The effect of laser assisted local heating on the mechanical properties of a hot stamping steel tube was in vestigated. A heated region with a spiral shape was generated on the surface of the tube by combining the lin...The effect of laser assisted local heating on the mechanical properties of a hot stamping steel tube was in vestigated. A heated region with a spiral shape was generated on the surface of the tube by combining the linear movement of the laser and the rotation of the tube. The results of axial crush tests show that the laser assisted local heating can be effectively used to modify the mechanical performance of the tube. A microstructural analysis confirms that the laser locally induces a martensitic phase transformation in the heated region and results in inhomogeneous microstructures alon- the length of the tube.展开更多
As a successively and locally plastic deformation process, ball spinning is applied to manufacturing thin-walled Nickel-Titanium shape memory alloy （NiTi SMA） tube at high temperature. NiTi SMA tube blank belongs to...As a successively and locally plastic deformation process, ball spinning is applied to manufacturing thin-walled Nickel-Titanium shape memory alloy （NiTi SMA） tube at high temperature. NiTi SMA tube blank belongs to the as-cast state which consists of a lot of dendritic grains and a few equiaxed grains. The compression tests of NiTi SMA were carried out at various strain rates at high temperature in order to obtain the constitutive model of NiTi SMA. Because NiTi SMA is sensitive to the strain rates at high temperature, rigid-viscoplastic finite element method （FEM） is used to simulate ball spinning of thin-walled NiTi SMA tube in order to analyze the deformation behavior of ball spinning of NiTi SMA tube. Stress fields, strain fields as well as velocity fields is obtained by means of rigid-viscoplastic FEM, which lays the profound foundations for studying the metal flow rule in ball spinning and forming perfect spun NiTi SMA tube.展开更多
The isothermal compression tests of C71500 copper-nickel alloy at different temperatures (1 073-1 273 K) and strain rates (0.01-10 s^-1) were carried out on Gleeble-3500 thermo-mechanical simulator.The real stress-str...The isothermal compression tests of C71500 copper-nickel alloy at different temperatures (1 073-1 273 K) and strain rates (0.01-10 s^-1) were carried out on Gleeble-3500 thermo-mechanical simulator.The real stress-strain data were obtained.On the basis of dynamic material model,the power dissipation was established.The peak efficiency of the power dissipation is 57%.At the same time,Prasad’s,Murty’s and Babu’s instability criteria based on Ziegler’s expectant rheology theory,and Gegel’s and Malas’s instability criteria based on Lyaponov’s function theory,were used to predict the unstable regions in the processing map.The maximum entropy generation rate and large plastic deformation principle are more in line with the hot deformation process of C71500 alloy,so the accuracy of Prasad’s instability criterion is much better.According to the obtained macro-crack and micro-metallographic structure morphologies,the temperature range of 1 098-1 156 K and the strain rate range of 2.91-10 s^-1,and the temperature range of 1 171-1 273 K and the strain rate range of 0.01-0.33 s^-1 are more suitable for the processing area of C71500 alloy.The accuracy of the above conclusions were verified by the forging of materials and the analysis of hot piercing tubes.The significance of this paper is to provide theoretical basis and technological conditions for hot-press processing of C71500 alloy.展开更多
Ni/NiO nanoparticles were synthesized by metal organics chemical vapor deposition of nickel acetylacetonate in an externally heated tube flow reactor at moderate temperatures, up to 500°C. Particle production and...Ni/NiO nanoparticles were synthesized by metal organics chemical vapor deposition of nickel acetylacetonate in an externally heated tube flow reactor at moderate temperatures, up to 500°C. Particle production and characteristics were studied by evaluating the effects of reactor temperature, precursor concentration, and flow rate through the reactor. In addition, two precursor decomposition methods were examined: thermal decomposition and reduction by hydrogen. Particle production was monitored with a scanning mobility particle sizer, and particle characteristics were studied using transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive spectroscopy. The presence of hydrogen in the reaction mixture influenced significantly both particle production and their characteristics.展开更多
基金Sponsored by IT R&D Program of MOTIE/KEIT(10044807)National Research Foundation of Korea Grant Funded by the Korean Government(NRF-2013R1A1A2010145)+2 种基金NRF Grant by the Ministry of ScienceICT&Future Planning(MSIP)(NRF-2015R1A5A1037627)Small and Medium Business Support Program(World-class 300Project,S2317960)
文摘The effect of laser assisted local heating on the mechanical properties of a hot stamping steel tube was in vestigated. A heated region with a spiral shape was generated on the surface of the tube by combining the linear movement of the laser and the rotation of the tube. The results of axial crush tests show that the laser assisted local heating can be effectively used to modify the mechanical performance of the tube. A microstructural analysis confirms that the laser locally induces a martensitic phase transformation in the heated region and results in inhomogeneous microstructures alon- the length of the tube.
基金the National Natural Science Foundation of China(No.51071056)the Fundamental Research Funds for the Central Universities of China(No.HEUCF121712)
文摘As a successively and locally plastic deformation process, ball spinning is applied to manufacturing thin-walled Nickel-Titanium shape memory alloy （NiTi SMA） tube at high temperature. NiTi SMA tube blank belongs to the as-cast state which consists of a lot of dendritic grains and a few equiaxed grains. The compression tests of NiTi SMA were carried out at various strain rates at high temperature in order to obtain the constitutive model of NiTi SMA. Because NiTi SMA is sensitive to the strain rates at high temperature, rigid-viscoplastic finite element method （FEM） is used to simulate ball spinning of thin-walled NiTi SMA tube in order to analyze the deformation behavior of ball spinning of NiTi SMA tube. Stress fields, strain fields as well as velocity fields is obtained by means of rigid-viscoplastic FEM, which lays the profound foundations for studying the metal flow rule in ball spinning and forming perfect spun NiTi SMA tube.
基金Funded by the National Natural Science Foundation of China(No.51801149)the Ministry of Industry and Information Technology of the People’s Republic of China(TC170A2KN-8)。
文摘The isothermal compression tests of C71500 copper-nickel alloy at different temperatures (1 073-1 273 K) and strain rates (0.01-10 s^-1) were carried out on Gleeble-3500 thermo-mechanical simulator.The real stress-strain data were obtained.On the basis of dynamic material model,the power dissipation was established.The peak efficiency of the power dissipation is 57%.At the same time,Prasad’s,Murty’s and Babu’s instability criteria based on Ziegler’s expectant rheology theory,and Gegel’s and Malas’s instability criteria based on Lyaponov’s function theory,were used to predict the unstable regions in the processing map.The maximum entropy generation rate and large plastic deformation principle are more in line with the hot deformation process of C71500 alloy,so the accuracy of Prasad’s instability criterion is much better.According to the obtained macro-crack and micro-metallographic structure morphologies,the temperature range of 1 098-1 156 K and the strain rate range of 2.91-10 s^-1,and the temperature range of 1 171-1 273 K and the strain rate range of 0.01-0.33 s^-1 are more suitable for the processing area of C71500 alloy.The accuracy of the above conclusions were verified by the forging of materials and the analysis of hot piercing tubes.The significance of this paper is to provide theoretical basis and technological conditions for hot-press processing of C71500 alloy.
基金supported by the Grant Agency of the Czech Republic No.104/07/1093 and by the Finnish Academy of Sciences and Letters.
文摘Ni/NiO nanoparticles were synthesized by metal organics chemical vapor deposition of nickel acetylacetonate in an externally heated tube flow reactor at moderate temperatures, up to 500°C. Particle production and characteristics were studied by evaluating the effects of reactor temperature, precursor concentration, and flow rate through the reactor. In addition, two precursor decomposition methods were examined: thermal decomposition and reduction by hydrogen. Particle production was monitored with a scanning mobility particle sizer, and particle characteristics were studied using transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive spectroscopy. The presence of hydrogen in the reaction mixture influenced significantly both particle production and their characteristics.
