We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surf...We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.展开更多
To investigate the ballistic performance and damage characteristics of quasi threedimensional（3D） needle-punched Cf/SiC composites prepared by chemical vapor infiltration（CVI）,penetration experiments were conducte...To investigate the ballistic performance and damage characteristics of quasi threedimensional（3D） needle-punched Cf/SiC composites prepared by chemical vapor infiltration（CVI）,penetration experiments were conducted by using 7.62 mm armor piercing incendiary（API）.Macro and micro fracture morphologies were then observed on recycled targets.The results show that the protection coefficient of 3D Cf/SiC composites is 2.54.High porosity and many micro thermal stress cracks may directly lead to the lower ballistic performance.Flat fracture morphology was observed on the crater surface.The low dynamic fracture strength along layer direction may be attributed to the voids and microcracks caused by residual thermal stress.The damage characteristics of Cf/Si C composites include matrix cracking,fiber bundle cracking,interfacial debonding,fiber fracture,and fiber bundle pull-out.And interfacial debonding and fiber fracture may play major roles in energy absorption.展开更多
Carbon fibers （CFs） were surface treated with air-oxidation, rare earths （RE） after air-oxidation, and rare earths, respectively. Erichsen test was conducted to study the interfacial adhesion of PTFE composites fi...Carbon fibers （CFs） were surface treated with air-oxidation, rare earths （RE） after air-oxidation, and rare earths, respectively. Erichsen test was conducted to study the interfacial adhesion of PTFE composites filled with carbon fibers treated with different treatment methods. Tribological properties of the PTFE composites, sliding against GCr15 steel under water-lubricated condition, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the composites were examined using scanning electron microscopy. Experimental results reveal that RE treatment is superior to air oxidation in promoting tribological properties of CF reinforced PTFE （CF/PTFE） composite. The friction and wear properties of PTFE composite filled with RE treated CF are the best of the PTFE composites. RE treatment is more effective than air oxidation to improve the tribological properties of CF/PTFE composite owing to the effective improvement of interfacial adhesion between carbon fibers and PTFE matrix.展开更多
The effect of rare earths （RE） surface treatment of carbon fibers （CF） on tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites under oil-lubricated condition was investigated. Exper...The effect of rare earths （RE） surface treatment of carbon fibers （CF） on tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites under oil-lubricated condition was investigated. Experimental results revealed that RE treated CF reinforced PTFE （CF/PTFE） composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air-oxidated composites. X-ray photoelectron spectroscopy （XPS） study of carbon fiber surface showed that, after RE treatment, oxygen concentration increased obviously, and the amount of oxygen-containing groups on CF surfaces were largely increased. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with VITE matrix, and large scale rubbing-off of PTFE be prevented, therefore, tribological properties of the composite was improved.展开更多
Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstrueture was investigated by XRD, SEM and EDS. The arc eros...Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstrueture was investigated by XRD, SEM and EDS. The arc erosion rate of Cf/Cu composite was investigated in vacuum. The results showed that the Ti and Cr could improve the wettability between Cu and C/C preform and the infiltration ability of Cu into C/ C preform greatly. A TiC interface formed between the fibers and matrix. The good bonding between the fiber and matrix guaranteed that part of the Cu matrix can still be bonded on the fibers even when the material was exposed to the plasma. Consequently, the carbon fibers were protected from the erosion. In comparison, Cu was completely consumed by the arc erosion. Hence, the graphite was eroded and presented a cauliflower-like morphology. Therefore, the prepared C/Cu bad better ability to resist the arc erosion, compared with common Cu-C material.展开更多
The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge...The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge-like coatings were found by scanning electro microscope (SEM) observations, and the Al matrix and carbon fibre reinforcement were both coated with Ce conversion coatings, with some minor cracks. The energy dispersive spectroscopy (EDS) plane scan analysis indicates that the major elements in the coating are Ce, O, Si, Al and the Ce content reaches 47.48%(mass fraction). The Ce conversion coatings increase the corrosion resisting properties of Cf/6061Al composite, with a higher free corrosion potential (Ecorr) and a lower free corrosion current density (icorr) for the coated composite than those of the bare composite. And the Boehmite-treatment would enhance the corrosion resistance of the REM conversion coating. The cathodic polarization and anodic polarization were retarded by REM conversion coating, resulting in an improved corrosion resistance.展开更多
Vacuum brazing experiments of Cf/C composites were carried out using pure Al and Al-5 Ti-B as brazing fillers , and shearing strength of the joints was measured. The microstructures of the brazed joints were studied b...Vacuum brazing experiments of Cf/C composites were carried out using pure Al and Al-5 Ti-B as brazing fillers , and shearing strength of the joints was measured. The microstructures of the brazed joints were studied by means of scanning electron microscopy （SEM） and energy dispersive X-ray spectrometer. The results indicate that the brazing temperature is the important processing parameter affecting the quality of the brazed joints. Vacuum brazing of Cf/C composites can be achieved employing the pure Al and AI-S Ti-B brazing fillers at a brazing temperature of 730 ℃ or 750 ℃ , respectively. Moreover, the joints have excellent microstructures with shear strength reaching the level of practical applications.展开更多
The precise microscopic feature of carbon-carbon(C/C)composites is essential for an accurate prediction of their mechanical behavior.After fabrication,actual microscopic feature differs from simple ideal spatial model...The precise microscopic feature of carbon-carbon(C/C)composites is essential for an accurate prediction of their mechanical behavior.After fabrication,actual microscopic feature differs from simple ideal spatial model.Micro-computed-tomography(CT)scan can well describe internal microstructures of composites.Therefore,a reconstructed model is developed based on mirco-CT,by a series of prodcedures including extracting components,generating new binary images and establishing a finite element(FE)model.Compared with the model designed by reconstructed commercial software MIMICS,the presented reconstructed FE model is superior in terms of high mesh quality and controllable mesh quantity.The precision of the model is verified by experiment.展开更多
The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coati...The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coatings on corrosion behaviors of composites was investigated by electrochemical polarization technology and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The higher Ecorr and lower icorr were obtained by Ce conversion coatings. EIS results showed that the higher values of R2 were obtained by treatment containing CeCl3, the high corrosion resistance occured in treatment containing CeCl3, the low corrosion resistance in uncoating sample, the coating of treatment containing Ce(NO3)3 was medium. The microstructure of Ce conversion coatings was observed by scanning electron microscopy (SEM), and the elements of corresponding for coatings was characterized by energy dispersive spectrometer (EDS). The micro-cracks and Ce-riched spherical particles were characteristics of these coatings.展开更多
Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing （PP-HP） and precursor impregnation-pyrolysis （PIP）, respectively. The effect of fabrication methods on the microstructure an...Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing （PP-HP） and precursor impregnation-pyrolysis （PIP）, respectively. The effect of fabrication methods on the microstructure and mechanical properties of the composites was investigated. It was found that the composite prepared by PP-HP exhibits a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface and the degradation of the fibers caused by a higher processing temperature. On the contrary, the composite prepared by PIP shows a tough fracture behavior, which could be rationalized on the basis of a weakly bonded fiber/matrix interface as well as a higher strength retention of the fibers. As a result, in comparison with the composite prepared by PP-HP, the composite prepared by PIP achieves better mechanical properties with a flexural strength of 573.4 MPa and a fracture toughness of 17.2 MPa.m^1/2.展开更多
The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd：YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy （CF-LIBS）. ...The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd：YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy （CF-LIBS）. The composition change in AZ31 magnesium alloy under different laser pulse width was also investigated. The experimental results showed that CF-LIBS can obtain satisfactory quantitative or semi-quantitative results for matrix or major elements, while only qualitative analysis was possible for minor or trace elements. Moreover, it is found that the chemical composition of molten metal will change after laser processing. The concentration of magnesium in molten metal is lower than that present in the base metal. The Mg loss increases with an increase of pulse width in the laser processing. This result shows that the selective vaporization of different elements is affected by the pulse width during laser processing.展开更多
基金Supported by Innovation and Technology Fund (No.ITP/045/19AP)Commercial Research&Development (CRD) Funding Supported by Hong Kong Productivity Council (No.10008787)。
文摘We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.
基金Funded by the National Natural Science Foundation of China(No.51271036)
文摘To investigate the ballistic performance and damage characteristics of quasi threedimensional（3D） needle-punched Cf/SiC composites prepared by chemical vapor infiltration（CVI）,penetration experiments were conducted by using 7.62 mm armor piercing incendiary（API）.Macro and micro fracture morphologies were then observed on recycled targets.The results show that the protection coefficient of 3D Cf/SiC composites is 2.54.High porosity and many micro thermal stress cracks may directly lead to the lower ballistic performance.Flat fracture morphology was observed on the crater surface.The low dynamic fracture strength along layer direction may be attributed to the voids and microcracks caused by residual thermal stress.The damage characteristics of Cf/Si C composites include matrix cracking,fiber bundle cracking,interfacial debonding,fiber fracture,and fiber bundle pull-out.And interfacial debonding and fiber fracture may play major roles in energy absorption.
基金Project supported bythe National Natural Science Foundation of China (50275093)
文摘Carbon fibers （CFs） were surface treated with air-oxidation, rare earths （RE） after air-oxidation, and rare earths, respectively. Erichsen test was conducted to study the interfacial adhesion of PTFE composites filled with carbon fibers treated with different treatment methods. Tribological properties of the PTFE composites, sliding against GCr15 steel under water-lubricated condition, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the composites were examined using scanning electron microscopy. Experimental results reveal that RE treatment is superior to air oxidation in promoting tribological properties of CF reinforced PTFE （CF/PTFE） composite. The friction and wear properties of PTFE composite filled with RE treated CF are the best of the PTFE composites. RE treatment is more effective than air oxidation to improve the tribological properties of CF/PTFE composite owing to the effective improvement of interfacial adhesion between carbon fibers and PTFE matrix.
基金the National Natural Science Foundation of China (50275093)
文摘The effect of rare earths （RE） surface treatment of carbon fibers （CF） on tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites under oil-lubricated condition was investigated. Experimental results revealed that RE treated CF reinforced PTFE （CF/PTFE） composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air-oxidated composites. X-ray photoelectron spectroscopy （XPS） study of carbon fiber surface showed that, after RE treatment, oxygen concentration increased obviously, and the amount of oxygen-containing groups on CF surfaces were largely increased. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with VITE matrix, and large scale rubbing-off of PTFE be prevented, therefore, tribological properties of the composite was improved.
基金Funded by the National Natural Science Foundation of China(No.51002121)Postgraduate Technology Innovation Project of Taiyuan University of Science and Technology(No.20134008)
文摘Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstrueture was investigated by XRD, SEM and EDS. The arc erosion rate of Cf/Cu composite was investigated in vacuum. The results showed that the Ti and Cr could improve the wettability between Cu and C/C preform and the infiltration ability of Cu into C/ C preform greatly. A TiC interface formed between the fibers and matrix. The good bonding between the fiber and matrix guaranteed that part of the Cu matrix can still be bonded on the fibers even when the material was exposed to the plasma. Consequently, the carbon fibers were protected from the erosion. In comparison, Cu was completely consumed by the arc erosion. Hence, the graphite was eroded and presented a cauliflower-like morphology. Therefore, the prepared C/Cu bad better ability to resist the arc erosion, compared with common Cu-C material.
文摘The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge-like coatings were found by scanning electro microscope (SEM) observations, and the Al matrix and carbon fibre reinforcement were both coated with Ce conversion coatings, with some minor cracks. The energy dispersive spectroscopy (EDS) plane scan analysis indicates that the major elements in the coating are Ce, O, Si, Al and the Ce content reaches 47.48%(mass fraction). The Ce conversion coatings increase the corrosion resisting properties of Cf/6061Al composite, with a higher free corrosion potential (Ecorr) and a lower free corrosion current density (icorr) for the coated composite than those of the bare composite. And the Boehmite-treatment would enhance the corrosion resistance of the REM conversion coating. The cathodic polarization and anodic polarization were retarded by REM conversion coating, resulting in an improved corrosion resistance.
文摘Vacuum brazing experiments of Cf/C composites were carried out using pure Al and Al-5 Ti-B as brazing fillers , and shearing strength of the joints was measured. The microstructures of the brazed joints were studied by means of scanning electron microscopy （SEM） and energy dispersive X-ray spectrometer. The results indicate that the brazing temperature is the important processing parameter affecting the quality of the brazed joints. Vacuum brazing of Cf/C composites can be achieved employing the pure Al and AI-S Ti-B brazing fillers at a brazing temperature of 730 ℃ or 750 ℃ , respectively. Moreover, the joints have excellent microstructures with shear strength reaching the level of practical applications.
基金supported by the National Natural Science Foundation of China (Nos.11272147,10772078)the Aviation Science Foundation (No.2013ZF52074)+1 种基金the State Key Laboratory of Mechanical Structural Mechanics and Control (No.0214G02)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The precise microscopic feature of carbon-carbon(C/C)composites is essential for an accurate prediction of their mechanical behavior.After fabrication,actual microscopic feature differs from simple ideal spatial model.Micro-computed-tomography(CT)scan can well describe internal microstructures of composites.Therefore,a reconstructed model is developed based on mirco-CT,by a series of prodcedures including extracting components,generating new binary images and establishing a finite element(FE)model.Compared with the model designed by reconstructed commercial software MIMICS,the presented reconstructed FE model is superior in terms of high mesh quality and controllable mesh quantity.The precision of the model is verified by experiment.
文摘The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coatings on corrosion behaviors of composites was investigated by electrochemical polarization technology and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The higher Ecorr and lower icorr were obtained by Ce conversion coatings. EIS results showed that the higher values of R2 were obtained by treatment containing CeCl3, the high corrosion resistance occured in treatment containing CeCl3, the low corrosion resistance in uncoating sample, the coating of treatment containing Ce(NO3)3 was medium. The microstructure of Ce conversion coatings was observed by scanning electron microscopy (SEM), and the elements of corresponding for coatings was characterized by energy dispersive spectrometer (EDS). The micro-cracks and Ce-riched spherical particles were characteristics of these coatings.
基金This research was financially supported by the National Natural Science Foundation of China (No. 50404012)
文摘Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing （PP-HP） and precursor impregnation-pyrolysis （PIP）, respectively. The effect of fabrication methods on the microstructure and mechanical properties of the composites was investigated. It was found that the composite prepared by PP-HP exhibits a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface and the degradation of the fibers caused by a higher processing temperature. On the contrary, the composite prepared by PIP shows a tough fracture behavior, which could be rationalized on the basis of a weakly bonded fiber/matrix interface as well as a higher strength retention of the fibers. As a result, in comparison with the composite prepared by PP-HP, the composite prepared by PIP achieves better mechanical properties with a flexural strength of 573.4 MPa and a fracture toughness of 17.2 MPa.m^1/2.
基金supported by National Natural Science Foundation of China(Nos.61405147,51375348)the Scientific Research Fund of Zhejiang Provincial Education Department,China(No.Y201430387)
文摘The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd：YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy （CF-LIBS）. The composition change in AZ31 magnesium alloy under different laser pulse width was also investigated. The experimental results showed that CF-LIBS can obtain satisfactory quantitative or semi-quantitative results for matrix or major elements, while only qualitative analysis was possible for minor or trace elements. Moreover, it is found that the chemical composition of molten metal will change after laser processing. The concentration of magnesium in molten metal is lower than that present in the base metal. The Mg loss increases with an increase of pulse width in the laser processing. This result shows that the selective vaporization of different elements is affected by the pulse width during laser processing.
