Inclusions in nickel-based superalloys significantly influence their mechanical properties which limit the application and development.A two-dimensional axisymmetric model coupling electromagnetic flow,heat transfer,a...Inclusions in nickel-based superalloys significantly influence their mechanical properties which limit the application and development.A two-dimensional axisymmetric model coupling electromagnetic flow,heat transfer,and inclusions transport was developed using the finite element method.The effects of current intensity and frequency on the transport behavior of inclusions and removal rate during vacuum induction melting were investigated using this model.To verify the accuracy of the mathematical model,experiments were conducted using the vacuum induction furnace model VIF200.A comparison of the experimental results with the simulation results reveals an excellent agreement.Four eddies exist in the central section of the molten pool,with any two eddies flowing in opposite directions.The drag force exerted by the eddies causes the inclusions converge toward the four corners of the cut surface.Due to buoyancy,an increase in the particle size of inclusions makes it easier for them to be adsorbed by the free surface,a phenomenon that is particularly noticeable for inclusions with a particle size of 400μm.An increase in current intensity changes the adsorption interface of certain 400-μm inclusions from the free surface to the sidewall.Increasing both current intensity and frequency enhances the crucible removal rate of inclusions,with current intensity exerting a more significant effect,increasing the removal rate by approximately 1% for every 150 A.Upon completion of melting,the ingot is typically obtained by pouring or bottom pouring,and inclusions adsorbed to the free surface are difficult to separate.Therefore,higher current intensity and frequency should be employed during melting to enhance the crucible removal rate.展开更多
This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories.Three different crucibles were tested—MgO,Al2O3,and MgO–spinel.We studied the variations...This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories.Three different crucibles were tested—MgO,Al2O3,and MgO–spinel.We studied the variations in the compositions of the inclusions and the alloy–crucible interface with the reaction time using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and Xray diffraction.The results showed that the MgO and MgO–spinel crucibles form MgO-containing inclusions(Al–Mg oxides and Al–Mg–Ti oxides),whereas the inclusions formed when using the Al2O3 crucible are Al2O3 and Al–Ti oxides.We observed a new MgAl2O4 phase at the inner wall of the MgO crucible,with the alloy melted in the MgO crucible exhibiting fewer inclusions.No new phase occurred at the inner wall of the Al2O3 crucible.We discuss the mechanism of interaction between the refractories and the Ni-based superalloy.Physical erosion was found to predominate in the Al2O3 crucible,whereas dissolution and chemical reactions dominated in the MgO crucible.No reaction was observed between three crucibles and the Ti of the melt although the Ti content(3.8wt%)was higher than that of Al(2.1wt%).展开更多
The developing of large size superalloy vacuum induction melting(VIM)ingots is limited owing to hot cracking,The hot cracking behavior of the large size GH4742 superalloy VIM ingot was investigated via experiment and ...The developing of large size superalloy vacuum induction melting(VIM)ingots is limited owing to hot cracking,The hot cracking behavior of the large size GH4742 superalloy VIM ingot was investigated via experiment and simulation.The microstructure was examined by optical microscopy,and element segregation was investigated by electron probe microanalysis.The solidification temperature range and yield strength at high temperature(YSHT)were calculated by JMatPro software.The results show that the variations of microstructure and element segregation in different locations are caused by different cooling rates.Moreover,the larger secondary dendrite arm spacing and serious element segregation of Nb accelerate hot cracking of the VIM ingot.In addition,the solidification temperature range is wider,and YSHT is lower in center than at edge of the ingot.Therefore,the hot cracking susceptibility is the highest in the center of the GH4742 superalloy VIM ingot.The critical criterion of element segregation for hot cracking is that the partition coeffcient of Nb should be larger than 0.5.展开更多
The effects of rare earth element Y on the purification of K4169 superalloy during vacuum induction melting were investigated at different superheating temperatures. The corresponding interaction mechanisms were also ...The effects of rare earth element Y on the purification of K4169 superalloy during vacuum induction melting were investigated at different superheating temperatures. The corresponding interaction mechanisms were also clarified. Results showed that the addition of Y remarkably promoted the purification effect on the K4169 melt. The contents of O and S in the K4169 as-cast alloy ingots after purification were 3–4 and 8–10 ppm, respectively. The degrees of deoxidation and desulfurization increased to 50% and 57%, respectively, upon the addition of 0.1 wt% Y. The yttrium-rich phase that precipitated at the grain boundary blocked the diffusion of C and the accumulation of S, thereby contributing to the purification of the alloy.展开更多
The variation law of inclusions type and size in the vacuum induction melting process and ingot of Ni-based superalloy containing 70%return material was studied by industrial test sampling,and the mechanism of inclusi...The variation law of inclusions type and size in the vacuum induction melting process and ingot of Ni-based superalloy containing 70%return material was studied by industrial test sampling,and the mechanism of inclusions formation was analyzed with thermodynamic calculations.The results show that there are mainly two types of composite inclusions in the vacuum induction melting of Ni-based superalloys,which are nitride-and oxide-based composite inclusions,like Al_(2)O_(3)-SiO_(2)-Cr_(2)O_(3),TiN-(Mo,Nb)C,etc.The type and proportion of inclusions from the center to the edge of the vacuum induction ingot did not change significantly.The number density of inclusions from the center to the edge of the ingot varied less,and the size of inclusions became smaller from the center to the edge.In addition,thermodynamic calculations show that oxides(M_(2)O_(3))are present in the liquid phase and mainly contain Al,Ti,Cr,Fe and O elements.The nitride consists mainly of Ti and N and contains small amounts of Cr,C,Nb,and Mo elements.This is consistent with the results of industrial tests.As the temperature decreases,the precipitation phases such as M_(2)O_(3),MN,γ,MC,δ,γ'andμphases are gradually precipitated,where oxides and nitrides are present in the liquid phase.The contents of O and N elements are the main influencing factors for the inclusions content and precipitation temperature;when the nitrogen content is reduced to below 0.0015%,it can make MN precipitate below the liquid-phase line.展开更多
In this study,yttrium as desulfurizer on the purification of Ni-20Co-20Cr-10Al-Y alloy during vac-uum induction melting(VIM)process using Y_(2)O_(3)cru-cibles was investigated experimentally.It is found that Y plays a...In this study,yttrium as desulfurizer on the purification of Ni-20Co-20Cr-10Al-Y alloy during vac-uum induction melting(VIM)process using Y_(2)O_(3)cru-cibles was investigated experimentally.It is found that Y plays an important role on the desulfurizing of the NiCo-CrAIY alloy.Without any addition of Y,merely the employment of Y_(2)O_(3)crucibles could effectively reduce S content of the alloy melts from 28×10^(-6)to 6×10^(-6)-7×10^(-6).With addition of 0.8 wt%Y in the alloy,the concentration of S could further reduce 2×10^(7)3×10^(-6).The primary interactive mechanism between Y and molten alloy was concluded to be the synthesis reac-tion of NisY phase,Y2S3 phases and YAIO_(3)phase.In the desulfurize slags,Y2S3 phases and Y_(2)O_(3)phase are found.No secondary contamination is present in the alloy melts after addition of Y.展开更多
The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace.A numerical model for the electromagnetic-thermal-hydrodynamic coupling...The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace.A numerical model for the electromagnetic-thermal-hydrodynamic coupling fields have been developed by using the finite element method(FEM)and a 2D numerical simulation for electromagnetic、 temperature and velocity fields of metallurgical-grade silicon melting in vacuum induction furnace were performed with a software Multi-physics Comsol 3.5a in this paper.The results showed that the temperature field was dependent observably on input power of coils and induction heating times and the maximum temperature gradient in melting pool was 215K in holding time.With the silicon molted gradually a clockwise vortex was come into being for electromagnetic stirring in the smelting poor.The variation of velocity field in melting silicon is mainly influenced with the change of the current intensity and power frequency.The numerical predications of temperature distribution are in good agreement with experiments.展开更多
CuCr25W1Ni2 alloy was prepared by means of vacuum induction melting (VIM). A series of Cu/Cr alloys with different compositions (mass fraction, 25%～75%) and Cr grain sizes (up to 150 μm) were investigated for their ...CuCr25W1Ni2 alloy was prepared by means of vacuum induction melting (VIM). A series of Cu/Cr alloys with different compositions (mass fraction, 25%～75%) and Cr grain sizes (up to 150 μm) were investigated for their differences in physical properties and breakdown voltage. The influence of alloy elements and microstructure on the performance of CuCr25W1Ni2 alloy was also discussed. Experimental results show that the chromium phase is strengthened and its size is minimized by the addition of tungsten powder. After electrical breakdown, very fine tungsten particles in the melt layer form the external nuclei in the solidification process. The microstructure of surface melt layer of CuCr25W1Ni2 alloy is much flatter. It can notably improve the dielectric strength. On the other hand, the nickel can enhance the mutual solubility of copper and chromium, and the whole alloy is strengthened. [展开更多
The grain size of TiAl alloy castings prepared by traditional casting process is coarse,thus showing poor mechanical properties.In this study,a new type of high performance Ti-46Al alloy tube prepared by vacuum centri...The grain size of TiAl alloy castings prepared by traditional casting process is coarse,thus showing poor mechanical properties.In this study,a new type of high performance Ti-46Al alloy tube prepared by vacuum centrifugal casting technology was introduced.This research comprehensively examined the influence of pouring time on the microstructure and mechanical performance of the castings,employing both experimental approaches and ProCast simulation methodologies.The findings indicate that prolonging the pouring time facilitates a microstructural evolution from coarse columnar grains to refined equiaxed grains.Under the condition of pouring temperature of 1,600℃,rotation speed of 800 r·min^(-1) and pouring time of 6 s,the tensile strength of Ti-46Al alloy at room temperature reaches 650 MPa,and the tensile strength at 800℃ reaches 705 MPa,which is significantly higher than that of traditional as-cast Ti-Al alloy.展开更多
A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas...A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.展开更多
CuCr25 alloys containing different Ni content were prepared by vacuum induction melting (VIM). The micro structure and properties were tested. The results show that with the increase of Ni content in CuCr25 alloys, th...CuCr25 alloys containing different Ni content were prepared by vacuum induction melting (VIM). The micro structure and properties were tested. The results show that with the increase of Ni content in CuCr25 alloys, the Cr phase changed from developed dendrite into nodular grains and was drastically refined; the electrical conductivity significantly decrease, but still reach the level of conventional CuCr50 when the Ni content is below 0.5%. The Ni content had little influence on their breakdown strength. The first breakdown sites transferred to the boundary of Cu and Cr phase for CuCr25Ni compared to the Cr phase for CuCr25 without Ni.展开更多
Losses of the alloying elements during vacuum induction melting of the binary NiTi alloys were evaluated by visual observation and chemical analysis of the NiTi melted specimens and the scalp formed on the internal su...Losses of the alloying elements during vacuum induction melting of the binary NiTi alloys were evaluated by visual observation and chemical analysis of the NiTi melted specimens and the scalp formed on the internal surface of the crucible. The results indicated that the major sources of the losses were （a） evaporation of the metals, （b） formation of the NiTi scalp and （c） the sprinkling drops splashed out of the melt due to the exothermic reactions occurring between Ni and Ti to form the NiTi parent phase. Quantitative evaluations were made for the metallic losses by holding the molten alloy for 0.5, 3, 5, 10 and 15 min at around 100℃ above the melting point inside the crucible.Chemical analysis showed that there existed an optimum holding time of 3 min during which the alloying elements were only dropped to a predictable limit. Microstructure, chemical composition, shape memory and mechanical properties of the cast metal ingots were determined to indicate the appropriate achievements with the specified 3 min optimum holding time.展开更多
As the aircraft and aerospace industry and the automobile industry are developed, the demand of reliable materials with high strength and high toughness is steadily increased. The grain miniature method which improves...As the aircraft and aerospace industry and the automobile industry are developed, the demand of reliable materials with high strength and high toughness is steadily increased. The grain miniature method which improves the ductility and the toughness simultaneously under high strength is the miniature of the casting microstructure. In this paper, the Nb which affects the austenite grain miniature is added by 0.00%, 0.03% and 0.06% in this steel and the ingot is manufactured in a vacuum induction melting furnace （VIM）. The casting microstructure and the mechanical property of the maraging steel according to Nb contents are analyzed by conducting the solution annealing and the age hardening after hot rolling. In this result, a specimen containing 0.03% Nb is most miniature. When it does the long time age hardening, the precipitation estimated as the carbide is appeared. The mechanical properties are excellent if a specimen containing 0.06% Nb does the age hardening during 8 h in 482℃.展开更多
Processing technologies for the mass production of aero and industrial gas turbine engine hot-section components made by the investment casting process are discussed. Howmet Corporation is involved in most of these te...Processing technologies for the mass production of aero and industrial gas turbine engine hot-section components made by the investment casting process are discussed. Howmet Corporation is involved in most of these technologies because of the end-user's desire for a finished part. These technologies include pattern-making (using a variety of wax and plastic materials, rapid prototyping, 'hard' tooling, and wax injection machines), silica-zircon and alumina cores that produce internal passages, shells for very large parts and for use with alloys containing reactive elements, Ni, Co, and Ti alloys that are cleaner than ever before,zirconia, silica, and mullite crucibles;computer-controls,robotics,and the manufacture of vacuum casting furnaces; cleaning and finishing equipment designed to quickly process parts with minimal variation,and post-casting operations including hot isostatic pressing (HIP),heat treating,coating,and machining. These technologies will be discussed along with process capabilities required by today's turbine hot-section component suppliers.展开更多
V_(x)FeCoNiCu high entropy alloy matrix composites reinforced by in situ TiC particles(10 vol.%),i.e.,V_(x)FeCoNiCu/TiC composites,were fabricated from V–Fe–Co–Ni–Cu–Ti–C system using vacuum inductive melting me...V_(x)FeCoNiCu high entropy alloy matrix composites reinforced by in situ TiC particles(10 vol.%),i.e.,V_(x)FeCoNiCu/TiC composites,were fabricated from V–Fe–Co–Ni–Cu–Ti–C system using vacuum inductive melting method.With the content of vanadium increasing,the size of TiC particles decreased gradually.Meanwhile,vanadium agglomeration occurred slightly.The reaction mechanism of the mixed powder(Fe,V,Ti and C)and the mechanical properties of obtaining V_(x)FeCoNiCu/TiC composites were studied.It was found that three reactions occurred(Fe-Ti-FeTi-Fe_(2)Ti,FeTi-Fe_(2)Ti-Fe-Ti and Ti-C-TiC)in the heating process.The apparent activation energy for these three reactions was calculated and found to be 26.4,698.3 and 1879.0 kJ/mol,respectively.At room temperature,tensile strength and elongation increased first and then decreased with the increase in vanadium content and the microhardness increased gradually.The maximum tensile strength of the composites was determined to be 666 MPa,representing a 17.7%increase over that of FeCoNiCu/TiC high entropy alloy composites.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52422408 and 52171031)Excellent Youth Fund of Liaoning Natural Science Foundation(No.2023JH3/10200001)Liaoning Xingliao Talents-Top-notch Young Talents Project(No.XLYC2203064).
文摘Inclusions in nickel-based superalloys significantly influence their mechanical properties which limit the application and development.A two-dimensional axisymmetric model coupling electromagnetic flow,heat transfer,and inclusions transport was developed using the finite element method.The effects of current intensity and frequency on the transport behavior of inclusions and removal rate during vacuum induction melting were investigated using this model.To verify the accuracy of the mathematical model,experiments were conducted using the vacuum induction furnace model VIF200.A comparison of the experimental results with the simulation results reveals an excellent agreement.Four eddies exist in the central section of the molten pool,with any two eddies flowing in opposite directions.The drag force exerted by the eddies causes the inclusions converge toward the four corners of the cut surface.Due to buoyancy,an increase in the particle size of inclusions makes it easier for them to be adsorbed by the free surface,a phenomenon that is particularly noticeable for inclusions with a particle size of 400μm.An increase in current intensity changes the adsorption interface of certain 400-μm inclusions from the free surface to the sidewall.Increasing both current intensity and frequency enhances the crucible removal rate of inclusions,with current intensity exerting a more significant effect,increasing the removal rate by approximately 1% for every 150 A.Upon completion of melting,the ingot is typically obtained by pouring or bottom pouring,and inclusions adsorbed to the free surface are difficult to separate.Therefore,higher current intensity and frequency should be employed during melting to enhance the crucible removal rate.
基金This work is financially supported by the Natural Science Foundation of China(No.51974029)the Natural Science and Technology Major Project(No.2017-VI-0014-0086)and Fundamental Research Funds for the Central Universities(Nos.FRF-AT-19-013 and FRF-NP-19-003).
文摘This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories.Three different crucibles were tested—MgO,Al2O3,and MgO–spinel.We studied the variations in the compositions of the inclusions and the alloy–crucible interface with the reaction time using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and Xray diffraction.The results showed that the MgO and MgO–spinel crucibles form MgO-containing inclusions(Al–Mg oxides and Al–Mg–Ti oxides),whereas the inclusions formed when using the Al2O3 crucible are Al2O3 and Al–Ti oxides.We observed a new MgAl2O4 phase at the inner wall of the MgO crucible,with the alloy melted in the MgO crucible exhibiting fewer inclusions.No new phase occurred at the inner wall of the Al2O3 crucible.We discuss the mechanism of interaction between the refractories and the Ni-based superalloy.Physical erosion was found to predominate in the Al2O3 crucible,whereas dissolution and chemical reactions dominated in the MgO crucible.No reaction was observed between three crucibles and the Ti of the melt although the Ti content(3.8wt%)was higher than that of Al(2.1wt%).
基金supported by the National Natural Science Foundation of China(Nos.Ui708253 and 51571052)。
文摘The developing of large size superalloy vacuum induction melting(VIM)ingots is limited owing to hot cracking,The hot cracking behavior of the large size GH4742 superalloy VIM ingot was investigated via experiment and simulation.The microstructure was examined by optical microscopy,and element segregation was investigated by electron probe microanalysis.The solidification temperature range and yield strength at high temperature(YSHT)were calculated by JMatPro software.The results show that the variations of microstructure and element segregation in different locations are caused by different cooling rates.Moreover,the larger secondary dendrite arm spacing and serious element segregation of Nb accelerate hot cracking of the VIM ingot.In addition,the solidification temperature range is wider,and YSHT is lower in center than at edge of the ingot.Therefore,the hot cracking susceptibility is the highest in the center of the GH4742 superalloy VIM ingot.The critical criterion of element segregation for hot cracking is that the partition coeffcient of Nb should be larger than 0.5.
基金financially supported by the National Science & Technology Pillar Program of China (No. 2013BAB11B04)the National Natural Science Foundation of China (Nos. 51404017 and 51604014)
文摘The effects of rare earth element Y on the purification of K4169 superalloy during vacuum induction melting were investigated at different superheating temperatures. The corresponding interaction mechanisms were also clarified. Results showed that the addition of Y remarkably promoted the purification effect on the K4169 melt. The contents of O and S in the K4169 as-cast alloy ingots after purification were 3–4 and 8–10 ppm, respectively. The degrees of deoxidation and desulfurization increased to 50% and 57%, respectively, upon the addition of 0.1 wt% Y. The yttrium-rich phase that precipitated at the grain boundary blocked the diffusion of C and the accumulation of S, thereby contributing to the purification of the alloy.
基金supported by the National Key R&D Program of China(2021YFB3700402)National Natural Science Foundation of China(51974020,52104318 and 52074030).
文摘The variation law of inclusions type and size in the vacuum induction melting process and ingot of Ni-based superalloy containing 70%return material was studied by industrial test sampling,and the mechanism of inclusions formation was analyzed with thermodynamic calculations.The results show that there are mainly two types of composite inclusions in the vacuum induction melting of Ni-based superalloys,which are nitride-and oxide-based composite inclusions,like Al_(2)O_(3)-SiO_(2)-Cr_(2)O_(3),TiN-(Mo,Nb)C,etc.The type and proportion of inclusions from the center to the edge of the vacuum induction ingot did not change significantly.The number density of inclusions from the center to the edge of the ingot varied less,and the size of inclusions became smaller from the center to the edge.In addition,thermodynamic calculations show that oxides(M_(2)O_(3))are present in the liquid phase and mainly contain Al,Ti,Cr,Fe and O elements.The nitride consists mainly of Ti and N and contains small amounts of Cr,C,Nb,and Mo elements.This is consistent with the results of industrial tests.As the temperature decreases,the precipitation phases such as M_(2)O_(3),MN,γ,MC,δ,γ'andμphases are gradually precipitated,where oxides and nitrides are present in the liquid phase.The contents of O and N elements are the main influencing factors for the inclusions content and precipitation temperature;when the nitrogen content is reduced to below 0.0015%,it can make MN precipitate below the liquid-phase line.
基金This study was financially supported by the National Science&Technology Pillar Program of China(No.2013BAB11B04)the National Natural Science Foundation of China(No.51404017)Furthermore,the authors wish to express their appreciation to the State Key Laboratory of Refractories and Metallurgy,Wuhan University of Science and Technology.
文摘In this study,yttrium as desulfurizer on the purification of Ni-20Co-20Cr-10Al-Y alloy during vac-uum induction melting(VIM)process using Y_(2)O_(3)cru-cibles was investigated experimentally.It is found that Y plays an important role on the desulfurizing of the NiCo-CrAIY alloy.Without any addition of Y,merely the employment of Y_(2)O_(3)crucibles could effectively reduce S content of the alloy melts from 28×10^(-6)to 6×10^(-6)-7×10^(-6).With addition of 0.8 wt%Y in the alloy,the concentration of S could further reduce 2×10^(7)3×10^(-6).The primary interactive mechanism between Y and molten alloy was concluded to be the synthesis reac-tion of NisY phase,Y2S3 phases and YAIO_(3)phase.In the desulfurize slags,Y2S3 phases and Y_(2)O_(3)phase are found.No secondary contamination is present in the alloy melts after addition of Y.
基金Item Sponsored by the NSFC project (51066003u1137601) +1 种基金National science & technology support plan project (2011BAE03B01) Scientific Research Foundation Project (2010Y408) of Yunnan Province Education Department
文摘The temperature and velocity distribution of melting pool fields is very important effect to the silicon purification in vacuum induction furnace.A numerical model for the electromagnetic-thermal-hydrodynamic coupling fields have been developed by using the finite element method(FEM)and a 2D numerical simulation for electromagnetic、 temperature and velocity fields of metallurgical-grade silicon melting in vacuum induction furnace were performed with a software Multi-physics Comsol 3.5a in this paper.The results showed that the temperature field was dependent observably on input power of coils and induction heating times and the maximum temperature gradient in melting pool was 215K in holding time.With the silicon molted gradually a clockwise vortex was come into being for electromagnetic stirring in the smelting poor.The variation of velocity field in melting silicon is mainly influenced with the change of the current intensity and power frequency.The numerical predications of temperature distribution are in good agreement with experiments.
文摘CuCr25W1Ni2 alloy was prepared by means of vacuum induction melting (VIM). A series of Cu/Cr alloys with different compositions (mass fraction, 25%～75%) and Cr grain sizes (up to 150 μm) were investigated for their differences in physical properties and breakdown voltage. The influence of alloy elements and microstructure on the performance of CuCr25W1Ni2 alloy was also discussed. Experimental results show that the chromium phase is strengthened and its size is minimized by the addition of tungsten powder. After electrical breakdown, very fine tungsten particles in the melt layer form the external nuclei in the solidification process. The microstructure of surface melt layer of CuCr25W1Ni2 alloy is much flatter. It can notably improve the dielectric strength. On the other hand, the nickel can enhance the mutual solubility of copper and chromium, and the whole alloy is strengthened. [
基金financially supported by the Natural Science Foundation of China(52071065)the Fundamental Research Funds for the Central Universities(N2007007)the National Key R&D Program of China(2016YFB-0301201)。
文摘The grain size of TiAl alloy castings prepared by traditional casting process is coarse,thus showing poor mechanical properties.In this study,a new type of high performance Ti-46Al alloy tube prepared by vacuum centrifugal casting technology was introduced.This research comprehensively examined the influence of pouring time on the microstructure and mechanical performance of the castings,employing both experimental approaches and ProCast simulation methodologies.The findings indicate that prolonging the pouring time facilitates a microstructural evolution from coarse columnar grains to refined equiaxed grains.Under the condition of pouring temperature of 1,600℃,rotation speed of 800 r·min^(-1) and pouring time of 6 s,the tensile strength of Ti-46Al alloy at room temperature reaches 650 MPa,and the tensile strength at 800℃ reaches 705 MPa,which is significantly higher than that of traditional as-cast Ti-Al alloy.
基金Item Sponsored by National Natural Science Foundation of China(50534010)
文摘A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.
基金We gratefully acknowledge the financial support from "863" program (Grant No.200lAA320714 and 715-005-0160)the National Natural Science Foundation of China (Grant No.50071043 and 50271050). The authors also appreciate Prof. Y.X. Zhu, Z. Zheng and A.P.
文摘CuCr25 alloys containing different Ni content were prepared by vacuum induction melting (VIM). The micro structure and properties were tested. The results show that with the increase of Ni content in CuCr25 alloys, the Cr phase changed from developed dendrite into nodular grains and was drastically refined; the electrical conductivity significantly decrease, but still reach the level of conventional CuCr50 when the Ni content is below 0.5%. The Ni content had little influence on their breakdown strength. The first breakdown sites transferred to the boundary of Cu and Cr phase for CuCr25Ni compared to the Cr phase for CuCr25 without Ni.
文摘Losses of the alloying elements during vacuum induction melting of the binary NiTi alloys were evaluated by visual observation and chemical analysis of the NiTi melted specimens and the scalp formed on the internal surface of the crucible. The results indicated that the major sources of the losses were （a） evaporation of the metals, （b） formation of the NiTi scalp and （c） the sprinkling drops splashed out of the melt due to the exothermic reactions occurring between Ni and Ti to form the NiTi parent phase. Quantitative evaluations were made for the metallic losses by holding the molten alloy for 0.5, 3, 5, 10 and 15 min at around 100℃ above the melting point inside the crucible.Chemical analysis showed that there existed an optimum holding time of 3 min during which the alloying elements were only dropped to a predictable limit. Microstructure, chemical composition, shape memory and mechanical properties of the cast metal ingots were determined to indicate the appropriate achievements with the specified 3 min optimum holding time.
基金supported by Research Funds from Chosun University,2007.
文摘As the aircraft and aerospace industry and the automobile industry are developed, the demand of reliable materials with high strength and high toughness is steadily increased. The grain miniature method which improves the ductility and the toughness simultaneously under high strength is the miniature of the casting microstructure. In this paper, the Nb which affects the austenite grain miniature is added by 0.00%, 0.03% and 0.06% in this steel and the ingot is manufactured in a vacuum induction melting furnace （VIM）. The casting microstructure and the mechanical property of the maraging steel according to Nb contents are analyzed by conducting the solution annealing and the age hardening after hot rolling. In this result, a specimen containing 0.03% Nb is most miniature. When it does the long time age hardening, the precipitation estimated as the carbide is appeared. The mechanical properties are excellent if a specimen containing 0.06% Nb does the age hardening during 8 h in 482℃.
文摘Processing technologies for the mass production of aero and industrial gas turbine engine hot-section components made by the investment casting process are discussed. Howmet Corporation is involved in most of these technologies because of the end-user's desire for a finished part. These technologies include pattern-making (using a variety of wax and plastic materials, rapid prototyping, 'hard' tooling, and wax injection machines), silica-zircon and alumina cores that produce internal passages, shells for very large parts and for use with alloys containing reactive elements, Ni, Co, and Ti alloys that are cleaner than ever before,zirconia, silica, and mullite crucibles;computer-controls,robotics,and the manufacture of vacuum casting furnaces; cleaning and finishing equipment designed to quickly process parts with minimal variation,and post-casting operations including hot isostatic pressing (HIP),heat treating,coating,and machining. These technologies will be discussed along with process capabilities required by today's turbine hot-section component suppliers.
基金the Jiangsu Province Science and Technology Plan Project(No.BE2018753/KJ185629)the National Natural Science Foundation of China(Nos.51571118 and 51371098).
文摘V_(x)FeCoNiCu high entropy alloy matrix composites reinforced by in situ TiC particles(10 vol.%),i.e.,V_(x)FeCoNiCu/TiC composites,were fabricated from V–Fe–Co–Ni–Cu–Ti–C system using vacuum inductive melting method.With the content of vanadium increasing,the size of TiC particles decreased gradually.Meanwhile,vanadium agglomeration occurred slightly.The reaction mechanism of the mixed powder(Fe,V,Ti and C)and the mechanical properties of obtaining V_(x)FeCoNiCu/TiC composites were studied.It was found that three reactions occurred(Fe-Ti-FeTi-Fe_(2)Ti,FeTi-Fe_(2)Ti-Fe-Ti and Ti-C-TiC)in the heating process.The apparent activation energy for these three reactions was calculated and found to be 26.4,698.3 and 1879.0 kJ/mol,respectively.At room temperature,tensile strength and elongation increased first and then decreased with the increase in vanadium content and the microhardness increased gradually.The maximum tensile strength of the composites was determined to be 666 MPa,representing a 17.7%increase over that of FeCoNiCu/TiC high entropy alloy composites.
