precursor infiltration and pyrolysis(PIP) method for preparation of BN/SiO2 composites was used to improve mechanical properties, dielectric properties and feasibility of high temperature dielectric parts with large dimensions and complex shapes. In the processing procedure, the porous BN ceramic matrix was first successfully prepared by compacting the mixed powders of B and BN and then sintering them at a certain temperature under normal pressure of N2. The polycarbosilane(PCS) solution was vacuum infiltrated into porous BN ceramics at the room temperature and then at 800℃ in the air to depolimerize out amorphous SiO2, and sintered further at 1 300℃ in N2 to get BN/SiO2 composites. The microstructure of materials was studied by means of X-ray diffraction and electron probe micro analysis. The thermo-decomposition mechanism of PCS was investigated by a TG-DTA and infrared (IR) spectrum analysis. The flexural strengths were measured by the three-point bending method. The dielectric constant and the loss tangent were measured by the wave-guide method. The results show BN/SiO2 composites were fabricated. The obtained composites posses a flexural strength of 61.96 - 93.31 MPa, the dielectric constant in the range of 3.50 - 3.78 and the order of magnitude of the loss tangent at 10^-3 , which are good for the high tempera turedielectric parts with large size and complex shapes.     

Low-cost oriented preparation of ultra fine xonotlite fibers

Nanometer-sized xonotlite fibers have great potential application in many fields. The traditional method of preparing ultra fine xonotlite fibers uses the ultra fine and highly active silica as the major raw materials, which is not only expensive but also difficult to prepare the xonotlite fibers with diameters around 100 nm. In this study, the ultra fine xonotlite fibers with diameters around 100 nm were prepared by an autoclaving method. The preparation was low-cost oriented by using natural powder quartz and lime as the major raw materials. The intergrowth of the fibers formed thin shell hollow balls or ellipsoids, namely the secondary particles.The length of the nanometer-sized xonotlite fibers was around several microns. The fibers and their secondary particles were produced at 216℃ for 6 h with a continuous stirring of 300-500 r/min. Zirconium oxychloride was used as an additive. The experiments show that zirconium oxychloride has an enormous effect on the growing habit of xonotlite crystals and plays an important role in controlling the diameter of the xonotlite fibers.     

Microstructures and Tensile Properties of Hot-extruded Mg-6Zn-xCe(x=0,0.6,1.0,2.0) Alloys

Mg-6Zn-x Ce(x = 0, 0.6, 1.0, 2.0) alloy ingots with diameter of 50 mm were extruded into bars with diameter of 12 mm at 300 ℃. The microstructures were analyzed by X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy, and mechanical properties were tested at room temperature. The results showed that major intermetallic composition in as-cast Mg-6Zn and Mg-6Zn-0.6Ce alloys was Mg_4Zn_7 phase, during extrusion Mg_4Zn_7 phase was dissolved into matrix and then precipitated as MgZn_2. In as-cast and as-extruded Mg-6Zn-1Ce and Mg-6Zn-2Ce alloys the major intermetallic composition was T phase. The microstructure of as-extruded alloy was refined due to complete dynamic recrystallization, the average grain size decreased with increasing Ce content, which were 12.1, 11.7, 11.0 and 10.0 mm, respectively. High density MgZn_2 precipitated in Mg-6Zn and Mg-6Zn-0.6Ce alloys. The broken T phase particles were distributed linearly along extrusion direction. Mg-6Zn-0.6Ce alloy exhibited a high yield strength of 226.3 MPa that was about 24 MPa higher than Mg-6Zn alloy. However, with increasing Ce contents, the strengths were decreased slightly because the effects of precipitation strengthening of MgZn_2 and solid solute strengthening of Zn were weakened though the strengthening effect of T phase was enhanced.     

Composite thermal protection coating on woven silica fiber fabrics

A composite coating with inner and outer layers was prepared for the thermal protection of woven silica fiber fabrics.Using a sol mixture of a silica sol and AlF3/SiO2 particles mixed in the stoichiometric molar ratio for mullite,hollow silica spheres and short mullite fibers were added to the inner layer and outer layer,respectively.The phase composition and thermal evolution of the coating,along with the interfacial microstructure between the coating and the matrix,were characterized by means of X-ray diffraction,differential scanning calorimetry/thermogravimetry,scanning electron microscopy,and tensile strength testing.Mullite whiskers grew between 950°C and 1200°C and helped prevent thermal cracking during the drying and densification processes.The hollow silica spheres might play dual roles,weakening the adhesion between the coating and the fibers by reducing their direct contact,but strengthening the joining between the coating and substrate by embedding themselves among the fabrics.     

Effect of Extrusion Temperatures on Friction-wear Behavior of Chain-wheel Fabricated by 40Cr Steel under Oil-lubrication Condition

A 40 Cr steel was formed into a chain-wheel using a warm extrusion technology. The surface roughness and micro-structure, micro-hardness and phases of the extruded samples at different temperatures were analyzed using a three-dimensional optical microscope(OM), micro-hardness tester, and X-ray diffraction(XRD), respectively. The morphologies, chemical element distributions and phases of worn tracks at the extrusion temperatures of 550, 650 and 750 ℃ were analyzed using a scanning electron microscopy(SEM), energy disperse spectroscopy(EDS), and XRD, respectively. The friction-wear behaviors of extruded samples under oil-lubrication condition were observed using a wear test. And the effects of extrusion temperatures on the wear mechanism were discussed. The results show that residual austenite and pearlite exist on the sample at the extrusion temperature of 550 ℃ with the corresponding grain size and surface micro-hardness of 32.7 nm and 370.33 HV, respectively. The average coefficient of friction(COF) of extruded sample at the temperature of 550 ℃ is 0.196 5, and the wear mechanism is fatigue and abrasive wear. While the acicular martensite exists on the extruded samples at the extrusion temperatures of 650 and 750 ℃, the corresponding grain sizes are 30.0 and 29.1 nm, respectively. The average COF(coefficient of friction) of extruded sample at the temperatures of 650 and 750 ℃ are 0.187 4 and 0.163 6, respectively, and the wear mechanism is abrasive wear. As a result, the friction performance of extruded sample at the temperatures of 650 and 750 ℃ is better than that at the temperature of 550 ℃.     

Superplasticity and superplastic bulging behavior of ZrO<Subscript>2</Subscript>/Ni nanocomposite

ZrO2/Ni nanocomposite was produced by pulse electrodeposition and its superplastic properties were investigated by the tensile and bulging tests. The as-deposited nickel matrix has a narrow grain size distribution with a mean grain size of 45 nm. A maximum elongation of 605% was observed at 723 K and a strain rate of 1.67×10-3s-1 by tensile test. Superplastic bulging tests were subsequently performed using dies with diameters of 1 mm and 5 mm respectively based on the optimal superplastic forming temperature. The effects of forming temperature and gas pressure on bulging process were experimentally investigated. The results indicated that ZrO2/Ni nanocomposite samples can be readily bulged at 723 K with H/d value (defined as dome apex height over the die diameter) larger than 0.5, indicating that the nanocomposite has good bulging ability. SEM and TEM were used to examine the microstructure of the as-deposited and bulged samples. The observations showed that significant grain coarsening occurs during superplastic bulging, and the microstructure is found to depend on the forming temperature.     

Mechanical,electrical, and thermal properties of the directionally solidified Bi-Zn-AI ternary eutectic alloy

A Bi-2.0Zn-0.2A1 （wt%） ternary eutectic alloy was prepared using a vacuum melting furnace and a casting furnace. The samples were directionally solidified upwards at a constant growth rate （V= 18.4 μm/s） under different temperature gradients （G = 1.15-3.44 K/mm） and at a constant temperature gradient （G = 2.66 K/mm） under different growth rates （V= 8.3-500 μm/s） in a Bridgman-type directional so- lidification furnace. The dependence ofmicrostructure parameter （2） on the solidification parameters （G and V） and that of the microhardness （Hv） on the microstructure and solidification parameters were investigated. The resistivity （ρ） measurements of the studied alloy were per- formed using the standard four-point-probe method, and the temperature coefficient of resistivity （α） was calculated from the ρ-Tcurve. The enthalpy （AH） and the specific heat （Cp） values were determined by differential scanning calorimetry analysis. In addition, the thermal conductivities of samples, obtained using the Wiedemann-Franz and Smith-Palmer equations, were compared with the experimental results. The results revealed that, the thermal conductivity values obtained using the Wiedemarm-Franz and Smith-Palmer equations for the Bi-2.0Zn-0.2Al （wt%） alloy are in the range of 5.2-6.5 W/Km and 15.2-16.4 W/Km, respectively.     

Thermal Cycling Stability of Mg-25Al-15Zn-14Cu PCM

Thermal cycling tests of repeated melting/freezing processes were performed to check the thermal stability of Mg-25Al-15Zn-14 Cu alloy as phase change thermal storage material(PCM). Latent heat storage capacity and phase transition temperature of the PCMs were determined by differential scanning calorimetry(DSC) technique as a function of repeated thermal cycles such as 0, 100, 200, and 1000. The present work also comprised the investigation of the density and microstructure of Mg-25Al-15Zn-14 Cu alloy before and after thermal cycles by using the hydrostatic method and optical microscopy(OM), X-ray diffraction(XRD), and electron probe microanalysis(EPMA), respectively. The results show that the melting temperature of alloy after 1000 thermal cycles is 415.1 ℃ and the latent heat value is 190.4 J/g. Compared with the original alloy, the phase transition temperature will increase by 1.87% and the value of phase change latent heat will decrease by 7.35%, which are in a suitable range. Therefore, Mg-25Al-15Zn-14 Cu alloy has a good thermal reliability in terms of the change in its thermal properties with respect to thermal cycling for 1000, and can be used for a middle-temperature thermal storage utility.     

Effect of PEG Addition on the Behavior of Aluminum Sol,Dry Gel,and Film

Aluminum sol,dry gel,and film were prepared by sol-gel and a dipping-withdrawing method.The effect of polyethylene glycol (PEG) on the behavior of aluminum sol,gel,and film was investigated by DLS,rotary viscometer,XRD,IR,EPMA,and light microscope,respectively.The solid gels drying at room temperature was identified as amorphous phase,and the addition of PEG nearly has no effect on the structure of aluminum dry gel.It is indicated that the sol viscosity decreases with the PEG content increasing,...     

Synthesis ofNanocrystalline RuO2（60%）-SnO2（40%） Powders by Amorphous Citrate Route

Nanometer RuO2-SnO2 was synthesized by the citrate-gel method using RuCl3, SnCl4 as cation sources, citric acid as complexing agent and anhydrous ethanol as solvent. The structures of the derived powders were characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, transmission electron microscope, and Brunauer-Emmett-Teller surface area measurement. The pure, fine and amorphous powders was obtained at 160℃. The materials calcined at above 400 ℃ were composed of rutile-type oxide phases having particle sizes of fairly narrow distribution and good thermal resistant properties. By adding SnO2 to RuO2, the Ru metallic phase can be effectively controlled under a traditional temperature of preparation for dimensional stable anode.     

Wear performance of Ni/ZrO<Subscript>2</Subscript> infiltrated composite layer

The Ni/ZrO2 was used as raw materials to fabricate the surface infiltrated composite layer with 1-4 mm thickness on cast steel substrate through vacuum infiltrated casting technology. The microstructure indicated that the infiltrated composite layer included surface composite layer and transition layer. Wear property was investigated under room temperature and 450 ℃. The results indicated that the abrasion volume of substrate was 8 times that of the infiltrated composite layer at room temperature. The friction coefficient of infiltrated composite layer decreased with the increasing load. The wear resistance of infiltrated composite layer with different ZrO2 contents had been improved obviously under high temperature. The friction coefficient of infiltrated composite layer was decreased comparing with that at room temperature. The oxidation, abrasive and fatigue abrasion was the main wear mechanism at room temperature. Oxidation abrasion, fatigue wear and adhesive wear dominated the wearing process under elevated temperature.     

Electrochemical properties of spinel LiMn2O4 and LiAl0.1Mn1.9O3.9F0.1 synthesized by solid-state reaction

Two types of spinel cathode powders, LiMn2O4 and LiAl0.1Mn1.9O3.9F0.1, were synthesized by solid-state reaction. X-ray diffraction (XRD) patterns of the prepared samples were identified as the spinel structure with a space group of Fd 3 m. The cubic lattice parameter was determined from least-squares fitting of the XRD data. The LiAl0.1Mn1.9O3.9F0.1 sample showed a little lower initial capacity, but better cycling performance than the LiMn2O4 sample at both room temperature and an elevated temperature. The Vanderbilt method was used to test the electrochemical conductivity of the LiMn2O4 samples. The electrochemical impedance spec-troscopy (EIS) method was employed to investigate the electrochemical properties of these spinel LiMn2O4 samples.     

Fracture toughness and fracture behavior of SA508-Ⅲ steel at different temperatures

The fracture toughness of SA508-Ⅲ steel was studied in the temperature range from room temperature to 320℃ using the J-integral method. The fracture behavior of the steel was also investigated. It was found that the conditional fracture toughness （JQ） of the steel first decreased and then increased with increasing test temperature. The maximum and minimum values of do were 517.4 kJ/m^2 at 25℃ and 304.5 kJ/m^2 at 180℃, respectively. Dynamic strain aging （DSA） was also observed to occur when the temperature exceeded 260℃ with a certain strain rate. Both the dislocation density and the number of small dislocation cells effectively increased because of the occurrence of DSA; as a consequence, crack propagation was more strongly inhibited in the steel. Simultaneously, an increasing number of fine carbides precipitated under high stress at temperatures greater than 260℃. Thus, the deformation resistance of the steel was improved and the Jo was enhanced.     

Silicon assistant carbothermal reduction for SiC powders

The silicon assistant method to increase the reaction yield of carbothermal reduction of silica at a lower temperature is reported. The effect of silicon on the carbothermal reduction process has been investigated in detail. Compared with traditional reduction, the introduction of silicon can change the reaction path and further increase the conversion of silicon carbide at a lower temperature. It is considered that the assistant reduction consists of three steps: vaporizing and melting of silicon, formation of silicon monoxide, and synthesis of silicon carbide. The morphology of the synthesized SiC powders through the silicon assistant method can be affected apparently by the experimental temperature.     

Microstructural,Mechanical,Electrical,and Thermal Properties of the Bi-Sn-Ag Ternary Eutectic Alloy

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries.Bi-Sn-Ag eutectic alloy has been considered as one of the lead-free solder materials that can replace the toxic Pb-Sn eutectic solder without increasing soldering temperature.We investigated the effects of temperature gradient and growth rate on the mechanical,electrical and thermal properties of the BiSn-Ag ternary eutectic alloy.Bi-47 wt%Sn-0.68 wt%Ag alloy was directionally solidified upward with different temperature gradients(G=2.33-5.66 K/mm) at a constant growth rate(V=13.25 μm/s) and with different growth rates(V=6.55-132.83 μm/s) at a constant temperature gradient(G=2.33 K/mm) in the growth apparatus.The microstructures(λ),microhardness(HV),tensile stress(σ),electrical resistivity(ρ),and thermal properties(△H,C_p,T_m) were measured on directionally solidified samples.The dependency of the λ,HV,σ,and ρ on G and V was investigated.According to the experimental results,X values decrease with increasing G and V,but HV,λ,and ρ values increase with increasing G and V.Variations of electrical resistivity(ρ) for cast samples with the temperature in the range of 300-400 K were also measured by using a standard dc four-point probe technique.The enthalpy of fusion(△H) and specific heat(C_p) for the same alloy was also determined by means of differential scanning calorimeter(DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.     

Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties, electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated. The results indicated that with elevating the aging temperature from 100℃ to 160℃, the aging response rate was greatly accelerated, and the UTS at peak aging condition decreased, while the corresponding TYS increased. However, the electrical conductivity of the alloy became higher. After aging for 24 h at 120℃, the peak UTS and TYS values were achieved as 591 MPa and 541 MPa, respectively; but the alloy achieved a lower conductivity, 20.4 MS/m. When T6 temper was performed at 140℃ for 14 h, the UTS decreased only by 1% of the former, whereas the TYS and the electrical conductivity increased obviously, which were up to 559 MPa and 22.6 MS/m, respectively. The major strengthening precipitates of the peak-aged alloy were GP zones and η′ phase. The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature. There were obvious PFZs along the grain boundary both in T6 conditions aged at 140℃ and 160℃.     

Effect of Pd doping on the acetone-sensing properties of NdFeO_3

The acetone-sensing properties of the undoped and Pd doped perovskite-type oxides NdFeO3 were investigated from room temperature to 400°C. The perovskite-type NdFeO3 was synthesized by a sol-gel method, and the dopants Pd with the content from 1wt% to 5wt% were implanted into NdFeO3 nanoparticles by thermal diffusion. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques show that NdFeO3 is an orthorhombic structure with the average particle size of about 40 nm. A giant acetone-sensing response of 675.7 is observed when the Pd content in NdFeO3 powders is about 3wt%. The response and recovery time of the sensor to the 5×10-4 acetone gas are 16 and 1 s, respectively. At the same time, it performs a good selectivity to acetone gas and may be a new promising material candidate for the acetone-sensor development.