In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process,the effects of different gating systems on mold filling,solidification process,and prediction of shrinkag...In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process,the effects of different gating systems on mold filling,solidification process,and prediction of shrinkage porosity of aero-engine turbine nozzle castings were investigated by simulation and experimental methods.Results show that the design of the vertical runner would cause greater turbulence of the melt in the riser during the mold filling process,and the outer runner is not necessary.With the decrease in number of runners,the hot spot moves down towards the casting,and the shrinkage and porosity defects are formed in the casting below the riser.In the original designs,a certain tendency of shrinkage and porosity defect is found in the vanes,inner rings,and outer rings of the castings by both simulation prediction and experiment.Finally,based on the processing optimization,the aero-engine turbine nozzle casting with no shrinkage and porosity defects is obtained.展开更多
Phosphate-bonded investments have already been widely utilized in dental restoration and micro-casting of artistic products for its outstanding rapid setting and high strength. However, the rapid setting rate of inves...Phosphate-bonded investments have already been widely utilized in dental restoration and micro-casting of artistic products for its outstanding rapid setting and high strength. However, the rapid setting rate of investment slurry has up to now been a barrier to extend the use of such slurry in preparation of medium-sized ceramic moulds. This paper proposes a new process of rapid fabrication of magnesia-phosphate-bonded investment ceramic moulds for medium-sized superalloy castings utilizing bauxite and mullite as refractory aggregates. In order to determine the properties of magnesia-phosphate-bonded bauxite-mullite investments (MPBBMI), a series of experiments were conducted, including modifciation of the workable time of slurry by liquid(mL)/powder(g)(L/P) ratio and addition of boric acid as retard agent and sodium tri-polyphosphate (STP) as strengthening agent, and adjustment of bauxite (g)/mullite(g)(B/M) ratio for mechanical strength. Mechanical vibration was applied to improve initial setting time and fluidity when pouring investment slurry; then an intermediate size ceramic mould for superalloy castings was manufactured by means of this rapid preparing process with MPBBMI material. The results showed that the MPBBMI slurry exhibits proper initial setting time and excellent fluidity when the L/P ratio is 0.64 and the boric acid content is 0.88wt.%. The fired specimens made from the MPBBMI material demonstrated adequate compression strength to withstand impact force of molten metal when the B/M ratio is 0.89 and the STP content is 0.92wt.%. The experimental results confirmed the feasibility of the proposed rapid fabricating process for medium-sized ceramic moulds with MPBBMI material by appropriate measures.展开更多
K439B nickel-based superalloy is a new type of high-temperature material.There is insufficient research on its constitutive equations and numerical modeling of thermal stress.Isothermal tensile experiments of K439B su...K439B nickel-based superalloy is a new type of high-temperature material.There is insufficient research on its constitutive equations and numerical modeling of thermal stress.Isothermal tensile experiments of K439B superalloy at different temperatures(20°C-1,000°C)and strain rates(1.33×10^(-3)s^(-1)-5.33×10^(-3)s^(-1))were performed by using a Gleeble-3800 simulator.The elastic moduli at different temperatures(20°C-650°C)were measured by resonance method.Subsequently,stress-strain curves were measured for K439B superalloy under different conditions.The elastic-viscoplastic constitutive equations were established and the correspongding parameters were solved by employing the Perzyna model.The verification results indicate that the calculated values of the constitutive equations are in good agreement with the experimental values.On this basis,the influence of process parameters on thermal stress was investigated by numerical simulation and orthogonal experimental design.The results of orthogonal experimental design reveal that the cooling mode of casting has a significant influence on the thermal stress,while pouring temperature and preheating temperature of shell mold have minimal impact.The distribution of physical fields under optimal process parameters,determined based on the orthogonal experimental design results,was simulated.The simulation results determine separately the specific positions with maximum values for effective stress,plastic strain,and displacement within the casting.The maximum stress is about 1,000.0 MPa,the plastic strain is about 0.135,and the displacement is about 1.47 mm.Moreover,the distribution states of thermal stress,strain,and displacement are closely related to the distribution of the temperature gradient and cooling rate in the casting.The research would provide a theoretical reference for exploring the stress-strain behavior and numerical modeling of the effective stress of the alloy during the casting process.展开更多
An integrated macro and micro multi-scale model for the three-dimensional microstructure simulation of Ni-based superalloy investment castings was developed, and applied to industrial castings to investigate grain evo...An integrated macro and micro multi-scale model for the three-dimensional microstructure simulation of Ni-based superalloy investment castings was developed, and applied to industrial castings to investigate grain evolution during solidification. A ray tracing method was used to deal with the complex heat radiation transfer. The rnicrostructure evolution was simulated based on the Modified Cellular Automaton method, which was coupled with three-dimensional nested macro and micro grids. Experi- ments for Ni-based superalloy turbine wheel investment casting were carried out, which showed a good correspondence with the simulated results. It is indicated that the proposed model is able to predict the microstructure of the casting precisely, which provides a tool for the optimizing process.展开更多
This paper presents a brief review of the current casting techniques for single-crystal （SC） blades, as well as an analysis of the solidification process in complex turbine blades. A series of novel casting methods ...This paper presents a brief review of the current casting techniques for single-crystal （SC） blades, as well as an analysis of the solidification process in complex turbine blades. A series of novel casting methods based on the Bridgman process were presented to illustrate the development in the production of SC blades from super- alloys. The grain continuator and the heat conductor techniques were developed to remove geometry-related grain defects. In these techniques, the heat barrier that hinders lateral SC growth from the blade airfoil into the extremities of the platform is minimized. The parallel heating and cooling system was developed to achieve symmetric thermal conditions for SC solidification in blade clusters, thus considerably decreasing the negative shadow effect and its related defects in the current Bridgman process. The dipping and heaving technique, in which thin- shell molds are utilized, was developed to enable the establishment of a high temperature gradient for SC growth and the freckle-free solidification of superalloy castings. Moreover, by applying the targeted cooling and heating technique, a novel concept for the three-dimen- sional and precise control of SC growth, a proper thermal arrangement may be dynamically established for the microscopic control of SC growth in the critical areas of large industrial gas turbine blades.展开更多
文摘In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process,the effects of different gating systems on mold filling,solidification process,and prediction of shrinkage porosity of aero-engine turbine nozzle castings were investigated by simulation and experimental methods.Results show that the design of the vertical runner would cause greater turbulence of the melt in the riser during the mold filling process,and the outer runner is not necessary.With the decrease in number of runners,the hot spot moves down towards the casting,and the shrinkage and porosity defects are formed in the casting below the riser.In the original designs,a certain tendency of shrinkage and porosity defect is found in the vanes,inner rings,and outer rings of the castings by both simulation prediction and experiment.Finally,based on the processing optimization,the aero-engine turbine nozzle casting with no shrinkage and porosity defects is obtained.
文摘Phosphate-bonded investments have already been widely utilized in dental restoration and micro-casting of artistic products for its outstanding rapid setting and high strength. However, the rapid setting rate of investment slurry has up to now been a barrier to extend the use of such slurry in preparation of medium-sized ceramic moulds. This paper proposes a new process of rapid fabrication of magnesia-phosphate-bonded investment ceramic moulds for medium-sized superalloy castings utilizing bauxite and mullite as refractory aggregates. In order to determine the properties of magnesia-phosphate-bonded bauxite-mullite investments (MPBBMI), a series of experiments were conducted, including modifciation of the workable time of slurry by liquid(mL)/powder(g)(L/P) ratio and addition of boric acid as retard agent and sodium tri-polyphosphate (STP) as strengthening agent, and adjustment of bauxite (g)/mullite(g)(B/M) ratio for mechanical strength. Mechanical vibration was applied to improve initial setting time and fluidity when pouring investment slurry; then an intermediate size ceramic mould for superalloy castings was manufactured by means of this rapid preparing process with MPBBMI material. The results showed that the MPBBMI slurry exhibits proper initial setting time and excellent fluidity when the L/P ratio is 0.64 and the boric acid content is 0.88wt.%. The fired specimens made from the MPBBMI material demonstrated adequate compression strength to withstand impact force of molten metal when the B/M ratio is 0.89 and the STP content is 0.92wt.%. The experimental results confirmed the feasibility of the proposed rapid fabricating process for medium-sized ceramic moulds with MPBBMI material by appropriate measures.
基金supported by the National Science and Technology Major Project of China(Grant No.J2019-VI-0004-0117)the State Key Laboratory of Special Rare Metal Materials(No.SKL2021K002)Northwest Rare Metal Materials Research Institute Ningxia Co.,Ltd.
文摘K439B nickel-based superalloy is a new type of high-temperature material.There is insufficient research on its constitutive equations and numerical modeling of thermal stress.Isothermal tensile experiments of K439B superalloy at different temperatures(20°C-1,000°C)and strain rates(1.33×10^(-3)s^(-1)-5.33×10^(-3)s^(-1))were performed by using a Gleeble-3800 simulator.The elastic moduli at different temperatures(20°C-650°C)were measured by resonance method.Subsequently,stress-strain curves were measured for K439B superalloy under different conditions.The elastic-viscoplastic constitutive equations were established and the correspongding parameters were solved by employing the Perzyna model.The verification results indicate that the calculated values of the constitutive equations are in good agreement with the experimental values.On this basis,the influence of process parameters on thermal stress was investigated by numerical simulation and orthogonal experimental design.The results of orthogonal experimental design reveal that the cooling mode of casting has a significant influence on the thermal stress,while pouring temperature and preheating temperature of shell mold have minimal impact.The distribution of physical fields under optimal process parameters,determined based on the orthogonal experimental design results,was simulated.The simulation results determine separately the specific positions with maximum values for effective stress,plastic strain,and displacement within the casting.The maximum stress is about 1,000.0 MPa,the plastic strain is about 0.135,and the displacement is about 1.47 mm.Moreover,the distribution states of thermal stress,strain,and displacement are closely related to the distribution of the temperature gradient and cooling rate in the casting.The research would provide a theoretical reference for exploring the stress-strain behavior and numerical modeling of the effective stress of the alloy during the casting process.
基金financially supported by the National Basic Research Program of China (Grant Nos. 2005CB724105 and 2011CB706801)the National Natural Science Foundation of China (Grant No. 10477010)+1 种基金the National High Technology Research, Development Program of China (Grant No. 2007AA04Z141)the Important National Science & Technology Specific Projects (Grant No. 2009ZX04006-041-04)
文摘An integrated macro and micro multi-scale model for the three-dimensional microstructure simulation of Ni-based superalloy investment castings was developed, and applied to industrial castings to investigate grain evolution during solidification. A ray tracing method was used to deal with the complex heat radiation transfer. The rnicrostructure evolution was simulated based on the Modified Cellular Automaton method, which was coupled with three-dimensional nested macro and micro grids. Experi- ments for Ni-based superalloy turbine wheel investment casting were carried out, which showed a good correspondence with the simulated results. It is indicated that the proposed model is able to predict the microstructure of the casting precisely, which provides a tool for the optimizing process.
文摘This paper presents a brief review of the current casting techniques for single-crystal （SC） blades, as well as an analysis of the solidification process in complex turbine blades. A series of novel casting methods based on the Bridgman process were presented to illustrate the development in the production of SC blades from super- alloys. The grain continuator and the heat conductor techniques were developed to remove geometry-related grain defects. In these techniques, the heat barrier that hinders lateral SC growth from the blade airfoil into the extremities of the platform is minimized. The parallel heating and cooling system was developed to achieve symmetric thermal conditions for SC solidification in blade clusters, thus considerably decreasing the negative shadow effect and its related defects in the current Bridgman process. The dipping and heaving technique, in which thin- shell molds are utilized, was developed to enable the establishment of a high temperature gradient for SC growth and the freckle-free solidification of superalloy castings. Moreover, by applying the targeted cooling and heating technique, a novel concept for the three-dimen- sional and precise control of SC growth, a proper thermal arrangement may be dynamically established for the microscopic control of SC growth in the critical areas of large industrial gas turbine blades.
