The influence of Si on the stability of TiC in Al melts was studied.It is found that TiC particles in Al melts become unstable with the addition of Si.When the melting temperature is below 890 °C,TiC will react w...The influence of Si on the stability of TiC in Al melts was studied.It is found that TiC particles in Al melts become unstable with the addition of Si.When the melting temperature is below 890 °C,TiC will react with Al and Si to form TiAlxSiy and Al4C3 phases.But if the melt temperature is above 890 ℃,TiC will react with Al and Si to form to Ti3SiC2 and Al4C3.It is considered that the influence of Si on the stability of TiC in Al melts is due to its incursion into TiC crystal lattice during the holding,which will cause serious lattice distortion in TiC and then speed up the out-diffusion of surrounded C atoms.展开更多
A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R...A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. <展开更多
The mechanical properties of the SiC fiber-reinforced Mg-Al metal matrix composite materials have been studied on internal microstructure by (scanning electron microscopy) SEM in-situ tensile test. The emergence and p...The mechanical properties of the SiC fiber-reinforced Mg-Al metal matrix composite materials have been studied on internal microstructure by (scanning electron microscopy) SEM in-situ tensile test. The emergence and propagation of the crack, and the fracture behavior in materials have been observed and studied. It is found that in the case of the tensile test, the crack emerged in SiC fiber initially. In the case of the strong cohesion of the fiber-metal interface, the crack propagated in the fiber, meanwhile the fibers in the neighborhood of the cracked fiber began to crack and the Mg-Al metal deformed plastically, and at last the material fractured. Otherwise the toughness of the materials grows in the case of the lower cohesion of the fiber-metal matrix interface.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
Two types of composites were prepared with Al-4.5Cu alloy as a matrix using stir casting method.One was reinforced with 10wt.%of Si C and 2wt.%of MoS2.The other was reinforced with 10wt.%of Si C and 4wt.%of MoS2.Their...Two types of composites were prepared with Al-4.5Cu alloy as a matrix using stir casting method.One was reinforced with 10wt.%of Si C and 2wt.%of MoS2.The other was reinforced with 10wt.%of Si C and 4wt.%of MoS2.Their surfaces were remelted using a CO2 laser beam with an objective to study the influence of laser surface melting(LSM).The topography,microhardness,corrosion resistance and wear resistance of the laser melted surfaces were studied.Overall surface integrity after LSM was compared with as-cast surface.LSM enhanced the microhardness and wear resistance of the surface in each case.Porosity of the laser melted surface was low and corrosion resistance was high.Thus,LSM can be conveniently applied to enhancing the surface integrity of the aluminium composites.However,there is an optimum laser specific energy,around 38 J/m^2 in this study,for obtaining the best surface integrity.展开更多
Theductility and hardness of AA6011/SiCp composites using NaCl, SnCl2, NH4Cl and PdCl2 as wetting reagents were investigated. SiCp was cleaned with the wetting reagents, and used as reinforcement in AA6011 alloy using...Theductility and hardness of AA6011/SiCp composites using NaCl, SnCl2, NH4Cl and PdCl2 as wetting reagents were investigated. SiCp was cleaned with the wetting reagents, and used as reinforcement in AA6011 alloy using the stir casting method. Ductility and hardness responses of the composites were measured using standard methods. Microstructural features were examined using scanning electron microscopy and the phases were determined with the help of an X-ray diffractometer. The results show that for all wetting agents, the increase in cleaning time leads to initial increase in ductility to a certain value, but a decrease afterwards with further increase in cleaning time. The best combination of hardness （BHN 57.88） and ductility （11.91%） was shown under conditions of 40 g/L SnCl2and cleaning time of 60 min. A minor formation of Al4C3was noted in diffraction patterns, indicating that the formation of deleterious precipitate was hindered by the cleaning process.展开更多
The influences of SiC content on the microstructure, porosity, hardness and wear resistance of A356？SiCp composites processed via two different methods of compocasting and vibrating cooling slope （VCS） were compare...The influences of SiC content on the microstructure, porosity, hardness and wear resistance of A356？SiCp composites processed via two different methods of compocasting and vibrating cooling slope （VCS） were compared with each other. In the as-cast condition, the matrix of VCS and compocast processed composites exhibited globular and dendritric structures, respectively. While a more uniform distribution of SiC particulates in the matrix alloy as well as higher hardness values were obtained for the VCS processed samples, the composites produced via compocasting exhibited less porosity. The increased SiC content （up to 20% in volume fraction） resulted in a more uniform distribution of SiC particles within the matrix alloy and improved wear resistance for both the composite series. However, for the VCS processed composites, the increased SiC content, resulted in the decreased size and shape factor of globules as well as better tribological properties when compared with compocast composites. It was concluded that the improved properties of the VCS processed composites when compared with their compocast counterparts was a consequence of a more uniform distribution of SiC particulates in the matrix alloy as well as the globular microstructure generated during the VCS process.展开更多
The rheological behavior and gelcasting of composite suspensions of SiC and synthesized Al 2O 3-Y 2O 3-La 2O 3 powder as sintering aid were investigated. It was found that the rheological behavior of SiC particles cou...The rheological behavior and gelcasting of composite suspensions of SiC and synthesized Al 2O 3-Y 2O 3-La 2O 3 powder as sintering aid were investigated. It was found that the rheological behavior of SiC particles could be modified with a slightly oxidized surface that was similar to silica in colloidal behavior. The smaller the particles were, the more similar to silica the SiC powder was. The pH value of Al 2O 3-Y 2O 3-La 2O 3 synthesized powder slurry at isoelectric points (IEP) is higher than that of SiC powder. The dispersant PAA-NH 4 changes the IEP of both SiC and Al 2O 3-Y 2O 3-La 2O 3 powder slurry to higher pH values. The experimental results indicate that the composite suspension could possess satisfactory stability and lower viscosity at pH =10.1 and PAA-NH 4 as dispersant. The optimum solid loading was 550 0 in volume. Machinable green bodies with uniform complex shape are gained after molding.展开更多
In this paper the corrosion characteristics of Silicon carbide particulate-reinforced 6061 aluminum composite （ 6061 AI/SiCp composite ） and the base alloy are experimentally assessed. The corrosion tests are carrie...In this paper the corrosion characteristics of Silicon carbide particulate-reinforced 6061 aluminum composite （ 6061 AI/SiCp composite ） and the base alloy are experimentally assessed. The corrosion tests are carried out at different temperatures in the concentration range of 0.01N to 1N sulphuric acid as corrosion media using Tafel extrapolation technique and Electrochemical Impedance Spectroscopy （EIS）. The results obtained from Tafel extrapolation technique and Electrochemical Impedance Spectroscopy are in good agreement. The results show an increase in the corrosion rate with increase in temperature as well as with increase in the concentration of the corrosion media. The thermodynamic parameters like energy of activation are calculated using Arrhenius theory equation and, enthalpy of activation and entropy of activation are calculated using transition state theory equation.展开更多
A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other...A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains,Al2O3 grains,as well as Al2O3 long and short fibres which were also aligned normally to the grinding wheel surface,respectively.The main research contents concern grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal volume,wheel-wear rates,integrity of the ground surfaces,grinding ratios and grinding efficiency.Furthermore,grinding wheels of whiskers and fibres have a common disadvantage:they tend to load easily.The authors have proposed a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.展开更多
基金Project(50625101) supported by the National Natural Science Fund for Distinguished Young Scholars,China Project(51071097) supported by the National Natural Science Foundation of ChinaProject(11QG67) supported by the Fundamental Research Funds for the Central Universities,China
文摘The influence of Si on the stability of TiC in Al melts was studied.It is found that TiC particles in Al melts become unstable with the addition of Si.When the melting temperature is below 890 °C,TiC will react with Al and Si to form TiAlxSiy and Al4C3 phases.But if the melt temperature is above 890 ℃,TiC will react with Al and Si to form to Ti3SiC2 and Al4C3.It is considered that the influence of Si on the stability of TiC in Al melts is due to its incursion into TiC crystal lattice during the holding,which will cause serious lattice distortion in TiC and then speed up the out-diffusion of surrounded C atoms.
文摘A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. <
文摘The mechanical properties of the SiC fiber-reinforced Mg-Al metal matrix composite materials have been studied on internal microstructure by (scanning electron microscopy) SEM in-situ tensile test. The emergence and propagation of the crack, and the fracture behavior in materials have been observed and studied. It is found that in the case of the tensile test, the crack emerged in SiC fiber initially. In the case of the strong cohesion of the fiber-metal interface, the crack propagated in the fiber, meanwhile the fibers in the neighborhood of the cracked fiber began to crack and the Mg-Al metal deformed plastically, and at last the material fractured. Otherwise the toughness of the materials grows in the case of the lower cohesion of the fiber-metal matrix interface.
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Two types of composites were prepared with Al-4.5Cu alloy as a matrix using stir casting method.One was reinforced with 10wt.%of Si C and 2wt.%of MoS2.The other was reinforced with 10wt.%of Si C and 4wt.%of MoS2.Their surfaces were remelted using a CO2 laser beam with an objective to study the influence of laser surface melting(LSM).The topography,microhardness,corrosion resistance and wear resistance of the laser melted surfaces were studied.Overall surface integrity after LSM was compared with as-cast surface.LSM enhanced the microhardness and wear resistance of the surface in each case.Porosity of the laser melted surface was low and corrosion resistance was high.Thus,LSM can be conveniently applied to enhancing the surface integrity of the aluminium composites.However,there is an optimum laser specific energy,around 38 J/m^2 in this study,for obtaining the best surface integrity.
基金the University of Lagos, Nigeria, for providing the platform for the Tetfund Research Grant (CRC/ TETFUND/No.2011/2013) used for this research
文摘Theductility and hardness of AA6011/SiCp composites using NaCl, SnCl2, NH4Cl and PdCl2 as wetting reagents were investigated. SiCp was cleaned with the wetting reagents, and used as reinforcement in AA6011 alloy using the stir casting method. Ductility and hardness responses of the composites were measured using standard methods. Microstructural features were examined using scanning electron microscopy and the phases were determined with the help of an X-ray diffractometer. The results show that for all wetting agents, the increase in cleaning time leads to initial increase in ductility to a certain value, but a decrease afterwards with further increase in cleaning time. The best combination of hardness （BHN 57.88） and ductility （11.91%） was shown under conditions of 40 g/L SnCl2and cleaning time of 60 min. A minor formation of Al4C3was noted in diffraction patterns, indicating that the formation of deleterious precipitate was hindered by the cleaning process.
文摘The influences of SiC content on the microstructure, porosity, hardness and wear resistance of A356？SiCp composites processed via two different methods of compocasting and vibrating cooling slope （VCS） were compared with each other. In the as-cast condition, the matrix of VCS and compocast processed composites exhibited globular and dendritric structures, respectively. While a more uniform distribution of SiC particulates in the matrix alloy as well as higher hardness values were obtained for the VCS processed samples, the composites produced via compocasting exhibited less porosity. The increased SiC content （up to 20% in volume fraction） resulted in a more uniform distribution of SiC particles within the matrix alloy and improved wear resistance for both the composite series. However, for the VCS processed composites, the increased SiC content, resulted in the decreased size and shape factor of globules as well as better tribological properties when compared with compocast composites. It was concluded that the improved properties of the VCS processed composites when compared with their compocast counterparts was a consequence of a more uniform distribution of SiC particulates in the matrix alloy as well as the globular microstructure generated during the VCS process.
文摘The rheological behavior and gelcasting of composite suspensions of SiC and synthesized Al 2O 3-Y 2O 3-La 2O 3 powder as sintering aid were investigated. It was found that the rheological behavior of SiC particles could be modified with a slightly oxidized surface that was similar to silica in colloidal behavior. The smaller the particles were, the more similar to silica the SiC powder was. The pH value of Al 2O 3-Y 2O 3-La 2O 3 synthesized powder slurry at isoelectric points (IEP) is higher than that of SiC powder. The dispersant PAA-NH 4 changes the IEP of both SiC and Al 2O 3-Y 2O 3-La 2O 3 powder slurry to higher pH values. The experimental results indicate that the composite suspension could possess satisfactory stability and lower viscosity at pH =10.1 and PAA-NH 4 as dispersant. The optimum solid loading was 550 0 in volume. Machinable green bodies with uniform complex shape are gained after molding.
文摘In this paper the corrosion characteristics of Silicon carbide particulate-reinforced 6061 aluminum composite （ 6061 AI/SiCp composite ） and the base alloy are experimentally assessed. The corrosion tests are carried out at different temperatures in the concentration range of 0.01N to 1N sulphuric acid as corrosion media using Tafel extrapolation technique and Electrochemical Impedance Spectroscopy （EIS）. The results obtained from Tafel extrapolation technique and Electrochemical Impedance Spectroscopy are in good agreement. The results show an increase in the corrosion rate with increase in temperature as well as with increase in the concentration of the corrosion media. The thermodynamic parameters like energy of activation are calculated using Arrhenius theory equation and, enthalpy of activation and entropy of activation are calculated using transition state theory equation.
文摘A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains,Al2O3 grains,as well as Al2O3 long and short fibres which were also aligned normally to the grinding wheel surface,respectively.The main research contents concern grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal volume,wheel-wear rates,integrity of the ground surfaces,grinding ratios and grinding efficiency.Furthermore,grinding wheels of whiskers and fibres have a common disadvantage:they tend to load easily.The authors have proposed a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.
