The high-temperature oxidation resistance of AISI 321 stainless steel used in solar thermal power heat exchangers determines its service life.In this study,aluminizing and subsequent laser shock peening(LSP)treatments...The high-temperature oxidation resistance of AISI 321 stainless steel used in solar thermal power heat exchangers determines its service life.In this study,aluminizing and subsequent laser shock peening(LSP)treatments were employed to improve the high-temperature oxidation resistance of AISI 321 stainless steel at 620°C.These two treatments decreased the oxidation rate of AISI 321 steel.Specifically,the optimal oxidation resistance was observed in aluminized steel before oxidation for 144 h owing to the increased entropy of the LSP-treated specimen.After 144 h,LSP-treated steel achieved the best oxidation resistance because of the formation of a protectiveα-Al2O3film.Moreover,the large amount of subgrain boundaries formed on the aluminized layer of the LSP-treated samples could act as short-circuit paths for the outward diffusion of Al,facilitating the rapid nucleation ofα-Al2O3.Meanwhile,the aluminized layer could isolate the contact between the oxidation environment and matrix,thereby decreasing the oxidation rate.Furthermore,the minimum oxidation parabolic constant was calculated for LSP-treated steel(6.45787×10^(-14)),which was 69.18%and 36.36%that of aluminized and 321 steel,respectively,during the entire oxidation process.Therefore,the combination of aluminizing and LSP treatments can improve the high-temperature oxidation resistance of 321 stainless steel,providing a new idea for its surface treatment to achieve a long service life at high temperatures.展开更多
Pure titanium samples were aluminized at 950,1025 and 1100 ℃ for 0-6 h in a pack containing 10%Al＋5%NaF＋85%Al2O3 in mass traction.The aluminized layers formed on the samples were characterized.The kinetic studies i...Pure titanium samples were aluminized at 950,1025 and 1100 ℃ for 0-6 h in a pack containing 10%Al＋5%NaF＋85%Al2O3 in mass traction.The aluminized layers formed on the samples were characterized.The kinetic studies indicated that the diffusion of Al-bearing gases through the pack is the rate-controlling step in this process.The activation energy of 161.8 kJ/mol was calculated for this step.In addition,the mass gains of the aluminized samples were predicted using the partial pressures of gases in the pack and those adjacent to the samples surface.The predicted values are in good agreement wim the experimental measurements at 950 ℃ but are higher than those measured at 1025 and 1100 ℃.展开更多
This study reports the significantly enhanced aluminizing behaviors of a low carbon steel at temperatures far below the austenitizing temperature, with a nanostructured surface layer produced by surface mechanical att...This study reports the significantly enhanced aluminizing behaviors of a low carbon steel at temperatures far below the austenitizing temperature, with a nanostructured surface layer produced by surface mechanical attrition treatment （SMAT）. A much thicker iron aluminide compound layer with a much enhanced growth kinetics of η-Fe2Al5 in the SMAT sample has been observed relative to the coarse-grained steel sample. Compared to the coarse-grained sample, a weakened texture is formed in the aluminide layer in the SMAT sample. The aluminizing kinetics is analyzed in terms of promoted difusivity and nucleation frequency in the nanostructured surface layer.展开更多
Aluminizing coating and aluminizing-dispersed Y 2O 3 composite coating were prepared on 20 steel specimens by pulsed spark technique, which exhibited a micro-crystallized structure with grain size in the range of se...Aluminizing coating and aluminizing-dispersed Y 2O 3 composite coating were prepared on 20 steel specimens by pulsed spark technique, which exhibited a micro-crystallized structure with grain size in the range of several ten to several hundred nanometers. It is shown that, after oxidation at 600 ℃ in air for 100 h, these two kinds of coatings have excellent resistance to high temperature oxidation and scale spallation, and the aluminizing-dispersed Y 2O 3 composite coating has even better property than the aluminizing coating. AFM, SEM, EDS and XRD were applied to analyze the surface morphology, composition and phases structure of these coatings and the oxide scale formed in oxidation. The mechanism for these coatings that how to enhance the oxidation resistance and scale spallation resistance was discussed by considering the factors, such as Al concentration on the selective oxidation of Fe-Al alloy, the effect of micro-crystallization, reactive element effect (REE) caused by dispersed Y 2O 3, etc.展开更多
Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity.Although the pulling speed is one of the most important parameters to control the coating t...Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity.Although the pulling speed is one of the most important parameters to control the coating thickness of aluminizing products,however,there are few publications on the mathematical modeling of pulling speed during the hot dip process.In order to describe the correlation among the pulling speed,coating thickness and solidification time,the principle of mass and heat transfer during the aluminizing process is investigated in this paper.The mathematical models are based on Navier-Stokes equation and heat transfer analysis.Experiments using the self-designed equipment are carried out to validate the mathematical models.Specifically,aluminum melt is purified at 730 ℃.The Cook-Norteman method is used for the pretreatment of Q235 steel plates.The temperature of hot dip aluminizing is set to 690 ℃ and thedipping time is set to 3 min.A direct current motor with stepless speed variation is used to adjust the pulling speed.The temperature change of the coating is recorded by an infrared thermometer,and the coating thickness is measured by using image analysis.The validate experiment results indicate that the coating thickness is proportional to the square root of pulling speed for the Q235 steel plate,and that there is a linear relationship between coating thickness and solidification time when the pulling speed is lower than 0.11 m/s.The prediction of the proposed model fits well with the experimental observations of the coating thickness.展开更多
Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the micro...Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the microstructure and the thickness of the aluminide coating of Cu was investigated. Pack aluminizing of Cu significantly improved the microhardness and the oxidation resistance. The microhardness was increased about seven times and the oxidation resistance,after 96 h exposure in air at 900℃, was extremely increased ten times by aluminizing Cu at 900℃ for 3 h.展开更多
In this study, the two kinds of Fe-Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures. The corrosion behavior of the Fe-Al coatings in artificial seawater was investigated by...In this study, the two kinds of Fe-Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures. The corrosion behavior of the Fe-Al coatings in artificial seawater was investigated by the electrochemical and weight loss techniques. Results show that the thickness of coating layer increases with increasing aluminizing temperature. The coatings exhibit high micro-hardness and good metallurgical bonding with the substrate. In comparison with the steel substrate, the corrosion current density Ico^r of the Fe-AI coatings is always lower than that of substrate, about 1/38 or 1/33 after 2 h immersion, and 1/3 or 1/6 for 720 h immersion. As can be seen from the weight loss curve, the Fe-AI coatings show less loss than that of the substrate within 30-day immersion. The corrosion products formed on the surface of the coatings include oxides of Al, Mg, Fe and Ca, and pitting defect has also been found. The Fe-Al coating with higher content of Fe2Al5 has better corrosion resistance.展开更多
The steel surface treatment by rare-earth aluminithermic aluminizing,which was utilized onthermal couple,buried parts of lightning arrester and silencer of automobile,has met with success.This new technique was studie...The steel surface treatment by rare-earth aluminithermic aluminizing,which was utilized onthermal couple,buried parts of lightning arrester and silencer of automobile,has met with success.This new technique was studied by Beijing University of Science and Technology,BeijingIron-steel Institute and Jingdong Work of Corrosion-protective Materials cooperatively.The steel展开更多
Aluminum was deposited by diffusion into Cu-Al-Y alloy substrates by the pack-cementation process.Diffusion was carried out in two kinds of container with pot-type and can-type,and the results are presented.The effect...Aluminum was deposited by diffusion into Cu-Al-Y alloy substrates by the pack-cementation process.Diffusion was carried out in two kinds of container with pot-type and can-type,and the results are presented.The effects of various time and temperature on the coating characteristics of Cu-Al-Y was also investigated.The result shows that the diffusion layer is nearly 170-200μm in thickness by aluminizing treatment at 900-950℃for 6-8 h in pot-type container.The aluminized layers were observed by a scanning electron micrograph(SEM),we can found:A uniform coating was achieved on Cu-Al-Y alloy surface,relatively uniform thickness and even interfaces between the layers and the substrate.The diffusion coefficient of Al in Cu-Al-Y alloys at 900℃in pot-type container can be calculated is 3.65×10-12 m 2 /s.展开更多
Dissolution kinetics of CaO·2Al_(2)O_(3)(CA_(2))particles in a synthetic CaO-Al_(2)O_(3)-SiO_(2)steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope.Effects...Dissolution kinetics of CaO·2Al_(2)O_(3)(CA_(2))particles in a synthetic CaO-Al_(2)O_(3)-SiO_(2)steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope.Effects of temperature(i.e.,1500,1550,and 1600℃)and slag composition on the dissolution time of CA_(2)particles are investigated,along with the time dependency of the projection area of the particle during the dissolution process.It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity.Moreover,a higher ratio of CaO/Al_(2)O_(3)(C/A)leads to an increased dissolution rate of CA_(2)particle at 1600℃.Thermodynamic calculations suggested the dissolution product,i.e.,melilite,formed on the surface of the CA_(2)particle during dissolution in slag with a C/A ratio of 3.8 at 1550℃.Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA_(2)particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA_(2)particle.The formation of this layer during the dissolution process was identified as a hindrance,impeding the dissolution of CA_(2)particle.A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided,especially using calcium treatment during the secondary refining process.展开更多
In order to prepare high density magnesium aluminate spinel materials,the light-burned magnesia and alumina powder were used as the main raw materials.Active magnesium aluminate spinel powders were synthesized at diff...In order to prepare high density magnesium aluminate spinel materials,the light-burned magnesia and alumina powder were used as the main raw materials.Active magnesium aluminate spinel powders were synthesized at different temperatures,and the sintering properties of the synthesized materials were characterized.The results show that the optimal light-burned temperature for synthesizing active magnesium aluminate spinel raw materials with small grain sizes and high sintering activity is 1400℃.The active spinel raw materials were sintered at 1750℃ for 3 h to form a dense spinel material,in which the spinel grains were well developed,exhibited a dense interlocking structure,and were uniformly distributed,with an average grain size of about 7.26μm.The bulk density and apparent porosity of the dense spinel material were 3.29 g·cm^(-3) and 3.5%,respectively.展开更多
The new CL-20(hexanitrohexaazaisowurtzitane)type aluminized explosives in the overdrive detonation(ODD)conditions of the core problem is how to accurately represent the state of the overdrive detonation products.To th...The new CL-20(hexanitrohexaazaisowurtzitane)type aluminized explosives in the overdrive detonation(ODD)conditions of the core problem is how to accurately represent the state of the overdrive detonation products.To this end,this paper is based on the impedance matching method to test the ODD conditions of CL-20 type aluminium explosive particle velocity.Calculated the interfacial pressure of the shock wave in different media.Determined the characteristic parameters of the reaction zone of the detonation of CL-20 aluminized explosives.Calibrated the parameters of the JoneseWilkinseLee(JWL)+γ equation for the detonation products(DPs).Revealed the effect of different DPs equation of state(EOS)on the Hugoniot pressure of ODD.The results indicate that when the content of aluminum powder ranges from 0%to 30%,the duration of the ODD reaction zone and the width of the detonation reaction zone of the CL-20-based aluminized explosive are directly proportional to the content of aluminum powder.The width of the detonation reaction zone is increased by 1.97 times to 2.7 times compared to that of the reaction zone without the addition of aluminum powder.However,the energy release efficiency of the detonation reaction zone is inversely proportional to the content of aluminum powder.When the aluminum powder content was held constant,the incorporation of AP caused a 25%reduction in the energy release efficiency of the detonation reaction zone.Compared with existing ODD state equations,the JWL +γ equation is superior in calibrating overpressure Hugoniot data and the isentropic expansion in the C-J state.The deviation between calculated pressure results and experimental measurements is within 6%.展开更多
The effect of platinum(a rare metal)-aluminide coating parameters on the tensile properties of nickel-based superalloy Rene■80 was evaluated at 871℃.For this purpose,initial layers of platinum with different thickne...The effect of platinum(a rare metal)-aluminide coating parameters on the tensile properties of nickel-based superalloy Rene■80 was evaluated at 871℃.For this purpose,initial layers of platinum with different thicknesses(2,4,6 and 8μm)were coated on tensile samples Then,low-temperature high-activity(LTHA)and hightemperature low-activity(HTLA)processes were used for aluminizing.Results of microstructural evaluations using scanning electron microscope(SEM)and phase analysis by X-ray diffraction(XRD)showed a three-layer structure coating for different platinum layer thicknesses and both aluminizing processes.Increasing the thickness of the platinum layer from 2 to 8μm led to the improvement in the final coating thickness from 91.6 to 102.1μm in HTLA.This increase was from 128.1 to 148.6μm in LTHA.The results of hot tensile tests at 871℃ showed a decrease in strength properties of the coated samples compared to the uncoated ones.However,HTLA and high thicknesses of the initial platinum layer showed an intense reduction.The results of fractographic evaluations abou uncoated samples showed a ductile fracture.On the other hand,coated samples showed a simultaneous ductile and brittle fracture failure mechanism.But the main fracture morphology was brittle cleavage fracture which was for the HTLA.展开更多
We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement(CAC)and anhydrite.The effects of anhydrite on the visible efflorescence,and the corre...We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement(CAC)and anhydrite.The effects of anhydrite on the visible efflorescence,and the corresponding capillary absorption of CAC-anhydrite mortars were revealed.The composition and microstructure of efflorescence-causing substances were investigated by optical microscope,in-situ Raman spectroscopy,scanning electron microscope,energy dispersive spectrometer,thermogravimetric analysis,and differential scanning calorimetry,at multi-scales.Results indicate that,besides the calcium carbonate,ettringite is another main component of efflorescence-causing substances.Compared with the neat CAC mortars,the addition of anhydrite has a significant effect on the degree of efflorescence by acting on the composition of hydration products and pore structure.In addition,methods are proposed for the prevention of efflorescence of CAC-anhydrite binary system.展开更多
In order to investigate the modification behavior and regularity of inclusions in X80 pipeline steel by Mg-treatment, the comparative industrial experiments of Mg-treatment and Ca-treatment in X80 pipeline steel were ...In order to investigate the modification behavior and regularity of inclusions in X80 pipeline steel by Mg-treatment, the comparative industrial experiments of Mg-treatment and Ca-treatment in X80 pipeline steel were carried out. Mg and Ca were added to the steel in the form of cored wire after RH (Ruhrstahl-Hereaeus vacuum degassing) process. After adding Ca-containing cored wire, the inclusions were transformed into CaO–Al_(2)O_(3) in the steel. With the progress of smelting, the cleanliness of molten steel became worse, and the equivalent diameter of inclusions was at a higher level. Mg-treatment had a good effect on the modification of inclusions. After Mg-containing cored wire was added to the steel, Al_(2)O_(3) and CaO–Al_(2)O_(3) in the steel were transformed into MgO, MgO·Al_(2)O_(3), and CaO–MgO–Al_(2)O_(3) inclusions, which were basically spherical. The initial precipitated MgO became the core of other inclusions in the steel, which promotes the precipitation of MgO·Al_(2)O_(3). After Mg-treatment, almost no unmodified calcium aluminate inclusions existed in the hot rolled plate, and the cleanliness of the steel was improved. The effect of Ca and Mg on the transformation of inclusions in pipeline steel was studied by thermodynamic calculation, the result of which is consistent with the experimental results.展开更多
Based on the data of outcrop,core,logging,gas testing,and experiments,the natural gas accumulation and aluminous rock mineralization integrated research was adopted to analyze the controlling factors of aluminous rock...Based on the data of outcrop,core,logging,gas testing,and experiments,the natural gas accumulation and aluminous rock mineralization integrated research was adopted to analyze the controlling factors of aluminous rock series effective reservoirs in the Ordos Basin,NW China,as well as the configuration of coal-measure source rocks and aluminous rock series reservoirs.A natural gas accumulation model was constructed to evaluate the gas exploration potential of aluminous rock series under coal seam in the basin.The effective reservoirs of aluminous rock series in the Ordos Basin are composed of honeycomb-shaped bauxites with porous residual pisolitic and detrital structures,with the diasporite content of greater than 80%and dissolved pores as the main storage space.The bauxite reservoirs are formed under a model that planation controls the material supply,karst paleogeomorphology controls diagenesis,and land surface leaching improves reservoir quality.The hot humid climate and sea level changes in the Late Carboniferous–Early Permian dominated the development of a typical coal-aluminum-iron three-stage stratigraphic structure.The natural gas generated by the extensive hydrocarbon generation of coal-measure source rocks was accumulated in aluminous rock series under the coal seam,indicating a model of hydrocarbon accumulation under the source.During the Upper Carboniferous–Lower Permian,the relatively low-lying area on the edge of an ancient land or island in the North China landmass was developed.The gas reservoirs of aluminous rock series,which are clustered at multiple points in lenticular shape,are important new natural gas exploration fields with great potential in the Upper Paleozoic of North China Craton.展开更多
To provide theoretical guidance for performance stability control of low-reactive mold fluxes,the effects of BaO and MgO on the structure and properties of aluminate slag with various CaO/Al_(2)0_(3)(C/A)ratios were i...To provide theoretical guidance for performance stability control of low-reactive mold fluxes,the effects of BaO and MgO on the structure and properties of aluminate slag with various CaO/Al_(2)0_(3)(C/A)ratios were investigated using the Fourier transform infrared spectrometer,Raman spectroscope,hemispherical melting point instrument,rotational viscometer and X-ray diffractometer.The results indicated that with BaO and MgO addition,the structure polymerization was first weakened and then enhanced at C/A of 1.1,and the transition contents corresponded to 8 wt.%BaO and 2 wt.%MgO,respectively,while the structure polymerization decreased continuously at C/A of 1.3.Since the viscosity change was well consistent with the structure evolution,the polymerization degree played a more prominent role in the slag viscosity than superheat degree when the melting temperature difference was within 40℃.The break temperature decreased initially and then increased with augment of BaO and MgO at C/A of 1.1,while it manifested a decrease trend with BaO addition,and it decreased obviously but then turned to increase with MgO increment at C/A of 1.3.The crystallization phase and crystallization ratio kept stable with BaO increment,while the crystallization ratio rose greatly with MgO promoting LiAlO_(2)precipitation at C/A of 1.1.The crystal types of all experimental slags were mainly Ca_(12)Al_(14)O_(33)and CaF_(2)at C/A of 1.3,and the precipitation of crystalline phase BaAl2O4 demonstrated a rising trend,while that of Ca_(12)Al_(14)O_(33)gradually declined with BaO augment.展开更多
Free water available in calcium aluminate cement(CAC)-bonded castables is crucial for the hydration of CAC and the conversion of hydration products in the curing and drying processes,as both the hydration and conversi...Free water available in calcium aluminate cement(CAC)-bonded castables is crucial for the hydration of CAC and the conversion of hydration products in the curing and drying processes,as both the hydration and conversion reactions are dissolution–precipitation reactions.To elucidate the effect of different levels of free water loss upon the hydration of CAC,the conversion of hydration products and the mechanical strength of the CAC-bonded castables,the CAC-bonded castables were subjected to sealed and unsealed curing conditions at 50℃ and drying at 110℃.The results demonstrate that the fast removal of free water during unsealed curing would hinder the conversion from 2CaO·Al_(2)O_(3)·8H_(2)O to 3CaO·Al_(2)O_(3)·6H_(2)O and consequently prevent the deterioration of strength.As a comparison,although sealed-cured samples have less water loss and high degree of hydration of CAC,they still show lower strength than the unsealed samples after curing.The following drying process further accelerates the hydration of residual calcium aluminate clinkers for both the sealed and unsealed samples,but still does not favor the conversion from 2CaO·Al_(2)O_(3)·8H_(2)O to 3CaO·Al_(2)O_(3)·6H_(2)O in the unsealed-cured samples.展开更多
Afterburning behind the detonation front of an aluminized explosive releases energy on the millisecond timescale,which prolong the release of detonation energy and the energy release at different stages also shows sig...Afterburning behind the detonation front of an aluminized explosive releases energy on the millisecond timescale,which prolong the release of detonation energy and the energy release at different stages also shows significant differences.However,at present,there are few effective methods for evaluating the energy release characteristics of the middle reaction stage of such explosives,which can have a duration of tens to hundreds of microseconds.The present work demonstrates an approach to assessing the midstage of an aluminized explosive detonation based on a water push test employing a high degree of confinement.In this method,the explosive is contained in a steel cylinder having one end closed that is installed at the bottom of a transparent water tank.Upon detonation,the gaseous products expand in one direction while forcing water ahead of them.The resulting underwater shock wave and the interface between the gas phase products and the water are tracked using an ultra-high-speed framing and streak camera.The shock wave velocity in water and the expansion work performed by the gaseous detonation products were calculated to assess the energy release characteristics of aluminized explosives such as CL-20 and RDX in the middle stage of the detonation reaction.During the middle stage of the detonation process of these aluminized explosives,the aluminum reaction reduced the attenuation of shock waves and increased the work performed by gas phase products.A higher aluminum content increased the energy output while the presence of oxidants slowed the energy release rate.This work demonstrates an effective means of evaluating the performance of aluminized explosives.展开更多
The effect of Si on the growth kinetics of intermetallic compounds during the reaction of solid iron and molten aluminum was investigated with a scanning electron microscope coupled with an energy dispersive X-ray spe...The effect of Si on the growth kinetics of intermetallic compounds during the reaction of solid iron and molten aluminum was investigated with a scanning electron microscope coupled with an energy dispersive X-ray spectroscope, and hot-dip aluminized experiments. The results show that the intermetallic layer is composed of major Fe2Al5 and minor FeAl3. The Al-Fe-Si ternary phase, rl/rg, is formed in the Fe2Al5 layer. The tongue-like morphology of the Fe2Als layer becomes less distinct and disappears finally as the content of Si in aluminum bath increases. Si in the bath improves the prohibiting ability to the growth of Fe2Als and FeAl3. When the contents of Si are 0, 0.5%, 1.0%, 1.5%, 2.0% and 3.0%, the activation energies of Fe2Al5 are evaluated to be 207, 186, 169, 168, 167 and 172 kJ/mol, respectively. The reduction of the activation energy might result from the lattice distortion caused by Si atom penetrating into the Fe2Al5 phase. When Si atom occupies the vacancy site, it blocks easy diffusion path and results in the disappearance of tongue-like morphology.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.52075048,51675058,12232004)Hunan Provincial Excellent Youth Project of the Education Department(Grant No.21B0304)+2 种基金Natural Science Foundation of Hunan Province(Grant No.2023JJ30025)Science and Technology Innovation Program of Hunan Province(Grant No.2023RC1058)Scientific Research Innovation Project for Graduate Student of Changsha University of Science and Technology(Grant No.CLSJCX22096)。
文摘The high-temperature oxidation resistance of AISI 321 stainless steel used in solar thermal power heat exchangers determines its service life.In this study,aluminizing and subsequent laser shock peening(LSP)treatments were employed to improve the high-temperature oxidation resistance of AISI 321 stainless steel at 620°C.These two treatments decreased the oxidation rate of AISI 321 steel.Specifically,the optimal oxidation resistance was observed in aluminized steel before oxidation for 144 h owing to the increased entropy of the LSP-treated specimen.After 144 h,LSP-treated steel achieved the best oxidation resistance because of the formation of a protectiveα-Al2O3film.Moreover,the large amount of subgrain boundaries formed on the aluminized layer of the LSP-treated samples could act as short-circuit paths for the outward diffusion of Al,facilitating the rapid nucleation ofα-Al2O3.Meanwhile,the aluminized layer could isolate the contact between the oxidation environment and matrix,thereby decreasing the oxidation rate.Furthermore,the minimum oxidation parabolic constant was calculated for LSP-treated steel(6.45787×10^(-14)),which was 69.18%and 36.36%that of aluminized and 321 steel,respectively,during the entire oxidation process.Therefore,the combination of aluminizing and LSP treatments can improve the high-temperature oxidation resistance of 321 stainless steel,providing a new idea for its surface treatment to achieve a long service life at high temperatures.
文摘Pure titanium samples were aluminized at 950,1025 and 1100 ℃ for 0-6 h in a pack containing 10%Al＋5%NaF＋85%Al2O3 in mass traction.The aluminized layers formed on the samples were characterized.The kinetic studies indicated that the diffusion of Al-bearing gases through the pack is the rate-controlling step in this process.The activation energy of 161.8 kJ/mol was calculated for this step.In addition,the mass gains of the aluminized samples were predicted using the partial pressures of gases in the pack and those adjacent to the samples surface.The predicted values are in good agreement wim the experimental measurements at 950 ℃ but are higher than those measured at 1025 and 1100 ℃.
基金supported by the National Science Foundation of China (Nos.50701044 and 50890171)the Ministry of Science and Technology of China (No.2005CB623604)
文摘This study reports the significantly enhanced aluminizing behaviors of a low carbon steel at temperatures far below the austenitizing temperature, with a nanostructured surface layer produced by surface mechanical attrition treatment （SMAT）. A much thicker iron aluminide compound layer with a much enhanced growth kinetics of η-Fe2Al5 in the SMAT sample has been observed relative to the coarse-grained steel sample. Compared to the coarse-grained sample, a weakened texture is formed in the aluminide layer in the SMAT sample. The aluminizing kinetics is analyzed in terms of promoted difusivity and nucleation frequency in the nanostructured surface layer.
文摘Aluminizing coating and aluminizing-dispersed Y 2O 3 composite coating were prepared on 20 steel specimens by pulsed spark technique, which exhibited a micro-crystallized structure with grain size in the range of several ten to several hundred nanometers. It is shown that, after oxidation at 600 ℃ in air for 100 h, these two kinds of coatings have excellent resistance to high temperature oxidation and scale spallation, and the aluminizing-dispersed Y 2O 3 composite coating has even better property than the aluminizing coating. AFM, SEM, EDS and XRD were applied to analyze the surface morphology, composition and phases structure of these coatings and the oxide scale formed in oxidation. The mechanism for these coatings that how to enhance the oxidation resistance and scale spallation resistance was discussed by considering the factors, such as Al concentration on the selective oxidation of Fe-Al alloy, the effect of micro-crystallization, reactive element effect (REE) caused by dispersed Y 2O 3, etc.
基金supported by Guangxi Provincial Natural Science Foundation of China (Grant No. 0832001)
文摘Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity.Although the pulling speed is one of the most important parameters to control the coating thickness of aluminizing products,however,there are few publications on the mathematical modeling of pulling speed during the hot dip process.In order to describe the correlation among the pulling speed,coating thickness and solidification time,the principle of mass and heat transfer during the aluminizing process is investigated in this paper.The mathematical models are based on Navier-Stokes equation and heat transfer analysis.Experiments using the self-designed equipment are carried out to validate the mathematical models.Specifically,aluminum melt is purified at 730 ℃.The Cook-Norteman method is used for the pretreatment of Q235 steel plates.The temperature of hot dip aluminizing is set to 690 ℃ and thedipping time is set to 3 min.A direct current motor with stepless speed variation is used to adjust the pulling speed.The temperature change of the coating is recorded by an infrared thermometer,and the coating thickness is measured by using image analysis.The validate experiment results indicate that the coating thickness is proportional to the square root of pulling speed for the Q235 steel plate,and that there is a linear relationship between coating thickness and solidification time when the pulling speed is lower than 0.11 m/s.The prediction of the proposed model fits well with the experimental observations of the coating thickness.
文摘Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the microstructure and the thickness of the aluminide coating of Cu was investigated. Pack aluminizing of Cu significantly improved the microhardness and the oxidation resistance. The microhardness was increased about seven times and the oxidation resistance,after 96 h exposure in air at 900℃, was extremely increased ten times by aluminizing Cu at 900℃ for 3 h.
基金supported by the Foundation of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology (No. ASMA 201403)Cooperative Innovation Fund of Jiangsu Province (No. BY 2014004-09)
文摘In this study, the two kinds of Fe-Al coatings were fabricated by pack aluminizing on low-carbon steel at different temperatures. The corrosion behavior of the Fe-Al coatings in artificial seawater was investigated by the electrochemical and weight loss techniques. Results show that the thickness of coating layer increases with increasing aluminizing temperature. The coatings exhibit high micro-hardness and good metallurgical bonding with the substrate. In comparison with the steel substrate, the corrosion current density Ico^r of the Fe-AI coatings is always lower than that of substrate, about 1/38 or 1/33 after 2 h immersion, and 1/3 or 1/6 for 720 h immersion. As can be seen from the weight loss curve, the Fe-AI coatings show less loss than that of the substrate within 30-day immersion. The corrosion products formed on the surface of the coatings include oxides of Al, Mg, Fe and Ca, and pitting defect has also been found. The Fe-Al coating with higher content of Fe2Al5 has better corrosion resistance.
文摘The steel surface treatment by rare-earth aluminithermic aluminizing,which was utilized onthermal couple,buried parts of lightning arrester and silencer of automobile,has met with success.This new technique was studied by Beijing University of Science and Technology,BeijingIron-steel Institute and Jingdong Work of Corrosion-protective Materials cooperatively.The steel
基金Basic Research Priorities Program of the Science and Technology Committee of Shanghai(03JC14063)Shanghai Leading Academic Discipline Project(J50503)Innovative Program of the Education Commission of Shanghai(11YZ112)
文摘Aluminum was deposited by diffusion into Cu-Al-Y alloy substrates by the pack-cementation process.Diffusion was carried out in two kinds of container with pot-type and can-type,and the results are presented.The effects of various time and temperature on the coating characteristics of Cu-Al-Y was also investigated.The result shows that the diffusion layer is nearly 170-200μm in thickness by aluminizing treatment at 900-950℃for 6-8 h in pot-type container.The aluminized layers were observed by a scanning electron micrograph(SEM),we can found:A uniform coating was achieved on Cu-Al-Y alloy surface,relatively uniform thickness and even interfaces between the layers and the substrate.The diffusion coefficient of Al in Cu-Al-Y alloys at 900℃in pot-type container can be calculated is 3.65×10-12 m 2 /s.
基金the Natural Sciences and Engineering Research Council of Canada(NSERC)for funding this researchThis research used a high temperature confocal laser scanning microscope-VL2000DX-SVF17SP funded by Canada Foundation for Innovation John Evans Leaders Fund(CFI JELF,Project Number:32826),a PANalytical X’Pert diffraction instrument located at the Centre for crystal growth,Brockhouse Institute for Materials Research,and a scanning electron microscope-JEOL 6610 located at the Canadian Centre for Electron Microscopy at McMaster University.W.Mu would like to acknowledge Swedish Iron and Steel Research Office(Jernkonteret),STINT and SSF for supporting the time for international collaboration research regarding clean steel.
文摘Dissolution kinetics of CaO·2Al_(2)O_(3)(CA_(2))particles in a synthetic CaO-Al_(2)O_(3)-SiO_(2)steelmaking slag system have been investigated using the high-temperature confocal laser scanning microscope.Effects of temperature(i.e.,1500,1550,and 1600℃)and slag composition on the dissolution time of CA_(2)particles are investigated,along with the time dependency of the projection area of the particle during the dissolution process.It is found that the dissolution rate was enhanced by either an increase in temperature or a decrease in slag viscosity.Moreover,a higher ratio of CaO/Al_(2)O_(3)(C/A)leads to an increased dissolution rate of CA_(2)particle at 1600℃.Thermodynamic calculations suggested the dissolution product,i.e.,melilite,formed on the surface of the CA_(2)particle during dissolution in slag with a C/A ratio of 3.8 at 1550℃.Scanning electron microscopy equipped with energy dispersive X-ray spectrometry analysis of as-quenched samples confirmed the dissolution path of CA_(2)particles in slags with C/A ratios of 1.8 and 3.8 as well as the melilite formed on the surface of CA_(2)particle.The formation of this layer during the dissolution process was identified as a hindrance,impeding the dissolution of CA_(2)particle.A valuable reference for designing or/and choosing the composition of top slag for clean steel production is provided,especially using calcium treatment during the secondary refining process.
文摘In order to prepare high density magnesium aluminate spinel materials,the light-burned magnesia and alumina powder were used as the main raw materials.Active magnesium aluminate spinel powders were synthesized at different temperatures,and the sintering properties of the synthesized materials were characterized.The results show that the optimal light-burned temperature for synthesizing active magnesium aluminate spinel raw materials with small grain sizes and high sintering activity is 1400℃.The active spinel raw materials were sintered at 1750℃ for 3 h to form a dense spinel material,in which the spinel grains were well developed,exhibited a dense interlocking structure,and were uniformly distributed,with an average grain size of about 7.26μm.The bulk density and apparent porosity of the dense spinel material were 3.29 g·cm^(-3) and 3.5%,respectively.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11872120,12102050)Key Laboratory of Explosion Science and Technology(Grant No.QNKT22-01).
文摘The new CL-20(hexanitrohexaazaisowurtzitane)type aluminized explosives in the overdrive detonation(ODD)conditions of the core problem is how to accurately represent the state of the overdrive detonation products.To this end,this paper is based on the impedance matching method to test the ODD conditions of CL-20 type aluminium explosive particle velocity.Calculated the interfacial pressure of the shock wave in different media.Determined the characteristic parameters of the reaction zone of the detonation of CL-20 aluminized explosives.Calibrated the parameters of the JoneseWilkinseLee(JWL)+γ equation for the detonation products(DPs).Revealed the effect of different DPs equation of state(EOS)on the Hugoniot pressure of ODD.The results indicate that when the content of aluminum powder ranges from 0%to 30%,the duration of the ODD reaction zone and the width of the detonation reaction zone of the CL-20-based aluminized explosive are directly proportional to the content of aluminum powder.The width of the detonation reaction zone is increased by 1.97 times to 2.7 times compared to that of the reaction zone without the addition of aluminum powder.However,the energy release efficiency of the detonation reaction zone is inversely proportional to the content of aluminum powder.When the aluminum powder content was held constant,the incorporation of AP caused a 25%reduction in the energy release efficiency of the detonation reaction zone.Compared with existing ODD state equations,the JWL +γ equation is superior in calibrating overpressure Hugoniot data and the isentropic expansion in the C-J state.The deviation between calculated pressure results and experimental measurements is within 6%.
文摘The effect of platinum(a rare metal)-aluminide coating parameters on the tensile properties of nickel-based superalloy Rene■80 was evaluated at 871℃.For this purpose,initial layers of platinum with different thicknesses(2,4,6 and 8μm)were coated on tensile samples Then,low-temperature high-activity(LTHA)and hightemperature low-activity(HTLA)processes were used for aluminizing.Results of microstructural evaluations using scanning electron microscope(SEM)and phase analysis by X-ray diffraction(XRD)showed a three-layer structure coating for different platinum layer thicknesses and both aluminizing processes.Increasing the thickness of the platinum layer from 2 to 8μm led to the improvement in the final coating thickness from 91.6 to 102.1μm in HTLA.This increase was from 128.1 to 148.6μm in LTHA.The results of hot tensile tests at 871℃ showed a decrease in strength properties of the coated samples compared to the uncoated ones.However,HTLA and high thicknesses of the initial platinum layer showed an intense reduction.The results of fractographic evaluations abou uncoated samples showed a ductile fracture.On the other hand,coated samples showed a simultaneous ductile and brittle fracture failure mechanism.But the main fracture morphology was brittle cleavage fracture which was for the HTLA.
基金Funded by the National Key Research and Development Program of China(No.2022YFC3803400)National Natural Science Foundation of China(Nos.52378255,52278270)+1 种基金Shanghai Municipal Science and Technology Major Project(No.2021SHZDZX0100)the Fundamental Research Funds for the Central Universities and the Experimental Center of Materials Science and Engineering in Tongji University。
文摘We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement(CAC)and anhydrite.The effects of anhydrite on the visible efflorescence,and the corresponding capillary absorption of CAC-anhydrite mortars were revealed.The composition and microstructure of efflorescence-causing substances were investigated by optical microscope,in-situ Raman spectroscopy,scanning electron microscope,energy dispersive spectrometer,thermogravimetric analysis,and differential scanning calorimetry,at multi-scales.Results indicate that,besides the calcium carbonate,ettringite is another main component of efflorescence-causing substances.Compared with the neat CAC mortars,the addition of anhydrite has a significant effect on the degree of efflorescence by acting on the composition of hydration products and pore structure.In addition,methods are proposed for the prevention of efflorescence of CAC-anhydrite binary system.
基金funded by the National Natural Science Foundation of China(Nos.52104334,51874195 and 52074179)Center for Advanced Solidification Technology(CAST)and State Key Laboratory of Advanced Special Steel.
文摘In order to investigate the modification behavior and regularity of inclusions in X80 pipeline steel by Mg-treatment, the comparative industrial experiments of Mg-treatment and Ca-treatment in X80 pipeline steel were carried out. Mg and Ca were added to the steel in the form of cored wire after RH (Ruhrstahl-Hereaeus vacuum degassing) process. After adding Ca-containing cored wire, the inclusions were transformed into CaO–Al_(2)O_(3) in the steel. With the progress of smelting, the cleanliness of molten steel became worse, and the equivalent diameter of inclusions was at a higher level. Mg-treatment had a good effect on the modification of inclusions. After Mg-containing cored wire was added to the steel, Al_(2)O_(3) and CaO–Al_(2)O_(3) in the steel were transformed into MgO, MgO·Al_(2)O_(3), and CaO–MgO–Al_(2)O_(3) inclusions, which were basically spherical. The initial precipitated MgO became the core of other inclusions in the steel, which promotes the precipitation of MgO·Al_(2)O_(3). After Mg-treatment, almost no unmodified calcium aluminate inclusions existed in the hot rolled plate, and the cleanliness of the steel was improved. The effect of Ca and Mg on the transformation of inclusions in pipeline steel was studied by thermodynamic calculation, the result of which is consistent with the experimental results.
基金Supported by the PetroChina Science and Technology Major Project(2021DJ2101).
文摘Based on the data of outcrop,core,logging,gas testing,and experiments,the natural gas accumulation and aluminous rock mineralization integrated research was adopted to analyze the controlling factors of aluminous rock series effective reservoirs in the Ordos Basin,NW China,as well as the configuration of coal-measure source rocks and aluminous rock series reservoirs.A natural gas accumulation model was constructed to evaluate the gas exploration potential of aluminous rock series under coal seam in the basin.The effective reservoirs of aluminous rock series in the Ordos Basin are composed of honeycomb-shaped bauxites with porous residual pisolitic and detrital structures,with the diasporite content of greater than 80%and dissolved pores as the main storage space.The bauxite reservoirs are formed under a model that planation controls the material supply,karst paleogeomorphology controls diagenesis,and land surface leaching improves reservoir quality.The hot humid climate and sea level changes in the Late Carboniferous–Early Permian dominated the development of a typical coal-aluminum-iron three-stage stratigraphic structure.The natural gas generated by the extensive hydrocarbon generation of coal-measure source rocks was accumulated in aluminous rock series under the coal seam,indicating a model of hydrocarbon accumulation under the source.During the Upper Carboniferous–Lower Permian,the relatively low-lying area on the edge of an ancient land or island in the North China landmass was developed.The gas reservoirs of aluminous rock series,which are clustered at multiple points in lenticular shape,are important new natural gas exploration fields with great potential in the Upper Paleozoic of North China Craton.
基金The authors would like to deeply appreciate the fund support from the Natural Science Foundation of Anhui Provincial Education Department(KJ2021A0358)the National Natural Science Foundation of China(51804004)。
文摘To provide theoretical guidance for performance stability control of low-reactive mold fluxes,the effects of BaO and MgO on the structure and properties of aluminate slag with various CaO/Al_(2)0_(3)(C/A)ratios were investigated using the Fourier transform infrared spectrometer,Raman spectroscope,hemispherical melting point instrument,rotational viscometer and X-ray diffractometer.The results indicated that with BaO and MgO addition,the structure polymerization was first weakened and then enhanced at C/A of 1.1,and the transition contents corresponded to 8 wt.%BaO and 2 wt.%MgO,respectively,while the structure polymerization decreased continuously at C/A of 1.3.Since the viscosity change was well consistent with the structure evolution,the polymerization degree played a more prominent role in the slag viscosity than superheat degree when the melting temperature difference was within 40℃.The break temperature decreased initially and then increased with augment of BaO and MgO at C/A of 1.1,while it manifested a decrease trend with BaO addition,and it decreased obviously but then turned to increase with MgO increment at C/A of 1.3.The crystallization phase and crystallization ratio kept stable with BaO increment,while the crystallization ratio rose greatly with MgO promoting LiAlO_(2)precipitation at C/A of 1.1.The crystal types of all experimental slags were mainly Ca_(12)Al_(14)O_(33)and CaF_(2)at C/A of 1.3,and the precipitation of crystalline phase BaAl2O4 demonstrated a rising trend,while that of Ca_(12)Al_(14)O_(33)gradually declined with BaO augment.
基金the National Natural Science Foundation of China(52172030)for the financial support.
文摘Free water available in calcium aluminate cement(CAC)-bonded castables is crucial for the hydration of CAC and the conversion of hydration products in the curing and drying processes,as both the hydration and conversion reactions are dissolution–precipitation reactions.To elucidate the effect of different levels of free water loss upon the hydration of CAC,the conversion of hydration products and the mechanical strength of the CAC-bonded castables,the CAC-bonded castables were subjected to sealed and unsealed curing conditions at 50℃ and drying at 110℃.The results demonstrate that the fast removal of free water during unsealed curing would hinder the conversion from 2CaO·Al_(2)O_(3)·8H_(2)O to 3CaO·Al_(2)O_(3)·6H_(2)O and consequently prevent the deterioration of strength.As a comparison,although sealed-cured samples have less water loss and high degree of hydration of CAC,they still show lower strength than the unsealed samples after curing.The following drying process further accelerates the hydration of residual calcium aluminate clinkers for both the sealed and unsealed samples,but still does not favor the conversion from 2CaO·Al_(2)O_(3)·8H_(2)O to 3CaO·Al_(2)O_(3)·6H_(2)O in the unsealed-cured samples.
基金supported by the National Natural Science Foundation of China(Grant No.11832006)。
文摘Afterburning behind the detonation front of an aluminized explosive releases energy on the millisecond timescale,which prolong the release of detonation energy and the energy release at different stages also shows significant differences.However,at present,there are few effective methods for evaluating the energy release characteristics of the middle reaction stage of such explosives,which can have a duration of tens to hundreds of microseconds.The present work demonstrates an approach to assessing the midstage of an aluminized explosive detonation based on a water push test employing a high degree of confinement.In this method,the explosive is contained in a steel cylinder having one end closed that is installed at the bottom of a transparent water tank.Upon detonation,the gaseous products expand in one direction while forcing water ahead of them.The resulting underwater shock wave and the interface between the gas phase products and the water are tracked using an ultra-high-speed framing and streak camera.The shock wave velocity in water and the expansion work performed by the gaseous detonation products were calculated to assess the energy release characteristics of aluminized explosives such as CL-20 and RDX in the middle stage of the detonation reaction.During the middle stage of the detonation process of these aluminized explosives,the aluminum reaction reduced the attenuation of shock waves and increased the work performed by gas phase products.A higher aluminum content increased the energy output while the presence of oxidants slowed the energy release rate.This work demonstrates an effective means of evaluating the performance of aluminized explosives.
基金Project (51071135) supported by the National Natural Science Foundation of ChinaProject (20114301110005) supported by the Ph. D.Programs Foundation of Ministry of Education of ChinaProject (10XZX15) supported by the Science Foundation of Xiangtan University,China
文摘The effect of Si on the growth kinetics of intermetallic compounds during the reaction of solid iron and molten aluminum was investigated with a scanning electron microscope coupled with an energy dispersive X-ray spectroscope, and hot-dip aluminized experiments. The results show that the intermetallic layer is composed of major Fe2Al5 and minor FeAl3. The Al-Fe-Si ternary phase, rl/rg, is formed in the Fe2Al5 layer. The tongue-like morphology of the Fe2Als layer becomes less distinct and disappears finally as the content of Si in aluminum bath increases. Si in the bath improves the prohibiting ability to the growth of Fe2Als and FeAl3. When the contents of Si are 0, 0.5%, 1.0%, 1.5%, 2.0% and 3.0%, the activation energies of Fe2Al5 are evaluated to be 207, 186, 169, 168, 167 and 172 kJ/mol, respectively. The reduction of the activation energy might result from the lattice distortion caused by Si atom penetrating into the Fe2Al5 phase. When Si atom occupies the vacancy site, it blocks easy diffusion path and results in the disappearance of tongue-like morphology.
