Microwave boriding layer microstructure of carbon steels and its diffusion mechanics were studied. The results show that the existence of microwave field in the boriding can＇t change the growth mechanics of boriding ...
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Microwave boriding layer microstructure of carbon steels and its diffusion mechanics were studied. The results show that the existence of microwave field in the boriding can＇t change the growth mechanics of boriding layer. Compared with conventional boriding, if the treatment temperature and time remain constantly, the descend rate of the boriding layer thickness with the increase of carbon content of steel is smaller. The diffusion activation energy ofT8 steel is 2.6× 10^5 J/mol between the temperature of 750 ℃ and 900 ℃ in microwave field, which is in the same order of conventional boriding.
The morphology, mechanical properties of unsaturated polyester（UP） resin modified with TDI were studied via dynamic FT-1R spectra, SEM, DMA and mechanical property testing. Results show that companying with the cure...
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The morphology, mechanical properties of unsaturated polyester（UP） resin modified with TDI were studied via dynamic FT-1R spectra, SEM, DMA and mechanical property testing. Results show that companying with the cured cross-linking reaction of UP resin, TDI can firstly react with UP and produce polyurethane（PU）, and then UP and PU form the cross-linking nets together. The impact fracture section morphology of modified UP resin manifested the typical sea- islands structure. Testing of mechanical properties showes that for introducing of PU, the TDI has an obvious effect on the toughness and strength of UP resin. When the ratio of TDI/UP （w/w） was 7.5%, the modified UP resin exhibited the best mechanical properties with flexural strength of 125 MPa, impact strength of 18 kJ·m^-2 and tensile strength of 72 MPa.
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...
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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.
The influences of mass concentration of nickel chloride hexahydrate, sodium borohydride, ethylenediamine, pH value, bath temperature on deposition rate were studied with orthogonal experiments by a series of pre-treat...
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The influences of mass concentration of nickel chloride hexahydrate, sodium borohydride, ethylenediamine, pH value, bath temperature on deposition rate were studied with orthogonal experiments by a series of pre-treatments on micro-diamond particle, and the optimized parameters were obtained. Both the morphology and the composition of original diamond and the diamond with Ni-B coating were analyzed by SEM and XRD respectively. The SEM image shows that the spherical Ni-B particle is coated upon diamond. XRD pattern shows that the coating compositions are Ni and Ni2B.
With industrial grade Al（OH）3 as raw materials, the self dispersion nanosized AlOOH crystal powder were prepared by the sol-hydrothermal method. The results of XRD and TEM show that the nanosized AlOOH could automat...
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With industrial grade Al（OH）3 as raw materials, the self dispersion nanosized AlOOH crystal powder were prepared by the sol-hydrothermal method. The results of XRD and TEM show that the nanosized AlOOH could automatically disperse to a single-dispersing state in water without surface modification, dispersant, additive and accessional conditions （ultrasonic wave dispersing, ball-mill dispersing）. The application results of the product indicate that the nanosized AlOOH can be composed into a toughened nanocomposites without surface modification. Accordingly, the self dispersion characteristic and mechanism of hydrothermal crystallization and charging composite dispersion of nanosized AIOOH are found, and a new technique of preparing polymer/inorganic nanocomposites is proposed, which is called blending compositing new techniques of sol even dispersing at auasi-homogeneous phase.
The influence of different relative density on the cyclic oxidation behaviors of MoSi2 at 1 273 K were studied. ＂Pesting＂ was not found in all MoSi2 materials after being oxidized for 480 h. All samples exhibited co...
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The influence of different relative density on the cyclic oxidation behaviors of MoSi2 at 1 273 K were studied. ＂Pesting＂ was not found in all MoSi2 materials after being oxidized for 480 h. All samples exhibited continuous mass gain during the oxidation process. The mass gains of MoSi2 with the lowest relative density （78.6%） and the highest relative density （94.8%） are increased by 8.15 mg·cm^-2 and 3.48 mg·cm^-2, respectively. The surface of the material with lower relative density formed a loose, porous and discontinuous oxidation scale, which accelerated oxygen diffusion and aggravated the oxidation process. However, a dense scale in the material with higher relative density is formed, which acts a diffusion barrier to the oxygen atoms penetrating into the matrix. The high temperature oxidation resistance of MoSi2 can be improved by increasing its relative density.
Controlled Al doped Si3N4 single-crystal nanobelts were synthesized by catalyst-assisted pyrolysis of polymeric precursors. The Al-doping levels can be tailored by varying the Al concentration in the polymeric precurs...
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Controlled Al doped Si3N4 single-crystal nanobelts were synthesized by catalyst-assisted pyrolysis of polymeric precursors. The Al-doping levels can be tailored by varying the Al concentration in the polymeric precursors. The as-synthesized nanobelts were characterized by SEM, XRD, EDS, TEM and HRTEM. The single-crystal belts had perfect crystal structures with few defects such as dislocations and stacking faults. The nanobelts obtained are several tens nanometers in thickness, several hundreds nanometers in width. The growth direction of the Al doped α-Si3N4 nanobelts was [011]. The growth mechanisms of α-Si3N4 nanobelts were proposed to be solid-liquid-gas-sold (SLGS). The optical properties of Al doping Si3N4 nanobelts were measured. Current results suggested that the optical properties of the nanomaterials can be controlled by adjusting Al doping contents.
Mg2Si is a kind of narrow-band-gap n-type semiconductor, which is a promising environmental friendly thermoelectric material for its high electrical conductivity, low thermal conductivity, as well as non-toxicity and ...
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ISBN:
(纸本)9788880800842
Mg2Si is a kind of narrow-band-gap n-type semiconductor, which is a promising environmental friendly thermoelectric material for its high electrical conductivity, low thermal conductivity, as well as non-toxicity and non-pollution. In the present study, the fabrication process of Mg2Si thermoelectric material is systematically explored by spark plasma sintering technique (SPS) from Mg and Si raw powders. The density, phase and microstructure of the specimen are analyzed by XRD and FE-SEM. The results suggest that the complete reaction temperature for Mg and Si is 550°C, and the excessive content of Mg is helpful for obtaining the high purity Mg2Si. The relative density can reach 97% when the sample is prepared under the condition of 550°C-250MPa-10min, but crack is observed on the sample surface. Therefore, Mg and Si powder firstly react at 550°C-20MPa-30min, followed by sintering at 750°C-20MPa-5min. The sintered sample contains only Mg2Si phase with a high relative density near 100% and Mg2Si grains are fine and homogeneous.
The dynamic compressive behavior of Al2O3 (10% vol.) / TiB2 ceramic composite had been tested by using a split Hopkinson pressure bar in this paper. The results show that the main failure modes of the ceramic composit...
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The dynamic compressive behavior of Al2O3 (10% vol.) / TiB2 ceramic composite had been tested by using a split Hopkinson pressure bar in this paper. The results show that the main failure modes of the ceramic composite include crushed failure and split fracture along the loading direction. The former is the typical compressive failure of brittle materials. The later is tensile failure along the flaws produced during the composite manufacturing. The numerical simulation was also used to study the effect of the diameter/length ratio of the samples on the experimental results. The effect of the deformation in the bars' ends, which contacted with the samples, was also studied in the numerical models.
A series of B-C ceramics was simultaneously synthesized and densified from boron and carbon elements by using a Spark Plasma Sintering (SPS) method. A high relative density (>95%) was successfully obtained at 1900 ...
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ISBN:
(纸本)9788880800842
A series of B-C ceramics was simultaneously synthesized and densified from boron and carbon elements by using a Spark Plasma Sintering (SPS) method. A high relative density (>95%) was successfully obtained at 1900 °C. The main phases of the B-C ceramics were proved to be B4C and B13C2 with a small amount of unreacted free-C, and the grain size was ~500 nm. B/C ratios in the ceramics were measured by chemical analysis and the B/C ratio could be well controlled.
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