Microstructure and phase evolutions of Mg-A1 powders ball milled in hydrogen atmosphere were investigated. Both in Mg-3%A1 (mass fraction) and Mg-9%AI systems, fl-MgH2 phase was observed upon a short milling time of...Microstructure and phase evolutions of Mg-A1 powders ball milled in hydrogen atmosphere were investigated. Both in Mg-3%A1 (mass fraction) and Mg-9%AI systems, fl-MgH2 phase was observed upon a short milling time of 4 h and its maximum content of-80% was reached after 32 h. Neither as-milled powders of the in the two systems contain Mgl7All2. However, heating the milled powders of Mg-9%AI powders to 350 ~C resulted in the precipitation of Mg17A112. DTA/TG analyses of those powders milled for 8-40 h showed that either well-developed peak doublets or shoulders were observed, which plausibly corresponded to the separate hydrogen desorption from different particle fractions offl-MgH2.展开更多
Microstructure and tribological properties of copper-based hybrid nanocomposites reinforced with copper coatedmultiwalled carbon nanotubes (MWCNTs) and silicon carbide (SiC) were studied. Carbon nanotube was varied fr...Microstructure and tribological properties of copper-based hybrid nanocomposites reinforced with copper coatedmultiwalled carbon nanotubes (MWCNTs) and silicon carbide (SiC) were studied. Carbon nanotube was varied from 1% to 4% withsilicon carbide content being fixed at 4%. The synthesis of copper hybrid nanocomposites involves ball milling, cold pressing andsintering followed by hot pressing. The developed hybrid nanocomposites were subjected to density, grain size, and hardness tests.The tribological performances of the nanocomposites were assessed by carrying out dry sliding wear tests using pin-on-steel disctribometer at different loads. A significant decrease in grain size was observed for the developed hybrid composites when comparedwith pure copper. An improvement of 80% in the micro-hardness of the hybrid nanocomposite has been recorded for 4% carbonnanotubes reinforced hybrid composites when compared with pure copper. An increase in content of CNTs in the hybridnanocomposites results in lowering of the friction coefficient and wear rates of hybrid nanocomposites.展开更多
AZ31B magnesium alloy and nano-composite were manufactured by hybrid casting process and hot extruded at 350 °C. The sliding wear behaviour of alloy and nano-composite was estimated at room temperature using the ...AZ31B magnesium alloy and nano-composite were manufactured by hybrid casting process and hot extruded at 350 °C. The sliding wear behaviour of alloy and nano-composite was estimated at room temperature using the standard pin-on-disc wear test equipment. The tests were conducted under a normal load of 10 N at different sliding speeds ranging from 0.60 to 1.2 m/s for distance up to 2000 m. The wear mechanisms of the worn out surface were studied using SEM analysis. The influence of test parameters on wear rate of the pins was established using a linear regression model statistically. Compared with the AZ31B magnesium alloy, the nano-composite shows lower wear rates due to higher hardness improvement caused by the reinforcement. The wear mechanism appears to be a mix-up of ploughing, rows of furrows, delamination and oxidation.展开更多
Tribological behaviors of monolithic A356 aluminum alloy castings and A356.CNT nanocomposite castings, fabricated by fully liquid and semisolid routes were examined. Samples were prepared by melt agitation, rheocastin...Tribological behaviors of monolithic A356 aluminum alloy castings and A356.CNT nanocomposite castings, fabricated by fully liquid and semisolid routes were examined. Samples were prepared by melt agitation, rheocasting, stir casting, and compocasting techniques. Effects of addition of carbon nanotubes (CNTs), casting process and the applied load on wear properties and mechanisms were investigated. It was found that wear loss, wear rate and friction coefficient of nanocomposite samples remarkably declined by the addition of CNTs. Moreover, changing the casting process from fully liquid to semisolid routes, plus increasing fractions of the primary phase were the two factors that improved the wear properties of the investigated samples, especially nanocomposite ones. In addition, it was revealed that adhesion and delamination were the dominant wear mechanism of the monolithic samples produced by fully liquid and semisolid routes, respectively. However, regardless of fabrication techniques, the abrasion was the main wear mechanism of nanocomposite samples.展开更多
The formation mechanism and wear behavior of a gradient nanostructured(GNS) Inconel 625 alloy were investigated using SEM, TEM and ball-on-disc sliding wear tester. The results show that surface mechanical grinding tr...The formation mechanism and wear behavior of a gradient nanostructured(GNS) Inconel 625 alloy were investigated using SEM, TEM and ball-on-disc sliding wear tester. The results show that surface mechanical grinding treatment(SMGT) induced an approximately 800 μm-deep gradient microstructure, consisting of surface nano-grained,nano-laminated, nano-twined, and severely deformed layers, which resulted in a reduced gradient in micro-hardness from 6.95 GPa(topmost surface) to 2.77 GPa(coarse-grained matrix). The nano-grained layer resulted from the formation of high-density nano-twins and subsequent interaction between nano-twins and dislocations. The width and depth of the wear scar, wear loss volume, and wear rate of the SMGT-treated sample were smaller than those of untreated coarse-grained sample. Moreover, the wear mechanisms for both samples were mainly abrasive wear and adhesive wear, accompanied with mild oxidation wear. The notable wear resistance enhancement of the GNS Inconel 625 alloy was attributed to the high micro-hardness, high residual compressive stress, and high strain capacity of the GNS surface layer.展开更多
The corrosion, corrosive wear and dry sliding wear of nanocomposites, are extremely complicated and involve various chemical, physical anbd mechanical factors. The aim of this work is to investigate the effects of nan...The corrosion, corrosive wear and dry sliding wear of nanocomposites, are extremely complicated and involve various chemical, physical anbd mechanical factors. The aim of this work is to investigate the effects of nanosized SiC content on the hardness, dry sliding wear, corrosion and corrosive wear of Al/SiC nanocomposites synthesized by mechanical milling cold pressing and hot extrusion. The corrosion resistance of these composites in 3%NaCl solution was investigated by electrochemical polarization testing and their dry sliding as well as corrosive wear resistance in the same solution was evaluated using a pin-on-disc tester. The microstructures of the samples and their worn surfaces were examined using scanning electron microscopy. It was shown that the dry sliding wear and corrosion resistance of these nanocomposites were improved with the increase of SiC content. It was concluded that due to the lubrication effect of the solution, both the friction coefficient and frictional heat that might soften the material were reduced. In addition, the improved strength of the nanocomposites combined with their better corrosion resistance contributed to their increased corrosive wear resistance, compared with the base alloy. The prominent wear mechanism in the unreinforced alloy was adhesive wear, in the Al/SiC nanocomposites, the wear mechanism changed to abrasive.展开更多
Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE (polytetrafluoroethylene) which is a very common materia...Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE (polytetrafluoroethylene) which is a very common material for sliding bearing applications has been investigated to contribute related literature. PTFE is well-known for its exceptional tribological properties, and good toughness, and high thermal stability. It can also be used in dry sliding applications. PTFE is commonly used to reduce friction between relatively moving surfaces, lts wear rate can be reduced by adding micro or nano-sized fillers such as Al2O3, TiO2, SiO2, MoS2, Al, Pb, ZnO, Cu, ZrO2, Ni, CNF (carbon nano fiber), carbon fiber, glass fiber, bronze, and graphite powder into the PTFE. In this study, an experimental research was carried out for filled and unfilled PTFE to compare their behaviors under different speeds and loads. Test materials were unfilled PTFE, PTFE + wt. 5% Al2O3, PTFE + wt. 15% Al2O3. Formation of transfer film was examined in dry sliding condition against stainless steel counter faces. All tribological tests were carried out in a commercially available tribo-tester sliding against AISI-416 C stainless steel. As a result of a series of systematic experiments, remarkable results have been obtained to make a distinctive comparison between unfilled and filled PTFE. The variation of friction coefficient with sliding distance during the tests has also been recorded. At the end of the tests, wear rate of related PTFE specimen was calculated based on measured data. Wear rate is found very high for unfilled PTFE, however, the lowest wear rate is recorded for PTFE + wt. 15% Al2O3 as expected. The coefficient of friction remained approximately stable during the wear tests. Transfer films were inspected by observing the discs' surface with optical microscope.展开更多
The tribological properties of combinative addition of nano-MoS2 and nano-SiO2 to the base oil have been investigated with a reciprocating ball-on-plate tribotester for magnesium alloy-steel contacts. The results demo...The tribological properties of combinative addition of nano-MoS2 and nano-SiO2 to the base oil have been investigated with a reciprocating ball-on-plate tribotester for magnesium alloy-steel contacts. The results demonstrate that the optimum mass ratio of nano-SiO2 to nano-MoS2 is 0.25:0.75. The optimum combinative addition into the base oil reduces the friction coefficient by 43.8% and the surface roughness (Sa) by 31.7% when compared to that found with the base oil. Meanwhile, the combinative addition of nano-MoS2 and nano-SiO〉 in comparison with single nanoparticles addition, is more pronounced in terms of the lubrication film stability. The excellent tribological properties of the SiO2/MoS2 combinations are attributed to the formation of physical adsorption films and tribochemical products during the rubbing process and the micro-cooperation of various nano- particles with different shapes and lubrication mechanisms.展开更多
The ultrathin polyelectrolyte molecular deposition films and polyelectrolyte composite nanoparticles molecular deposition films were prepared using layer-by-layer molecular deposition method and in situ growth method....The ultrathin polyelectrolyte molecular deposition films and polyelectrolyte composite nanoparticles molecular deposition films were prepared using layer-by-layer molecular deposition method and in situ growth method.A micro-tribometer has been developed to measure the shear response of those ultrathin molecular deposition films.By using a smooth steel sphere in a ball-on-flat configuration,the shear force was determined for molecular deposition films on glass substrate for different layers.The results indicate that the shear behaviors of molecular deposition film were mainly determined with the contact area and film layers.Moreover,the composite molecular deposition film with nanoparticles has better shear behaviors than the polyelectrolyte molecular deposition film.The shear force of polyelectrolyte molecular deposition film is more dependent on the speed than that of composite nanoparticle molecular deposition film.展开更多
基金Projects(10JC407700,11ZR1417600)supported by the Science and Technology Committee of Shanghai,ChinaProject(12zz017)supported by the Shanghai Education Committee,China
文摘Microstructure and phase evolutions of Mg-A1 powders ball milled in hydrogen atmosphere were investigated. Both in Mg-3%A1 (mass fraction) and Mg-9%AI systems, fl-MgH2 phase was observed upon a short milling time of 4 h and its maximum content of-80% was reached after 32 h. Neither as-milled powders of the in the two systems contain Mgl7All2. However, heating the milled powders of Mg-9%AI powders to 350 ~C resulted in the precipitation of Mg17A112. DTA/TG analyses of those powders milled for 8-40 h showed that either well-developed peak doublets or shoulders were observed, which plausibly corresponded to the separate hydrogen desorption from different particle fractions offl-MgH2.
文摘Microstructure and tribological properties of copper-based hybrid nanocomposites reinforced with copper coatedmultiwalled carbon nanotubes (MWCNTs) and silicon carbide (SiC) were studied. Carbon nanotube was varied from 1% to 4% withsilicon carbide content being fixed at 4%. The synthesis of copper hybrid nanocomposites involves ball milling, cold pressing andsintering followed by hot pressing. The developed hybrid nanocomposites were subjected to density, grain size, and hardness tests.The tribological performances of the nanocomposites were assessed by carrying out dry sliding wear tests using pin-on-steel disctribometer at different loads. A significant decrease in grain size was observed for the developed hybrid composites when comparedwith pure copper. An improvement of 80% in the micro-hardness of the hybrid nanocomposite has been recorded for 4% carbonnanotubes reinforced hybrid composites when compared with pure copper. An increase in content of CNTs in the hybridnanocomposites results in lowering of the friction coefficient and wear rates of hybrid nanocomposites.
文摘AZ31B magnesium alloy and nano-composite were manufactured by hybrid casting process and hot extruded at 350 °C. The sliding wear behaviour of alloy and nano-composite was estimated at room temperature using the standard pin-on-disc wear test equipment. The tests were conducted under a normal load of 10 N at different sliding speeds ranging from 0.60 to 1.2 m/s for distance up to 2000 m. The wear mechanisms of the worn out surface were studied using SEM analysis. The influence of test parameters on wear rate of the pins was established using a linear regression model statistically. Compared with the AZ31B magnesium alloy, the nano-composite shows lower wear rates due to higher hardness improvement caused by the reinforcement. The wear mechanism appears to be a mix-up of ploughing, rows of furrows, delamination and oxidation.
基金financial support of the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISi S” (No. К2-2019-007)
文摘Tribological behaviors of monolithic A356 aluminum alloy castings and A356.CNT nanocomposite castings, fabricated by fully liquid and semisolid routes were examined. Samples were prepared by melt agitation, rheocasting, stir casting, and compocasting techniques. Effects of addition of carbon nanotubes (CNTs), casting process and the applied load on wear properties and mechanisms were investigated. It was found that wear loss, wear rate and friction coefficient of nanocomposite samples remarkably declined by the addition of CNTs. Moreover, changing the casting process from fully liquid to semisolid routes, plus increasing fractions of the primary phase were the two factors that improved the wear properties of the investigated samples, especially nanocomposite ones. In addition, it was revealed that adhesion and delamination were the dominant wear mechanism of the monolithic samples produced by fully liquid and semisolid routes, respectively. However, regardless of fabrication techniques, the abrasion was the main wear mechanism of nanocomposite samples.
基金financially supported by the National Key Research and Development Program of China (No. 2017YFA07007003)the National Natural Science Foundation of China (No. 51661019)+4 种基金the Program for Major Projects of Science and Technology in Gansu Province, China (No. 145RTSA004)the Hongliu First-class Discipline Construction Plan of Lanzhou University of Technology, Chinathe Incubation Program of Excellent Doctoral Dissertation, Lanzhou University of Technology, Chinathe Lanzhou University of Technology Excellent Students Studying Abroad Learning Exchange Fundthe State Key Laboratory of Cooperation and Exchange Fund。
文摘The formation mechanism and wear behavior of a gradient nanostructured(GNS) Inconel 625 alloy were investigated using SEM, TEM and ball-on-disc sliding wear tester. The results show that surface mechanical grinding treatment(SMGT) induced an approximately 800 μm-deep gradient microstructure, consisting of surface nano-grained,nano-laminated, nano-twined, and severely deformed layers, which resulted in a reduced gradient in micro-hardness from 6.95 GPa(topmost surface) to 2.77 GPa(coarse-grained matrix). The nano-grained layer resulted from the formation of high-density nano-twins and subsequent interaction between nano-twins and dislocations. The width and depth of the wear scar, wear loss volume, and wear rate of the SMGT-treated sample were smaller than those of untreated coarse-grained sample. Moreover, the wear mechanisms for both samples were mainly abrasive wear and adhesive wear, accompanied with mild oxidation wear. The notable wear resistance enhancement of the GNS Inconel 625 alloy was attributed to the high micro-hardness, high residual compressive stress, and high strain capacity of the GNS surface layer.
基金Iranian Nanotechnology Initiative (INI) for finical support of the research work
文摘The corrosion, corrosive wear and dry sliding wear of nanocomposites, are extremely complicated and involve various chemical, physical anbd mechanical factors. The aim of this work is to investigate the effects of nanosized SiC content on the hardness, dry sliding wear, corrosion and corrosive wear of Al/SiC nanocomposites synthesized by mechanical milling cold pressing and hot extrusion. The corrosion resistance of these composites in 3%NaCl solution was investigated by electrochemical polarization testing and their dry sliding as well as corrosive wear resistance in the same solution was evaluated using a pin-on-disc tester. The microstructures of the samples and their worn surfaces were examined using scanning electron microscopy. It was shown that the dry sliding wear and corrosion resistance of these nanocomposites were improved with the increase of SiC content. It was concluded that due to the lubrication effect of the solution, both the friction coefficient and frictional heat that might soften the material were reduced. In addition, the improved strength of the nanocomposites combined with their better corrosion resistance contributed to their increased corrosive wear resistance, compared with the base alloy. The prominent wear mechanism in the unreinforced alloy was adhesive wear, in the Al/SiC nanocomposites, the wear mechanism changed to abrasive.
文摘Since the wear problems play a crucial role in the relatively moving systems, in this paper, the effect of counter-face roughness on the wear of extruded PTFE (polytetrafluoroethylene) which is a very common material for sliding bearing applications has been investigated to contribute related literature. PTFE is well-known for its exceptional tribological properties, and good toughness, and high thermal stability. It can also be used in dry sliding applications. PTFE is commonly used to reduce friction between relatively moving surfaces, lts wear rate can be reduced by adding micro or nano-sized fillers such as Al2O3, TiO2, SiO2, MoS2, Al, Pb, ZnO, Cu, ZrO2, Ni, CNF (carbon nano fiber), carbon fiber, glass fiber, bronze, and graphite powder into the PTFE. In this study, an experimental research was carried out for filled and unfilled PTFE to compare their behaviors under different speeds and loads. Test materials were unfilled PTFE, PTFE + wt. 5% Al2O3, PTFE + wt. 15% Al2O3. Formation of transfer film was examined in dry sliding condition against stainless steel counter faces. All tribological tests were carried out in a commercially available tribo-tester sliding against AISI-416 C stainless steel. As a result of a series of systematic experiments, remarkable results have been obtained to make a distinctive comparison between unfilled and filled PTFE. The variation of friction coefficient with sliding distance during the tests has also been recorded. At the end of the tests, wear rate of related PTFE specimen was calculated based on measured data. Wear rate is found very high for unfilled PTFE, however, the lowest wear rate is recorded for PTFE + wt. 15% Al2O3 as expected. The coefficient of friction remained approximately stable during the wear tests. Transfer films were inspected by observing the discs' surface with optical microscope.
基金supported by the National Natural Science Foundation of China(Grant No.51171212)Chongqing Science and Technology Commission(Grant Nos.CSTC2012JJJQ50001,CSTC2013jcyj C60001&cstc2012gg B50003)+2 种基金the National Science and Technology Program of China(Grant No.2013DFA71070)the Fundamental Research Funds for the Central Universities(Grant No.CDJZR13138801)the Fundamental Research Funds for the Yangtze Normal University(Grant No.CJSF2010C025)
文摘The tribological properties of combinative addition of nano-MoS2 and nano-SiO2 to the base oil have been investigated with a reciprocating ball-on-plate tribotester for magnesium alloy-steel contacts. The results demonstrate that the optimum mass ratio of nano-SiO2 to nano-MoS2 is 0.25:0.75. The optimum combinative addition into the base oil reduces the friction coefficient by 43.8% and the surface roughness (Sa) by 31.7% when compared to that found with the base oil. Meanwhile, the combinative addition of nano-MoS2 and nano-SiO〉 in comparison with single nanoparticles addition, is more pronounced in terms of the lubrication film stability. The excellent tribological properties of the SiO2/MoS2 combinations are attributed to the formation of physical adsorption films and tribochemical products during the rubbing process and the micro-cooperation of various nano- particles with different shapes and lubrication mechanisms.
基金supported by the National Natural Science Foundation of China (Grant No. 50975288)the National Basic Research Program of China ("973" Program) (Grant No. 2007CB607604)
文摘The ultrathin polyelectrolyte molecular deposition films and polyelectrolyte composite nanoparticles molecular deposition films were prepared using layer-by-layer molecular deposition method and in situ growth method.A micro-tribometer has been developed to measure the shear response of those ultrathin molecular deposition films.By using a smooth steel sphere in a ball-on-flat configuration,the shear force was determined for molecular deposition films on glass substrate for different layers.The results indicate that the shear behaviors of molecular deposition film were mainly determined with the contact area and film layers.Moreover,the composite molecular deposition film with nanoparticles has better shear behaviors than the polyelectrolyte molecular deposition film.The shear force of polyelectrolyte molecular deposition film is more dependent on the speed than that of composite nanoparticle molecular deposition film.