Low cost hydride-dehydride (HDH) Ti-6Al-4V (Ti-64) alloy powder was employed to investigate the metallurgical quality and mechanical properties of laser formed samples. With appropriate control of the laser forming pr...Low cost hydride-dehydride (HDH) Ti-6Al-4V (Ti-64) alloy powder was employed to investigate the metallurgical quality and mechanical properties of laser formed samples. With appropriate control of the laser forming processing parameters and the loose density of HDH powder, two kinds of defect, i.e. porosity and ill-bonding, can be avoided. Rare earth Nd powder was added to HDH Ti-64 powder to purify laser formed alloy. The results show that with a few additive of Nd, the microstructure of laser formed alloy changes from Widmanstatten morphology to a basket weave microstructure. Accordingly an appropriate addition of Nd is effective to improve both the strength and ductility of laser formed HDH Ti-64 alloy. The values of tensile test meet the wrought specification with the content of Nd ranging from 0.1%-0.2%(mass fraction).展开更多
A model for simulating the spray forming process with scanning atomizer was developed.Models for the scanning atomization and the deposition processes were coupled together in order to obtain a new description of the ...A model for simulating the spray forming process with scanning atomizer was developed.Models for the scanning atomization and the deposition processes were coupled together in order to obtain a new description of the spray forming process.The model,which is able to predict the shape of a spray-formed billet prepared with scanning atomizer,was established after analyzing the changes in droplet size and density distribution along the r-axis in the spray cone in scanning atomization.The effects of the two kinds of atomization were compared,showing that the scanning atomization is good for deposition.展开更多
In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on the population dynamic...In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on the population dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains. The model is coupled with droplets heat transfer controlling equations and solved for AI-4.5 wt pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.展开更多
To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconven...To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconventional innovative technological procedures.One of these technologies is the forming in semi-solid state involving rapid solidification of miniature components from steels.Production of such components is complicated by a number of technical problems.To explain phenomena of the process and structure development,the production of miniature components from the tool steel X210Cr12 difficult to form was experimentally tested.The structure of this originally ledeburite steel consisted of 95 % of metastable austenite after the treatment.Metastable austenite was located particularly in globular and polygonal grains while the remaining interspaces were filled by lamellar network.The detected high stability of extremely high fraction of metastable austenite was tested under different conditions of thermal exposition and mechanical loading.展开更多
The flow field formed when an aluminum ribbon is produced by twin-belt rapid solidification is simulated with the solution algorithm （SOLA）-volume of fluid （VOF） method, and the influence of casting speed and cool...The flow field formed when an aluminum ribbon is produced by twin-belt rapid solidification is simulated with the solution algorithm （SOLA）-volume of fluid （VOF） method, and the influence of casting speed and cooling-belt velocity on the flow field is analyzed for a given ejection nozzle size. It has been found that the flow field can be filled well when the width of the ejection nozzle outlet is the same as that of the up slit of the cooling belt. When the ejection nozzle outlet is wider than the up slit of the cooling belt, the aluminum fluid can fill well if only the casting speed matches the cooling-belt velocity properly, otherwise under filling occurs in some areas in the cooling zone.展开更多
Several tensile samples were prepared using laser rapid forming (LRF) with Ti-6Al-4V alloy as powder material, and the samples were annealed. The microstructure and high temperature mechanical properties of laser form...Several tensile samples were prepared using laser rapid forming (LRF) with Ti-6Al-4V alloy as powder material, and the samples were annealed. The microstructure and high temperature mechanical properties of laser formed Ti-6Al-4V alloy through annealing treatment were investigated. The short-term and long-term tensile tests at 350℃were performed. The results show that the microstructure of LRF samples consists of the large columnar priorβgrains which grow epitaxially from the substrate along the deposition direction. There are Widmanstatten a laths in priorβgrains, but a laths in annealed microstructure are coarser, and their aspect ratio is lower than that in as-deposited microstructure. In addition, the priorβgrain boundary is also coarsened and broken off through the annealing treatment. The high temperature mechanical properties of the annealed LRF samples exceed those of casting alloy significantly, especially the stress-rupture lifetime reaches 661.7 h even while the test stress increases from initial value of 490 MPa to the final stress of 800 MPa gradually.展开更多
The formability of light-weight alloy, such as aluminum alloy, magnesium alloy, can be improved significantly when formed at elevated temperature. Superplastic forming (SPF) is a well-known manufacturing method to for...The formability of light-weight alloy, such as aluminum alloy, magnesium alloy, can be improved significantly when formed at elevated temperature. Superplastic forming (SPF) is a well-known manufacturing method to form complex part of these materials. In order to realize mass production of SPF in industry, forming at high strain rate should be realized. In this study, the mechanical properties of 5A06 sheet were tested by uniaxial tensile test at high strain rate and elevated temperatures up to 550 ℃. Free bulging test and forming of round cup were carried out to evaluate the formability of the 5A06 sheet. Results show that the total elongation of the 5A06 sheet began to increase rapidly after 200 ℃, and reached the maximum value at 450 ℃. At higher temperature, early brittle fracture occurred. In free bulging test, the bulging height remained almost constant about 27.0 mm, which means the formability of the sheet is not sensitive to forming temperature at elevated temperature. In the forming of round cup part, temperature has direct effect on the corner filling ability of the sheet, especially at temperature lower than 400 ℃.展开更多
Nickel-based superalloy Rene88DT,has been laser-deposited using laser rapid forming (LRF) route.The mechanical properties and microstructure characteristics of LRF Rene88DT at 25℃ and 750℃ were evaluated.The results...Nickel-based superalloy Rene88DT,has been laser-deposited using laser rapid forming (LRF) route.The mechanical properties and microstructure characteristics of LRF Rene88DT at 25℃ and 750℃ were evaluated.The results shows that both strength and ductility of LRF Rene88DT can be improved significantly by the integration of optimized heat treatment (solution treatment (1160℃,2h/AC) + aging (760℃,8h/AC)) and the HIP treatment(1160℃,2h/200MPa).25℃ tensile properties is comparable to that of the Powder Metallurgy standard.The 750℃ tensile strength and ductility are also comparable to those of the Powder Metallurgy standard,but the yield strength is still a little lower at 750℃.As compared with the as-deposited state,g' precipitates of LRF Rene88DT are evolved gradually to be spherical in shape and uniformly distribute in the g matrix after optimized heat treatment and HIP treatment.Fracture surface shows that crack initiates at the edge for all the samples of LRF Rene88DT after tensile deformation.The deformation is found to be homogeneous in the whole sample.Necking phenomenon exists near the fracture surface,which corresponds with the superior strength and ductility of LRF Rene88DT.展开更多
Additive manufacturing(AM)is widely used in the automotive industry and has been expanded to include aerospace,marine,and rail.High flexibility and the possibility of manufacturing complex parts in AM motivate the int...Additive manufacturing(AM)is widely used in the automotive industry and has been expanded to include aerospace,marine,and rail.High flexibility and the possibility of manufacturing complex parts in AM motivate the integration of additive manu-facturing with classical forming technologies,which can improve tooling concepts and reduce costs.This study presents three applications of this integration.First,the possibility of successful utilization of selective laser melting for manufacturing extrusion tools with complex cooling channels and paths for thermocouples is reported,leading to significantly reduced inner die temperatures during the extrusion process.Second,sheet lamination is integrated with laser metal deposition(LMD)to manufacture deep-drawing dies.Promising results are achieved in reducing the stair step effect,which is the main challenge in sheet lamination,by LMD and following post-processing such as milling,ball burnishing,and laser polishing.The new manufacturing route shows that LMD can economically and efficiently reduce the stair step effect and omit the hardening step from the conventional manufacturing process route.Finally,LMD is used to manufacture a hot stamping punch with improved surface roughness by ball burnishing and near-surface complex cooling channels.The experimental results show that the manufactured punch has lower temperatures during hot stamping compared with the conventionally manufactured punch.This study shows the successful integration of AM processes with classical forming processes.展开更多
The one-step finite element method （FEM）, based on plastic deformation theory, has been widely used to simulate sheet metal forming processes, but its application in bulk metal forming simulation has been seldom inv...The one-step finite element method （FEM）, based on plastic deformation theory, has been widely used to simulate sheet metal forming processes, but its application in bulk metal forming simulation has been seldom investigated, because of the complexity involved. Thus, a bulk metal forming process was analyzed using a rapid FEM based on deformation theory. The material was assumed to be rigid-plastic and strain-hardened. The constitutive relationship between stress and total strain was adopted, whereas the incompressible condition was enforced by penalty function. The geometrical non-linearity in large plastic deformation was taken into consideration. Furthermore, the force boundary condition was treated by a simplified equivalent approach, considering the contact history. Based on constraint variational principle, the deformation FEM was proposed. The one-step forward simulation of axisymmettic upsetting process was performed using this method. The results were compared with those obtained by the traditional incremental FEM to verify the feasibility of the proposed method.展开更多
基金Projects (S0331010) supported by the National Natural Science Foundation of Chinaproject (05XE0131) supported by the Talent Cultivating Program of Northwestern Polytechnical University
文摘Low cost hydride-dehydride (HDH) Ti-6Al-4V (Ti-64) alloy powder was employed to investigate the metallurgical quality and mechanical properties of laser formed samples. With appropriate control of the laser forming processing parameters and the loose density of HDH powder, two kinds of defect, i.e. porosity and ill-bonding, can be avoided. Rare earth Nd powder was added to HDH Ti-64 powder to purify laser formed alloy. The results show that with a few additive of Nd, the microstructure of laser formed alloy changes from Widmanstatten morphology to a basket weave microstructure. Accordingly an appropriate addition of Nd is effective to improve both the strength and ductility of laser formed HDH Ti-64 alloy. The values of tensile test meet the wrought specification with the content of Nd ranging from 0.1%-0.2%(mass fraction).
基金This work is financially supported by Program of 863 Project ( No 2006AA03Z114)Programon National Key Laboratory Foundation (No 9140C500101060C50)
文摘A model for simulating the spray forming process with scanning atomizer was developed.Models for the scanning atomization and the deposition processes were coupled together in order to obtain a new description of the spray forming process.The model,which is able to predict the shape of a spray-formed billet prepared with scanning atomizer,was established after analyzing the changes in droplet size and density distribution along the r-axis in the spray cone in scanning atomization.The effects of the two kinds of atomization were compared,showing that the scanning atomization is good for deposition.
文摘In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on the population dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains. The model is coupled with droplets heat transfer controlling equations and solved for AI-4.5 wt pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.
基金the project 1M06032 Research Centre of Forming TechnologySlovak and Czech Project SK-CZ-0180-09
文摘To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconventional innovative technological procedures.One of these technologies is the forming in semi-solid state involving rapid solidification of miniature components from steels.Production of such components is complicated by a number of technical problems.To explain phenomena of the process and structure development,the production of miniature components from the tool steel X210Cr12 difficult to form was experimentally tested.The structure of this originally ledeburite steel consisted of 95 % of metastable austenite after the treatment.Metastable austenite was located particularly in globular and polygonal grains while the remaining interspaces were filled by lamellar network.The detected high stability of extremely high fraction of metastable austenite was tested under different conditions of thermal exposition and mechanical loading.
基金This work was financially supported by the National Natural Science Foundation of China (No.50171007)the Natural Science Foundation of Liaoning Province, China (No.972072).
文摘The flow field formed when an aluminum ribbon is produced by twin-belt rapid solidification is simulated with the solution algorithm （SOLA）-volume of fluid （VOF） method, and the influence of casting speed and cooling-belt velocity on the flow field is analyzed for a given ejection nozzle size. It has been found that the flow field can be filled well when the width of the ejection nozzle outlet is the same as that of the up slit of the cooling belt. When the ejection nozzle outlet is wider than the up slit of the cooling belt, the aluminum fluid can fill well if only the casting speed matches the cooling-belt velocity properly, otherwise under filling occurs in some areas in the cooling zone.
基金Project (50331010) supported by the National Natural Science Foundation of ChinaProject (05XE0131) supported by Talent Cultivating Program of Northwestern Polytechnical University
文摘Several tensile samples were prepared using laser rapid forming (LRF) with Ti-6Al-4V alloy as powder material, and the samples were annealed. The microstructure and high temperature mechanical properties of laser formed Ti-6Al-4V alloy through annealing treatment were investigated. The short-term and long-term tensile tests at 350℃were performed. The results show that the microstructure of LRF samples consists of the large columnar priorβgrains which grow epitaxially from the substrate along the deposition direction. There are Widmanstatten a laths in priorβgrains, but a laths in annealed microstructure are coarser, and their aspect ratio is lower than that in as-deposited microstructure. In addition, the priorβgrain boundary is also coarsened and broken off through the annealing treatment. The high temperature mechanical properties of the annealed LRF samples exceed those of casting alloy significantly, especially the stress-rupture lifetime reaches 661.7 h even while the test stress increases from initial value of 490 MPa to the final stress of 800 MPa gradually.
基金National Nature Science Foundation of China (50805033)Natural Science Foundation of Heilongjiang Province of China (E200804)
文摘The formability of light-weight alloy, such as aluminum alloy, magnesium alloy, can be improved significantly when formed at elevated temperature. Superplastic forming (SPF) is a well-known manufacturing method to form complex part of these materials. In order to realize mass production of SPF in industry, forming at high strain rate should be realized. In this study, the mechanical properties of 5A06 sheet were tested by uniaxial tensile test at high strain rate and elevated temperatures up to 550 ℃. Free bulging test and forming of round cup were carried out to evaluate the formability of the 5A06 sheet. Results show that the total elongation of the 5A06 sheet began to increase rapidly after 200 ℃, and reached the maximum value at 450 ℃. At higher temperature, early brittle fracture occurred. In free bulging test, the bulging height remained almost constant about 27.0 mm, which means the formability of the sheet is not sensitive to forming temperature at elevated temperature. In the forming of round cup part, temperature has direct effect on the corner filling ability of the sheet, especially at temperature lower than 400 ℃.
文摘Nickel-based superalloy Rene88DT,has been laser-deposited using laser rapid forming (LRF) route.The mechanical properties and microstructure characteristics of LRF Rene88DT at 25℃ and 750℃ were evaluated.The results shows that both strength and ductility of LRF Rene88DT can be improved significantly by the integration of optimized heat treatment (solution treatment (1160℃,2h/AC) + aging (760℃,8h/AC)) and the HIP treatment(1160℃,2h/200MPa).25℃ tensile properties is comparable to that of the Powder Metallurgy standard.The 750℃ tensile strength and ductility are also comparable to those of the Powder Metallurgy standard,but the yield strength is still a little lower at 750℃.As compared with the as-deposited state,g' precipitates of LRF Rene88DT are evolved gradually to be spherical in shape and uniformly distribute in the g matrix after optimized heat treatment and HIP treatment.Fracture surface shows that crack initiates at the edge for all the samples of LRF Rene88DT after tensile deformation.The deformation is found to be homogeneous in the whole sample.Necking phenomenon exists near the fracture surface,which corresponds with the superior strength and ductility of LRF Rene88DT.
基金was carried out within the projects 198180216,426515407 and 417202720 funded by the German Research Foundation(DFG).
文摘Additive manufacturing(AM)is widely used in the automotive industry and has been expanded to include aerospace,marine,and rail.High flexibility and the possibility of manufacturing complex parts in AM motivate the integration of additive manu-facturing with classical forming technologies,which can improve tooling concepts and reduce costs.This study presents three applications of this integration.First,the possibility of successful utilization of selective laser melting for manufacturing extrusion tools with complex cooling channels and paths for thermocouples is reported,leading to significantly reduced inner die temperatures during the extrusion process.Second,sheet lamination is integrated with laser metal deposition(LMD)to manufacture deep-drawing dies.Promising results are achieved in reducing the stair step effect,which is the main challenge in sheet lamination,by LMD and following post-processing such as milling,ball burnishing,and laser polishing.The new manufacturing route shows that LMD can economically and efficiently reduce the stair step effect and omit the hardening step from the conventional manufacturing process route.Finally,LMD is used to manufacture a hot stamping punch with improved surface roughness by ball burnishing and near-surface complex cooling channels.The experimental results show that the manufactured punch has lower temperatures during hot stamping compared with the conventionally manufactured punch.This study shows the successful integration of AM processes with classical forming processes.
基金Sponsored by National Natural Science Foundation of China(50575143)Specialized Research Fund for Doctoral Program of Higher Education of China(20040248005)
文摘The one-step finite element method （FEM）, based on plastic deformation theory, has been widely used to simulate sheet metal forming processes, but its application in bulk metal forming simulation has been seldom investigated, because of the complexity involved. Thus, a bulk metal forming process was analyzed using a rapid FEM based on deformation theory. The material was assumed to be rigid-plastic and strain-hardened. The constitutive relationship between stress and total strain was adopted, whereas the incompressible condition was enforced by penalty function. The geometrical non-linearity in large plastic deformation was taken into consideration. Furthermore, the force boundary condition was treated by a simplified equivalent approach, considering the contact history. Based on constraint variational principle, the deformation FEM was proposed. The one-step forward simulation of axisymmettic upsetting process was performed using this method. The results were compared with those obtained by the traditional incremental FEM to verify the feasibility of the proposed method.
