Abstract: The feasibility of fabrication in situ TiB and TiC hybrid titanium matrix composites based on a Ti-B4C-C system was analyzed in theory and chemical reactions among the blended powders of Ti, B4C and C powders during the heating process was studied by differential scanning calorimetry (DSC). The results of DSC show that drastic exothermal reactions take place during the course of heating, which indicates that some new phases are formed. X-ray diffraction (XRD) patterns of the as-sintered composites reveal that TiB and TiC would be formed in the as-sintered composites and the peak intensity of TiC increases with increasing amount of graphite powder, showing that both the reactions of Ti-B4C and Ti-C systems have taken place completely within the range of 940~1150℃. OM and SEM results show that rodlike TiB whiskers and equiaxed TiC particulates distribute uniformly in titanium matrix. It is suggested that in situ TiB whisker and TiC particulate hybrid reinforced titanium matrix composites can be prepared by hot pressing of a Ti-B4C-C system.
Abstract: A Ⅱb type diamond has semiconductivity and superconductivity as well as better heat resistance, wear and chemical inertia than a common synthetic diamond because of the doping of boron. In order to change the condition of high cost and hard to industrialization on Ⅱb type diamond synthesizing, this paper put forward a new synthesizing method using an Fe-Ni-C-B catalyst alloy made by powder metallurgy at high temperature and high pressure. Because of the presence of boron, a Ⅱb type diamond needs a higher temperature and pressure than a common Ⅰb type diamond. Due to the action of boron, the diamond has rough grain size, bad crystal shape and complex surface structure. The presence of boron was primarily ascertained by the color of crystal, X-ray diffraction and Raman spectrum. In addition, the thermal stability of the diamond was characterized with the results of static compressive strength and impact toughness at different temperatures, as well as DSC and TGA analyses. The experimental results show that the thermal stability of the Ⅱb type diamond is improved rapidly. Resistance-temperature characteristics measurement with a self-made clamp proved the semiconductivity of the diamond crystal. Based on summarization and analysis of experimental data, it is obvious that synthesizing a Ⅱb type diamond by this method can be realized easily with low producing cost and is available for synthetic diamond industry.
Abstract: ZrO2/Cu composite powder was prepared by in-situ chemical route, with which a nano ZrO2/Cu composite material was prepared by powder metallurgy. TEM observation reveals that there are two crystal types of tetragonal and monoclinic Zirconia particles, and different interracial characterizations exist between the different zirconia particles and copper matrix. With Ansys software, interracial stress was simulated in zirconia with different crystal structures and copper matrix. The results show that the stress is easily concentrated in the tip of monoclinic Zirconia particles and cracks are easily brought than the tetragonal zirconia interface.
Abstract: An austenitic high silicon iron-base alloy with Ni or Mn was devised based on the study on the mechanical properties and microstructure of a general high silicon iron-base alloy. The new austenitic high silicon iron-base alloy with Ni or Mn was designed by means of austenitic stainless steel and the three-element phase graph of Fe-Ni-Si or Fe-Mn-Si. The microstructure, mechanical properties and corrosion resistance of the alloy were investigated by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), test equipment of mechanical properties, and test instrument of corrosion. The results show that the base structure of a general high silicon iron-base alloy is high silicon ferrite, which is mainly the long-range ordered Fe3Si. Fe3Si has low-temperature brittleness and is the main reason for silicon brittleness. The addition of 18% Ni produces austenite and causes an impact toughness up to 5.52 J·cm-2, which is 7 times higher than a general high silicon iron-base alloy, while the corrosion resistance is equivalent with a general high silicon iron-base alloy.
Abstract: Polyaluminocarbosilane (PACS) is a precursor of ultra-high-temperature-resistance Si-Al-C fiber. In order to get a desirable precursor of the fiber, polysilacarbosilane (PSCS) was used to react with aluminum acetylacetonate (Al(acac)3) to get PACS, the reaction process was traced by FTIR, GPC, 1H-NMR, 27Al-NMR and UV-Vis spectra, and the production mechanism was studied in detail. The result shows that PSCS is a kind of oligomers with Si-Si-Si and Si-C-Si bonds. There are two kinds of reactions during the whole process. One is Kumada rearrangement that Si-Si-Si bond translated into Si-C-Si bond, the other is Al(acac)3 with the silicon carbon compounds. The obtained PACS has a higher relative molecular mass and branching degree because of the cross linkage of Al(acac)3. The crosslink mainly occurs below 330℃ and above 400℃. In PACS, Al is in the state of Si-O-Al.
Abstract: An amount of Al powder was added to toughen Al2O3 porous supports by dry press forming. Based on the toughening mechanism of Al2O3/Al composite, the effects of heating temperature on the fracture toughness and bending strength of macroporous Al2O3/Al supports were investigated in detail, and the microstructure of specimens made of the supports was analyzed by SEM. The results show that the fracture toughness of the supports is influenced by calcining temperature. When the calcining temperature is low, unoxidized Al phase can absorb amount of fracture energy to make the fracture toughness of the supports high. But when the temperature is above 1200℃, the cracks which is occurred in the oxidation processing of Al phase can improve the fracture toughness of the supports, and the contribution of cracks is more important than the amount of Al phase to the fracture toughness of supports.
Abstract: The band gap of GaN can be changed by substituting some Ga and N atoms by Zn and O atoms in order to improve its quantum efficiencies. Under NH3 gas flow, the mixture of Ga2O3 and ZnO was calcined at 1123 K for 900 min. Gal-xZnxNO yellow powders were prepared by the gas solid phase synthesis method. The influence of different synthesis process on the physical properties of the samples was investigated. The crystal structure and optical properties of Gal-xZnxNO were characterized by XRD, TEM, UV-Vis measurements. The results indicate that the synthesized Gal-xZnxNO is hexagonl wurtzite structure and has absorption peak around a wavelength of 400~450 nm.
Abstract: Monodisperse silica spheres with a diameter of 640 nm were used as template, carbon nitride precursor was made by refluxing and stirring ethylendiamine (CH2NH2)2 and carbon tetrachloride (CCl4). The precursor was infiltrated into the interstitial regions of the silica template and heat-treated in nitrogen atmosphere to form a carbon nitride/silica composite, then macroporous carbon nitride was gained by removing the silica template with HF solution treatment. The composition and structure of a macroporous carbon nitride sample was detected by X-ray powder diffraction (XRD), elemental analysis, selected area electron diffraction (SAED), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectra (XPS). The in vitro anticoagulation activity of the sample was evaluated by activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT). It is found that the macroporous carbon nitride has no influence on the anticoagulation activity of plasma. It indicates that the potential application of the 3D macroporous carbon nitride as blood compatibility materials in the biomedical area will be realized in the future.
Abstract: The nearest atomic distance and cohesive energy of cubic and spherical Au nanoparticles were studied by the tight binding molecular dynamics method. The results show that the cubic nanoparticles with 108 and 256 atoms are amorphous in structure while the other nanoparticles are fcc in structure. For the nanoparticles in fcc structure, both the nearest atomic distance and cohesive energy decrease with decreasing particle size for a certain particle shape. And both variation quantities of the nearest atomic distance and cohesive energy of the spherical particles are lower than those of cubic ones. Since the nearest atomic distance is sensitive to the structure variation between amorphous and fcc, the nearest atomic distance can be regarded as a criteria for structure transition. By fitted the simulation results, it is found that the shape effect can lead to 2 96 of the total nearest atomic distance variation and 15 96 of the total cohesive energy variation. The present results on the nearest atomic distance of Au nanoparticles is well consistent with the corresponding experimental ones.
Abstract: Utilizing Maker fringe method, second-harmonic generation (SHG) was observed from electrically poled chalcohalide glass in a GeS2-Ga2S3-PbI2 pseudo-ternary system for the first time. The 70GeS2·15Ga2S3·15PbI2 composition glass was poled by applying various high dc voltages at various temperatures for different poling durations. SHG was observable from 190℃ under 4.0 kV, and the second harmonic (SH) intensity increased with the enhancement of applied voltage and poling duration until reached saturation. When conducted under 6 kV for 40 min, with increasing poling temperature the SH intensity gradually increased, experienced a maximum, and then decreased. A maximum second-order nonlinearity susceptibility, χ(2), value of 4 pm·V-1 was obtained under the optimal poling condition of an applied voltage of 6 kV, a temperature of 250℃ and a poling duration of 40 min. The SHG phenomenon is considered to be the result of the breakage of glassy macroscopic isotropy originated from reorientation of dipoles during electrical poling treatment and the dependence of poling parameters on the SH intensity is also discussed.
Abstract: An Al-Si fusing coating was successfully produced by low-oxygen pressure high-temperature fusing technology for improvement of the high-temperature oxidation resistance of Ti alloys. Compared with other technologies, this technology was correspondingly simple without long-term treatment and the concentrations of Al and Si in the fusing coating could be controlled by adjusting the powders' mixing ratio. It is verified by XRD that the Al-Si fusing coating is mainly composed of Al, Si, Ti5Si3, and TiAl3 phases. Cyclic oxidation tests at 1073 K for 105 h in air reveals that the mass gain of the uncoated Ti alloy keeps rapidly increasing during oxidation, while the Al-Si fusing coating obeys a parabolic law and remarkably improves the oxidation resistance.
Abstract: Electroless plating of a Ni-Cu-P ternary alloy was carried out on sintered NdFeB magnets to improve their corrosion resistance. The effects of complexing agent concentration, metallic-ion ratio[Cu2+]/[Ni2+], pH value, and temperature on the deposition rate and coatings' composition were studied. Surface morphologies of the coatings were observed through SEM (Model FEI SIRION), and the element composition of the coatings was analyzed through EDAX. The corrosion resistance of the Ni-Cu-P ternary alloy was investigated through polarization curves in a 3.5% NaCl solution and neutral salt spray tests. The results show that good adhesion of the Ni-Cu-P deposits to the magnets can be achieved after ultrasonic cleaned with alkaline solution and activated by acid; with increasing[Cu2+]/[Ni2+], the deposits transformed from amorphous to crystalline and became more smooth and compact, the phosphorus content of the deposits firstly increased then decreased. It is indicated that the electroless deposits on sintered NdFeB surface exhibited a superior corrosion resistance than electroless Ni-P deposits; the corrosion resistance of the Ni-Cu-P ternary alloy obtained from the solution with a metallic-ion ratio of 0.02 was the best.
Abstract: The glass-ceramic was produced by nickel slag as primary raw material. The crystallization process of the glass-ceramic was analyzed and the crystallization temperature was determined by DSC. The activation E and crystallization kinetic parameter k (Tp) of the glass added 2% Cr2O3 by weight as nucleation agent were calculated by the modified Johnson-Mehl-Avrami (JMA) method, and the results were 371. 1 kJ· mol-1 and 0.29, respectively. The characters of crystals appearing in glass were analyzed by XRD, SEM and optical microscope observation methods. It is shown that the crystallization process is observed between 930℃ and 950℃, and the size of crystals is 10~15μm after heat treatment at 950℃ for 30 min.
Abstract: Polycaprolactone-grafted-starch (PCL-g-St) was synthesized with caprolactone and corn starch using tetrabutyl titanate as initiator via coordination-insertion ring-opening polymerization. PCL-g-St and corn starch were compared using FTIR and DSC. The blend of PCL and PCL-g-St was prepared, and the mechanical properties, hydrophobicity, interface properties of the blend were investigated. The results show that the compatibility of the two phases in the blend is effectively improved after the starch was grafted with PCL and the mechanical properties are also increased compared with a non-modified St/PCL blend. The hydrophobicity of the PCL-g-St/PCL blend is improved, and its mechanical properties are not much influenced after being soaked into the water.
Abstract: High-temperature adhesive was prepared using phenol-formaldehyde resin (PF) as matrix and boron carbide (B4C) as modifier, silicon nitride (Si3N4) ceramics were bonded by the adhesive, and the bonded specimens were heat-treated within 300-800℃ subsequently. The adhesive properties of the high-temperature adhesive were tested. The results indicate that the adhesive has outstanding high-temperature bonding properties for Si3N4 at high temperature. The failure of bonded joints treated at 700 and 800℃ were due to the broken of Si3N4 matrix. The micro-morphologies at bonding interfaces were also investigated by SEM. It is shown that complex physical and chemical changes occurred during the heat-treatment process. By means of the modification reaction between B4C and the volatiles of PF resin, the value of carbon residue was prompted effectively; and the formation of fibers and the nanocrystallization of B2O3 benefit the achievement of satisfactory high-temperature bonding properties.
Abstract: Modification of potassium titanate whiskers (PTW) by sol-gel, FSO and NDZ-102 methods was studied. The water contact angle of modified PTW and the friction and wear properties of PEEK composites filled with various modified PTW were investigated. The worn surfaces and transfer films were observed by SEM and optical microscope, and the abrasion mechanism of PEEK composites filled with modified PTW was discussed. The results show that the water contact angle of PTW is improved after surface modification, and the highest is FSO modification. The friction coefficient of PEEK composites filled with modified PTW decreases, and the wear resistances of PEEK composites filled with FSO and sol-gel modified PTW are better than that without modification, which increases the wear resistance 2.64 and 2.11 times respectively under 300 N. But NDZ-102 decreases the wear resistance of PEEK composites.
Abstract: The crystallization behavior of a polymer is simultaneously influenced by temperature and temperature experience, but its temperature field is dependent on crystallization. A coupling analysis of cooling and crystallization process was carried out to exactly simulate the temperature field and crystallization behavior of se-mi-crystalline polymer melt. In the coupling method the result of temperature field was considered as the input of crystallization analysis and then the result of spherulites evolution was used as the input of temperature field simulation, so simulation results of the double scales, macroscopic and mesoscopic, was obtained at the same time. Because the coupling analysis has the physical background, the result of numerical simulation can be thought reasonable.
Abstract: In order to overcome the shortcomings of acellular dermal matrix used as tissue engineering scaffold material, such as bad permeability, low degradation speed, and strong immunogenicity, a new type of collagen scaffold was prepared by applying various chemical, biological and physical comprehensive methods to deal with pigskin. The microstructure of the scaffold was observed under photomicroscope and scanning electron microscopy (SEM), and the in vitro degradation time, permeability, tensile-strength, porosity, shrinkage temperature were tested. The experimental results show that its dermal fibroblasts, lipocytes and interstitial substances between collagen fibers have been removed completely, simultaneously collagen fibers have been appropriately loosen, and the original natural three-dimensional meshwork porous structure is maintained; the permeability is about 3 000 g·m-2·d-1, which is fit for wound healing; the degradation time is between 25 h and 50 h and can be controlled by adjusting technological conditions; the tensile-strength is between 10.20 MPa and 11.50 MPa which is better; the shrinkage temperature is between 70℃ and 85℃. All of those indicate that the material overcomes the shortcomings of acellular dermal matrix and has high permeability, tensile-strength, and proper degradation speed. So it conforms to tissue engineering scaffold material requirements.
Abstract: The microstructures of Mg-4Al alloys containing alkaline earth Sr and Ca were investigated by optical microscope (OM), scanning electronic microscope (SEM) and transmission electron microscope (TEM), and creep properties were also tested. The as-cast microstructure of the studied alloys consists of dendritic a-Mg and grain boundary second-phases. Divorced eutectic and lamellar eutectic Al4Sr, and bulky ternary τ phase are observed along grain boundary with 2% of Sr addition to the based alloy. 2% of Ca addition results in the formation of lamellar eutectic Mg2Ca at grain boundary and Al2Ca particles in grains. In the Mg-4Al-2Sr-ICa alloy, grain boundary phases are r phase and lamellar eutectic Mg2Ca, and Al2Ca particles are also precipitated in grains. With the increase of Al content in the Mg-4Al-2Sr-ICa, the coarse irregular-shaped (Mg, Al)2Ca eutectic forms along grain boundary and its volume fraction gradually increases, meanwhile Mg2Ca and τ phase gradually decrease. The new fine lamellar Al4Sr appears when the Al content reaches to 7%. The additions of Sr and Ca improve the creep resistance of Mg-Al alloys significantly, and the Mg-5Al-2Sr-ICa and Mg-6Al-2Sr -1Ca alloys indicate the best creep properties in all studied alloys. According to the power-law equation, under conditions of 175℃/50~80 MPa and 70 MPa/150~200℃, the creep behavior of the Mg-4Al-2Sr alloy is diffusion controlled dislocation climb at lower stresses (〈 60 MPa) and shows the breakdown of power-law at higher stresses. The creep mechanism of the Mg-4Al-2Sr-1Ca alloy seems controlled dislocation movement and grain boundary sliding.
Abstract: Directionally solidified Al2O3/YAG/ZrO2 eutectic ceramics were prepared by laser zone remelting technique to investigate the rapid solidification microstructure characteristic under ultra-high temperature gradient and different laser processing conditions. The fracture toughness and toughen mechanism were analyzed and discussed. The results show the following. (1) The directionally solidified Al2O3/YAG/ZrO2 eutectic ceramic shows a ‘Chinese script’ microstructure consisting of only three phases of Al2O3, YAG and ZrO2, and no other phases and colonies. The three phases distribute homogeneously and continuously, connect and finely couple each other to form an interpenetrating network, which belongs to the typical lamellar structure of a rapidly solidified irregular eutectic. (2) The eutectic spacing decreases with the increase of scanning rate under certain laser power intensity, and the smallest spacing is only about 0.2~0.3 μm. (3) Some amount of Y2O3 dissolves in ZrO2 phase and this influences the micro-patterns of ZrO2. (4) The maximum hardness reaches 18.67 GPa and the room-temperature fracture toughness is 8.O MPa·m1/2. Adding the third component of ZrO2, small size of phases and crack branching may contribute to the increased fracture toughness.
Abstract: The Cu-6% Ag and Cu-24% Ag were cast and annealed or aging treated to precipitate Ag secondary particles from supersaturated Cu matrix. The interface and orientation relationship between Ag precipitates and Cu matrix were investigated. The effect of Ag precipitates on the mechanical and electrical properties of the alloys was discussed. There are a strict orientation relationship, (100)Cu//(100)Ag and <110>Cu//<110>Ag, and semi-coherence interface between Ag precipitates and Cu matrix. One dislocation exists in average nine (111)Cu lattice intervals to adjust the lattice misfit at the interface. The strict orientation relationship and semi-coherence interface may produce significant strengthening affect and hardly increase the electron scattering in the alloys. With prolonging aging time the amount of Ag precipitates and the hardness of the alloys increase but the electrical resistivity decreases. The changes of the amount, morphology and interface structure of the precipitates should be responsible for the change of the properties during aging treatment.
Abstract: The exfoliation corrosion susceptibility and electrochemical impedance spectroscopy (EIS) of Al-Cu-Mg alloys with different corrosive grades were studied to analyze the dynamic process of exfoliation corrosion by TEM and electrochemical. The results show that 2524-T4 aluminum alloy is good in exfoliation corrosion property, Cu-rich particles are the main influence factor of exfoliation corrosion behavior of the alloy, pitting corrosion occurs after 2d and light exfoliation corrosion can be found after 4d. Using EIS and equivalent circuit to analyze the corrosion dynamic process, the corrosion process includes formation of pitting corrosion, development of pitting corrosion, and formation of exfoliation corrosion. The interface reaction in the corrosion process contains dissolution of oxide film, formation, adsorption and exfoliation of surface corrosion products.
Abstract: The signification of using heat insulation technology in a military armored vehicle was discussed. The difficulties and key problems of heat insulation technology in an engine were also analyzed. Based on the semisolid processing theory, material property research method and analogy testing method, hot simulation experiments were carried out to study the distortion rule and quality of cermets, such as TiC-Ni, at high temperature. The broken mechanism of cermets at high temperature was explored. The experimental and research results indicate that non-elasticity strain associate with time in nature according to constitutive equations of the classical elastic-plastic and creep theory. Non-elasticity strain should be expressed by uniform method for it is controlled by the single mechanism. Namely, it should be disposed by elastic-viscoplasticity constitutive equations which associate with plastic strain and creep strain. The mathematical model which can reflect the distortion character of cermets at high temperature was established by multiple regression analysis based on hot simulation experiment data, and statistical test of the mathematical model revealed that the mathematical model is reasonable.
Abstract: Seventeen plain groups, which were associated with 2D braided geometry of composites, were deduced from the combination of ten plain point groups and five plain dot lattices. The simplified method, combination and crossover principle of the point symbol on a 2D braided composites yarn segment were proposed. The construction methods of non-symmetry unit and basic symmetry unit were investigated, and the fabric-braided procedure from non-symmetry unit to basic symmetry unit was discussed. The 2D braided fabric of composites was classified four braided families, each braided family included several plain groups, each plain group was corresponding a group of braided structures, and each group of braided structures had one or several braided modes whose interwoven methods were homologous. The possible 2D braided composites geometry of majority plain groups was illustrated.
Abstract: The effect of MnS inclusions on hydrogen diffusion in steel was investigated by experiment and finite element method (FEM). The results show that with increasing MnS inclusion content the appearance diffusivity of hydrogen in steel increases when the elongated inclusions parallel to the direction of permeation and decreases when perpendicular to the direction of permeation. If the inclusions can both transport and trap hydrogen, the effect of inclusion on hydrogen diffusion in steel is determined by their strength of transportation and trap, density, figure and orientation.
Abstract: SEM and TEM were employed to study the structure stability of a new developed 718 alloy after aging at 680℃ for 1000 h. The results indicate that the main strengthening phase in a standard alloy 718 is γ″, while it is γ″ precipitated on increasing amount γ' in the new developed alloy and a compact morphology forms. The new developed alloy was proved to be very stable after long-time aging at 680℃. The morphology of phase on grain boundary in the standard alloy is long needle-like or lamellar while it is short rod-shaped or granular in the new developed alloy. The tensile properties of the two alloys at room temperature and 680℃ have a slight difference but the stress rupture and creep properties of the new developed alloy are greatly superior to the standard alloy. In comparison with the standard alloy, the new developed alloy has a better combination of mechanical properties and microstructure stability at 680℃.
Abstract: A method based on atomic radius and electro-negativity of alloying constituents was proposed to estimate the glass forming ability (GFA) of a bulk metallic glass. The mathematical model of the ratio of radiuses difference to electro-negativity difference and the critical cooling rate Rc was established. The same relationships with a shape of upturned parabola in all five kinds of alloys were obtained with this model. Based on the above results, four different compositions of Zr-Al-Ni-Cu bulk metallic glasses were designed and prepared, and their critical size Zmax, super-cooling liquid region ΔTx and the reduced glass temperature Trg were all measured respectively. The results show that the glass forming ability of Zr54Al13Ni15Cu18 is the best in the four alloys and the GFA order of these alloys predicted using the Δd/Δe model is basically consistent with experimental parameters (including Zmax ΔTx, and Trg). It is concluded that the prediction using the Δd/Δe model is a reliable method to compare the glass forming ability between different compositions in a same alloying series.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
