Jingpei XIE
,
Yaomin ZHU
,
Xiaoping WANG
材料科学技术（英文）
The M-s temperature, Delta G(gamma-->alpha), Delta G(gamma-->M) and mechanical energy under a non-severe impact loading in a medium manganese steel (Fe-7Mn-1.2C) have been calculated by means of Xu's Fe-X-C model. The relation between the yield strength of austenite and the driving force for martensite transformation has been established. It is proved that the martensite transformation can take place in a medium manganese steel (Fe-7Mn-1.2C alloy) under a non-severe impact loading.
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Acta Materialia
A Hf-Al-C composite composed of Hf(3)Al(3)C(5), Hf(2)Al(4)C(5) and Hf(3)Al(4)C(6) has been successfully synthesized by a hot pressing method; its microstructure and mechanical and thermal properties were systematically characterized. Hf-Al-C composite conserves the high hardness and stiffness similar to HfC. Interestingly, the composite exhibits Much higher strength and fracture toughness than HfC due to its fine and anisotropic grains. Diffusion-accommodated grain-boundary sliding of Hf-Al-C ceramics at high temperature is inhibited by glass-free grain boundaries and tight interlocking of grains at grain-edge triple junctions, resulting in high remaining stiffness up to 1600 degrees C. Dislocations on the basal planes of Hf-Al-C ceramics with a Burgers vector of 1/3 < 11 (2) over bar0 > can be activated at high temperature. Hf-Al-C composite shows higher coefficient of thermal expansion and specific heat capacity as well as lower thermal conductivity than HfC. The superior mechanical and thermal properties make Hf-Al-C compounds good high-temperature structural materials. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Carbides;TEM;High temperature;Mechanical property;Thermal property;high-temperature;elastic properties;crystal-structure;thermoelectric;properties;internal-friction;silicon carbides;grain-boundary;bulk;zr2al3c4;ceramics;oxidation
A. Alizadeh
材料科学技术（英文）
In this study, aluminum alloy (Al-2 wt% Cu) matrix composites reinforced with 1, 2 and 4 wt% boron carbide nanoparticles fabricated through mechanical milling with average size of 100 nm were fabricated via stir casting method at 850°C. Cast ingots of the matrix alloy and the composites were extruded at 500°C at an extrusion ratio of 10:1 to investigate the effects of hot extrusion on the mechanical properties of the composites. The microstructures of the as-cast and the extruded composites were investigated by scanning electron microscopy (SEM). Density measurement, hardness and tensile tests were carried out to identify the mechanical properties of the composites. The extruded samples revealed a more uniform distribution of B4C nanoparticles. Also, the extruded samples had strength and ductility values superior to those of the as-cast counterparts. In the as-cast and the extruded samples, with increasing amount of B4C nanoparticles, yield strength and tensile strength increased but elongation to fracture decreased.
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Stir casting
International Journal of Hydrogen Energy
A highly active photocatalyst based on g-C(3)N(4) coated SrTiO(3) has been synthesized simply by decomposing urea in the presence of SrTiO(3) at 400 degrees C. The catalyst demonstrates a high H(2) production rate similar to 440 mu mol h(-1)/g catalyst in aqueous solution under visible light irradiation, which is much higher than conventional anion doped SrTiO(3) or physical mixtures of g-C(3)N(4) and SrTiO(3). The improved photocatalytic activity can be ascribed to the close interfacial connections between g-C(3)N(4) and SrTiO(3) where photo-generated electron and holes are effectively separated. The newly synthesized catalyst also exhibited a stable performance in the repeated experiments. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
关键词:
Carbon nitride;Photocatalyst;Visible light;SrTiO(3);tio2 nanotube photocatalyst;hydrogen-production;water;generation;oxynitride
Materials Letters
Mechanical alloying (MA) of elemental powder mixtures of Fe50Nb35C15, Fe60Nb30C10 and Fe50Nb40C10 was performed using a high energy ball mill. In the MA processing, ball milling first leads to a Fe-Nb-C amorphous phase and nanocrystalline NbC. Further milling results in the formation of a nanocrystalline solid solution of Fe(Nb, C) and nanocrystalline NbC in Fe50Nb35C15 and Fe60Nb30C10, while the final product for Fe50Nb40C10 is a mixture of amorphous Fe-Nb-C and nanocrystalline NbC.
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mechanical alloying;Fe;Fe, Nb and C powders;amorphous;nanocrystalline;solid solution
Journal of Applied Physics
The effects of further addition, of carbon on structure and magnetic properties of the Sm20Fe70C10 alloy synthesized by mechanical alloying have been investigated. The main phase is Sm2Fe17Cx or Sm2Fe14C, depending on the composition of starting materials. The Sm2Fe14C phase tends to form when more carbon is added. Remilling and reannealing at a low temperature (600 degrees C) improve the magnetic properties of the alloys. The ratio of remanence to saturation magnetization as high as 0.79 indicates the existence of enhanced exchange coupling between the hard Sm2Fe17Cx and soft Sm2Fe14C/alpha-Fe magnetic phases in the Sm20Fe70C15 alloy. (C) 2000 American Institute of Physics. [S0021-8979(00)21208-5].
关键词:
phase-transformation;behavior;r2fe14c
Journal of Applied Physics
The Nd-Fe-Ti intermetallic compounds with a ThMn12 structure have been successfully prepared by mechanical alloying and then annealed. It has been found that the phase of the hexagonal TbCu7 structure is formed in Nd8Fe84Ti8 mechanical alloy powders annealed at temperatures ranging from 650 to 850 degrees C. With an increase in the annealing temperature T-a, the metastable TbCu7 structure transforms into a ThMn12 structure at T-a=900 degrees C. Consequently, the Curie temperature increases from 180 degrees C of TbCu7 structure at T-a=650 to 300 degrees C of ThMn12 structure at T-a=1050 degrees C. In the series of Nd-x-Fe92-xTi8 annealed at 960 degrees C for 30 min, it has been observed that the ThMn12 structure exists only over the range of compositions of 5 less than or equal to x<11, and the structure of the type Th2Zn17 is formed for x greater than or equal to 11. All the compounds are nitrited at 400 degrees C for 15 h, and the Curie temperatures are raised from 400 to 450 degrees C. The Nd9Fe83Ti8 powder, annealed at 960 degrees C for 30 min, and nitrided at 400 degrees C for 15 h, has a coercivity H-i(c)=2.3 kOe. The low coercivity perhaps mainly results from an excessive growth of alpha-Fe grains due to the high annealing temperature necessary for forming the hard magnetic phase Nd(Fe,Ti)(12)N delta. (C) 1996 American Institute of Physics.
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