Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively r...Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.展开更多
The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys be...The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy,respectively.The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing.After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494℃for 1.5 h and aging at 180℃for 4 h,its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa.Its wear resistance was also enhanced.The factors leading to the enhanced strength,hardness,and wear resistance of the alloy were discussed in detail.展开更多
Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VⅢB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of t...Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VⅢB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of the total energy plane wave pseudopotential method in first-principles. The lattice stabilities of Rh and Ir are ΔG^ bcc-hcp 〉 Δ G^fcc-hcp 〉 0, agreeing well with those of the projector augmented wave method in first-principles and the CALPHAD method in spite of elemental Co. Analyses of the electronic structures to lattice stability show that crystalline Rh and Ir with fcc structures have the obvious characteristic of a stable phase, agreeing with the results of total energy calculations. Analyses of atomic populations show that the transition rate of electrons from the s state to the p or d state for hcp, fcc, and bcc crystals of Co and Rh increases with the elemental period number to form a stronger cohesion, a higher cohesive energy, or a more stable lattice between atoms in heavier metals.展开更多
To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 wer...To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 were prepared, and the Al2O3 content of the prepared balls was 75%. It is found that the effect of calcia and magnesia on the wear resistance of ceramic balls is contrast to the accepted one: the wear rate of the ceramic balls prepared in CaO-Al2O3-SiO2 system is the lowest and the wear rate of the ceramic balls prepared in MgO-Al2O3-SiO2 is the highest. The main crystal phase of the ceramic ball is mullite and corundum. The ceramic ball granular is uniform and fine with 4-5 μm average size. The pore diameter is about 2 μm. The wear way of the ceramic balls is mainly transcrystalline fracture.展开更多
With industrial grade Al(OH)3 as raw materials, the self dispersion nanosized AlOOH crystal powder were prepared by the sol-hydrothermal method. The results of XRD and TEM show that the nanosized AlOOH could automat...With industrial grade Al(OH)3 as raw materials, the self dispersion nanosized AlOOH crystal powder were prepared by the sol-hydrothermal method. The results of XRD and TEM show that the nanosized AlOOH could automatically disperse to a single-dispersing state in water without surface modification, dispersant, additive and accessional conditions (ultrasonic wave dispersing, ball-mill dispersing). The application results of the product indicate that the nanosized AlOOH can be composed into a toughened nanocomposites without surface modification. Accordingly, the self dispersion characteristic and mechanism of hydrothermal crystallization and charging composite dispersion of nanosized AIOOH are found, and a new technique of preparing polymer/inorganic nanocomposites is proposed, which is called blending compositing new techniques of sol even dispersing at auasi-homogeneous phase.展开更多
pH value is a key factor in the preparation of nano-sized TiO2 with hydrothermal method. Using Ti(SO4)2 as the titanium source, H2O2 as the complexing agent, NaOH and HCl as the pH value regulator, nano- sized TiO2 ...pH value is a key factor in the preparation of nano-sized TiO2 with hydrothermal method. Using Ti(SO4)2 as the titanium source, H2O2 as the complexing agent, NaOH and HCl as the pH value regulator, nano- sized TiO2 powder with various morphologies and sizes was synthesized. Changes in morphology, size and phase type with pH values of samples were characterized by X-ray diffraction (XRD) and transmission electron micro- scopy (TEM) measurements. Results show that under the present preparation conditions, TiO2 powder is an anatase phase with pH value less than 11, but is more likely to be a brookite phase with pH value more than 11. With the increase in pH value from 1 to 11 in hydrothermal envi- ronment, nano-sized anatase TiO2 gradually grows up in all directions. {001 }, { 101 } and { 100} groups of crystal plane are the exposed crystal planes of nano-sized anatase TiO2 for the (004), (101) and (200) facets found in high-reso- lution TEM image. The photocatalytic performance of nano-sized TiO2 with different morphologies was com- pared by measuring their photocatalytic degradation rates for methylene blue under ultraviolet light. Results show that anatase TiO2 prepared under the alkalescenthydrothermal environment (pH = 9, 11) has a better pho- tocatalytic degrading performance. Different sizes and phases of nanoscaled TiO2 powders with different photo- catalytic performances can be prepared by the control of pH value of hydrothermal solutions.展开更多
In the present work,the sheets of Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy were hot rolled with different reductions(10%,30%,50%,and 60%) at 1023 K and 1073 K.The micro structure evolutions including grain micro structure,textu...In the present work,the sheets of Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy were hot rolled with different reductions(10%,30%,50%,and 60%) at 1023 K and 1073 K.The micro structure evolutions including grain micro structure,texture,and dislocation were investigated,using electron backscattering diffraction and transmission electron microscope.The results showed that dislocation slip,twinning,and dynamic recrystallization(DRX) were the main deformation mechanisms.DRX was found to be promoted by larger reduction and higher rolling temperature.The predominant texture formed during hot rolling was basal <0001>//ND,whose intensity reached peak value after 30% reduction hot rolling.While the intensity of DRX texture <10-10>//ND and<1-210>//ND increased with increasing reduction and temperature.This study provided an effective way to tailor the texture and microstructure of the alloy,for optimizing process parameters.展开更多
In the present work,Zn-10 Al-2 Cu-0.05 Ti(ZA10)alloy tubes with a diameter of 12.5 mm and wall thickness of 1.2 mm were fabricated by one-pass and double-pass Conform continuous extrusion.A stabilizing heat treatment[...In the present work,Zn-10 Al-2 Cu-0.05 Ti(ZA10)alloy tubes with a diameter of 12.5 mm and wall thickness of 1.2 mm were fabricated by one-pass and double-pass Conform continuous extrusion.A stabilizing heat treatment[350℃,30 min(furnace cooling)+120℃,12 h(air cooling)]was also applied to some of the double-pass tubes to improve the quality of their weld seams.The yield strength,ultimate tensile strength,elongation and expansion ratio of the one-pass continuous extrusion tube were 268.4 MPa,294.3 MPa,13.8%and 5.5%,respectively.Double-pass continuous extrusion improved these values to 278.4 MPa,317.2 MPa,15.4%and 11.4%,respectively.Double-pass tubes also had fewer aggregations of Al-αprecipitates along the welding seam,which improved seam quality and caused cracks to appear in the matrix,away from the weld-affected zone,during expansion testing.Heat-treated double-pass tubes exhibited superior yield strength(283.9 MPa)and ultimate tensile strength(328.5 MPa)but lower elongation(10.2%)and expansion ratios(10.3%).Additionally,the heat-treated tubes exhibited markedly lower elongation at room temperature due to the remarkable blockage of dislocation motions by fine-scale lamellar(α+η)eutectoid structures and a lower size effect when stretched.展开更多
基金Project(12JJ2028)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(201308430093)supported by the China Scholarship CouncilProjects(201012200006,2013zzts185,2012zzts066)supported by the Freedom Explore Program of Central South University,China
文摘Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.
基金financially supported by the National Natural Science Foundation of China (No.51274245)
文摘The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy,respectively.The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing.After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494℃for 1.5 h and aging at 180℃for 4 h,its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa.Its wear resistance was also enhanced.The factors leading to the enhanced strength,hardness,and wear resistance of the alloy were discussed in detail.
基金supported by the Doctoral Discipline Foundation of the Ministry of Education of China (No. 20070533118)the National Natural Science Foundation of China (No. 50871124)the Postdoctoral Foundation of Central South University
文摘Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VⅢB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of the total energy plane wave pseudopotential method in first-principles. The lattice stabilities of Rh and Ir are ΔG^ bcc-hcp 〉 Δ G^fcc-hcp 〉 0, agreeing well with those of the projector augmented wave method in first-principles and the CALPHAD method in spite of elemental Co. Analyses of the electronic structures to lattice stability show that crystalline Rh and Ir with fcc structures have the obvious characteristic of a stable phase, agreeing with the results of total energy calculations. Analyses of atomic populations show that the transition rate of electrons from the s state to the p or d state for hcp, fcc, and bcc crystals of Co and Rh increases with the elemental period number to form a stronger cohesion, a higher cohesive energy, or a more stable lattice between atoms in heavier metals.
基金the National Natural Science Fundation of China(No.50272016),Guangxi 2003 Degree Authorzation Office academic Construction Fun,and Natural Science Fund of Guangxi Education Department(No.[2004]4)
文摘To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 were prepared, and the Al2O3 content of the prepared balls was 75%. It is found that the effect of calcia and magnesia on the wear resistance of ceramic balls is contrast to the accepted one: the wear rate of the ceramic balls prepared in CaO-Al2O3-SiO2 system is the lowest and the wear rate of the ceramic balls prepared in MgO-Al2O3-SiO2 is the highest. The main crystal phase of the ceramic ball is mullite and corundum. The ceramic ball granular is uniform and fine with 4-5 μm average size. The pore diameter is about 2 μm. The wear way of the ceramic balls is mainly transcrystalline fracture.
基金Guangxi Provincial Natural Sciences Foundation, (No.0640041)Guangxi Provincial Scientific Research and Technical Develop-ment Program Project (No. 0141033)Prior Period Research Special Fund of Significant Basic Research of National Science and Technology Depart-ment (No. 2005CCA00200)
文摘With industrial grade Al(OH)3 as raw materials, the self dispersion nanosized AlOOH crystal powder were prepared by the sol-hydrothermal method. The results of XRD and TEM show that the nanosized AlOOH could automatically disperse to a single-dispersing state in water without surface modification, dispersant, additive and accessional conditions (ultrasonic wave dispersing, ball-mill dispersing). The application results of the product indicate that the nanosized AlOOH can be composed into a toughened nanocomposites without surface modification. Accordingly, the self dispersion characteristic and mechanism of hydrothermal crystallization and charging composite dispersion of nanosized AIOOH are found, and a new technique of preparing polymer/inorganic nanocomposites is proposed, which is called blending compositing new techniques of sol even dispersing at auasi-homogeneous phase.
基金Project(21373273)supported by the National Natural Science Foundation of ChinaProject(2019CG033)supported by the Deepening Reform Project of Innovation and Entrepreneurship Education of Central South University,China+1 种基金Project(2019JG067)supported by the Graduate Education and Teaching Reform Research Project of Central South University,ChinaProject(201810533278)supported by the National College Students’ Innovative Experiment Project of Central South University,China
基金financially supported by the National Natural Science Foundation of China (Nos.51302322 and 21373273)the Open-End Fund for the Valuable and Precision Instruments of Central South University (No.CSUZC201613)+1 种基金the Open Foundation of Guangdong Provincial Key Laboratory for Technology and Application of Metal Toughening,Guangdong Institute of Materials and Processing (No.GKL201605)the Education Reform Project of Central South University (No.2016jy03)
文摘pH value is a key factor in the preparation of nano-sized TiO2 with hydrothermal method. Using Ti(SO4)2 as the titanium source, H2O2 as the complexing agent, NaOH and HCl as the pH value regulator, nano- sized TiO2 powder with various morphologies and sizes was synthesized. Changes in morphology, size and phase type with pH values of samples were characterized by X-ray diffraction (XRD) and transmission electron micro- scopy (TEM) measurements. Results show that under the present preparation conditions, TiO2 powder is an anatase phase with pH value less than 11, but is more likely to be a brookite phase with pH value more than 11. With the increase in pH value from 1 to 11 in hydrothermal envi- ronment, nano-sized anatase TiO2 gradually grows up in all directions. {001 }, { 101 } and { 100} groups of crystal plane are the exposed crystal planes of nano-sized anatase TiO2 for the (004), (101) and (200) facets found in high-reso- lution TEM image. The photocatalytic performance of nano-sized TiO2 with different morphologies was com- pared by measuring their photocatalytic degradation rates for methylene blue under ultraviolet light. Results show that anatase TiO2 prepared under the alkalescenthydrothermal environment (pH = 9, 11) has a better pho- tocatalytic degrading performance. Different sizes and phases of nanoscaled TiO2 powders with different photo- catalytic performances can be prepared by the control of pH value of hydrothermal solutions.
基金financially supported by the National Natural Science Foundation of China (No. U1867201).
文摘In the present work,the sheets of Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy were hot rolled with different reductions(10%,30%,50%,and 60%) at 1023 K and 1073 K.The micro structure evolutions including grain micro structure,texture,and dislocation were investigated,using electron backscattering diffraction and transmission electron microscope.The results showed that dislocation slip,twinning,and dynamic recrystallization(DRX) were the main deformation mechanisms.DRX was found to be promoted by larger reduction and higher rolling temperature.The predominant texture formed during hot rolling was basal <0001>//ND,whose intensity reached peak value after 30% reduction hot rolling.While the intensity of DRX texture <10-10>//ND and<1-210>//ND increased with increasing reduction and temperature.This study provided an effective way to tailor the texture and microstructure of the alloy,for optimizing process parameters.
基金financially supported by the National 11th Five-Year Science and Technology Support Program of China(No.2009BAE71B00)Hunan Science and Technology Plan Key Project(No.2012GK4012)。
文摘In the present work,Zn-10 Al-2 Cu-0.05 Ti(ZA10)alloy tubes with a diameter of 12.5 mm and wall thickness of 1.2 mm were fabricated by one-pass and double-pass Conform continuous extrusion.A stabilizing heat treatment[350℃,30 min(furnace cooling)+120℃,12 h(air cooling)]was also applied to some of the double-pass tubes to improve the quality of their weld seams.The yield strength,ultimate tensile strength,elongation and expansion ratio of the one-pass continuous extrusion tube were 268.4 MPa,294.3 MPa,13.8%and 5.5%,respectively.Double-pass continuous extrusion improved these values to 278.4 MPa,317.2 MPa,15.4%and 11.4%,respectively.Double-pass tubes also had fewer aggregations of Al-αprecipitates along the welding seam,which improved seam quality and caused cracks to appear in the matrix,away from the weld-affected zone,during expansion testing.Heat-treated double-pass tubes exhibited superior yield strength(283.9 MPa)and ultimate tensile strength(328.5 MPa)but lower elongation(10.2%)and expansion ratios(10.3%).Additionally,the heat-treated tubes exhibited markedly lower elongation at room temperature due to the remarkable blockage of dislocation motions by fine-scale lamellar(α+η)eutectoid structures and a lower size effect when stretched.