The pure α-Ti samples were heated at an extremely high rate （～10^6 K/s） to the temperature of β phase zone followed by a rapidly quenching in an electro-pulsing treatment. After the treatment, micrometer-thick la...The pure α-Ti samples were heated at an extremely high rate （～10^6 K/s） to the temperature of β phase zone followed by a rapidly quenching in an electro-pulsing treatment. After the treatment, micrometer-thick lamellar substructures were generated within the original equiaxed α-Ti coarse grains. Misorientations across adjacent lamellae are of a few degrees. The ultrafine lamellar substructures originated from a non-equilibrium α-β-α’ phase transformation during rapidly heating-quenching process with a short exposure time at high temperatures. Tensile strength was increased by about 100 MPa due to the formation of the ultrafine lamellar substructure while the same tensile plasticity （elongation-to-failure） was maintained relative to the original sample. The strengthening effect could be attributed to the effective blockage of dislocation motions by a high density of sub-boundaries.展开更多
In this paper the preparation technique of surface nanocrystallization in commercial pure titanium was carried out by surface mechanical attrition treatment (SMAT). The mean grain size was calculated by using X-ray di...In this paper the preparation technique of surface nanocrystallization in commercial pure titanium was carried out by surface mechanical attrition treatment (SMAT). The mean grain size was calculated by using X-ray diffraction (XRD) and transmission electron microscope (TEM), and the results showed that the mean grain size of the surface was refined to nm Ievel after SMAT treatment. Nanocrystallized surface layers were formed after treated for 5, 15, 30 and 60 min. Microhardness experimental results implied the microhardness obviously increased on the surface layer and it also showed the variation of microhardness at the cross section. Corrosion test results showed the corrosion resistance of the surfaces in the original commercial pure titanium treated by SMAT was not improved in HCI solution. The corrosion micrographs were observed by scanning electron microscope (SEM).展开更多
A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained a...A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP).Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests.The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior.The basal and prismaticslip are suppressed either for tension or compression,which is the easiest to activate.The tension twin system{1012}<1011> easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor,consequently resulting in a lower yield strength under compression than tension.ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement.The interaction among the dislocations,grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation,while the interaction between the dislocations and grain boundaries for tension deformation.Deformation twins lead to the higher work hardening under compression than tension.展开更多
Nanocrystalline diamond （NCD） film deposition on pure titanium and Ti alloys is extraordinarily difficult because of the high diffusion coefficient of carbon in Ti, the large mismatch in their thermal expansion coef...Nanocrystalline diamond （NCD） film deposition on pure titanium and Ti alloys is extraordinarily difficult because of the high diffusion coefficient of carbon in Ti, the large mismatch in their thermal expansion coefficients, the complex nature of the interlayer formed during diamond deposition, and the difficulty to achieve very high nucleation density. In this investigation, NCD films were successfully deposited on pure Ti substrate by using a novel substrate pretreatment of ultrasonic scratching in a diamond powder-ethanol suspension and by a two-step process at moderate temperature. It was shown that by scratching with a 30-μm diamond suspension for 1 h, followed by a 10-h diamond deposition, a continuous NCD film was obtained with an average grain size of about 200 nm. Detailed experimental results on the preparation, characterization, and successful deposition of the NCD films on Ti were discussed.展开更多
Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produc...Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α′-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67%,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220%in its nanohardness,H/E_(r),and H_(3)/E_(r)^(2)indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(R_(a))and the skewness(R_(sk))of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223%,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(~100%)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-µm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58%,and 20 and 17%,respectively.展开更多
TiB2/TiB/TiNx(x=1,0.3)/Ti composite coating was prepared on pure Ti by laser surface alloying by using powders of boron as starting materials.The composite coating was examined by X-ray diffraction(XRD),high-resolutio...TiB2/TiB/TiNx(x=1,0.3)/Ti composite coating was prepared on pure Ti by laser surface alloying by using powders of boron as starting materials.The composite coating was examined by X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM)and scanning electron microscopy(SEM).The friction and wear properties of the composite coating were examined using a pin-on-disk tester under dry sliding wear condition.The results showed that the top surface of the composite coating was mainly composed of TiB2,TiB,TiN0.3,TiN and Ti phases,while the interface of the composite coating was composed of TiB and Ti phases.The composite coating showed sticklike structure near the top surface,and dendrites structure near the interface.The friction and wear test showed that the composite coating had better wear resistance than pure Ti due to their higher microhardness than that of pure Ti substrate.展开更多
In this study, the influence of annealing processes for cold-rolled sheets on the microstructure and mechanical performance of ultra-pure 430 ferritic stainless steel was investigated. Thermo-Calc calculation, organiz...In this study, the influence of annealing processes for cold-rolled sheets on the microstructure and mechanical performance of ultra-pure 430 ferritic stainless steel was investigated. Thermo-Calc calculation, organization observation, SEM detection,and tensile tests were used to discern the optimal annealing process. It is found that the microstructure is made up by the fine and uniform recrystallized ferritic grains after annealing. The optimum annealing process for ultra-pure 430 stainless steel is 950 ℃ for 90 s. After annealing, the stainless steel can obtain the optimum microstructure,recrystallization texture, and mechanical properties.展开更多
基金Financial supports from the National Natural Science Foundation of China(Grants Nos.50021101,50371091,90206044)the Ministry of Science and Technology of China(Grants Nos.1999064505 and 1999065009)are acknowledged.Fruitful discussion with Dr.Ruichun WANG are gratefully acknowledged.
文摘The pure α-Ti samples were heated at an extremely high rate （～10^6 K/s） to the temperature of β phase zone followed by a rapidly quenching in an electro-pulsing treatment. After the treatment, micrometer-thick lamellar substructures were generated within the original equiaxed α-Ti coarse grains. Misorientations across adjacent lamellae are of a few degrees. The ultrafine lamellar substructures originated from a non-equilibrium α-β-α’ phase transformation during rapidly heating-quenching process with a short exposure time at high temperatures. Tensile strength was increased by about 100 MPa due to the formation of the ultrafine lamellar substructure while the same tensile plasticity （elongation-to-failure） was maintained relative to the original sample. The strengthening effect could be attributed to the effective blockage of dislocation motions by a high density of sub-boundaries.
文摘In this paper the preparation technique of surface nanocrystallization in commercial pure titanium was carried out by surface mechanical attrition treatment (SMAT). The mean grain size was calculated by using X-ray diffraction (XRD) and transmission electron microscope (TEM), and the results showed that the mean grain size of the surface was refined to nm Ievel after SMAT treatment. Nanocrystallized surface layers were formed after treated for 5, 15, 30 and 60 min. Microhardness experimental results implied the microhardness obviously increased on the surface layer and it also showed the variation of microhardness at the cross section. Corrosion test results showed the corrosion resistance of the surfaces in the original commercial pure titanium treated by SMAT was not improved in HCI solution. The corrosion micrographs were observed by scanning electron microscope (SEM).
基金National Natural Science Foundation of China (No.51474170)Natural Science Foundation of Shaanxi Province (No.2023-JC-YB-312)Key Laboratory Project of Shaanxi Province Educational Committee (No.20JS075)。
文摘A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP).Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests.The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior.The basal and prismaticslip are suppressed either for tension or compression,which is the easiest to activate.The tension twin system{1012}<1011> easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor,consequently resulting in a lower yield strength under compression than tension.ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement.The interaction among the dislocations,grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation,while the interaction between the dislocations and grain boundaries for tension deformation.Deformation twins lead to the higher work hardening under compression than tension.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50572007) and the Foundation forDoctorial Stations of the Ministry of Education of China
文摘Nanocrystalline diamond （NCD） film deposition on pure titanium and Ti alloys is extraordinarily difficult because of the high diffusion coefficient of carbon in Ti, the large mismatch in their thermal expansion coefficients, the complex nature of the interlayer formed during diamond deposition, and the difficulty to achieve very high nucleation density. In this investigation, NCD films were successfully deposited on pure Ti substrate by using a novel substrate pretreatment of ultrasonic scratching in a diamond powder-ethanol suspension and by a two-step process at moderate temperature. It was shown that by scratching with a 30-μm diamond suspension for 1 h, followed by a 10-h diamond deposition, a continuous NCD film was obtained with an average grain size of about 200 nm. Detailed experimental results on the preparation, characterization, and successful deposition of the NCD films on Ti were discussed.
文摘Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α′-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67%,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220%in its nanohardness,H/E_(r),and H_(3)/E_(r)^(2)indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(R_(a))and the skewness(R_(sk))of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223%,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(~100%)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-µm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58%,and 20 and 17%,respectively.
基金National Natural Science Foundations of China(51045004)
文摘TiB2/TiB/TiNx(x=1,0.3)/Ti composite coating was prepared on pure Ti by laser surface alloying by using powders of boron as starting materials.The composite coating was examined by X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM)and scanning electron microscopy(SEM).The friction and wear properties of the composite coating were examined using a pin-on-disk tester under dry sliding wear condition.The results showed that the top surface of the composite coating was mainly composed of TiB2,TiB,TiN0.3,TiN and Ti phases,while the interface of the composite coating was composed of TiB and Ti phases.The composite coating showed sticklike structure near the top surface,and dendrites structure near the interface.The friction and wear test showed that the composite coating had better wear resistance than pure Ti due to their higher microhardness than that of pure Ti substrate.
文摘In this study, the influence of annealing processes for cold-rolled sheets on the microstructure and mechanical performance of ultra-pure 430 ferritic stainless steel was investigated. Thermo-Calc calculation, organization observation, SEM detection,and tensile tests were used to discern the optimal annealing process. It is found that the microstructure is made up by the fine and uniform recrystallized ferritic grains after annealing. The optimum annealing process for ultra-pure 430 stainless steel is 950 ℃ for 90 s. After annealing, the stainless steel can obtain the optimum microstructure,recrystallization texture, and mechanical properties.
