Bridgman directional solidification of investment castings is a key technology for the production of reliable and highly efficient gas turbine blades. In this paper, a mathematical model for three-dimensional （3D） s...Bridgman directional solidification of investment castings is a key technology for the production of reliable and highly efficient gas turbine blades. In this paper, a mathematical model for three-dimensional （3D） simulation of solidification process of single crystal investment castings was developed based on basic heat transfer equations. Complex heat radiation among the multiple blade castings and the furnace wall was considered in the model. Temperature distribution and temperature gradient in superalloy investment castings of single blade and multiple ones were investigated, respectively. The calculated cooling curves were compared with the experimental results and agreed well with the latter. It is indicated that the unsymmetrical temperature distribution and curved liquid-solid interface caused by the circle distribution of multiple turbine blades are probably main reasons why the stray grain and other casting defects occur in the turbine blade.展开更多
The three dimensional solidification simulation of the single crystal investment castings at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7 mm祄in was performed with the finite element thermal analysis method. The cal...The three dimensional solidification simulation of the single crystal investment castings at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7 mm祄in was performed with the finite element thermal analysis method. The calculated results were in accordance with the experimental ones. The results showed that with the increase of with-drawal rate the concave curvature of the liquidus isotherm was bigger and bigger and the temperature gradient of the castings decreased. No effects of withdrawal rate on the distribution of the temperature gradient of the starter and helical grain selector of the castings were observed at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7mm祄in. The relatively high temperature gradient between 500癈礳m and 1000癈礳m in the starter and helical grain selector was obtained at three withdrawal rates. The study indicates the three dimensional solidification simulation by finite element method is a powerful tool for understanding solidification and predicting defects in single crystal investment castings.展开更多
The density of vacuum counter-pressure cast aluminum alloy samples under grade-pressuring condition was studied. The effect of grade pressure difference and time on the density of aluminum alloys was discussed, and th...The density of vacuum counter-pressure cast aluminum alloy samples under grade-pressuring condition was studied. The effect of grade pressure difference and time on the density of aluminum alloys was discussed, and the solidification feeding model under grade-pressuring condition was established. The results indicate the grade-pressured solidification feeding ability of vacuum counter-pressure casting mainly depends on grade pressure difference and time. With the increase of grade pressure difference, the density of all the aluminum alloy samples increases, and the trend of change in density from the pouring gate to the top location is first decreasing gradually and then increasing. In addition, in obtaining the maximum density, the optimal grade-pressuring time is different for samples with different wall thicknesses, and the solidification time when the solid volume fraction of aluminum alloy reaches about 0.65 appears to be the optimal beginning time for gradepressuring.展开更多
To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different pro...To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.展开更多
A three-dimensional finite element method was developed to simulate the fluid flow,heat transfer and solidification for twin roll strip casting.An improved two-equationκ-εmodel was used to incorporate the turbulence...A three-dimensional finite element method was developed to simulate the fluid flow,heat transfer and solidification for twin roll strip casting.An improved two-equationκ-εmodel was used to incorporate the turbulence in fluid flow.The influence of vertical feeding and submerged entry nozzle feeding on the flow and temperature field was discussed.The optimum submersion depth and entry angle of submerged nozzle were obtained through comparison of the simulation results.展开更多
CA (Computer aided) investment casting technique used in superalloy castings of aerospace engine parts was presented. CA investment casting integrated computer application, RP (Rapid Prototyping) process, solidificati...CA (Computer aided) investment casting technique used in superalloy castings of aerospace engine parts was presented. CA investment casting integrated computer application, RP (Rapid Prototyping) process, solidification simulation and investment casting process. It broke the bottle neck of making metal die. Solid model of complex parts were produced by UGII or other software, then translated into STL(Stereolithography) file, after RP process of SLS(Selective Laser Sintering), wax pattern used in investment casting can be acquired without metal die in short time. These can reduce period and cost greatly of complex superalloy parts development of engine. The key processes of CA investment casting were discussed. The accuracy of model translation should match that of RP system. Choice of RP material, surface polishing, sintering parameter plays important role in RP process. Other processes, like solidification simulating and optimization of gate system were introduced. The conclusion was that complex parts can be produced by CA investment casting with lots of advantages. The accuracy of castings can reach CT5～7,and the smoothness can get Ra3～13 mm. These parts of engines worked well.展开更多
A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuouscasting to study the microstructure evolution during solidification and its mechanical properties. The so...A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuouscasting to study the microstructure evolution during solidification and its mechanical properties. The solidification of the alloy startedwith the primary crystallization of FCC-γ, followed by a binary eutectic reaction, with the formation of a heterogeneous constituent：FCC-γ＋G-phase, which replaced the low-melting eutectic （FCC-γ＋NiBe） in the Be-bearing alloys. AlNi6Si3 and γ′ formed during theterminal stages of solidification by investment casting, while the formation of AlNi6Si3 was suppressed by continuous casting. TheScheil solidification model agreed very well with the experimental results.展开更多
Steel strip feeding into the mold during continuous casting is known as an innovative technology.The newly applied technology is designed to further improve the slab quality.To analyze the complex phase change process...Steel strip feeding into the mold during continuous casting is known as an innovative technology.The newly applied technology is designed to further improve the slab quality.To analyze the complex phase change processes,molten sodium thiosulphate(Na2S2O3-5H2O)was used in the experimental investigation as a transparent analog for metallic alloys.Then,a numerical model incorporating fluid flow,heat transfer and phase change during strip feeding into the mold process was developed.The generalized enthalpy-based method was applied to describe the phase change behavior,and the porous media theory was used to model the blockage of fluid flow by the dendrites in the mushy zone between the strip and melt as well as the solidified shell and melt.The validated model was then used for the simulation of the real strip feeding into the mold process in an industrial scale.The whole shape of the strip under the effect of jet flow from the submerged entry nozzle(SEN)was presented.Results show that the strip will reach a pseudo-steady state after experiencing steel sheath formation,steel sheath melting and strip melting processes.When using the feeding method that is the strip narrow side toward the SEN in the present condition,the strip immersion length can reach 4.5 m below the meniscus and the slab centerline temperature can be decreased by 21 K to a maximum.When the strip feeding speed increased from 0.3 to 0.5 m/s,the minimum temperature of the centerline could be lowered by 4 K or so.展开更多
The cast-steel creeper tread is a part with complex external surface and internal shape, having a hot spot cased by the uneven wall thickness. As the hot spot is far away from the gating system and the feeding channel...The cast-steel creeper tread is a part with complex external surface and internal shape, having a hot spot cased by the uneven wall thickness. As the hot spot is far away from the gating system and the feeding channel is narrow, it is difficult to be fed by setting up a casting head, leading easily to shrinkage and causing great problems for investment casting. In this paper, the qualified castings can be successfully poured by feeding method of insert chill iron melt, smart design and placement process of chill, to realize simultaneous solidification of castings. The shrinkage of creeper tread is solved and the precision of castings is improved. This method exhibits easy operation, excellent feeding effect and simplified gating system to improve yield rate. Furthermore, it could save raw material, reduce waste product and lower product cost by using the insert chill iron melt in investment casting. The production practices showed that the qualified castings can be successfully poured by increasing feeding pressure, placing an internal chill to adjust the temperature of hot junction segments and realizing simultaneous solidification of castings.展开更多
An integrative computer aided investment casting (CAIC) technology for making complicated superalloy castings was described. Key processes of CAIC were discussed including the choice of SLS (Selectively Laser Sinterin...An integrative computer aided investment casting (CAIC) technology for making complicated superalloy castings was described. Key processes of CAIC were discussed including the choice of SLS (Selectively Laser Sintering) materials, sintering parameters, solidification simulation and gating and risering system optimization. Using CAIC process, many large-sized quality superalloy castings with complicated shape and thin wall have been produced successfully and economically in Central Iron & steel Research Institute (CISRI).展开更多
文摘Bridgman directional solidification of investment castings is a key technology for the production of reliable and highly efficient gas turbine blades. In this paper, a mathematical model for three-dimensional （3D） simulation of solidification process of single crystal investment castings was developed based on basic heat transfer equations. Complex heat radiation among the multiple blade castings and the furnace wall was considered in the model. Temperature distribution and temperature gradient in superalloy investment castings of single blade and multiple ones were investigated, respectively. The calculated cooling curves were compared with the experimental results and agreed well with the latter. It is indicated that the unsymmetrical temperature distribution and curved liquid-solid interface caused by the circle distribution of multiple turbine blades are probably main reasons why the stray grain and other casting defects occur in the turbine blade.
文摘The three dimensional solidification simulation of the single crystal investment castings at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7 mm祄in was performed with the finite element thermal analysis method. The calculated results were in accordance with the experimental ones. The results showed that with the increase of with-drawal rate the concave curvature of the liquidus isotherm was bigger and bigger and the temperature gradient of the castings decreased. No effects of withdrawal rate on the distribution of the temperature gradient of the starter and helical grain selector of the castings were observed at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7mm祄in. The relatively high temperature gradient between 500癈礳m and 1000癈礳m in the starter and helical grain selector was obtained at three withdrawal rates. The study indicates the three dimensional solidification simulation by finite element method is a powerful tool for understanding solidification and predicting defects in single crystal investment castings.
基金financially supported by the National Natural Science Foundation of China(No.51261025)
文摘The density of vacuum counter-pressure cast aluminum alloy samples under grade-pressuring condition was studied. The effect of grade pressure difference and time on the density of aluminum alloys was discussed, and the solidification feeding model under grade-pressuring condition was established. The results indicate the grade-pressured solidification feeding ability of vacuum counter-pressure casting mainly depends on grade pressure difference and time. With the increase of grade pressure difference, the density of all the aluminum alloy samples increases, and the trend of change in density from the pouring gate to the top location is first decreasing gradually and then increasing. In addition, in obtaining the maximum density, the optimal grade-pressuring time is different for samples with different wall thicknesses, and the solidification time when the solid volume fraction of aluminum alloy reaches about 0.65 appears to be the optimal beginning time for gradepressuring.
基金financially supported by the National Natural Science Foundation of China(No.51375391)the Xi’an Municipal Science and Technology Bureau in China(No.CX12180(5))
文摘To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.
基金Item Sponsored by National Natural Science Foundation of China(59995440)
文摘A three-dimensional finite element method was developed to simulate the fluid flow,heat transfer and solidification for twin roll strip casting.An improved two-equationκ-εmodel was used to incorporate the turbulence in fluid flow.The influence of vertical feeding and submerged entry nozzle feeding on the flow and temperature field was discussed.The optimum submersion depth and entry angle of submerged nozzle were obtained through comparison of the simulation results.
文摘CA (Computer aided) investment casting technique used in superalloy castings of aerospace engine parts was presented. CA investment casting integrated computer application, RP (Rapid Prototyping) process, solidification simulation and investment casting process. It broke the bottle neck of making metal die. Solid model of complex parts were produced by UGII or other software, then translated into STL(Stereolithography) file, after RP process of SLS(Selective Laser Sintering), wax pattern used in investment casting can be acquired without metal die in short time. These can reduce period and cost greatly of complex superalloy parts development of engine. The key processes of CA investment casting were discussed. The accuracy of model translation should match that of RP system. Choice of RP material, surface polishing, sintering parameter plays important role in RP process. Other processes, like solidification simulating and optimization of gate system were introduced. The conclusion was that complex parts can be produced by CA investment casting with lots of advantages. The accuracy of castings can reach CT5～7,and the smoothness can get Ra3～13 mm. These parts of engines worked well.
基金supported by the ARRS under the framework of the Slovenian-Brazilian Bilateral Project BI-BR/12-14-003funding from the European Union Seventh Framework Programme under Grant Agreement 312483-ESTEEM2(Integrated Infrastructure InitiativeI3)
文摘A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuouscasting to study the microstructure evolution during solidification and its mechanical properties. The solidification of the alloy startedwith the primary crystallization of FCC-γ, followed by a binary eutectic reaction, with the formation of a heterogeneous constituent：FCC-γ＋G-phase, which replaced the low-melting eutectic （FCC-γ＋NiBe） in the Be-bearing alloys. AlNi6Si3 and γ′ formed during theterminal stages of solidification by investment casting, while the formation of AlNi6Si3 was suppressed by continuous casting. TheScheil solidification model agreed very well with the experimental results.
基金This work was funded by the National Natural Science Foundation of China(Nos.51574068 and 51974071)Yong Elite Scientists Sponsorship Program by China Association for Science and Technology(No.2018QNRC001).
文摘Steel strip feeding into the mold during continuous casting is known as an innovative technology.The newly applied technology is designed to further improve the slab quality.To analyze the complex phase change processes,molten sodium thiosulphate(Na2S2O3-5H2O)was used in the experimental investigation as a transparent analog for metallic alloys.Then,a numerical model incorporating fluid flow,heat transfer and phase change during strip feeding into the mold process was developed.The generalized enthalpy-based method was applied to describe the phase change behavior,and the porous media theory was used to model the blockage of fluid flow by the dendrites in the mushy zone between the strip and melt as well as the solidified shell and melt.The validated model was then used for the simulation of the real strip feeding into the mold process in an industrial scale.The whole shape of the strip under the effect of jet flow from the submerged entry nozzle(SEN)was presented.Results show that the strip will reach a pseudo-steady state after experiencing steel sheath formation,steel sheath melting and strip melting processes.When using the feeding method that is the strip narrow side toward the SEN in the present condition,the strip immersion length can reach 4.5 m below the meniscus and the slab centerline temperature can be decreased by 21 K to a maximum.When the strip feeding speed increased from 0.3 to 0.5 m/s,the minimum temperature of the centerline could be lowered by 4 K or so.
文摘The cast-steel creeper tread is a part with complex external surface and internal shape, having a hot spot cased by the uneven wall thickness. As the hot spot is far away from the gating system and the feeding channel is narrow, it is difficult to be fed by setting up a casting head, leading easily to shrinkage and causing great problems for investment casting. In this paper, the qualified castings can be successfully poured by feeding method of insert chill iron melt, smart design and placement process of chill, to realize simultaneous solidification of castings. The shrinkage of creeper tread is solved and the precision of castings is improved. This method exhibits easy operation, excellent feeding effect and simplified gating system to improve yield rate. Furthermore, it could save raw material, reduce waste product and lower product cost by using the insert chill iron melt in investment casting. The production practices showed that the qualified castings can be successfully poured by increasing feeding pressure, placing an internal chill to adjust the temperature of hot junction segments and realizing simultaneous solidification of castings.
文摘An integrative computer aided investment casting (CAIC) technology for making complicated superalloy castings was described. Key processes of CAIC were discussed including the choice of SLS (Selectively Laser Sintering) materials, sintering parameters, solidification simulation and gating and risering system optimization. Using CAIC process, many large-sized quality superalloy castings with complicated shape and thin wall have been produced successfully and economically in Central Iron & steel Research Institute (CISRI).
