Interstitial oxygen(O)contamination remains a substantial challenge for metal injection molding(MIM)of titanium alloys.Herein,this critical problem is successfully addressed by regulating the thermal debinding tempera...Interstitial oxygen(O)contamination remains a substantial challenge for metal injection molding(MIM)of titanium alloys.Herein,this critical problem is successfully addressed by regulating the thermal debinding temperature and incorporating the oxygen scavenger LaB_(6).Results indicate that the surface oxide layer(with a thickness of(13.4±0.5)nm)of Ti_(6)Al4V powder begins to dissolve into the Ti matrix within the temperature range of 663–775℃.O contamination in MIM Ti alloys can be effectively mitigated by lowering the thermal debinding temperature and adding LaB6powder.As a result of reduced dissolved O content,the slips of mixedanddislocations are effectively accelerated,leading to improved ductility.Moreover,grain refinement,along with the in situ formation of Ti B whiskers and second-phase La_(2)O_(3)particles,enhances the strength of the material.The fabricated MIM Ti6Al4V sample exhibits excellent mechanical properties,achieving an ultimate tensile strength of(967±5)MPa,a yield strength of(866±8)MPa,and an elongation of 21.4%±0.7%.These tensile properties represent some of the best results reported in the literature for MIM Ti_(6)Al4V alloys.This study offers valuable insights into the development of high-performance MIM Ti alloys and other metal materials.展开更多
The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on th...The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on the continuum mechanics and thermal elasto-viseoplastic constitutive law. Model parameters were identified from the dilatometer sintering experiment. The real density distribution of green body was measured by X-ray computed tomography （CT）, which was regarded as the initial condition of sintering model. Numerical calculation of the above sintering model was carried out with the finite element soRware Abaqus, through the user-defined material mechanical behavior （UMAT）. The calculation results showed that shrinkages of low density regions were faster than those of high density regions during sintering, which led to internal stresses. Compressive stresses existed in high density regions and tensile stresses existed in low density regions. The densification of local regions depended on not only the initial density, but also the evolution of stresses during the sintering stage.展开更多
The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerge...The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerged entry nozzles,form floaters in the molds,and produce various surface defects on the cast slabs.This review summarizes the effects of nonmetallic inclusions on traditional CaO-SiO_(2)-based(CS)mold fluxes and novel CaO-Al_(2)O_(3)-based(CA)low-or non-reactive fluxes containing TiO_(2),BaO,and B_(2)O_(3)additives to avoid undesirable steel,slag,and inclusion reactions,with the aim of providing a new perspective for research and practice related to balancing the lubrication and heat transfer of mold fluxes to promote smooth operation and reduce surface defects on cast slabs.For traditional CS mold flux,although the addition of solvents such as Na_(2)O,Li_(2)O,and B_(2)O_(3)can enhance flowability,steel-slag reactions persist,limiting the effectiveness of CS mold fluxes in high-Ti steel casting.Low-or non-reactive CA mold fluxes with reduced SiO_(2)content are a research focus,where adding other components can significantly change flux characteristics.Replacing CaO with BaO can lower the melting point and inhibit crystallization,allowing the flux to maintain good flowability at low temperatures.Replacing SiO_(2)with TiO_(2)can stabilize the viscosity and enhance heat transfer.To reduce the environmental impact,fluorides are replaced with components such as TiO_(2),B_(2)O_(3),BaO,Li_(2)O,and Na_(2)O for F-frce mold fluxes with similar lubrication,crystallization,and heat-transfer effects.When TiO_(2)replaces CaF_(2),it stabilizes the viscosity and enhances the heat conductivity,forming CaTiO_(3)and CaSiTiO_(5)phases instead of cuspidine to control crystallization.B_(2)O_(3)lowers the melting point and suppresses crystallization,forming phases such as Ca_(3)B_(2)O_(6)and Ca_(11)Si_(4)B_(2)O_(22).BaO introduces non-bridging oxygen to reduce viscosity and ensure flux flowability at low temperatures.However,further studies are required to determine the optimal mold flux compositions corresponding to the steel grades and the interactions between the various components of the mold flux.In the future,the practical application of new mold fluxes for high-Ti steel will become the focus of further verification to achieve a balance between lubrication and heat transfer,which is expected to minimize the occurrence of casting problems and slab defects.展开更多
At present, the technology of biomass fuel composite molding technique is relatively lagging in China, which brings several negative influences, such as high energy consumption, short service life of the equipment. Th...At present, the technology of biomass fuel composite molding technique is relatively lagging in China, which brings several negative influences, such as high energy consumption, short service life of the equipment. The current situation of the biomass pellet fuel molding technology at home and abroad was introduced, and the development direction in China was put forward, which was of great significance for enhancing the level of pellet fuel molding technology in China.展开更多
A mathematical model of resin flow and temperature variation in the filling stage of the resin transfer molding (RTM) is developed based on the control volume/finite element method (CV/FEM). The effects of the heat tr...A mathematical model of resin flow and temperature variation in the filling stage of the resin transfer molding (RTM) is developed based on the control volume/finite element method (CV/FEM). The effects of the heat transfer and chemical reaction of the resin on the flow and temperature are considered. The numerical algorithm of the resin flow and temperature variation in the process of RTM are studied. Its accuracy and convergence are analyzed. The comparison of temperature variations between experimental results and model predictions is carried out for two RTM cases. Result shows that the model is efficient for evaluating the flow and temperature variation in the filling stage of RTM and there is a good coincidence between theory and experiment.展开更多
Laser powder bed fusion(LPBF)is highly suitable for forming 18Ni300 mold steel,thanks to its excellent capability in manufacturing complex shapes and outstanding capacity for regulating microstructures.It is widely us...Laser powder bed fusion(LPBF)is highly suitable for forming 18Ni300 mold steel,thanks to its excellent capability in manufacturing complex shapes and outstanding capacity for regulating microstructures.It is widely used in fields such as injection molding,die casting,and stamping dies.Adding reinforcing particles into steel is an effective means to improve its performance.Nb/18Ni300 composites were fabricated by LPBF using two kinds of Nb powders with different particle sizes,and their microstructures and properties were studied.The results show that the unmelted Nb particles are uniformly distributed in the 18Ni300 matrix and the grains are refined,which is particularly pronounced with fine Nb particles.In addition,element diffusion occurs between the particles and the matrix.The main phases of the base alloy are α-Fe and a small amount of γ-Fe.With the addition of Nb,part of the α-Fe is transformed into γ-Fe,and unmelted Nb phases appear.The addition of Nb also enhances the hardness and wear resistance of the composites but slightly reduces their tensile properties.After aging treatment,the molten pools and grain boundaries become blurred,grains are further refined,and the interfaces around the particles are thinned.The aging treatment also promotes the formation of reverted austenite.The hardness,ultimate tensile strength,and volumetric wear rate of the base alloy reach 51.9 HRC,1704 MPa,and 17.8×10^(-6) mm^(3)/(N·m),respectively.In contrast,the sample added with fine Nb particles has the highest hardness(56.1 HRC),ultimate tensile strength(1892 MPa)and yield strength(1842 MPa),and the volume wear rate of the sample added with coarse Nb particles is reduced by 90%to 1.7×10^(-6) mm^(3)/(N·m).展开更多
Carbon-fiber-reinforced plastics(CFRP)with improved mechanical properties based on modified epoxy binders were investigated in this study.By adding 15 parts by weight(p.b.w.)of copolymer of polysulfone with cardo phth...Carbon-fiber-reinforced plastics(CFRP)with improved mechanical properties based on modified epoxy binders were investigated in this study.By adding 15 parts by weight(p.b.w.)of copolymer of polysulfone with cardo phthalide group(PSFP-70C)to the epoxyanhydride binder,the flexural strength of the epoxy polymer was increased by 60%,the CFRP based on it by 57%,the flexural modulus of the epoxy polymer was increased by 83%,and the composite by 96%.The adhesion strength of the binder to carbon fiber reached a high level at 10 p.b.w.of thermoplastic modifier and increased by 65%compared to the unmodified binder.Scanning electron microscopy(SEM)was used to determine that in epoxyanhydride systems with a polysulfone content of 5–15 p.b.w.,the structure belongs to the"matrix dispersion"type and with a content of 20 p.b.w.to the"interpenetrating phase"type.A heterogeneous structure was also observed using dynamic mechanical analysis.展开更多
The dissolution of MgO-refractory into the slag had an obvious influence on the steel-slag reaction and the slag property,especially for high-aluminum steels.The dissolution behavior of MgO-refractory was investigated...The dissolution of MgO-refractory into the slag had an obvious influence on the steel-slag reaction and the slag property,especially for high-aluminum steels.The dissolution behavior of MgO-refractory was investigated under various conditions,including the temperature,the initial steel composition,and the initial slag composition.A steel-slag-refractory kinetic model for high-aluminum steel was developed,which incorporated the process of MgO-refractory dissolution.The dependence of the MgO mass transfer coefficient k_(MgO)^(r)on temperature T during MgO-refractory dissolution process was established,as described by ln k_(MgO)^(r)=63,754/T+24.38524.It was indicated that the MgO dissolution rate was significantly influenced by the temperature.A higher temperature increased the dissolution rate of MgO.The initial steel composition had a slight impact on the MgO dissolution rate.Additionally,the initial slag composition strongly impacted the MgO saturation concentration and the dissolution rate.A lower initial Al_(2)O_(3)/SiO_(2)ratio increased the MgO dissolution rate.The steel-slag-refractory kinetic model accurately predicted the dissolution of MgO-refractory and the influence of dissolved MgO on the viscosity and composition change during steel-slag-refractory reactions.It was suggested that a higher temperature can hardly reduce the viscosity due to the dissolution of the MgO-refractory.展开更多
A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysi...A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.展开更多
The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was est...The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.展开更多
In order to investigate the effect of die wall thickness on morphologies of defect band,a stepped mold with a wall thickness of 5 mm,4 mm,3 mm,2 mm,and 1 mm was designed to carry out high pressure die casting experime...In order to investigate the effect of die wall thickness on morphologies of defect band,a stepped mold with a wall thickness of 5 mm,4 mm,3 mm,2 mm,and 1 mm was designed to carry out high pressure die casting experiments with AlSi10 MgMn alloy.For castings with wall thickness of 2-4 mm,the ratio of the mean defect band width(w)and mean grain size(d)in the defect band(w/d)ranges 7-18,while it increases to 24.47 for the 5 mm-thick casting.This difference is related with the filling speed and the distribution of externally solidified crystals(ESCs).The mold flow analysis indicates that the filling speed decreases from 25.41 m·s^(-1)to 11.07 m·s^(-1)when wall thickness increases from 2 mm to 5 mm.Due to the decreasing filling speed along the wall thickness,ESCs gradually diffuse from the center to the defect band,which keep the shear strength in the defect band at a high-level during filling.Meanwhile,the shear strength generated during the filling also decreases as the shear rate drops.Finally,the defect bands in the 5 mm-thick region become widen and indistinct,and the porosity is as high as 5.25%.展开更多
An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. Th...An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. The injection molding, debinding, and sintering process were studied. An ideal control of carbon and oxygen contents was achieved by thermal debinding in vacuum atmosphere （10^-3 Pa）. The mechanical properties of as-sintered specimens were less than those of titanium made by the conventional press-sintering process. Good shape retention and ±0.04 mm dimension deviation were achieved.展开更多
Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor co...Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor compatibility and the powder-binder segregation between ceramic powders and binders. The objective of this study was to obtain a sintered part with excellent properties by introducing a small quantity of oleic acid to the surface of zirconia powders before the mixing process. As opposed to many previous investigations that focused only on the rheological behavior and modification mechanism, the sintering behavior and densification process were systematically investigated in this study. With the modified powders, debound parts with a more homogeneous and smaller pore size distribution were fabricated. Also, a higher density and greater flexural strength were achieved in the sintered parts fabricated using the modified powders.展开更多
Over the last half-century,polyether ether ketone(PEEK)has emerged as a widely adopted thermoplastic polymer,primarily due to its lower density,exceptional mechanical properties,high-temperature and chemical resistanc...Over the last half-century,polyether ether ketone(PEEK)has emerged as a widely adopted thermoplastic polymer,primarily due to its lower density,exceptional mechanical properties,high-temperature and chemical resistance,and biocompatibility.PEEK and its composites have found extensive applications across various fields,including machinery,aerospace,military equipment,electronics,and biomedicine,positioning themselves as promising substitutes for traditional metal structures.Nevertheless,achieving optimal performance and functional molding of PEEK and its composites presents a formidable challenge,given their inherent characteristics,such as semi-crystallinity,high melting temperature,heightened viscosity,low dielectric coefficient,and hydrophobic properties.In this paper,we present a comprehensive review of the molding methods and processes of PEEK and its composites,including extrusion molding,hot compression molding,injection molding,and 3D printing.We also introduce typical innovative applications within the fields of mechanics,electricity,and biomedicine while elucidating methodologies that leverage the distinctive advantages of PEEK and its composites.Additionally,we summarize research findings related to manipulating the properties of PEEK and its composites through the optimization of machine parameters,process variables,and material structural adjustments.Finally,we contemplate the prevailing development trends and outline prospective avenues for further research in the advancement and molding of PEEK and its composites.展开更多
Micro/nanostructured components play an important role in micro-optics and optical engineering,tribology and surface engineering,and biological and biomedical engineering,among other fields.Precision glass molding tec...Micro/nanostructured components play an important role in micro-optics and optical engineering,tribology and surface engineering,and biological and biomedical engineering,among other fields.Precision glass molding technology is the most efficient method of manufacturing micro/nanostructured glass components,the premise of which is meld manufacturing with complementary micro/nanostructures.Numerous mold manufacturing methods have been developed to fabricate extremely small and high-quality micro/nanostructures to satisfy the demands of functional micro/nanostructured glass components for various applications.Moreover,the service performance of the mold should also be carefully considered.This paper reviews a variety of technologies for manufacturing micro/nanostructured molds.The authors begin with an introduction of the extreme requirements of mold materials.The following section provides a detailed survey of the existing micro/nanostructured mold manufacturing techniques and their corresponding mold materials,including nonmechanical and mechanical methods.This paper concludes with a detailed discussion of the authors recent research on nickel-phosphorus(Ni-P)mold manufacturing and its service performance.展开更多
A non-isothermal injection molding process for a non-Newtonian viscous pseudoplastic fluid is simulated.A conservative interface capturing technique and the flow field solving method are coupled to perform a dynamic s...A non-isothermal injection molding process for a non-Newtonian viscous pseudoplastic fluid is simulated.A conservative interface capturing technique and the flow field solving method are coupled to perform a dynamic simulation.The validity of the numerical method is verified by a benchmark problem.The melt interface evolution versus time is captured and the physical quantities such as temperature,velocity and pressure at each time step are obtained with corresponding analysis.A"frozen skin"layer with the thickness increasing versus time during the injection process is found.The fact that the"frozen skin"layer can be reduced by increasing the injection velocity is numerically verified.The fountain flow phenomenon near the melt interface is also captured.Moreover,comparisons with the non-isothermal Newtonian case show that the curvatures of the interface arcs and the pressure contours near the horizontal mid-line of the cavity for the non-Newtonian pseudoplastic case is larger than that for the Newtonian case.The velocity profiles are different at different positions for the non-Newtonian pseudoplastic case,while in the case of Newtonian flow the velocity profiles are parabolic and almost the same at different positions.展开更多
To investigate value in use of liquefied wood-based resin applications in molding material, Chinese fir （Cunninghamia lanceolata） and poplar （Populus tomentosa） wood meal were liquefied in phenol. The reactant was...To investigate value in use of liquefied wood-based resin applications in molding material, Chinese fir （Cunninghamia lanceolata） and poplar （Populus tomentosa） wood meal were liquefied in phenol. The reactant was co-condensed with formaldehyde to obtain liquefied wood-based resin. For this paper, we investigated the characterization of the resin and its application in molding material. The result shows that the basic properties of liquefied wood-based resin were satisfactory; the bonding strength of plywood prepared with liquefied Chinese fir and liquefied poplar resin can reach 1.54 and 1.00 MPa, respectively. The compression strengths of the molding material prepared with two kinds of liquefied wood resin were 73.01 and 73.58 MPa, almost the same as that of PF resin molding material. The limiting volume swelling of molding material made with liquefied Chinese resin and liquefied poplar resin were 8.5% and 8.3%, thickness swelling rates of water absorption were 3.3% and 4.2%, and the maximum weight ratios of water absorption were 25.9% and 26.2%, respectively. The soil burial test result shows that the weight loss rate of the molding materials made with liquefied Chinese resin and liquefied poplar resin were 8.3% and 9.1% and that of the PF resin molding material was 7.9%. After the soil internment test, the reduction ratio of compression strength of the two kinds of molding material achieved 16.9% and 17.7%, while that of the PF resin molding material was 15.4%. The test results of wood fungi inoculation on the three surfaces of the molding material indicate the breeding rate of molding material prepared with liquefied Chinese resin and liquefied poplar resin were at level 4 and that of PF resin molding material was at level 1 of the ISO standard.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52274359 and 52304379)Beijing Natural Science Foundation,China(No.L212021)+4 种基金China National Postdoctoral Program for Innovative Talents(No.BX20220034)China Postdoctoral Science Foundation(No.2022M720403)Fundamental Research Funds for the Central Universities,China(Nos.FRFTP-19005C1Z and 00007718)AECC University Research Cooperation Project,China(No.HFZL2021CXY021)State Key Lab of Advanced Metals and Materials,University of Science and Technology Beijing,China(Nos.2021Z-03 and 2022Z-14)。
文摘Interstitial oxygen(O)contamination remains a substantial challenge for metal injection molding(MIM)of titanium alloys.Herein,this critical problem is successfully addressed by regulating the thermal debinding temperature and incorporating the oxygen scavenger LaB_(6).Results indicate that the surface oxide layer(with a thickness of(13.4±0.5)nm)of Ti_(6)Al4V powder begins to dissolve into the Ti matrix within the temperature range of 663–775℃.O contamination in MIM Ti alloys can be effectively mitigated by lowering the thermal debinding temperature and adding LaB6powder.As a result of reduced dissolved O content,the slips of mixedanddislocations are effectively accelerated,leading to improved ductility.Moreover,grain refinement,along with the in situ formation of Ti B whiskers and second-phase La_(2)O_(3)particles,enhances the strength of the material.The fabricated MIM Ti6Al4V sample exhibits excellent mechanical properties,achieving an ultimate tensile strength of(967±5)MPa,a yield strength of(866±8)MPa,and an elongation of 21.4%±0.7%.These tensile properties represent some of the best results reported in the literature for MIM Ti_(6)Al4V alloys.This study offers valuable insights into the development of high-performance MIM Ti alloys and other metal materials.
基金Project(2011CB606306)supported by the National Basic Research Program of ChinaProject(FRF-TP-10-003B)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(51274040)supported by the National Natural Science Foundation of China
文摘The evolution of stresses due to inhomogeneity in metal injection molding （MIM） parts during sintering was investigated. The sintering model of porous materials during densification process was developed based on the continuum mechanics and thermal elasto-viseoplastic constitutive law. Model parameters were identified from the dilatometer sintering experiment. The real density distribution of green body was measured by X-ray computed tomography （CT）, which was regarded as the initial condition of sintering model. Numerical calculation of the above sintering model was carried out with the finite element soRware Abaqus, through the user-defined material mechanical behavior （UMAT）. The calculation results showed that shrinkages of low density regions were faster than those of high density regions during sintering, which led to internal stresses. Compressive stresses existed in high density regions and tensile stresses existed in low density regions. The densification of local regions depended on not only the initial density, but also the evolution of stresses during the sintering stage.
基金financially supported by the National Natural Science Foundation of China(Nos.52204345 and 52474361)the Scientific Research Innovation Projects of Graduate Student of Jiangsu province,China(No.KYCX24_4184)。
文摘The large-scale production of high-Ti steels is limited by the formation of Ti-containing oxides or nitrides in steel-slag reactions during continuous casting.These processes degrade mold flux properties,clog submerged entry nozzles,form floaters in the molds,and produce various surface defects on the cast slabs.This review summarizes the effects of nonmetallic inclusions on traditional CaO-SiO_(2)-based(CS)mold fluxes and novel CaO-Al_(2)O_(3)-based(CA)low-or non-reactive fluxes containing TiO_(2),BaO,and B_(2)O_(3)additives to avoid undesirable steel,slag,and inclusion reactions,with the aim of providing a new perspective for research and practice related to balancing the lubrication and heat transfer of mold fluxes to promote smooth operation and reduce surface defects on cast slabs.For traditional CS mold flux,although the addition of solvents such as Na_(2)O,Li_(2)O,and B_(2)O_(3)can enhance flowability,steel-slag reactions persist,limiting the effectiveness of CS mold fluxes in high-Ti steel casting.Low-or non-reactive CA mold fluxes with reduced SiO_(2)content are a research focus,where adding other components can significantly change flux characteristics.Replacing CaO with BaO can lower the melting point and inhibit crystallization,allowing the flux to maintain good flowability at low temperatures.Replacing SiO_(2)with TiO_(2)can stabilize the viscosity and enhance heat transfer.To reduce the environmental impact,fluorides are replaced with components such as TiO_(2),B_(2)O_(3),BaO,Li_(2)O,and Na_(2)O for F-frce mold fluxes with similar lubrication,crystallization,and heat-transfer effects.When TiO_(2)replaces CaF_(2),it stabilizes the viscosity and enhances the heat conductivity,forming CaTiO_(3)and CaSiTiO_(5)phases instead of cuspidine to control crystallization.B_(2)O_(3)lowers the melting point and suppresses crystallization,forming phases such as Ca_(3)B_(2)O_(6)and Ca_(11)Si_(4)B_(2)O_(22).BaO introduces non-bridging oxygen to reduce viscosity and ensure flux flowability at low temperatures.However,further studies are required to determine the optimal mold flux compositions corresponding to the steel grades and the interactions between the various components of the mold flux.In the future,the practical application of new mold fluxes for high-Ti steel will become the focus of further verification to achieve a balance between lubrication and heat transfer,which is expected to minimize the occurrence of casting problems and slab defects.
基金Supported by the Special Fund for Agro-Scientific Research in the Public Interest(201003063)the Key Technology R&D Program of Jiangsu Province(BE2013412)the Fund for Independent Innovation of Agricultural Sciences in Jiangsu Province(XC(13)3030)~~
文摘At present, the technology of biomass fuel composite molding technique is relatively lagging in China, which brings several negative influences, such as high energy consumption, short service life of the equipment. The current situation of the biomass pellet fuel molding technology at home and abroad was introduced, and the development direction in China was put forward, which was of great significance for enhancing the level of pellet fuel molding technology in China.
文摘A mathematical model of resin flow and temperature variation in the filling stage of the resin transfer molding (RTM) is developed based on the control volume/finite element method (CV/FEM). The effects of the heat transfer and chemical reaction of the resin on the flow and temperature are considered. The numerical algorithm of the resin flow and temperature variation in the process of RTM are studied. Its accuracy and convergence are analyzed. The comparison of temperature variations between experimental results and model predictions is carried out for two RTM cases. Result shows that the model is efficient for evaluating the flow and temperature variation in the filling stage of RTM and there is a good coincidence between theory and experiment.
基金Key-Area Research and Development Program of Guangdong Province(2023B0909020004)Project of Innovation Research Team in Zhongshan(CXTD2023006)+1 种基金Natural Science Foundation of Guangdong Province(2023A1515011573)Zhongshan Social Welfare Science and Technology Research Project(2024B2022)。
文摘Laser powder bed fusion(LPBF)is highly suitable for forming 18Ni300 mold steel,thanks to its excellent capability in manufacturing complex shapes and outstanding capacity for regulating microstructures.It is widely used in fields such as injection molding,die casting,and stamping dies.Adding reinforcing particles into steel is an effective means to improve its performance.Nb/18Ni300 composites were fabricated by LPBF using two kinds of Nb powders with different particle sizes,and their microstructures and properties were studied.The results show that the unmelted Nb particles are uniformly distributed in the 18Ni300 matrix and the grains are refined,which is particularly pronounced with fine Nb particles.In addition,element diffusion occurs between the particles and the matrix.The main phases of the base alloy are α-Fe and a small amount of γ-Fe.With the addition of Nb,part of the α-Fe is transformed into γ-Fe,and unmelted Nb phases appear.The addition of Nb also enhances the hardness and wear resistance of the composites but slightly reduces their tensile properties.After aging treatment,the molten pools and grain boundaries become blurred,grains are further refined,and the interfaces around the particles are thinned.The aging treatment also promotes the formation of reverted austenite.The hardness,ultimate tensile strength,and volumetric wear rate of the base alloy reach 51.9 HRC,1704 MPa,and 17.8×10^(-6) mm^(3)/(N·m),respectively.In contrast,the sample added with fine Nb particles has the highest hardness(56.1 HRC),ultimate tensile strength(1892 MPa)and yield strength(1842 MPa),and the volume wear rate of the sample added with coarse Nb particles is reduced by 90%to 1.7×10^(-6) mm^(3)/(N·m).
基金financially supported by the Ministry of Science and Higher Education of the Russian Federation。
文摘Carbon-fiber-reinforced plastics(CFRP)with improved mechanical properties based on modified epoxy binders were investigated in this study.By adding 15 parts by weight(p.b.w.)of copolymer of polysulfone with cardo phthalide group(PSFP-70C)to the epoxyanhydride binder,the flexural strength of the epoxy polymer was increased by 60%,the CFRP based on it by 57%,the flexural modulus of the epoxy polymer was increased by 83%,and the composite by 96%.The adhesion strength of the binder to carbon fiber reached a high level at 10 p.b.w.of thermoplastic modifier and increased by 65%compared to the unmodified binder.Scanning electron microscopy(SEM)was used to determine that in epoxyanhydride systems with a polysulfone content of 5–15 p.b.w.,the structure belongs to the"matrix dispersion"type and with a content of 20 p.b.w.to the"interpenetrating phase"type.A heterogeneous structure was also observed using dynamic mechanical analysis.
基金support from the National Key R&D Program of China(Grant No.2023YFB3709901)the National Natural Science Foundation of China(Grant No.U22A20171)+1 种基金China Baowu Low Carbon Metallurgy Innovation Foundation(Grant No.BWLCF202315)the High Steel Center(HSC)at North China University of Technology and University of Science and Technology Beijing,China.
文摘The dissolution of MgO-refractory into the slag had an obvious influence on the steel-slag reaction and the slag property,especially for high-aluminum steels.The dissolution behavior of MgO-refractory was investigated under various conditions,including the temperature,the initial steel composition,and the initial slag composition.A steel-slag-refractory kinetic model for high-aluminum steel was developed,which incorporated the process of MgO-refractory dissolution.The dependence of the MgO mass transfer coefficient k_(MgO)^(r)on temperature T during MgO-refractory dissolution process was established,as described by ln k_(MgO)^(r)=63,754/T+24.38524.It was indicated that the MgO dissolution rate was significantly influenced by the temperature.A higher temperature increased the dissolution rate of MgO.The initial steel composition had a slight impact on the MgO dissolution rate.Additionally,the initial slag composition strongly impacted the MgO saturation concentration and the dissolution rate.A lower initial Al_(2)O_(3)/SiO_(2)ratio increased the MgO dissolution rate.The steel-slag-refractory kinetic model accurately predicted the dissolution of MgO-refractory and the influence of dissolved MgO on the viscosity and composition change during steel-slag-refractory reactions.It was suggested that a higher temperature can hardly reduce the viscosity due to the dissolution of the MgO-refractory.
基金supported by the National Natural Science Foundation of China(No.52274318).
文摘A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.
基金support from the National Natural Science Foundation of China(Grant Nos.52174313 and 52304350)thank all members of the Hebei High Quality Steel Continuous Casting Engineering Technology Research Center at North China University of Science and Technology,Tangshan,China.
文摘The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.
基金supported by the National Natural Science Foundation of China(No.52474396 and 52175284)the National Key Research and Development Program of China(Grant No.2022YFB3404201)。
文摘In order to investigate the effect of die wall thickness on morphologies of defect band,a stepped mold with a wall thickness of 5 mm,4 mm,3 mm,2 mm,and 1 mm was designed to carry out high pressure die casting experiments with AlSi10 MgMn alloy.For castings with wall thickness of 2-4 mm,the ratio of the mean defect band width(w)and mean grain size(d)in the defect band(w/d)ranges 7-18,while it increases to 24.47 for the 5 mm-thick casting.This difference is related with the filling speed and the distribution of externally solidified crystals(ESCs).The mold flow analysis indicates that the filling speed decreases from 25.41 m·s^(-1)to 11.07 m·s^(-1)when wall thickness increases from 2 mm to 5 mm.Due to the decreasing filling speed along the wall thickness,ESCs gradually diffuse from the center to the defect band,which keep the shear strength in the defect band at a high-level during filling.Meanwhile,the shear strength generated during the filling also decreases as the shear rate drops.Finally,the defect bands in the 5 mm-thick region become widen and indistinct,and the porosity is as high as 5.25%.
文摘An improved wax-based binder was developed for powder injection molding of pure titanium. A critical powder loading of 69 vol.% and a pseudo-plastic flow behavior were obtained by the feedstock based on the binder. The injection molding, debinding, and sintering process were studied. An ideal control of carbon and oxygen contents was achieved by thermal debinding in vacuum atmosphere （10^-3 Pa）. The mechanical properties of as-sintered specimens were less than those of titanium made by the conventional press-sintering process. Good shape retention and ±0.04 mm dimension deviation were achieved.
基金financially supported by the National Natural Science Foundation of China (Nos. 51572035 and 51502041)
文摘Despite its unique high efficiency and good environmental compatibility, the water-soluble binder system still encounters problems achieving a desired sintered part via ceramic injection molding because of the poor compatibility and the powder-binder segregation between ceramic powders and binders. The objective of this study was to obtain a sintered part with excellent properties by introducing a small quantity of oleic acid to the surface of zirconia powders before the mixing process. As opposed to many previous investigations that focused only on the rheological behavior and modification mechanism, the sintering behavior and densification process were systematically investigated in this study. With the modified powders, debound parts with a more homogeneous and smaller pore size distribution were fabricated. Also, a higher density and greater flexural strength were achieved in the sintered parts fabricated using the modified powders.
基金supported by the National Key R&D Program of China(No.2022YFC2401903)the“Pioneer”and the“Leading Goose”R&D Program of Zhejiang Province(No.2023C01170)+1 种基金the National Natural Science Foundation of China(No.52205424)the Key Project of Science and Technology Innovation 2025 of Ningbo(No.2023Z029),China.
文摘Over the last half-century,polyether ether ketone(PEEK)has emerged as a widely adopted thermoplastic polymer,primarily due to its lower density,exceptional mechanical properties,high-temperature and chemical resistance,and biocompatibility.PEEK and its composites have found extensive applications across various fields,including machinery,aerospace,military equipment,electronics,and biomedicine,positioning themselves as promising substitutes for traditional metal structures.Nevertheless,achieving optimal performance and functional molding of PEEK and its composites presents a formidable challenge,given their inherent characteristics,such as semi-crystallinity,high melting temperature,heightened viscosity,low dielectric coefficient,and hydrophobic properties.In this paper,we present a comprehensive review of the molding methods and processes of PEEK and its composites,including extrusion molding,hot compression molding,injection molding,and 3D printing.We also introduce typical innovative applications within the fields of mechanics,electricity,and biomedicine while elucidating methodologies that leverage the distinctive advantages of PEEK and its composites.Additionally,we summarize research findings related to manipulating the properties of PEEK and its composites through the optimization of machine parameters,process variables,and material structural adjustments.Finally,we contemplate the prevailing development trends and outline prospective avenues for further research in the advancement and molding of PEEK and its composites.
基金This work was financially supported by National Natural Science Foundation of China(Nos.51775046&51875043&52005040)the China Postdoctoral Science Foundation(No.2019M660480)+1 种基金the Beijing Municipal Natural Sci-ence Foundation(JQ20014)The authors would also like to acknowledge support from the Fok Ying-Tong Education Foundation for Young Teachers in the Higher Education Insti-tutions of China(No.151052).
文摘Micro/nanostructured components play an important role in micro-optics and optical engineering,tribology and surface engineering,and biological and biomedical engineering,among other fields.Precision glass molding technology is the most efficient method of manufacturing micro/nanostructured glass components,the premise of which is meld manufacturing with complementary micro/nanostructures.Numerous mold manufacturing methods have been developed to fabricate extremely small and high-quality micro/nanostructures to satisfy the demands of functional micro/nanostructured glass components for various applications.Moreover,the service performance of the mold should also be carefully considered.This paper reviews a variety of technologies for manufacturing micro/nanostructured molds.The authors begin with an introduction of the extreme requirements of mold materials.The following section provides a detailed survey of the existing micro/nanostructured mold manufacturing techniques and their corresponding mold materials,including nonmechanical and mechanical methods.This paper concludes with a detailed discussion of the authors recent research on nickel-phosphorus(Ni-P)mold manufacturing and its service performance.
基金Supported by the National Natural Science Foundation of China（10871159） the National Basic Research Program of China（2005CB321704）
文摘A non-isothermal injection molding process for a non-Newtonian viscous pseudoplastic fluid is simulated.A conservative interface capturing technique and the flow field solving method are coupled to perform a dynamic simulation.The validity of the numerical method is verified by a benchmark problem.The melt interface evolution versus time is captured and the physical quantities such as temperature,velocity and pressure at each time step are obtained with corresponding analysis.A"frozen skin"layer with the thickness increasing versus time during the injection process is found.The fact that the"frozen skin"layer can be reduced by increasing the injection velocity is numerically verified.The fountain flow phenomenon near the melt interface is also captured.Moreover,comparisons with the non-isothermal Newtonian case show that the curvatures of the interface arcs and the pressure contours near the horizontal mid-line of the cavity for the non-Newtonian pseudoplastic case is larger than that for the Newtonian case.The velocity profiles are different at different positions for the non-Newtonian pseudoplastic case,while in the case of Newtonian flow the velocity profiles are parabolic and almost the same at different positions.
基金This study was financially supported by the National Natural Science Foundation of China （Grant No. 30471351）.
文摘To investigate value in use of liquefied wood-based resin applications in molding material, Chinese fir （Cunninghamia lanceolata） and poplar （Populus tomentosa） wood meal were liquefied in phenol. The reactant was co-condensed with formaldehyde to obtain liquefied wood-based resin. For this paper, we investigated the characterization of the resin and its application in molding material. The result shows that the basic properties of liquefied wood-based resin were satisfactory; the bonding strength of plywood prepared with liquefied Chinese fir and liquefied poplar resin can reach 1.54 and 1.00 MPa, respectively. The compression strengths of the molding material prepared with two kinds of liquefied wood resin were 73.01 and 73.58 MPa, almost the same as that of PF resin molding material. The limiting volume swelling of molding material made with liquefied Chinese resin and liquefied poplar resin were 8.5% and 8.3%, thickness swelling rates of water absorption were 3.3% and 4.2%, and the maximum weight ratios of water absorption were 25.9% and 26.2%, respectively. The soil burial test result shows that the weight loss rate of the molding materials made with liquefied Chinese resin and liquefied poplar resin were 8.3% and 9.1% and that of the PF resin molding material was 7.9%. After the soil internment test, the reduction ratio of compression strength of the two kinds of molding material achieved 16.9% and 17.7%, while that of the PF resin molding material was 15.4%. The test results of wood fungi inoculation on the three surfaces of the molding material indicate the breeding rate of molding material prepared with liquefied Chinese resin and liquefied poplar resin were at level 4 and that of PF resin molding material was at level 1 of the ISO standard.
