Two types of titanium/steel composite plates with the same thickness were manufactured by parallel explosive welding and double vertical explosive welding and rolling, respectively. The comparative analysis of microst...Two types of titanium/steel composite plates with the same thickness were manufactured by parallel explosive welding and double vertical explosive welding and rolling, respectively. The comparative analysis of microstructure showed that the interface of double vertical explosive welding plate （B plate） tended to be straight while the interface of parallel explosive welding plate （A plate） was wavy bonding. Defects near the interface of B plate were extruded, and the thickness of the diffusion layer of B plate was thicker under the effects of preheating temperature and press-working. Comparative tests of mechanical properties indicated that the tensile shear strength of B plate was lower while its micro-hardness was higher. Specimens of these two types of plates were neither separated nor cracked after bending up to 180° in the three-point bending test. From the microstructural observation of tensile fracture characteristics, A plate had strong toughness fracture while B plate had mainly ductile fracture with cleavage fracture as the supplement. Macroscopically, the tensile strength of the latter was 7.9% less than that of the former. However, both satisfied the Chinese standard of tensile strength.展开更多
A multilayer tungsten carbide particle（WCp）-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology.The morphology,microstructure,and formation mechanism of the coating...A multilayer tungsten carbide particle（WCp）-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology.The morphology,microstructure,and formation mechanism of the coating were studied and discussed in different zones.The microstructure morphology and phase composition were investigated by scanning electron microscopy,optical microscopy,X-ray diffraction,and energy-dispersive X-ray spectroscopy.In the results,the coating presents a dense and homogeneous microstructure with few pores and is free from cracks.The whole coating shows a multilayer structure,including composite,transition,fusion,and diffusion-affected layers.Metallurgical bonding was achieved between the coating and substrate because of the formation of the fusion and diffusion-affected layers.The Ni-based alloy is mainly composed of y-Ni solid solution with finely dispersed Cr7C3/Cr（23）C6,CrB,and Ni＋Ni3Si.WC particles in the composite layer distribute evenly in areas among initial Ni-based alloying particles,forming a special three-dimensional reticular microstructure.The macrohardness of the coating is HRC 55,which is remarkably improved compared to that of the substrate.The microhardness increases gradually from the substrate to the composite zone,whereas the microhardness remains almost unchanged in the transition and composite zones.展开更多
An approach named direct reaction synthesis (DRS) has been developed to fabricate particulate composites with an extremely fine reinforcement size. ID situ Al matrix composites were fabri-cated by DRS. Extensive analy...An approach named direct reaction synthesis (DRS) has been developed to fabricate particulate composites with an extremely fine reinforcement size. ID situ Al matrix composites were fabri-cated by DRS. Extensive analysis of the composites microstructure using SEM and TEM identify that the reinforcement formed during the DRS process is Ti carbide (TiC) particle, generally less than 1.0 μm. The reacted, semisolid extruded samples exhibit a homogeneous distribution of fine TiC particles in Al-Cu matrix, Mechanical property evaluation of the composites has revealed a very high tensile strength relative to the matrix alloy. Fractographic analysis indicates ductile failure although the ductility and strength are limited by the presence of coarse titanium aluminides (Al3Ti).展开更多
The synthesis and characterization of a new class of cementitious composites filled with polymer emulsions were investigated, and their superior mechanical strength and durability properties compared to composites dev...The synthesis and characterization of a new class of cementitious composites filled with polymer emulsions were investigated, and their superior mechanical strength and durability properties compared to composites devoid of fi llers were reported. Polymer emulsions were utilized to mechanically reinforce the composite and bridge the cement, fly ash, aggregate and fibers. The results reveal that the epoxy emulsion and poly（ethylene-co-vinyl acetate） emulsion markedly enhance the mechanical and durability properties of cemetitious composites. The fi bers can be pulled out in the form of slip-hardening and the abrasion phenomenon can be observed clearly on the surface of the fibers. The hydration extent of cement is higher than that of the pristine composites. The polymer modified cementitious composites designed on micromechanics, have fl exibility and plasticity which could be applied for a novel form of multifunctional materials with a range of pipeline coatings applications.展开更多
2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between ...2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon（Py C） coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition（CVD）. Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_（17）Al_（12） precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.展开更多
Ni–Al powder and Ni–Al composite coatings were fabricated by twin-wire arc spraying（TWAS）. The microstructures of Ni-5wt%Al powder and Ni-20wt%Al powder were characterized by scanning electronic microscopy（SEM） ...Ni–Al powder and Ni–Al composite coatings were fabricated by twin-wire arc spraying（TWAS）. The microstructures of Ni-5wt%Al powder and Ni-20wt%Al powder were characterized by scanning electronic microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results showed that the obtained particle size ranged from 5 to 50 μm. The morphology of the Ni–Al powder showed that molten particles were composed of Ni solid solution, NiAl, Ni_3Al, Al_2O_3, and NiO. The Ni–Al phase and a small amount of Al_2O_3 particles changed the composition of the coating. The microstructures of the twin-wire-arc-sprayed Ni–Al composite coatings were characterized by SEM, EDS, X-ray diffraction（XRD）, and transmission electron microscopy（TEM）. The results showed that the main phase of the Ni-5wt%Al coating consisted of Ni solid solution and Ni Al in addition to a small amount of Al_2O_3. The main phase of the Ni-20wt%Al coating mainly consisted of Ni solid solution, Ni Al, and Ni_3Al in addition to a small amount of Al and Al_2O_3, and Ni Al and Ni_3Al intermetallic compounds effectively further improved the final wear property of the coatings. TEM analysis indicated that fine spherical NiAl_3 precipitates and a Ni–Al–O amorphous phase formed in the matrix of the Ni solid solution in the original state.展开更多
Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the ...Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented展开更多
TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and sh...TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and short bar-shape eutectic TiC. Al content has great effects on the morphology of TiC. With the increasing of Al content, the morphology of primary TiC changes from coarse developed dendrite into short bar-shape or plate--shape TiC with 35%Al. Meanwhile, the structure of the matrix changes from single Ti to Ti and Ti3Al, and to Ti3Al and TiAl. However, the C content has no influence on the microstructure of matrix. When the C content is less than 1.2%, the dendrite TiC disappears and only short bar-shape or plate-shape TiC exists in the composites. In addition, the effect of he3t treatment on the morphology of TiC has also Studied.展开更多
KAl（7075）alloy/Mg（AZ31）alloy laminated composite plates were successfully fabricated by the equalchannelangular processing（ECAP）by using route A for 1,2,and 3 passes at 573 K,respectively.After fabrication,the 1...KAl（7075）alloy/Mg（AZ31）alloy laminated composite plates were successfully fabricated by the equalchannelangular processing（ECAP）by using route A for 1,2,and 3 passes at 573 K,respectively.After fabrication,the 1-pass ECAPed laminated composite plates were annealed at different temperatures.The microstructure evolution,phase constituent,and bonding strength near the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates were evaluated with scanning electron microscopy,X-ray diffraction,and shear tests.The experimentalresults indicated that a 20 μm diffusion layer was observed at the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates fabricated by the 1-pass ECAP,which mainly included Al_3Mg_2 and Mg_（17）Al_（12） phases.With the increase of passes,the increase of diffusion layer thickness was not obvious and the form of crack in these processes led to the decrease of bonding strength.For 1-pass ECAPed composites,the thickness of diffusion layer remained unchanged after annealed at 473 K,while the bonding strength reached its maximum value 29.12 MPa.However,after elevating heat treatment temperature to 573 K,the thickness of diffusion layer increased rapidly,and thus the bonding strength decreased.展开更多
Carbon fiber reinforced phenolic based composites were prepared by laminating molding. The variation in mechanical characteristics of composites was evaluated with heating temperature and procedure. The microstructure...Carbon fiber reinforced phenolic based composites were prepared by laminating molding. The variation in mechanical characteristics of composites was evaluated with heating temperature and procedure. The microstructures of composites at different temperatures were observed by optical microscope and scanning electron microscope, respectively. The results showed that the main weight loss range of carbon/phenolic is from 300 to 800 ℃, before 700 ℃ the weight loss was resulted from pyrolysis and after that the weight loss was mainly by oxidation in the fiber phase; with the heat treatment temperature rising, the bonding at the interface of carbon fibers and resin matrix weakened; in the pyrolysis temperature range, the interlaminar shear strength（ILSS） of carbon/phenolic showed a rapid drop with temperature rising, and then decrease in the rate of ILSS became relatively slower; the fiber oxidation had little influence on the ILSS.展开更多
With the use of Ti/Ni/Cu/Ni multiple foils as interlayer,carbon/carbon（C/C） composite was bonded to Nibased superalloy GH3044 by partial transient liquid-phase bonding technique.The effect of bonding temperature on ...With the use of Ti/Ni/Cu/Ni multiple foils as interlayer,carbon/carbon（C/C） composite was bonded to Nibased superalloy GH3044 by partial transient liquid-phase bonding technique.The effect of bonding temperature on the microstructures and strengths of the joints was investigated.The results showed that gradient structural multiple interlayers composed of ‘‘C–Ti reaction layer/Ti–Ni intermetallic compound layer/Ni–Cu sosoloid/residual Cu layer/Ni-GH3044 diffusion layer＇＇ were formed between C/C composite and GH3044.The shear strength of the C/C composite/GH3044 joint reached the highest value of 26.1 MPa when the bonding temperature was 1,030 °C.In addition,the fracture morphology showed that the fracture mode changed with the increase of bonding temperature.展开更多
To obtain the compositions and microstructure of hydration products of cementitious material in different hydration ages and its growth law of filling strength, the optimal proportion of composite cementitious materia...To obtain the compositions and microstructure of hydration products of cementitious material in different hydration ages and its growth law of filling strength, the optimal proportion of composite cementitious material was determined according to the chemical composition of cement clinker which was composed of the Portland cement 32.5R, CSA 42.5 sulphoaluminate cement and two gypsum（CS）. The characterization of composite cementitious materials in different hydration ages was conducted by NMR, XRD and SEM techniques. The mechanism of hydration was explored. It is shown that the compressive strength of the test block increases gradually with the increase of hydration age. The microstructure of composite cementitious material can be changed from Al-O octahedron into Al-O tetrahedron in the hydration process. The hydrated alkali alumi niumsilicate formed with Si-O tetrahedron and Al-O tetrahedron. The degree of polymerization of Si-O tetrahedron gradually increased, and the structural strength of cementitious materials continued to increase. The diffraction peak of clinker minerals gradually decreased with the extension of hydration age. The CaSO4 completely hydrated to produce Aft during hydration which resulted in high early strength of cementitious material. The early hydration product of composite cementitious materials was Aft with a needle bar structure. The main middle and last hydration products were CSH gel and CH gel with dense prismatic shape. The microscopic pore of composite cementitious material gradually decreased and improved the later strength of filling block. The strong support was provided for mined-out area.展开更多
A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure ...A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370℃.展开更多
Hardness of the TiB2/7075 composite increased with increasing deformation temperature. In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about 1 mum in length) and small MgZn2 phases (abo...Hardness of the TiB2/7075 composite increased with increasing deformation temperature. In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about 1 mum in length) and small MgZn2 phases (about 100 nm in size) were precipitated nearby the grain boundaries where the TiB2 particles exist. After deformation at 300 degreesC, some of the large precipitates and all the small precipitates in these area dissolved into the matrix, meanwhile, fine precipitates were formed in grains. After deformation at 450 degreesC, all the precipitates in the annealed composite dissolved into the matrix, and new phases were precipitated in grains. The dissolution of the large fiber-like precipitate makes the saturation level of the matrix increased and leads to an increased solution hardening and natural aging, which contribute much to the hardening effect.展开更多
A new,innovative vibration cast-rolling technology of “electromagnetic stirring+dendrite breaking+asynchronous rolling” was proposed with the adoption of sinusoidal vibration of crystallization roller to prepare Ti/...A new,innovative vibration cast-rolling technology of “electromagnetic stirring+dendrite breaking+asynchronous rolling” was proposed with the adoption of sinusoidal vibration of crystallization roller to prepare Ti/Al laminated composites,and the effect of sinusoidal vibration of crystallization roller on composite microstructure was investigated in detail.The results show that the metallurgical bonding of titanium and aluminum is realized by mesh interweaving and mosaic meshing,instead of transition bonding by forming metal compound layer.The meshing depth between titanium and aluminum layers (6.6μm) of cast-rolling materials with strong vibration of crystallization roller (amplitude 0.87 mm,vibration frequency 25 Hz) is doubled compared with that of traditional cast-rolling materials (3.1μm),and the composite interfacial strength(27.0 N/mm) is twice as high as that of traditional cast-rolling materials (14.9 N/mm).This is because with the action of high-speed superposition of strong tension along the rolling direction,strong pressure along the width direction and rolling force,the composite linearity evolves from "straight line" with traditional casting-rolling to "curved line",and the depth and number of cracks in the interface increases greatly compared with those with traditional cast-rolling,which leads to the deep expansion of the meshing area between interfacial layers and promotes the stable enhancement of composite quality.展开更多
Two ingots were produced by centrifugal casting at mould rotational speeds of 600 rpm and 800 rpm using 20 vol%SiC p /AlSi9Mg composite melt,respectively.The microstructure along the radial direction of cross-sectiona...Two ingots were produced by centrifugal casting at mould rotational speeds of 600 rpm and 800 rpm using 20 vol%SiC p /AlSi9Mg composite melt,respectively.The microstructure along the radial direction of cross-sectional sample of ingots was presented.SiC particles migrated towards the external circumference of the tube,and the distribution of SiC particles became uniform under centrifugal force.Voids in 20 vol%SiC p /AlSi9Mg composite melt migrated towards the inner circumference of the tube.The quantitative analysis results indicated that not only SiC particles but also primaryαphases segregated greatly in centrifugal casting resulting from the transportation behavior of constitutions with different densities in the SiC p /AlSi9Mg composite melt.In addition,the eutectic Si was broken owing to the motion of SiC p /AlSi9Mg composite melt during centrifugal casting.展开更多
Pipelines are extensively used in environments such as nuclear power plants,chemical factories,and medical devices to transport gases and liquids.These tubular environments often feature complex geometries,confined sp...Pipelines are extensively used in environments such as nuclear power plants,chemical factories,and medical devices to transport gases and liquids.These tubular environments often feature complex geometries,confined spaces,and millimeter-scale height restrictions,presenting significant challenges to conventional inspection methods.Here,we present an ultrasonic microrobot(weight,80 mg;dimensions,24 mm×7 mm;thickness,210μm)to realize agile and bidirectional navigation in narrow pipelines.The ultrathin structural design of the robot is achieved through a high-performance piezoelectric composite film microstructure based on MEMS technology.The robot exhibits various vibration modes when driven by ultrasonic frequency signals,its motion speed reaches81 cm s-1 at 54.8 k Hz,exceeding that of the fastest piezoelectric microrobots,and its forward and backward motion direction is controllable through frequency modulation,while the minimum driving voltage for initial movement can be as low as 3 VP-P.Additionally,the robot can effortlessly climb slopes up to 24.25°and carry loads more than 36 times its weight.The robot is capable of agile navigation through curved L-shaped pipes,pipes made of various materials(acrylic,stainless steel,and polyvinyl chloride),and even over water.To further demonstrate its inspection capabilities,a micro-endoscope camera is integrated into the robot,enabling real-time image capture inside glass pipes.展开更多
It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of gr...It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of grains has its own domain and dislocation structure. There are mono- and polydomains with and without dislocations. The grains of the main phase of monoand polydomains without dislocations and polydomains with dislocations were formed by diffusion in the solid phase. In these conditions NiAl3 phase is located on the grain boundary of the main phase. The Ni2Al3 phase is located at the triple joints of the main phase.展开更多
Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique.Different mixing methods were used in this study to control the distribution of Al N particles.The microstru...Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique.Different mixing methods were used in this study to control the distribution of Al N particles.The microstructure,thermal diffusivity and thermal expansion of the Mg–Al/Al N composites using different mixing methods were investigated.The results showed that the intergranular and intragranular distributions of Al N particles were obtained,respectively,by controlling the mixing methods.The composite with intragranular particles exhibited lower thermal diffusivity because of the existences of more interfaces,defects and grain boundaries,which acted as scattering centers and reduced the mean free path of electrons and phonons.The existence of Al N particles lowered the coefficient of thermal expansion（CTE）and enhanced the dimensional stability of the composites.And the use of the improved mixing method further reduced the CTE of Mg–Al/Al N composites.展开更多
The influences of Mn and Ni contents on the impact toughness and microstructure in the weld metals of high strength low alloy steels were studied. The objective of this study was to determine the optimum composition r...The influences of Mn and Ni contents on the impact toughness and microstructure in the weld metals of high strength low alloy steels were studied. The objective of this study was to determine the optimum composition ranges of Mn and Ni to develop welding consumables with better resistance to cold cracking. The results indicated that Mn and Ni had considerable effect on the microstructure of weld metal, and both Mn and Ni promoted acicular ferrite at the expense of proeutectoid ferrite and ferrite side plates. Varying Ni content influenced the Charpy impact energy, the extent of which depended on Mn content. Based on the properties and impact resistance, the optimum levels of Mn and Ni were suggested to be 0.6%—0.9%,, and 2.5%—3.5%, respectively. Additions beyond this limit promoted the formation of segregation structures and other microstructural features, which may be detrimental to weld metal toughness.展开更多
基金This project was sponsored by the National Natural Science Foundation of China （No. 51541112） and Special Fund Achievement Transformation Projects in Jiangsu of China （No. BA2012030）.
文摘Two types of titanium/steel composite plates with the same thickness were manufactured by parallel explosive welding and double vertical explosive welding and rolling, respectively. The comparative analysis of microstructure showed that the interface of double vertical explosive welding plate （B plate） tended to be straight while the interface of parallel explosive welding plate （A plate） was wavy bonding. Defects near the interface of B plate were extruded, and the thickness of the diffusion layer of B plate was thicker under the effects of preheating temperature and press-working. Comparative tests of mechanical properties indicated that the tensile shear strength of B plate was lower while its micro-hardness was higher. Specimens of these two types of plates were neither separated nor cracked after bending up to 180° in the three-point bending test. From the microstructural observation of tensile fracture characteristics, A plate had strong toughness fracture while B plate had mainly ductile fracture with cleavage fracture as the supplement. Macroscopically, the tensile strength of the latter was 7.9% less than that of the former. However, both satisfied the Chinese standard of tensile strength.
基金supported by the National Natural Science Foundation of China(No.51205178)the Natural Science Foundation of Gansu Province,China(No.1208RJZA189)the Doctor Fund Project of Lanzhou University of Technology
文摘A multilayer tungsten carbide particle（WCp）-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology.The morphology,microstructure,and formation mechanism of the coating were studied and discussed in different zones.The microstructure morphology and phase composition were investigated by scanning electron microscopy,optical microscopy,X-ray diffraction,and energy-dispersive X-ray spectroscopy.In the results,the coating presents a dense and homogeneous microstructure with few pores and is free from cracks.The whole coating shows a multilayer structure,including composite,transition,fusion,and diffusion-affected layers.Metallurgical bonding was achieved between the coating and substrate because of the formation of the fusion and diffusion-affected layers.The Ni-based alloy is mainly composed of y-Ni solid solution with finely dispersed Cr7C3/Cr（23）C6,CrB,and Ni＋Ni3Si.WC particles in the composite layer distribute evenly in areas among initial Ni-based alloying particles,forming a special three-dimensional reticular microstructure.The macrohardness of the coating is HRC 55,which is remarkably improved compared to that of the substrate.The microhardness increases gradually from the substrate to the composite zone,whereas the microhardness remains almost unchanged in the transition and composite zones.
文摘An approach named direct reaction synthesis (DRS) has been developed to fabricate particulate composites with an extremely fine reinforcement size. ID situ Al matrix composites were fabri-cated by DRS. Extensive analysis of the composites microstructure using SEM and TEM identify that the reinforcement formed during the DRS process is Ti carbide (TiC) particle, generally less than 1.0 μm. The reacted, semisolid extruded samples exhibit a homogeneous distribution of fine TiC particles in Al-Cu matrix, Mechanical property evaluation of the composites has revealed a very high tensile strength relative to the matrix alloy. Fractographic analysis indicates ductile failure although the ductility and strength are limited by the presence of coarse titanium aluminides (Al3Ti).
基金Funded by the National Natural Science Foundation of China(No.21076227)
文摘The synthesis and characterization of a new class of cementitious composites filled with polymer emulsions were investigated, and their superior mechanical strength and durability properties compared to composites devoid of fi llers were reported. Polymer emulsions were utilized to mechanically reinforce the composite and bridge the cement, fly ash, aggregate and fibers. The results reveal that the epoxy emulsion and poly（ethylene-co-vinyl acetate） emulsion markedly enhance the mechanical and durability properties of cemetitious composites. The fi bers can be pulled out in the form of slip-hardening and the abrasion phenomenon can be observed clearly on the surface of the fibers. The hydration extent of cement is higher than that of the pristine composites. The polymer modified cementitious composites designed on micromechanics, have fl exibility and plasticity which could be applied for a novel form of multifunctional materials with a range of pipeline coatings applications.
基金supported by the National Nature Science Foundation of China (Nos. 51472203, 51521061, 51575447 and 51432008)
文摘2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon（Py C） coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition（CVD）. Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_（17）Al_（12） precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.
基金financially supported by the International Cooperation Project Foundation in Science and Technology of China(No.2008DFR50070)
文摘Ni–Al powder and Ni–Al composite coatings were fabricated by twin-wire arc spraying（TWAS）. The microstructures of Ni-5wt%Al powder and Ni-20wt%Al powder were characterized by scanning electronic microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results showed that the obtained particle size ranged from 5 to 50 μm. The morphology of the Ni–Al powder showed that molten particles were composed of Ni solid solution, NiAl, Ni_3Al, Al_2O_3, and NiO. The Ni–Al phase and a small amount of Al_2O_3 particles changed the composition of the coating. The microstructures of the twin-wire-arc-sprayed Ni–Al composite coatings were characterized by SEM, EDS, X-ray diffraction（XRD）, and transmission electron microscopy（TEM）. The results showed that the main phase of the Ni-5wt%Al coating consisted of Ni solid solution and Ni Al in addition to a small amount of Al_2O_3. The main phase of the Ni-20wt%Al coating mainly consisted of Ni solid solution, Ni Al, and Ni_3Al in addition to a small amount of Al and Al_2O_3, and Ni Al and Ni_3Al intermetallic compounds effectively further improved the final wear property of the coatings. TEM analysis indicated that fine spherical NiAl_3 precipitates and a Ni–Al–O amorphous phase formed in the matrix of the Ni solid solution in the original state.
文摘Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented
文摘TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and short bar-shape eutectic TiC. Al content has great effects on the morphology of TiC. With the increasing of Al content, the morphology of primary TiC changes from coarse developed dendrite into short bar-shape or plate--shape TiC with 35%Al. Meanwhile, the structure of the matrix changes from single Ti to Ti and Ti3Al, and to Ti3Al and TiAl. However, the C content has no influence on the microstructure of matrix. When the C content is less than 1.2%, the dendrite TiC disappears and only short bar-shape or plate-shape TiC exists in the composites. In addition, the effect of he3t treatment on the morphology of TiC has also Studied.
基金Funded by the National Natural Science Foundations of China(No.51301118)the Projects of International Cooperation in Shanxi(2014081002)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2013108)
文摘KAl（7075）alloy/Mg（AZ31）alloy laminated composite plates were successfully fabricated by the equalchannelangular processing（ECAP）by using route A for 1,2,and 3 passes at 573 K,respectively.After fabrication,the 1-pass ECAPed laminated composite plates were annealed at different temperatures.The microstructure evolution,phase constituent,and bonding strength near the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates were evaluated with scanning electron microscopy,X-ray diffraction,and shear tests.The experimentalresults indicated that a 20 μm diffusion layer was observed at the joining interface of Al（7075）alloy/Mg（AZ31）alloy laminated composites plates fabricated by the 1-pass ECAP,which mainly included Al_3Mg_2 and Mg_（17）Al_（12） phases.With the increase of passes,the increase of diffusion layer thickness was not obvious and the form of crack in these processes led to the decrease of bonding strength.For 1-pass ECAPed composites,the thickness of diffusion layer remained unchanged after annealed at 473 K,while the bonding strength reached its maximum value 29.12 MPa.However,after elevating heat treatment temperature to 573 K,the thickness of diffusion layer increased rapidly,and thus the bonding strength decreased.
基金the Innovation Foundation of Postgraduate of Jiangsu Province,China(No.CX08B_134Z)Beforehand Research Fund of Defense Technology(No.404040301)The Fundamental Research Funds for the Central Universities(No.NUST2011XQTR13)
文摘Carbon fiber reinforced phenolic based composites were prepared by laminating molding. The variation in mechanical characteristics of composites was evaluated with heating temperature and procedure. The microstructures of composites at different temperatures were observed by optical microscope and scanning electron microscope, respectively. The results showed that the main weight loss range of carbon/phenolic is from 300 to 800 ℃, before 700 ℃ the weight loss was resulted from pyrolysis and after that the weight loss was mainly by oxidation in the fiber phase; with the heat treatment temperature rising, the bonding at the interface of carbon fibers and resin matrix weakened; in the pyrolysis temperature range, the interlaminar shear strength（ILSS） of carbon/phenolic showed a rapid drop with temperature rising, and then decrease in the rate of ILSS became relatively slower; the fiber oxidation had little influence on the ILSS.
基金financially supported by the National Natural Science Foundation of China(Nos.51202193 and 51221001)the Fundamental Research Foundation of Northwestern Polytechnical University(No.GBKY1021)the‘‘111’’Project(No.08040)
文摘With the use of Ti/Ni/Cu/Ni multiple foils as interlayer,carbon/carbon（C/C） composite was bonded to Nibased superalloy GH3044 by partial transient liquid-phase bonding technique.The effect of bonding temperature on the microstructures and strengths of the joints was investigated.The results showed that gradient structural multiple interlayers composed of ‘‘C–Ti reaction layer/Ti–Ni intermetallic compound layer/Ni–Cu sosoloid/residual Cu layer/Ni-GH3044 diffusion layer＇＇ were formed between C/C composite and GH3044.The shear strength of the C/C composite/GH3044 joint reached the highest value of 26.1 MPa when the bonding temperature was 1,030 °C.In addition,the fracture morphology showed that the fracture mode changed with the increase of bonding temperature.
基金Funded by the National Natural Science Foundation of China(No.51574055)the Natural Science Foundation of Liaoning Province(No.20170540143)
文摘To obtain the compositions and microstructure of hydration products of cementitious material in different hydration ages and its growth law of filling strength, the optimal proportion of composite cementitious material was determined according to the chemical composition of cement clinker which was composed of the Portland cement 32.5R, CSA 42.5 sulphoaluminate cement and two gypsum（CS）. The characterization of composite cementitious materials in different hydration ages was conducted by NMR, XRD and SEM techniques. The mechanism of hydration was explored. It is shown that the compressive strength of the test block increases gradually with the increase of hydration age. The microstructure of composite cementitious material can be changed from Al-O octahedron into Al-O tetrahedron in the hydration process. The hydrated alkali alumi niumsilicate formed with Si-O tetrahedron and Al-O tetrahedron. The degree of polymerization of Si-O tetrahedron gradually increased, and the structural strength of cementitious materials continued to increase. The diffraction peak of clinker minerals gradually decreased with the extension of hydration age. The CaSO4 completely hydrated to produce Aft during hydration which resulted in high early strength of cementitious material. The early hydration product of composite cementitious materials was Aft with a needle bar structure. The main middle and last hydration products were CSH gel and CH gel with dense prismatic shape. The microscopic pore of composite cementitious material gradually decreased and improved the later strength of filling block. The strong support was provided for mined-out area.
文摘A coating of composition Si-40Mo (wt pct) was prepared by fused slurry coating method on the two-dimensional carbon/carbon (2D-C/C) composite to improve oxidation resistance. In the procedure of the fabrication, pure St slurry inner layer in the pre-coating was necessary to apply because of infiltration of liquid Si into the substrate during the sintering. The coating consists of Si continuous phase and MoSi2 particles. In addition, the infiltration of Si into the substrate and the SiC reaction layer between the coating and the C/C composite were observed. Oxidation behavior of coated and uncoated C/C composites was studied in cyclic mode. The oxidation resistance and the thermal shock resistance of the Si-Mo fused slurry coating were quite excellent at 1370℃.
基金This work was supported by Alexander von Humboldt Foundation of Germany and the National Natural Science Foundation of China under the grant number of
文摘Hardness of the TiB2/7075 composite increased with increasing deformation temperature. In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about 1 mum in length) and small MgZn2 phases (about 100 nm in size) were precipitated nearby the grain boundaries where the TiB2 particles exist. After deformation at 300 degreesC, some of the large precipitates and all the small precipitates in these area dissolved into the matrix, meanwhile, fine precipitates were formed in grains. After deformation at 450 degreesC, all the precipitates in the annealed composite dissolved into the matrix, and new phases were precipitated in grains. The dissolution of the large fiber-like precipitate makes the saturation level of the matrix increased and leads to an increased solution hardening and natural aging, which contribute much to the hardening effect.
基金Funded by the Hebei Province Natural Science Foundation (No.E2017203043)National Natural Science Foundation of China(No.U1604251)。
文摘A new,innovative vibration cast-rolling technology of “electromagnetic stirring+dendrite breaking+asynchronous rolling” was proposed with the adoption of sinusoidal vibration of crystallization roller to prepare Ti/Al laminated composites,and the effect of sinusoidal vibration of crystallization roller on composite microstructure was investigated in detail.The results show that the metallurgical bonding of titanium and aluminum is realized by mesh interweaving and mosaic meshing,instead of transition bonding by forming metal compound layer.The meshing depth between titanium and aluminum layers (6.6μm) of cast-rolling materials with strong vibration of crystallization roller (amplitude 0.87 mm,vibration frequency 25 Hz) is doubled compared with that of traditional cast-rolling materials (3.1μm),and the composite interfacial strength(27.0 N/mm) is twice as high as that of traditional cast-rolling materials (14.9 N/mm).This is because with the action of high-speed superposition of strong tension along the rolling direction,strong pressure along the width direction and rolling force,the composite linearity evolves from "straight line" with traditional casting-rolling to "curved line",and the depth and number of cracks in the interface increases greatly compared with those with traditional cast-rolling,which leads to the deep expansion of the meshing area between interfacial layers and promotes the stable enhancement of composite quality.
基金Funded by Natural Science Foundation Project of CQ CSTC(No.2008BB4177)
文摘Two ingots were produced by centrifugal casting at mould rotational speeds of 600 rpm and 800 rpm using 20 vol%SiC p /AlSi9Mg composite melt,respectively.The microstructure along the radial direction of cross-sectional sample of ingots was presented.SiC particles migrated towards the external circumference of the tube,and the distribution of SiC particles became uniform under centrifugal force.Voids in 20 vol%SiC p /AlSi9Mg composite melt migrated towards the inner circumference of the tube.The quantitative analysis results indicated that not only SiC particles but also primaryαphases segregated greatly in centrifugal casting resulting from the transportation behavior of constitutions with different densities in the SiC p /AlSi9Mg composite melt.In addition,the eutectic Si was broken owing to the motion of SiC p /AlSi9Mg composite melt during centrifugal casting.
基金supported by the National Key Research and Development Program of China(No.2024YFB3212901)National Natural Science Foundation of China(12072189)the Medicine and Engineering Interdisciplinary Research Fund of Shanghai Jiao Tong University(No.YG2025ZD05)。
文摘Pipelines are extensively used in environments such as nuclear power plants,chemical factories,and medical devices to transport gases and liquids.These tubular environments often feature complex geometries,confined spaces,and millimeter-scale height restrictions,presenting significant challenges to conventional inspection methods.Here,we present an ultrasonic microrobot(weight,80 mg;dimensions,24 mm×7 mm;thickness,210μm)to realize agile and bidirectional navigation in narrow pipelines.The ultrathin structural design of the robot is achieved through a high-performance piezoelectric composite film microstructure based on MEMS technology.The robot exhibits various vibration modes when driven by ultrasonic frequency signals,its motion speed reaches81 cm s-1 at 54.8 k Hz,exceeding that of the fastest piezoelectric microrobots,and its forward and backward motion direction is controllable through frequency modulation,while the minimum driving voltage for initial movement can be as low as 3 VP-P.Additionally,the robot can effortlessly climb slopes up to 24.25°and carry loads more than 36 times its weight.The robot is capable of agile navigation through curved L-shaped pipes,pipes made of various materials(acrylic,stainless steel,and polyvinyl chloride),and even over water.To further demonstrate its inspection capabilities,a micro-endoscope camera is integrated into the robot,enabling real-time image capture inside glass pipes.
文摘It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of grains has its own domain and dislocation structure. There are mono- and polydomains with and without dislocations. The grains of the main phase of monoand polydomains without dislocations and polydomains with dislocations were formed by diffusion in the solid phase. In these conditions NiAl3 phase is located on the grain boundary of the main phase. The Ni2Al3 phase is located at the triple joints of the main phase.
文摘Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique.Different mixing methods were used in this study to control the distribution of Al N particles.The microstructure,thermal diffusivity and thermal expansion of the Mg–Al/Al N composites using different mixing methods were investigated.The results showed that the intergranular and intragranular distributions of Al N particles were obtained,respectively,by controlling the mixing methods.The composite with intragranular particles exhibited lower thermal diffusivity because of the existences of more interfaces,defects and grain boundaries,which acted as scattering centers and reduced the mean free path of electrons and phonons.The existence of Al N particles lowered the coefficient of thermal expansion（CTE）and enhanced the dimensional stability of the composites.And the use of the improved mixing method further reduced the CTE of Mg–Al/Al N composites.
文摘The influences of Mn and Ni contents on the impact toughness and microstructure in the weld metals of high strength low alloy steels were studied. The objective of this study was to determine the optimum composition ranges of Mn and Ni to develop welding consumables with better resistance to cold cracking. The results indicated that Mn and Ni had considerable effect on the microstructure of weld metal, and both Mn and Ni promoted acicular ferrite at the expense of proeutectoid ferrite and ferrite side plates. Varying Ni content influenced the Charpy impact energy, the extent of which depended on Mn content. Based on the properties and impact resistance, the optimum levels of Mn and Ni were suggested to be 0.6%—0.9%,, and 2.5%—3.5%, respectively. Additions beyond this limit promoted the formation of segregation structures and other microstructural features, which may be detrimental to weld metal toughness.
