Friction stir processing （FSP） was used to incorporate SiC particles into the matrix of A356 Al alloy to form composite material. Constant tool rotation speed of 1800 r/min and travel speed of 127 mm/min were used i...Friction stir processing （FSP） was used to incorporate SiC particles into the matrix of A356 Al alloy to form composite material. Constant tool rotation speed of 1800 r/min and travel speed of 127 mm/min were used in this study. The base metal （BM） shows the hypoeutectic Al-Si dendrite structure. The microstructure of the stir zone （SZ） is very different from that of the BM. The eutectic Si and SiC particles are dispersed homogeneously in primary Al solid solution. The thermo-mechanically affected zone （TMAZ）, where the original microstructure is greatly deformed, is characterized by dispersed eutectic Si and SiC particles aligned along the rotational direction of the tool. The hardness of the SZ shows higher value than that of the BM because some defects are remarkably reduced and the eutectic Si and SiC particles are dispersed over the SZ.展开更多
The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing proc...The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing process. To carry out this investigation, Ag was added by 5.3, 10.6, and 16.0 wt.% to an AA2024 consumable rod by inserting holes in it. It was found that due to the strengthening by solid solution and the formation of precipitates and intermetallic containing Ag, the driving force for grain growth is reduced and consequently the grain size of the coating is decreased. After artificial aging heat treatment, the electrical conductivities of the coatings containing 0 and 16.0 wt.% Ag are increased by 4.15%(IACS) and decreased by 2.15%(IACS), respectively. While considering a linear relationship, it can be proposed that for a 1 wt.% Ag increase, the strength and hardness of the coating will be increased by 1.8% and 1.0%, respectively. It was established that the effect of Al6(Cu,Ag)Mg4 precipitate formation on strengthening is greater than that of Ag-rich intermetallic.展开更多
More than 80 million metric tons of fly ash is produced annually in the U.S. as coal combustion by-product. Coal fly ash can be converted to value-added products if unburned carbon is reduced to less than 2.5%. Howeve...More than 80 million metric tons of fly ash is produced annually in the U.S. as coal combustion by-product. Coal fly ash can be converted to value-added products if unburned carbon is reduced to less than 2.5%. However, most of fly ash is currently landfilled as waste due to lack of efficient purification technologies to separate unburned carbon from fly ash. A rotary triboelectrostatic separator has been developed and patented recently at the University of Kentucky with unique features. Several fly ash samples have been used to understand the effects of major process parameters on the separation performance. The results show that compared to existing triboelectrostatic separators, the rotary triboelectrostatic separator has significant advantages in particle charging efficiency, solids throughput, separation efficiency, applicable particle size range.展开更多
Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_...Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_(22)Co_(26)Cr_(20)Ni_(22)Ta_(10)−(BaF_(2)/CaF_(2))x(x=3−20,wt.%)composites were prepared by spark plasma sintering(SPS),with BaF_(2)/CaF_(2) eutectic powder used as solid lubricant.The lubrication behavior and mechanical properties were studied at both room and high temperatures.With the increase of the content of BaF_(2)/CaF_(2) eutectic powder,the friction coefficients and the wear rates of the composites at 600 and 800℃ decrease significantly.The composites with eutectic powder content of 15 and 20 wt.%have the best lubricating performance at 600℃,with low friction coefficient and wear rates,mainly due to the good mechanical properties of EHEA matrix,the lubrication effect of BaF_(2)/CaF_(2) phase and the oxides formed on the worn surface.展开更多
Brake friction materials with different zinc powder contents(0,2,4,6,8 wt.%)were fabricated via powder metallurgy method.The results indicate that with the increasing zinc powder content,the density and thermal conduc...Brake friction materials with different zinc powder contents(0,2,4,6,8 wt.%)were fabricated via powder metallurgy method.The results indicate that with the increasing zinc powder content,the density and thermal conductivity of the materials gradually increase,while the hardness decreases monotonously.With increasing zinc powder content,the curve of the nominal friction coefficient shows fluctuating trend but the lowest friction coefficient also shows an increase.However,the wear rate and braking noise of the friction material monotonously decrease with increasing zinc content.This effect may be attributed to the transformation of the tribological mechanism from adhesive wear and abrasive wear to adhesive wear.The brake friction material with 4 wt.%zinc powder exhibits both the best tribological and noise performance.展开更多
To quantize the difficulty level of dust production on the surface of different types of farmland,the Marticorena threshold frictional velocity pattern was used in this study to simulate the dust threshold frictional ...To quantize the difficulty level of dust production on the surface of different types of farmland,the Marticorena threshold frictional velocity pattern was used in this study to simulate the dust threshold frictional velocity.The results showed that the dust threshold frictional velocity of desertification farmland was 7.39cm/s,while it was 29.05 cm/s after the wheat harvested and the farmland ploughed; the turning green period was 46.85 cm/s; shooting period was 98.93 cm/s,the uncovered and the establishment period of fruit tree farmland was 26.0 and 139.15 cm/s.It was concluded that,bare desertification farmland could be changed into source of dust release easier.展开更多
The extruded plate of powder metallurgy AA2024 aluminum alloy was successfully solid-state joined by friction stir welding(FSW) to demonstrate potential applications in the aerospace and automotive industries. For det...The extruded plate of powder metallurgy AA2024 aluminum alloy was successfully solid-state joined by friction stir welding(FSW) to demonstrate potential applications in the aerospace and automotive industries. For determining the optimal processing parameters of FSW, the microstructure, mechanical properties, and fracture behavior of FSW joints were evaluated. When the processing parameters were optimized with 2000 r/min rotation speed and100 mm/min traverse speed, high quality welds were achieved. The ultimate tensile strength yield strength and elongation of the joint can reach 415 MPa(85% of the base metal strength), 282 MPa, and 9.5%, respectively. The hardness of the joint gradually decreased from the alloy matrix to the heat-affected zone. The lowest strength and hardness appeared near the heat-affected zone because of the over-aging caused by heat flow from repeated stirring during FSW. The average grain size of the stir zone(2.15 μm) was smaller than that of the base metal(4.43 μm) and the heat-affected zone(5.03 μm), whose grains had <110> preferred orientation.展开更多
The couette dusty flow between two horizontal parallel porous flat plates with transverse sinusoidal injection of the dusty fluid at the stationary plate and its corresponding removal by constant suction through the p...The couette dusty flow between two horizontal parallel porous flat plates with transverse sinusoidal injection of the dusty fluid at the stationary plate and its corresponding removal by constant suction through the plate in uniform motion was analyzed. Due to this type of injection velocity the dusty flow becomes 3D. Perturbation method is used to obtain the expressions for the velocity and temperature fields of both the fluid and dust. It was found that the velocity profiles of both the fluid and dust in the main flow direction decrease with the increase of the mass concentration of the dust particles, and those in cross flow direction increase with an increase in the mass concentration of the dust particles up to the middle of the channel and thereafter decrease with increase in mass concentration of the dust particles. The skin friction components Tx and Tz in the main flow and transverse directions respectively increase with an increase in the mass concentration of the dust particles (or) injection parameter. The heat transfer coefficient decreases with the increase of the injection parameter and increases with the increase in the mass concentration of the dust particles.展开更多
Ti-Fe-x TiC(x=0, 3, 6, 9, wt.%) composites were fabricated through low temperature ball milling of Ti, Fe and TiC powders, followed by spark plasma sintering. The results show that β-Ti, β-Ti-Fe, η-Ti4 Fe2 O0.4 and...Ti-Fe-x TiC(x=0, 3, 6, 9, wt.%) composites were fabricated through low temperature ball milling of Ti, Fe and TiC powders, followed by spark plasma sintering. The results show that β-Ti, β-Ti-Fe, η-Ti4 Fe2 O0.4 and TiC particles can be found in the composites. The microstructure can be obviously refined with increasing the content of TiC particles. The coefficient of friction(COF) decreases and the hardness increases with increasing the content of TiC particles. The adhesive wear is the dominant wear mechanism of all the Ti-Fe-x TiC composites. The Ti-Fe-6 TiC composite shows the best wear resistance, owing to the small size and high content of TiC particle as well as relatively fine microstructure. The wear rate of the Ti-Fe-6 TiC composite is as low as 1.869× 10-5 mm3/(N·m) and the COF is only 0.64. Therefore, TiC particle reinforced Ti-Fe based composites may be utilized as potential wear resistant materials.展开更多
UV is a high-energy electromagnetic radiation that has been widely used in industrial production and the scientific research domain. In this work, a deep UV light emission was obtained using triboelectrification induc...UV is a high-energy electromagnetic radiation that has been widely used in industrial production and the scientific research domain. In this work, a deep UV light emission was obtained using triboelectrification induced plasma discharge without any extra power supply. By a mechanical friction between polymer and quartz glass, the triboelectric charges cause a changing electric field, which may bring plasma discharge of low pressure gas （Ar-Hg） and give out 253.7 nm irradiation. The UV light caused by continuous friction can excite a trichromatic phosphor and afford a bright white light emission. A UV sterilization experiment shows that -98% of Escherichia coil can be killed in 30 min by UV irradiation, which reveals that a self-powered sterilization apparatus with good sterilization effect was fabricated. This work provides a novel design to fabricate a self- powered UV light emitting device using low-frequency mechanical friction and realizes the coupling of triboelectrificafion and plasma luminescence, which may further expand the application of UV light in special circumstances.展开更多
基金supported by a grant from the Fundamental R & D Program (No.10038688) for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea
文摘Friction stir processing （FSP） was used to incorporate SiC particles into the matrix of A356 Al alloy to form composite material. Constant tool rotation speed of 1800 r/min and travel speed of 127 mm/min were used in this study. The base metal （BM） shows the hypoeutectic Al-Si dendrite structure. The microstructure of the stir zone （SZ） is very different from that of the BM. The eutectic Si and SiC particles are dispersed homogeneously in primary Al solid solution. The thermo-mechanically affected zone （TMAZ）, where the original microstructure is greatly deformed, is characterized by dispersed eutectic Si and SiC particles aligned along the rotational direction of the tool. The hardness of the SZ shows higher value than that of the BM because some defects are remarkably reduced and the eutectic Si and SiC particles are dispersed over the SZ.
基金funding support of Babol Noshirvani University of Technology,Iran,through Grant Program No.BNUT/370167/99。
文摘The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing process. To carry out this investigation, Ag was added by 5.3, 10.6, and 16.0 wt.% to an AA2024 consumable rod by inserting holes in it. It was found that due to the strengthening by solid solution and the formation of precipitates and intermetallic containing Ag, the driving force for grain growth is reduced and consequently the grain size of the coating is decreased. After artificial aging heat treatment, the electrical conductivities of the coatings containing 0 and 16.0 wt.% Ag are increased by 4.15%(IACS) and decreased by 2.15%(IACS), respectively. While considering a linear relationship, it can be proposed that for a 1 wt.% Ag increase, the strength and hardness of the coating will be increased by 1.8% and 1.0%, respectively. It was established that the effect of Al6(Cu,Ag)Mg4 precipitate formation on strengthening is greater than that of Ag-rich intermetallic.
文摘More than 80 million metric tons of fly ash is produced annually in the U.S. as coal combustion by-product. Coal fly ash can be converted to value-added products if unburned carbon is reduced to less than 2.5%. However, most of fly ash is currently landfilled as waste due to lack of efficient purification technologies to separate unburned carbon from fly ash. A rotary triboelectrostatic separator has been developed and patented recently at the University of Kentucky with unique features. Several fly ash samples have been used to understand the effects of major process parameters on the separation performance. The results show that compared to existing triboelectrostatic separators, the rotary triboelectrostatic separator has significant advantages in particle charging efficiency, solids throughput, separation efficiency, applicable particle size range.
基金The authors acknowledge the financial support from the National Natural Science Foundation of China(51671217).
文摘Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_(22)Co_(26)Cr_(20)Ni_(22)Ta_(10)−(BaF_(2)/CaF_(2))x(x=3−20,wt.%)composites were prepared by spark plasma sintering(SPS),with BaF_(2)/CaF_(2) eutectic powder used as solid lubricant.The lubrication behavior and mechanical properties were studied at both room and high temperatures.With the increase of the content of BaF_(2)/CaF_(2) eutectic powder,the friction coefficients and the wear rates of the composites at 600 and 800℃ decrease significantly.The composites with eutectic powder content of 15 and 20 wt.%have the best lubricating performance at 600℃,with low friction coefficient and wear rates,mainly due to the good mechanical properties of EHEA matrix,the lubrication effect of BaF_(2)/CaF_(2) phase and the oxides formed on the worn surface.
基金Project(2016YFB1100103)supported by the National Key Research and Development Program of ChinaProject(KC1703004)supported by the Science and Technology Planning Project of Changsha City,ChinaProject(2018ZZTS127)supported by the Fundamental Research Funds for the Central Universities of Central South University,China。
文摘Brake friction materials with different zinc powder contents(0,2,4,6,8 wt.%)were fabricated via powder metallurgy method.The results indicate that with the increasing zinc powder content,the density and thermal conductivity of the materials gradually increase,while the hardness decreases monotonously.With increasing zinc powder content,the curve of the nominal friction coefficient shows fluctuating trend but the lowest friction coefficient also shows an increase.However,the wear rate and braking noise of the friction material monotonously decrease with increasing zinc content.This effect may be attributed to the transformation of the tribological mechanism from adhesive wear and abrasive wear to adhesive wear.The brake friction material with 4 wt.%zinc powder exhibits both the best tribological and noise performance.
文摘To quantize the difficulty level of dust production on the surface of different types of farmland,the Marticorena threshold frictional velocity pattern was used in this study to simulate the dust threshold frictional velocity.The results showed that the dust threshold frictional velocity of desertification farmland was 7.39cm/s,while it was 29.05 cm/s after the wheat harvested and the farmland ploughed; the turning green period was 46.85 cm/s; shooting period was 98.93 cm/s,the uncovered and the establishment period of fruit tree farmland was 26.0 and 139.15 cm/s.It was concluded that,bare desertification farmland could be changed into source of dust release easier.
基金Project(92066205) supported by the National Natural Science Foundation of ChinaProject(JCKY61420052008)supported by the National Defense Science and Technology Key Laboratory Foundation,China+2 种基金Project(311021013)supported by Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai),ChinaProject(FRF-MP-20-52) supported by the Fundamental Research Funds for the Central Universities,ChinaProject(075-15-2021-612) support from the Government of the Russian Federation。
文摘The extruded plate of powder metallurgy AA2024 aluminum alloy was successfully solid-state joined by friction stir welding(FSW) to demonstrate potential applications in the aerospace and automotive industries. For determining the optimal processing parameters of FSW, the microstructure, mechanical properties, and fracture behavior of FSW joints were evaluated. When the processing parameters were optimized with 2000 r/min rotation speed and100 mm/min traverse speed, high quality welds were achieved. The ultimate tensile strength yield strength and elongation of the joint can reach 415 MPa(85% of the base metal strength), 282 MPa, and 9.5%, respectively. The hardness of the joint gradually decreased from the alloy matrix to the heat-affected zone. The lowest strength and hardness appeared near the heat-affected zone because of the over-aging caused by heat flow from repeated stirring during FSW. The average grain size of the stir zone(2.15 μm) was smaller than that of the base metal(4.43 μm) and the heat-affected zone(5.03 μm), whose grains had <110> preferred orientation.
文摘The couette dusty flow between two horizontal parallel porous flat plates with transverse sinusoidal injection of the dusty fluid at the stationary plate and its corresponding removal by constant suction through the plate in uniform motion was analyzed. Due to this type of injection velocity the dusty flow becomes 3D. Perturbation method is used to obtain the expressions for the velocity and temperature fields of both the fluid and dust. It was found that the velocity profiles of both the fluid and dust in the main flow direction decrease with the increase of the mass concentration of the dust particles, and those in cross flow direction increase with an increase in the mass concentration of the dust particles up to the middle of the channel and thereafter decrease with increase in mass concentration of the dust particles. The skin friction components Tx and Tz in the main flow and transverse directions respectively increase with an increase in the mass concentration of the dust particles (or) injection parameter. The heat transfer coefficient decreases with the increase of the injection parameter and increases with the increase in the mass concentration of the dust particles.
基金financial support from the National Key Fundamental Research and Development Project of China (2014CB644002)。
文摘Ti-Fe-x TiC(x=0, 3, 6, 9, wt.%) composites were fabricated through low temperature ball milling of Ti, Fe and TiC powders, followed by spark plasma sintering. The results show that β-Ti, β-Ti-Fe, η-Ti4 Fe2 O0.4 and TiC particles can be found in the composites. The microstructure can be obviously refined with increasing the content of TiC particles. The coefficient of friction(COF) decreases and the hardness increases with increasing the content of TiC particles. The adhesive wear is the dominant wear mechanism of all the Ti-Fe-x TiC composites. The Ti-Fe-6 TiC composite shows the best wear resistance, owing to the small size and high content of TiC particle as well as relatively fine microstructure. The wear rate of the Ti-Fe-6 TiC composite is as low as 1.869× 10-5 mm3/(N·m) and the COF is only 0.64. Therefore, TiC particle reinforced Ti-Fe based composites may be utilized as potential wear resistant materials.
文摘UV is a high-energy electromagnetic radiation that has been widely used in industrial production and the scientific research domain. In this work, a deep UV light emission was obtained using triboelectrification induced plasma discharge without any extra power supply. By a mechanical friction between polymer and quartz glass, the triboelectric charges cause a changing electric field, which may bring plasma discharge of low pressure gas （Ar-Hg） and give out 253.7 nm irradiation. The UV light caused by continuous friction can excite a trichromatic phosphor and afford a bright white light emission. A UV sterilization experiment shows that -98% of Escherichia coil can be killed in 30 min by UV irradiation, which reveals that a self-powered sterilization apparatus with good sterilization effect was fabricated. This work provides a novel design to fabricate a self- powered UV light emitting device using low-frequency mechanical friction and realizes the coupling of triboelectrificafion and plasma luminescence, which may further expand the application of UV light in special circumstances.
