DR.Su Jinsan ran a clinic in the British concession in Tianjin during the early 1910s.He was believed to be the best orthopedic surgeon of the city.Even foreign horse racers whose limbs were broken would come to see h...DR.Su Jinsan ran a clinic in the British concession in Tianjin during the early 1910s.He was believed to be the best orthopedic surgeon of the city.Even foreign horse racers whose limbs were broken would come to see him.He was a tall man in his 50s with slim but strong fingers,bright eyes,rosy lips,white teeth,and a dark shiny goatee on his chin.He spoke in a clear and loud voice that resonated from his diaphragm and chest and could be heard from a far distance.If given proper training,he could have become a Peking Opera star as good as Jin Shaoshan.展开更多
In the context of additive manufacturing processes,the influence of specimen deformation from different welding paths is conducted by using CMT-AM.A least-squares method was used to quantitatively measure specimen def...In the context of additive manufacturing processes,the influence of specimen deformation from different welding paths is conducted by using CMT-AM.A least-squares method was used to quantitatively measure specimen deformation.The values of S(i.e.,the sum of the distance from each feature point in a plane to the ideal plane)from different welding paths had significant influence on deformation of deposited layer.With the value of S increasing,the deformation of deposited layer gradually increased.With this result,a suitable welding trace plan was ascertained,which was successfully used to acquire well-formed and densely organized specimens during the arc-welding additive manufacturing process.Our results provide a foundation for experiments based on deposited layer scanning trace planning.展开更多
SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properti...SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properties of these joints were investigated.The results revealed that SiC particle segregation was more likely during centered electron beam welding(than during deflection beam welding),and strong interface reactions led to the formation of many Al4C3 brittle intermetallic compounds.Moreover,the tensile strength of the joints was 104 MPa.The interface reaction was restrained via deflection electron beam welding,and only a few Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al.Quasi-cleavage fracture occurred at the interface reaction layer of the base metal.Both methods yielded a hardness transition zone near the SiCp/2024 fusion zone,and the brittle intermetallic Al4C3compounds formed in this zone resulted in high hardness.展开更多
Butt joints between Mg alloy AZ31 B and pure Al 1 060 sheets were produced via metal inert gas welding process with Zn-Cd alloy foil. Crack-free Al/Mg butt joints between AZ31 B Mg alloy and pure Al 1060 sheets were o...Butt joints between Mg alloy AZ31 B and pure Al 1 060 sheets were produced via metal inert gas welding process with Zn-Cd alloy foil. Crack-free Al/Mg butt joints between AZ31 B Mg alloy and pure Al 1060 sheets were obtained. Intermetallic compound layer 1 and layer 2 had formed in fusion zone/Mg alloy and the average thickness of the layer 1 was about 50 μm. The intermetallic compound layer 1 consisted of Al12Mg17 and Mg2Si phases while layer 2 consisted of Al12Mg17, Mg2Si and Mg Zn2 phases. The crack started from the IMC layer at the bottom of the joint and propagated along the brittle IMC layer, then expanded into weld metal during the SEM in situ tensile test. The highest tensile strength of the dissimilar metal butt joints could reach 46.8 MPa and the effect ofinterfacial IMC layer on mechanical property of the joint was discussed in detail in the present study.展开更多
Problems such as poor structural integrity,inhomogeneous dispersion,and agglomeration of graphene in the brazing seam are typically encountered for graphene additives in a brazed joint interface.To resolve these probl...Problems such as poor structural integrity,inhomogeneous dispersion,and agglomeration of graphene in the brazing seam are typically encountered for graphene additives in a brazed joint interface.To resolve these problems,a plasma-enhanced chemical vapor deposition process was employed for in-situ preparation of a high-quality graphene-coated copper(Cu)foam composite interlayer prior to be applied for brazing carbon/carbon composite and niobium.The prepared graphene and the brazed joints were characterized via Raman spectroscopy,scanning electron microscopy,and high-resolution transmission electron microscopy.The results revealed that graphene was evenly distributed in the brazing seam with the help of the Cu foam,which was characterized by interconnected porosity.Simultaneously,the excellent chemical inertia of graphene inhibited the collapse of the Cu foam,based on which the thermal residual stress in the joint was effectively mitigated due to the synergistic reinforcement effect of the Cu foam(with good plastic deformation capacity)and graphene(with extremely low coefficient of linear expansion).This effect led to significant improvement in the average shear strength of the joint.展开更多
Electron beam welding experiment of titanium alloy to chromium bronze with a vanadium filler metal was carried out. Microstructure of the joint was observed by optical microscopy and scanning electron microscopy. Tens...Electron beam welding experiment of titanium alloy to chromium bronze with a vanadium filler metal was carried out. Microstructure of the joint was observed by optical microscopy and scanning electron microscopy. Tensile strength of the joint was evaluated. The fracture surface of the joint was also analyzed. The results showed that the addition of vanadium filler metal reduced the brittleness of joint by increasing the amount of vanadium-based solid solution in the weld. But the melting point of vanadium.filler metal was so high that large heat input was needed to completely melt the filler metal. Thus, a large amount of interfacial compounds were produced. The tensile strength of joint was 280 MPa with a brittle fracture mode.展开更多
Flow field of weld pool during deep penetration electron beam welding of TA 15 titanium alloy was numerically and experimentally studied using a hybrid heat source of Gaussian surface heat source and rotational parabo...Flow field of weld pool during deep penetration electron beam welding of TA 15 titanium alloy was numerically and experimentally studied using a hybrid heat source of Gaussian surface heat source and rotational paraboloidal body heat source. And the formation mechanism of the weld pool flow field was analyzed. The results showed that the movement of the liquid metal in the top weld pool was the fiercest and weakened gradually in the middle and bottom of the weld pool. The maximum flow velocity of the liquid metal was about 0. 295 m/s in the top surface of weld pool. The primary driving forces of the movement of liquid metal in the weld pool were the recoil pressure of metal vapor and the surface tension.展开更多
SU Jinsan was Tianjin’s top orthopedist in the early years of the Republic of China(1912-1939).His reputation was such that expats who had broken limbs in horse riding accidents were among patients he saw at his mode...SU Jinsan was Tianjin’s top orthopedist in the early years of the Republic of China(1912-1939).His reputation was such that expats who had broken limbs in horse riding accidents were among patients he saw at his modest clinic in Xiaobailou.Of a tall and wiry build while in his 50s,the surgeon had powerful hands,piercing eyes and wore a coal black goatee.His deep,resonant,resounding voice could make even the best of Peking Opera per-展开更多
During the Spring Festival you lament about how time flies, how ruthless time is and how incapable you are facing life. But it also gives you satisfaction that no other festival can give. Only during these days can yo...During the Spring Festival you lament about how time flies, how ruthless time is and how incapable you are facing life. But it also gives you satisfaction that no other festival can give. Only during these days can you feel yesterday as if it were real; you seem to fall into the wonderful tunnel of time, yet you cannot help but crawl further.展开更多
Large-area single-or multilayer graphene of high quality is synthesized on Ni films by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at a relatively low temperature (650℃).In the deposition pro...Large-area single-or multilayer graphene of high quality is synthesized on Ni films by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at a relatively low temperature (650℃).In the deposition process,a trace amount of CH4 gas (2-8 sccm (sccm denotes standard cubic centimeter per minute at STP)) is introduced into the PECVD chamber and only a short deposition time (30-60 s) is used.Single-or multilayer graphene is obtained because carbon atoms from the discharging CH4 diffuse into the Ni film and then segregate out at its surface.The layer number of the obtained graphene increases when the deposition time or CH4 gas flow rate is increased.This investigation shows that PECVD is a simple,low-cost,and effective technique to synthesize large-area single-or multilayer graphene,which has potential for application as electronic devices.展开更多
文摘DR.Su Jinsan ran a clinic in the British concession in Tianjin during the early 1910s.He was believed to be the best orthopedic surgeon of the city.Even foreign horse racers whose limbs were broken would come to see him.He was a tall man in his 50s with slim but strong fingers,bright eyes,rosy lips,white teeth,and a dark shiny goatee on his chin.He spoke in a clear and loud voice that resonated from his diaphragm and chest and could be heard from a far distance.If given proper training,he could have become a Peking Opera star as good as Jin Shaoshan.
基金Project was supported by the National Natural Science Foundation of China(51475104,51435004)National Key Basic Research and Development Planning Project(973 plan)(No.2013CB035500).
文摘In the context of additive manufacturing processes,the influence of specimen deformation from different welding paths is conducted by using CMT-AM.A least-squares method was used to quantitatively measure specimen deformation.The values of S(i.e.,the sum of the distance from each feature point in a plane to the ideal plane)from different welding paths had significant influence on deformation of deposited layer.With the value of S increasing,the deformation of deposited layer gradually increased.With this result,a suitable welding trace plan was ascertained,which was successfully used to acquire well-formed and densely organized specimens during the arc-welding additive manufacturing process.Our results provide a foundation for experiments based on deposited layer scanning trace planning.
基金Project was supported by the National Nature Science Foundation of China(51375115).
文摘SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properties of these joints were investigated.The results revealed that SiC particle segregation was more likely during centered electron beam welding(than during deflection beam welding),and strong interface reactions led to the formation of many Al4C3 brittle intermetallic compounds.Moreover,the tensile strength of the joints was 104 MPa.The interface reaction was restrained via deflection electron beam welding,and only a few Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al.Quasi-cleavage fracture occurred at the interface reaction layer of the base metal.Both methods yielded a hardness transition zone near the SiCp/2024 fusion zone,and the brittle intermetallic Al4C3compounds formed in this zone resulted in high hardness.
文摘Butt joints between Mg alloy AZ31 B and pure Al 1 060 sheets were produced via metal inert gas welding process with Zn-Cd alloy foil. Crack-free Al/Mg butt joints between AZ31 B Mg alloy and pure Al 1060 sheets were obtained. Intermetallic compound layer 1 and layer 2 had formed in fusion zone/Mg alloy and the average thickness of the layer 1 was about 50 μm. The intermetallic compound layer 1 consisted of Al12Mg17 and Mg2Si phases while layer 2 consisted of Al12Mg17, Mg2Si and Mg Zn2 phases. The crack started from the IMC layer at the bottom of the joint and propagated along the brittle IMC layer, then expanded into weld metal during the SEM in situ tensile test. The highest tensile strength of the dissimilar metal butt joints could reach 46.8 MPa and the effect ofinterfacial IMC layer on mechanical property of the joint was discussed in detail in the present study.
基金Project was supported by the National Nature Science Foundation of China(51575135,51622503,U1537206).
文摘Problems such as poor structural integrity,inhomogeneous dispersion,and agglomeration of graphene in the brazing seam are typically encountered for graphene additives in a brazed joint interface.To resolve these problems,a plasma-enhanced chemical vapor deposition process was employed for in-situ preparation of a high-quality graphene-coated copper(Cu)foam composite interlayer prior to be applied for brazing carbon/carbon composite and niobium.The prepared graphene and the brazed joints were characterized via Raman spectroscopy,scanning electron microscopy,and high-resolution transmission electron microscopy.The results revealed that graphene was evenly distributed in the brazing seam with the help of the Cu foam,which was characterized by interconnected porosity.Simultaneously,the excellent chemical inertia of graphene inhibited the collapse of the Cu foam,based on which the thermal residual stress in the joint was effectively mitigated due to the synergistic reinforcement effect of the Cu foam(with good plastic deformation capacity)and graphene(with extremely low coefficient of linear expansion).This effect led to significant improvement in the average shear strength of the joint.
文摘Electron beam welding experiment of titanium alloy to chromium bronze with a vanadium filler metal was carried out. Microstructure of the joint was observed by optical microscopy and scanning electron microscopy. Tensile strength of the joint was evaluated. The fracture surface of the joint was also analyzed. The results showed that the addition of vanadium filler metal reduced the brittleness of joint by increasing the amount of vanadium-based solid solution in the weld. But the melting point of vanadium.filler metal was so high that large heat input was needed to completely melt the filler metal. Thus, a large amount of interfacial compounds were produced. The tensile strength of joint was 280 MPa with a brittle fracture mode.
文摘Flow field of weld pool during deep penetration electron beam welding of TA 15 titanium alloy was numerically and experimentally studied using a hybrid heat source of Gaussian surface heat source and rotational paraboloidal body heat source. And the formation mechanism of the weld pool flow field was analyzed. The results showed that the movement of the liquid metal in the top weld pool was the fiercest and weakened gradually in the middle and bottom of the weld pool. The maximum flow velocity of the liquid metal was about 0. 295 m/s in the top surface of weld pool. The primary driving forces of the movement of liquid metal in the weld pool were the recoil pressure of metal vapor and the surface tension.
文摘SU Jinsan was Tianjin’s top orthopedist in the early years of the Republic of China(1912-1939).His reputation was such that expats who had broken limbs in horse riding accidents were among patients he saw at his modest clinic in Xiaobailou.Of a tall and wiry build while in his 50s,the surgeon had powerful hands,piercing eyes and wore a coal black goatee.His deep,resonant,resounding voice could make even the best of Peking Opera per-
文摘During the Spring Festival you lament about how time flies, how ruthless time is and how incapable you are facing life. But it also gives you satisfaction that no other festival can give. Only during these days can you feel yesterday as if it were real; you seem to fall into the wonderful tunnel of time, yet you cannot help but crawl further.
基金supported by the National Natural Science Foundation of China(51105108)the Fundamental Research Funds for the Central Universities(HIT.NSRIF.2010113and2010115)the Foundation of the Key Laboratory for Advanced Materials Processing Technology,Ministry of Education(2010007)
文摘Large-area single-or multilayer graphene of high quality is synthesized on Ni films by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at a relatively low temperature (650℃).In the deposition process,a trace amount of CH4 gas (2-8 sccm (sccm denotes standard cubic centimeter per minute at STP)) is introduced into the PECVD chamber and only a short deposition time (30-60 s) is used.Single-or multilayer graphene is obtained because carbon atoms from the discharging CH4 diffuse into the Ni film and then segregate out at its surface.The layer number of the obtained graphene increases when the deposition time or CH4 gas flow rate is increased.This investigation shows that PECVD is a simple,low-cost,and effective technique to synthesize large-area single-or multilayer graphene,which has potential for application as electronic devices.
