Flexibility of the CSIR-RCS, induction stirring with simultaneous air cooling process, in combination with high pressure die casting is successfully demonstrated by semi-solid rheocasting of plates performed on commer...Flexibility of the CSIR-RCS, induction stirring with simultaneous air cooling process, in combination with high pressure die casting is successfully demonstrated by semi-solid rheocasting of plates performed on commercial 2024, 6082 and 7075 wrought aluminum alloys. Tensile properties were measured for the above mentioned rheocast wrought aluminum alloys in the T6 condition. The results showed that tensile properties were close to or even in some cases exceeded the minimum specifications. The yield strength and elongation of rheocast 2024-T6 exceeded the minimum requirements of the wrought alloy in the T6 condition but the ultimate tensile strength achieved only 90% of the specification because the Mg content of the starting alloy was below the commercial alloy specification. The strengths of rheocast 6082-T6 exceeded all of the wrought alloy T6 strength targets but the elongation only managed 36% of the required minimum due to porosity, caused by incipient melting during solution heat treatment, and the presence of fine intermetallie needles in the eutectic. The yield strength of rheocast 7075 exceeded the required one and the ultimate tensile strength also managed 97% of the specification; while the elongation only reached 46% of the minimum requirement also due to incipient melting porosity caused during the solution heat treatment process.展开更多
Near-net shape rheocasting with the Council for Scientific and Industrial Research Rheo casting system(CSIR-RCS) and a high pressure die casting machine was successfully performed on Al-5Ti-1B grain refined aluminum a...Near-net shape rheocasting with the Council for Scientific and Industrial Research Rheo casting system(CSIR-RCS) and a high pressure die casting machine was successfully performed on Al-5Ti-1B grain refined aluminum alloy 7075.Grain refinement levels used were 0.03% Ti,0.13% Ti and 0.29% Ti(mass fraction).Tensile tests reveal that the ultimate tensile strengths,at all levels of grain refinement,are at least 97% of the specified minimum.Elongation at fracture increases with the increase of level of grain refinement although a maximum elongation is only 76% of the required minimum elongation in the case of 0.29% Ti.Incipient melting,during solution treatment,of the low melting point multinary eutectic causes porosity in the material and accounts for poor elongation results.0.03% Ti has a coarse eutectic structure forming larger pores while 0.29% Ti has a fine structure forming fine pores in the multinary eutectic.The 0.2% offset yield strengths of all the grain refinement levels are at least equal to or above the specified minimum and a decrease is observed with the increase of grain refinement level.There is a clear reduction in grain size from 0.03% Ti to 0.29% Ti in the as-cast condition.An underlying grain structure develops in the T6 condition material which has an inverse size to the as-cast structure;coarse grained as-cast material results in fine grained T6 condition material after solution heat treatment.The decrease in the offset yield strength as grain refinement increases correlates very strongly with the T6 grain sizes according to a Hall-Petch type relationship.展开更多
Based on XRD,SEM and EDS analyses,the phases in GH4151 alloy were identified.Differential scanning calorimetry(DSC)experiment and metallographic method were carried out to determine the incipient melting temperature(I...Based on XRD,SEM and EDS analyses,the phases in GH4151 alloy were identified.Differential scanning calorimetry(DSC)experiment and metallographic method were carried out to determine the incipient melting temperature(IMT)of the alloy.The result shows that the IMT of alloy is situated between 1150 and 1160℃.Subsequently,the dissolution process of Laves phase was carried out,and the dissolution kinetic equations were obtained at different temperatures.And then based on the verification of experiments,the model was confirmed to be credible to predict the fraction of the Laves phase dissolution.Finally,the results of diffusion coefficients indicate that the diffusion of Nb element is a critical factor for homogenization process of GH4151 alloy.展开更多
The forming and growing mechanisms of homogenization-solution pores in a single crystal superalloy were investigated. The microstructures were observed with optical microscope （OM） and field emission microscope （FE...The forming and growing mechanisms of homogenization-solution pores in a single crystal superalloy were investigated. The microstructures were observed with optical microscope （OM） and field emission microscope （FEM） after homogenization-solution heat treated at 1328℃ and 1350 ℃ for 2 h, 6 h and 9 h. Results indicate that when heat treated at 1328 ℃, pores appear at the interface of eutectic and matrix at first and then leave in the matrix with the shrink of eutectic. When heat treated at 1350 ℃, incipient melting happens at first, and some of them have a pore in the center. After that, with the homogenization-solution process, incipient melting microstructure fades away gradually. By analyzing the results with thermodynamics and kinetics methods, it is concluded that some pores nucleate during directional solidification and then become larger and visible during homogenization-solution heat treatments; some pores are generated by incipient melting, yet such pores are difficult to be distinguished from other pores; imbalanced elements cross-diffusion induces to the forming and growing of pores too, and such imbalanced diffusion also plays an important part on the growth of all preexisting pores.展开更多
Numerical heat-transfer and turbulent flow model for an industrial high-pressure gas quenching vacuum furnace was established to simulate the heating,holding and gas fan quenching of a low rhenium-bearing Ni-based sin...Numerical heat-transfer and turbulent flow model for an industrial high-pressure gas quenching vacuum furnace was established to simulate the heating,holding and gas fan quenching of a low rhenium-bearing Ni-based single crystal turbine blade.The mesh of simplified furnace model was built using finite volume method and the boundary conditions were set up according to the practical process.Simulation results show that the turbine blade geometry and the mutual shielding among blades have significant influence on the uniformity of the temperature distribution.The temperature distribution at sharp corner,thin wall and corner part is higher than that at thick wall part of blade during heating,and the isotherms show a toroidal line to the center of thick wall.The temperature of sheltered units is lower than that of the remaining part of blade.When there is no shelteration among multiple blades,the temperature distribution for all blades is almost identical.The fluid velocity field,temperature field and cooling curves of the single and multiple turbine blades during gas fan quenching were also simulated.Modeling results indicate that the loading tray,free outlet and the location of turbine blades have important influences on the flow field.The high-speed gas flows out from the nozzle is divided by loading tray,and the free outlet enhanced the two vortex flow at the end of the furnace door.The closer the blade is to the exhaust outlet and the nozzle,the greater the flow velocity is and the more adequate the flow is.The blade geometry has an effect on the cooling for single blade and multiple blades during gas fan quenching,and the effects in double layers differs from that in single layer.For single blade,the cooing rate at thin-walled part is lower than that at thick-walled part,the cooling rate at sharp corner is greater than that at tenon and blade platform,and the temperature at regions close to the internal position is decreased more slowly than that close to the surface.For multiple blades in single layer,the tempe展开更多
The evolution of microstructure and formation mechanism of incipient melting microstructure of DD5 single crystal superalloy during solution heat treatment were studied by scanning electron microscopy(SEM),electron pr...The evolution of microstructure and formation mechanism of incipient melting microstructure of DD5 single crystal superalloy during solution heat treatment were studied by scanning electron microscopy(SEM),electron probe microanalysis(EPMA),and energy dispersive spectroscopy(EDS).The solidus and liquidus of single crystal alloy were obtained by differential scanning calorimetry(DSC).Results show that the mosaic-like eutectic and fan-like eutectic are dissolved at first,and the coarseγ'phase is dissolved later during the solution heat treatment of 1,390°C/2 h+1,310°C/4 h+1,320°C/10 h+air cooling(AC).The composition segregations of Al,Ta,W and Re are 0.99,0.96,1.04 and 1.16,respectively,which close to 1.The incipient melting is caused by the low local temperature of the alloy,and the micropore region with a lower melting point is the preferred position for incipient melting.展开更多
Beginning of the twentieth century was marked by coinage of a new rock name, Charnockite, first described as a hypersthene-bearing granite from Southern India. Since then charnockites have been described from most of ...Beginning of the twentieth century was marked by coinage of a new rock name, Charnockite, first described as a hypersthene-bearing granite from Southern India. Since then charnockites have been described from most of the conti-nents and mostly restricted to high-grade belts. Later half of the last century saw a lively debate over an igneous versus metamorphic origin. However, two factors acted as deterrents for the resolution of the debate. First, charnockites and associated rocks occur in a variety of different structural setting and display diverse field rela-tions, attesting to possible different mode of origin. Second and possibly more important is the lack of consensus on the nomenclature of charnockites and associated rocks and this is commonly linked with the metamorphic versus magmatic perspective. Scanning the literature of this period makes one believe that both metamorphic and magmatic hypotheses are valid, but applicable to different field setting only. Before critically evaluating individual cases, it is imperative that a uniform approach in nomenclature should be agreed upon. It is proposed that name charnockite be adopted for any quartzofeldspathic rock with orthopyroxene, irrespective of its mode of occurrence, struc-tural setting and mode of origin. The associated more mafic varieties, be better described as mafic granulite, rather than basic charnockite. For the patchy charnockites of east Gondwana (including parts of Peninsular India, Sri Lanka and Antarctica), metamorphic transformation from amphibolite facies gneiss, by two different mechanisms: CO2 ingress from deep level, and drop in fluid pressure, has been proposed. However, all such patchy occurrence is not amenable to explanation by metamorphic trans- formation. In some instances, migmatisation of older charnockitic rocks is evident. Also pro- gressive charnockitisation relating patchy char-nockite to banded variety could be argued against on two counts: grain-size relation and time-relation. Larger bodies or bands have been explained a展开更多
Hf lowers the incipient melting temperature of superalloy. As carbon content in Hf-bearing alloy decreases, the incipient melting temperature drops furthey. PD ingots have stronger tendency to incipient melting than H...Hf lowers the incipient melting temperature of superalloy. As carbon content in Hf-bearing alloy decreases, the incipient melting temperature drops furthey. PD ingots have stronger tendency to incipient melting than HRS ones. Even though in PD ingot, the sensitivities at both ends of the ingot are quite different. The melting of Ni_5Hf phase may be considered as one of the main factors affecting incipient melting. The more Ni_5Hf the alloy contains, the more serious the incipient melting becomes. The results of differential thermal analysis (DTA) have proved that the peak of 1135-1160℃ corresponds to the melting range or Ni_5Hf. By means of a pretreatment at 1150℃, 8h, Ni_5Hf phase can be eliminated in two ways: the reaction Ni_5Hf+γ(C)→MC_(2)+γ and solid solution, and therefore the final solid solution treatment can be carried out at 1260℃. This brings about a high homogenized structure and further increases the stress rupture properties of the alloy at 1040℃, 140 MPa.展开更多
The roles of hot isostatic pressing (HIP) temperatures (490 ℃/100 MPa/2 h,510 ℃/100 MPa/2 h,530 ℃/100 MPa/2 h) in the microstructure and properties of AlSi7Cu2Mg alloy step castings with three types wall thicknesse...The roles of hot isostatic pressing (HIP) temperatures (490 ℃/100 MPa/2 h,510 ℃/100 MPa/2 h,530 ℃/100 MPa/2 h) in the microstructure and properties of AlSi7Cu2Mg alloy step castings with three types wall thicknesses were studied.The experimental results show that HIP at 490 ℃ could effectively eliminate the internal closed porosity of the castings with a wall thickness of ≤40 mm,but for heavy castings (70 mm),even HIP at 530 ℃,a few loose defects remained inside the castings.Two types of incipient eutectics containing Al5Mg8Si6Cu2 and Al2Cu were observed in the samples that HIP at 530 ℃,which was responsible for the decrease of the tensile strength of the castings within the medium wall thickness (40 mm) compared with that HIP at 490 ℃.HIP could greatly reduce the difference of the tensile strength values of castings with wall thicknesses 17 mm and 70 mm from 117.93 MPa (without HIP) to 25.7 MPa (with HIP at 530 ℃).展开更多
文摘Flexibility of the CSIR-RCS, induction stirring with simultaneous air cooling process, in combination with high pressure die casting is successfully demonstrated by semi-solid rheocasting of plates performed on commercial 2024, 6082 and 7075 wrought aluminum alloys. Tensile properties were measured for the above mentioned rheocast wrought aluminum alloys in the T6 condition. The results showed that tensile properties were close to or even in some cases exceeded the minimum specifications. The yield strength and elongation of rheocast 2024-T6 exceeded the minimum requirements of the wrought alloy in the T6 condition but the ultimate tensile strength achieved only 90% of the specification because the Mg content of the starting alloy was below the commercial alloy specification. The strengths of rheocast 6082-T6 exceeded all of the wrought alloy T6 strength targets but the elongation only managed 36% of the required minimum due to porosity, caused by incipient melting during solution heat treatment, and the presence of fine intermetallie needles in the eutectic. The yield strength of rheocast 7075 exceeded the required one and the ultimate tensile strength also managed 97% of the specification; while the elongation only reached 46% of the minimum requirement also due to incipient melting porosity caused during the solution heat treatment process.
文摘Near-net shape rheocasting with the Council for Scientific and Industrial Research Rheo casting system(CSIR-RCS) and a high pressure die casting machine was successfully performed on Al-5Ti-1B grain refined aluminum alloy 7075.Grain refinement levels used were 0.03% Ti,0.13% Ti and 0.29% Ti(mass fraction).Tensile tests reveal that the ultimate tensile strengths,at all levels of grain refinement,are at least 97% of the specified minimum.Elongation at fracture increases with the increase of level of grain refinement although a maximum elongation is only 76% of the required minimum elongation in the case of 0.29% Ti.Incipient melting,during solution treatment,of the low melting point multinary eutectic causes porosity in the material and accounts for poor elongation results.0.03% Ti has a coarse eutectic structure forming larger pores while 0.29% Ti has a fine structure forming fine pores in the multinary eutectic.The 0.2% offset yield strengths of all the grain refinement levels are at least equal to or above the specified minimum and a decrease is observed with the increase of grain refinement level.There is a clear reduction in grain size from 0.03% Ti to 0.29% Ti in the as-cast condition.An underlying grain structure develops in the T6 condition material which has an inverse size to the as-cast structure;coarse grained as-cast material results in fine grained T6 condition material after solution heat treatment.The decrease in the offset yield strength as grain refinement increases correlates very strongly with the T6 grain sizes according to a Hall-Petch type relationship.
基金Project(50974016)supported by the National Natural Science Foundation of China。
文摘Based on XRD,SEM and EDS analyses,the phases in GH4151 alloy were identified.Differential scanning calorimetry(DSC)experiment and metallographic method were carried out to determine the incipient melting temperature(IMT)of the alloy.The result shows that the IMT of alloy is situated between 1150 and 1160℃.Subsequently,the dissolution process of Laves phase was carried out,and the dissolution kinetic equations were obtained at different temperatures.And then based on the verification of experiments,the model was confirmed to be credible to predict the fraction of the Laves phase dissolution.Finally,the results of diffusion coefficients indicate that the diffusion of Nb element is a critical factor for homogenization process of GH4151 alloy.
基金financially supported by the Foundation of Beijing Institute of Aeronautical Materials (No. 150109)
文摘The forming and growing mechanisms of homogenization-solution pores in a single crystal superalloy were investigated. The microstructures were observed with optical microscope （OM） and field emission microscope （FEM） after homogenization-solution heat treated at 1328℃ and 1350 ℃ for 2 h, 6 h and 9 h. Results indicate that when heat treated at 1328 ℃, pores appear at the interface of eutectic and matrix at first and then leave in the matrix with the shrink of eutectic. When heat treated at 1350 ℃, incipient melting happens at first, and some of them have a pore in the center. After that, with the homogenization-solution process, incipient melting microstructure fades away gradually. By analyzing the results with thermodynamics and kinetics methods, it is concluded that some pores nucleate during directional solidification and then become larger and visible during homogenization-solution heat treatments; some pores are generated by incipient melting, yet such pores are difficult to be distinguished from other pores; imbalanced elements cross-diffusion induces to the forming and growing of pores too, and such imbalanced diffusion also plays an important part on the growth of all preexisting pores.
基金financially supported by the National Natural Science Foundation of China(grant nos.51374137 and 51171089)National Science and Technology Major Special Project of China(grant no.2012ZX04012-011)National Basic Research Program of China(grant no.2011CB706801)
文摘Numerical heat-transfer and turbulent flow model for an industrial high-pressure gas quenching vacuum furnace was established to simulate the heating,holding and gas fan quenching of a low rhenium-bearing Ni-based single crystal turbine blade.The mesh of simplified furnace model was built using finite volume method and the boundary conditions were set up according to the practical process.Simulation results show that the turbine blade geometry and the mutual shielding among blades have significant influence on the uniformity of the temperature distribution.The temperature distribution at sharp corner,thin wall and corner part is higher than that at thick wall part of blade during heating,and the isotherms show a toroidal line to the center of thick wall.The temperature of sheltered units is lower than that of the remaining part of blade.When there is no shelteration among multiple blades,the temperature distribution for all blades is almost identical.The fluid velocity field,temperature field and cooling curves of the single and multiple turbine blades during gas fan quenching were also simulated.Modeling results indicate that the loading tray,free outlet and the location of turbine blades have important influences on the flow field.The high-speed gas flows out from the nozzle is divided by loading tray,and the free outlet enhanced the two vortex flow at the end of the furnace door.The closer the blade is to the exhaust outlet and the nozzle,the greater the flow velocity is and the more adequate the flow is.The blade geometry has an effect on the cooling for single blade and multiple blades during gas fan quenching,and the effects in double layers differs from that in single layer.For single blade,the cooing rate at thin-walled part is lower than that at thick-walled part,the cooling rate at sharp corner is greater than that at tenon and blade platform,and the temperature at regions close to the internal position is decreased more slowly than that close to the surface.For multiple blades in single layer,the tempe
基金The authors would like to express their sincere thanks to the financial support from the Key Project of National Natural Science Foundation of China(No.U16642548).
文摘The evolution of microstructure and formation mechanism of incipient melting microstructure of DD5 single crystal superalloy during solution heat treatment were studied by scanning electron microscopy(SEM),electron probe microanalysis(EPMA),and energy dispersive spectroscopy(EDS).The solidus and liquidus of single crystal alloy were obtained by differential scanning calorimetry(DSC).Results show that the mosaic-like eutectic and fan-like eutectic are dissolved at first,and the coarseγ'phase is dissolved later during the solution heat treatment of 1,390°C/2 h+1,310°C/4 h+1,320°C/10 h+air cooling(AC).The composition segregations of Al,Ta,W and Re are 0.99,0.96,1.04 and 1.16,respectively,which close to 1.The incipient melting is caused by the low local temperature of the alloy,and the micropore region with a lower melting point is the preferred position for incipient melting.
文摘Beginning of the twentieth century was marked by coinage of a new rock name, Charnockite, first described as a hypersthene-bearing granite from Southern India. Since then charnockites have been described from most of the conti-nents and mostly restricted to high-grade belts. Later half of the last century saw a lively debate over an igneous versus metamorphic origin. However, two factors acted as deterrents for the resolution of the debate. First, charnockites and associated rocks occur in a variety of different structural setting and display diverse field rela-tions, attesting to possible different mode of origin. Second and possibly more important is the lack of consensus on the nomenclature of charnockites and associated rocks and this is commonly linked with the metamorphic versus magmatic perspective. Scanning the literature of this period makes one believe that both metamorphic and magmatic hypotheses are valid, but applicable to different field setting only. Before critically evaluating individual cases, it is imperative that a uniform approach in nomenclature should be agreed upon. It is proposed that name charnockite be adopted for any quartzofeldspathic rock with orthopyroxene, irrespective of its mode of occurrence, struc-tural setting and mode of origin. The associated more mafic varieties, be better described as mafic granulite, rather than basic charnockite. For the patchy charnockites of east Gondwana (including parts of Peninsular India, Sri Lanka and Antarctica), metamorphic transformation from amphibolite facies gneiss, by two different mechanisms: CO2 ingress from deep level, and drop in fluid pressure, has been proposed. However, all such patchy occurrence is not amenable to explanation by metamorphic trans- formation. In some instances, migmatisation of older charnockitic rocks is evident. Also pro- gressive charnockitisation relating patchy char-nockite to banded variety could be argued against on two counts: grain-size relation and time-relation. Larger bodies or bands have been explained a
文摘Hf lowers the incipient melting temperature of superalloy. As carbon content in Hf-bearing alloy decreases, the incipient melting temperature drops furthey. PD ingots have stronger tendency to incipient melting than HRS ones. Even though in PD ingot, the sensitivities at both ends of the ingot are quite different. The melting of Ni_5Hf phase may be considered as one of the main factors affecting incipient melting. The more Ni_5Hf the alloy contains, the more serious the incipient melting becomes. The results of differential thermal analysis (DTA) have proved that the peak of 1135-1160℃ corresponds to the melting range or Ni_5Hf. By means of a pretreatment at 1150℃, 8h, Ni_5Hf phase can be eliminated in two ways: the reaction Ni_5Hf+γ(C)→MC_(2)+γ and solid solution, and therefore the final solid solution treatment can be carried out at 1260℃. This brings about a high homogenized structure and further increases the stress rupture properties of the alloy at 1040℃, 140 MPa.
基金Funded by the Natural Science Foundation of Shanxi Province,China(No.201801D121108)the Project by Zhaoqing Xijiang Innovation and Entrepreneurship Team Project Funding of China(No.2017A0109004)。
文摘The roles of hot isostatic pressing (HIP) temperatures (490 ℃/100 MPa/2 h,510 ℃/100 MPa/2 h,530 ℃/100 MPa/2 h) in the microstructure and properties of AlSi7Cu2Mg alloy step castings with three types wall thicknesses were studied.The experimental results show that HIP at 490 ℃ could effectively eliminate the internal closed porosity of the castings with a wall thickness of ≤40 mm,but for heavy castings (70 mm),even HIP at 530 ℃,a few loose defects remained inside the castings.Two types of incipient eutectics containing Al5Mg8Si6Cu2 and Al2Cu were observed in the samples that HIP at 530 ℃,which was responsible for the decrease of the tensile strength of the castings within the medium wall thickness (40 mm) compared with that HIP at 490 ℃.HIP could greatly reduce the difference of the tensile strength values of castings with wall thicknesses 17 mm and 70 mm from 117.93 MPa (without HIP) to 25.7 MPa (with HIP at 530 ℃).
