A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulat...A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulated by dynamic mesh techniques.The results show that as the ingot grows,the molten pool profile changes from shallow and flat to V-shaped,and both the molten pool depth and the mushy width increase.Meanwhile,the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis.As melt rate increases,both the molten pool depth and the mushy width increase.It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold.The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width.In addition,as melt rate increases,the local solidification time(LST)of ingot decreases obviously at first and then increases.When melt rate is controlled in a suitable range,LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest,which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.展开更多
A new technique IMS (Incremental Melting and Solidification Process) has been introduced. A kind of cast steel high Mn foundry alloy gradient rnalerial was produced by this process. The microstructure and mechanical ...A new technique IMS (Incremental Melting and Solidification Process) has been introduced. A kind of cast steel high Mn foundry alloy gradient rnalerial was produced by this process. The microstructure and mechanical properties of the alloy were tested. Fe and Mn in the samples were measured by EPMA. The experimental results show that the content and hardness of Fe-Mn alloy vary continuously and the IMS process is an alternative way in producing metal matrix gradient material. It is possible for these materials to be made into some parts such as camshaft.展开更多
A mathematical formulation is applied to represent the phenomena in theincremental melting and solidification process (IMSP), and the temperature and electromagneticfields and the depth of steel liquid phase are calcu...A mathematical formulation is applied to represent the phenomena in theincremental melting and solidification process (IMSP), and the temperature and electromagneticfields and the depth of steel liquid phase are calculated by a finite difference technique using thecontrol volume method. The result shows that the predicted values are in good agreement with theobservations. In accordance with the calculated values for different kinds of materials anddifferent size of molds, the technological parameter of the IMS process such as the power supply andthe descending speed rate can be determined.展开更多
The melting process of a phase change material(PCM) inside a capsule can be promising in the thermal management of spacecraft. Such spacecraft operate under various gravity conditions, but previous studies have mostly...The melting process of a phase change material(PCM) inside a capsule can be promising in the thermal management of spacecraft. Such spacecraft operate under various gravity conditions, but previous studies have mostly considered the influence of gravity conditions on the constrained melting process of a PCM and not on its unconstrained melting process. In this study, a numerical model was constructed to comprehensively analyze the constrained and unconstrained melting processes of a PCM inside a spherical capsule under low-gravity conditions. After validation, the model was then applied to investigating the effects of low-gravity conditions on the evolution of velocity, temperature, melt layer thickness, heat transfer, liquid fraction, and total melting time. For the unconstrained melting process, low-gravity conditions weaken buoyancy-driven natural convection and slow down the solid PCM downward trend, thereby limiting the melting rate. In addition, the melt layer thickness does not increase linearly with decreasing gravity. Specifically, the increase in melt layer thickness is smaller by about 1.06 mm when the gravity drops from 0.4g to 0.2g compared to when it drops from 0.2g to 0.1g. The local heat flux in the contact melting area gradually decreases with the reduction of gravity during the unconstrained melting process. During the constrained melting process, notable oscillations in the local heat flux were observed. Decreasing the gravity from g to 0g increased the total melting times of the constrained and unconstrained melting processes by 417% and 621%, respectively.展开更多
The purpose of this paper is to study large-sized copper billets refined with 5N ultrahigh purity after vacuum melting and directional solidifi-cation （VMDS）. The precise impurity analysis of copper billets was carr...The purpose of this paper is to study large-sized copper billets refined with 5N ultrahigh purity after vacuum melting and directional solidifi-cation （VMDS）. The precise impurity analysis of copper billets was carried out with a glow discharge mass spectrometer （GDMS）. The re-sults demonstrate that the total concentration of twenty-two impurities is decreased by 63.1wt.%-66.5 wt.%. Ag, P, S, Na, Mg, Se, Zn, In and Bi are easy to be removed due to lgPimp - lgPCu 1.5, and they can be removed effectively under the vacuum condition of 1650-1700 K for 30 min. The electrical conductivity of 5N copper is higher than that of the raw material as the impurity concentrations decrease. The segrega-tion effect in directional solidification can be remarkable when the equilibrium distribution coefficient （k0） value is less than 0.65 due to the strong affinity of Cu for some metallic and non-metallic impurities.展开更多
The effect of melt superheating treatment on the solidification microstructure and mechanical properties of theγ'phase precipitation-strengthened K424 superalloy was investigated.Differential scanning calorimetry...The effect of melt superheating treatment on the solidification microstructure and mechanical properties of theγ'phase precipitation-strengthened K424 superalloy was investigated.Differential scanning calorimetry(DSC)experiments were conducted to explore the influence of melt treatment temperature on the undercooling of the superalloy.Additionally,pouring experiments were carried out to assess how alterations in both the temperature and duration of melt treatment impacted the grain size,secondary dendrite arm spacing(SDAS),elemental segregation,and mechanical properties of the alloy.Metallographic analysis,scanning electron microscopy,energy dispersive spectroscopy(EDS)and Thermo-Calc software were employed for microstructure characterization.The test specimens were subjected to tensile testing at room temperature and stress rupture testing at 975℃ under 196 MPa.The findings reveal that appropriate melt treatment conditions result in decreased grain size,refined SDAS,minimized elemental segregation,and significant improvements in mechanical properties.Specifically,the study demonstrates that a melt treatment at 1,650℃ for 5 min results in the smallest average grain size of 949μm and the smallest SDAS of 25.38μm.Furthermore,the room temperature tensile properties and creep resistance are notably affected by the melt treatment parameters.It is shown that specific melt treatment conditions,such as holding at 1,650℃ for 5 min,result in superior room temperature strength and extended stress rupture life of the K424 superalloy,while a balance between strength and stability is achieved at 1,600℃ with a holding time of 10 min.These findings offer guidance for optimizing the melt treatment parameters for the K424 superalloy,laying a foundation for further investigations.展开更多
In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting r...In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were investigated using kinetic empirical equation by fitting and combining with X-ray diffraction,X-ray fluorescence,scanning electron microscopy,energy-dispersive spectrometry,and optical microscopy.The results show that iron reduction is controlled by the mass transfer process of(FeOx)in the slag,while vanadium reduction is controlled by both the mass transfer of(VOx)in the slag and the mass transfer of[V]in the molten iron,and the slag–metal interfacial reaction is the only pathway for vanadium reduction.The reduction of iron and vanadium is an obvious first-order reaction,with activation energy of 101.6051 and 197.416 kJ mol^(−1),respectively.Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency.The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe_(2)O_(3)→Fe_(3)O_(4)/FeV_(2)O_(4)→FeTiO_(3) and FeV_(2)O_(4)→MgV_(2)O_(5);titanium in slag is mainly in the form of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and CaTiO_(3).As the reaction time went on,the molar ratio(nTi/nMg)in Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and the Ti2O_(3) content in the slag gradually went up,while the area proportion of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)went up and then down,and the porosity of the slag and the grain size of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)got smaller.展开更多
Rapid solidification of Ti-50 at.%Al peritectic alloy is realized by laser melting technique at diferent conditions of laser power and scanning speed. The temperature field and the cooling rate under the corresponding...Rapid solidification of Ti-50 at.%Al peritectic alloy is realized by laser melting technique at diferent conditions of laser power and scanning speed. The temperature field and the cooling rate under the corresponding conditions are derived from the finite element simulation.℃omparing the measured pool size with the simulated result, the laser absorptivity of Ti-50 at.%Al peritectic alloy at diferent conditions can be deduced to establish the relationships between the laser absorptivity, the laser power and the scanning speed. The morphology evolution and the phase selection of Ti-50 at.%Al peritectic alloy are described by the temperature gradient and the cooling rate. With the increase of temperature gradient and cooling rate, β phase replaces α phase to become the leading growth phase. And the growth of α phase experiences the transition from facet to non-facet manner, while β phase is refined. To understand the underlying mechanism of the competition growth can bring benefit to the industrial application of Ti-Al alloy.展开更多
Ti-Zr-Cu alloy has garnered signifcant attention in the feld of dental implants due to its excellent biocompatibility,antibacterial properties,and potentially controllable mechanical properties.However,two critical ch...Ti-Zr-Cu alloy has garnered signifcant attention in the feld of dental implants due to its excellent biocompatibility,antibacterial properties,and potentially controllable mechanical properties.However,two critical challenges remain in the selective laser melting(SLM)fabrication of Ti-Zr-Cu alloy:First,the high thermal conductivity of the Cu element tends to destabilize the solidifcation behavior of the molten pool,leading to uncontrollable pore defect evolution;Second,the infuence of process parameters on the synergistic efects of zirconium solution strengthening and copper precipitation strengthening is not well understood,hindering precise control over the material's mechanical properties.To address these issues,this study systematically elucidates the quantitative impact of energy input on the defect formation mechanisms and strengthening efects in the SLM processing of Ti15Zr5Cu alloy.By optimizing laser power(120–200 W)and scanning speed(450–1200 mm/s)through a full-factor experimental design,we comprehensively analyze the efects of energy input on defect morphology,microstructure evolution,and mechanical performance.The results demonstrate that as energy density decreases,defect types transition from spherical pores to irregular pores,signifcantly infuencing mechanical properties.Based on the defect evolution trends,three distinct energy density regions are identifed:the high-energy region,the lowenergy region,and the transition region.Under the optimal processing conditions of a laser power of 180 W and a scanning speed of 1200 mm/s,the Ti15Zr5Cu alloy exhibits a relative density of 99.998%,a tensile strength of 1490±11 MPa,and an elongation at break of 6.0%±0.5%.These properties ensure that the material satisfes the stringent requirements for high strength in narrow-diameter implants used in the maxilloanterior region.This study provides theoretical and experimental support for the process-property optimization of Ti-Zr-Cu alloys in additive manufacturing and promotes their application in the fabrication of high-performance,antibacterial dental implants.展开更多
The impact and solidification processes of single melting tin dust at the micron scale on a spherical bead were numerically studied with hot flue gas flow. The geometrical evolution of dust impacting on hot bead and s...The impact and solidification processes of single melting tin dust at the micron scale on a spherical bead were numerically studied with hot flue gas flow. The geometrical evolution of dust impacting on hot bead and spreading without solidification involved initial spreading, retraction and oscillation, and stabilizing. The increased impact angle was found to reduce maximum spread area, weaken retraction and oscillation, and raise steady spread area. Dust impacting on cold bead completely solidified after liquid spreading and solidification without retraction and oscillation. Increased impact angle raised solidification sliding distance, whereas it reduced solidification spread area. Then, the effects of bead temperature, dust inlet velocity and size on the sliding and spreading of dust were studied, and the results indicated that increasing bead temperature, dust inlet velocity and size could raise solidification sliding distance and solidification spread area. With the dusts continually impacting on the bed, a dust layer forms at the front of bead, being different from that of solid dust, which becomes thick firstly, and then spreads from bead front to sides.展开更多
To investigate the nucleation behavior during the single-phased metallic solidification process,the commercial ultrapure ferritic stainless steels with no(Initial steel)and various melt treatments(R1,MR1,Y2,MY1,and M1...To investigate the nucleation behavior during the single-phased metallic solidification process,the commercial ultrapure ferritic stainless steels with no(Initial steel)and various melt treatments(R1,MR1,Y2,MY1,and M1 steels)were used to carry out the differential scanning colorimetry(DSC)and high-temperature confocal laser scanning microscope(HT-CLSM)experiments.Based on the results of DSC experiments,the equilibrium solidification process as well as the relationship among the critical undercooling degree(△T_(c)^(DSC)),latent heat of fusion/crystallization(△H_(f)/△H_(c)),equiaxed grain ratio(ER),and average grain size(△_(ave)^(ingot))was revealed.ER is increased with the decreasing△T_(c)^(DSC)and increasing△H_(f)/△H_(c);however,△_(ave)^(ingot)is decreased with them.Referring to the results of HT-CLSM experiments,the average sizes of micro-/macrostructures(d_(ave)/D_(ave)/)are decreased with the increasing cooling rate,as well as the difference between and apparent critical undercooling degree(△T_(c)^(CLSM))was revealed.The heterogeneous nucleation of the crystal nuclei occurs only if△T_(c)^(CLSM)>△T_(c)^(DSC).Combining with the interfacial wetting-lattice mismatch heterogeneous nucleation model,the dynamic mechanism of the metallic solidification was revealed.The as-cast grains of the melt-treated samples were obviously refined,owing to the much higher actual heterogeneous nucleation rates(I_(heter.,i))obtained through melt treatments,and the heterogeneous nucleation rates(I_(heter.,ij))for all samples are increased with the cooling rates,firmly confirming that the as-cast grains of each sample could be refined by the increasing cooling rates.展开更多
The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical ...The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical issue, in this study, Si is employed to assist the SLM printing of high-strength Al7075. The laser energy density during SLM is optimized, and the eff ects of Si element on solidification path, relative density, microstructure and mechanical properties of Al7075 alloy are studied systematically. With the modified solidification path, laser energy density, and the dense microstructure with refined grain size and semi-continuous precipitates network at grain boundaries, which consists of fine Si, β-MgSi, Q-phase and θ-AlCu, the hot cracking phenomenon and mechanical properties are eff ectively improved. As a result, the tensile strength of the SLM-processed Si-modified Al7075 can reach 486 ± 3 MPa, with a high relative density of ~ 99.4%, a yield strength of 291 ± 8 MPa, fracture elongation of(6.4 ± 0.4)% and hardness of 162 ± 2(HV) at the laser energy density of 112.5 J/mm~3. The main strengthening mechanism with Si modification is demonstrated to be the synergetic enhancement of grain refinement, solution strengthening, load transfer, and dislocation strengthening. This work will inspire more new design of high-strength alloys through SLM.展开更多
The relationships between microstructure and melting temperature of slag containing different heavy metals （Zn, Cu, Pb and Cr） were studied. Furthermore, the corresponding solidification mechanism and rule of heavy ...The relationships between microstructure and melting temperature of slag containing different heavy metals （Zn, Cu, Pb and Cr） were studied. Furthermore, the corresponding solidification mechanism and rule of heavy metals were analyzed by microscopic tests during melting and reconstructing process. Based on preliminary results, three conclusions were derived. Firstly, pure slag would begin to melt when the temperature reached 1 180℃; however, Zn did not play any fluxing action. Secondly, upon adding Cu and Pb, the initial melting temperature of slag decreased by 5-8℃ and their fluxing effect was observed. Thirdly, the initial melting temperature and the reaction time for slag decreased by 22℃ and 6 s respectively after adding Cr; the fluxing action was significant under Cr. The results of X-ray diffraction （XRD） and Fourier transform infrared spectroscope （FTIR） analyses showed that the above heavy metals had little influence on the reconstruction of slag. Toxicity characteristic leaching procedure （TCLP） leaching tests showed a good solidification effect of the heavy metals with melting slag, fixation rate of Zn, Cu, Pb and Cr was 36.3%, 24.6%, 9.2% and 93.2%, respectively. The leaching toxicity of the heavy metals met the requirements for environmental emission after solidification treatment.展开更多
A good understanding of melting and resolidification of the substrate will help us to achieve better bonding.Anumerical model is developed to investigate the solidification of the droplet,and melting and resolidificat...A good understanding of melting and resolidification of the substrate will help us to achieve better bonding.Anumerical model is developed to investigate the solidification of the droplet,and melting and resolidification of thesubstrate.The molybdenum powder spraying onto three different substrates:a stainless steel,brass(70%Cu)andaluminum by atmospheric plasma spraying has been investigated.The maximum melting depth of the substrate hasbeen measured and compared with the numerical prediction.Experimental results show that the material propertiesof the splat and substrate and melting temperature of the substrate play the important roles on substrate melting.A dimensionless parameter,temperature factor,has been proposed and served as an indicator for substrate melting.展开更多
The effect of melting rate on the temperature distribution,velocity field,macrosegregation and dendrite arm spacing during electroslag remelting continuous directional solidification process with a mould of 160 mm in ...The effect of melting rate on the temperature distribution,velocity field,macrosegregation and dendrite arm spacing during electroslag remelting continuous directional solidification process with a mould of 160 mm in diameter was investigated.The mechanism of solute transport and dendrite growth of austenitic hot-work die steel during electroslag remelting process was proposed.The results showed that a lower melting rate contributed to a higher temperature gradient as well as a shallower liquid metal molten pool.With the increase in the melting rate,the central counterclockwise vortex in the slag and clockwise vortex in the liquid metal molten pool grew,whereas the marginal clockwise vortex in the slag reduced.With increasing melting rate,the macrosegregation of carbon became more serious,whereas the average value of secondary dendrite arm spacing first decreased and then increased.The secondary dendrite arm spacing reached a minimum value at melting rate of 98 kg/h,which indicated that 98 kg/h was a proper melting rate for electroslag remelting continuous directional solidification process with a mould of 160 mm in diameter.展开更多
During the welding of AZ91 cast alloy,the presence of eutectic β-Mg17Al12 phase results in constitutional liquation in the original interdendritic regions and in the formation of a partially melted zone(PMZ). In this...During the welding of AZ91 cast alloy,the presence of eutectic β-Mg17Al12 phase results in constitutional liquation in the original interdendritic regions and in the formation of a partially melted zone(PMZ). In this study,gas tungsten arc welding(GTAW) and partial melting(simulated using furnace,salt bath and Gleeble) experiments were conducted. The results show that practically there would not be a critical heating rate during the welding to prevent constitutional liquation. The gradual change of the re-solidification microstructure within PMZ from base metal side to weld metal side was characterized. A sharp transition from base metal to PMZ has been observed. It is found that the original partially divorced eutectic has become a more regular eutectic in most of the PMZ,although close to the fusion boundary the re-solidified eutectic is again a more divorced one. Proceeding the eutectic re-solidification,α-Mg re-solidified with a cellular growth resulting in a serrated interface. The morphological change affected by the peak temperature and cooling rate will be presented and explained.展开更多
A heat and mass transfer modelling containing phase transformation dynamics is made for pure metals and binary alloys under pulsed laser processing. The nonequilibrium effects of processing parameters and physical pro...A heat and mass transfer modelling containing phase transformation dynamics is made for pure metals and binary alloys under pulsed laser processing. The nonequilibrium effects of processing parameters and physical properties are evaluated on the melting and solidification of pure metals (Al, Cu, Fe and Ni) and Al Cu alloys. It is shown that the energy intensity of laser beam and physical properties of metals and the solute concentration of alloys have important effect on the interface temperature, melting and solidification velocity, melting depth and non equilibrium partition coefficient. This situation is resulted from the interaction of heat transfer, redistribution of solute, solute trapping and growth kinetics.展开更多
The investigation on purification of metallurgical grade silicon by solidification of hypereutectic Al-Si melt with super gravity as an intensified separation way was carried out.The results indicate that the refined ...The investigation on purification of metallurgical grade silicon by solidification of hypereutectic Al-Si melt with super gravity as an intensified separation way was carried out.The results indicate that the refined silicon grains are successfully enriched at the bottom of the Al-Si alloy along the direction of super gravity.Then the refined silicon was collected by aqua regia leaching.The purity of the collected silicon is analyzed as 99.92%,which is obviously improved compared with the purity of the metallurgical grade silicon of 99.59%,proving the feasibility of this purification method.Furthermore,the mass fraction of B is reduced from 8.33×10-6 to 5.25×10-6 and that of P from 33.65×10-6 to13.50×10-6.展开更多
A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards a...A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards and distribute randomly inside the Al melt, which induces more nucleation sites resulting in grain refinement. At the same time, the effect of nuclei size on the nuclei distribution and refinement employing electric current pulse （ECP） was also investigated. The smaller nuclei migrate a short distance with the Al melt at lower speed. But for the larger nuclei, the migration downwards with higher speed benefits the refinement of interior grains of the melt. The research results help to better understand the refinement process and provide a more reasonable explanation of the grain refinement mechanism using ECP.展开更多
To improve the poor stability of casting process of Al alloy with high Mg content, which leads to poor final product quality, the melting purification process and the influences of the refiner on the microstructure an...To improve the poor stability of casting process of Al alloy with high Mg content, which leads to poor final product quality, the melting purification process and the influences of the refiner on the microstructure and defect of 5083 alloy were studied. The results show that the optimized process for the rotary impeller degassing of 5083 alloy is as follows： a rotary speed of 250-400 r/min; a gas flow of 1.2-2.0 L/s, a refining time of 10-15 min. This optimized process can reduce the gas content in the solid alloy to 2× 10^-3 mL/g or lower. Due to the addition of grain refiner, the cast microstructure of 5083 alloy is refined. The Al-5Ti-IB wire shows the best refining effect among all the refiners. The refining effect is improved with the increase of grain refiner addition amount. And the refinement effects become stable when Ti content reaches 0.1% or higher. The surface crinkling defect of the billet can be easily found in the alloy refined with Al-5Ti-IB wire compared with the alloys refined with other refiners.展开更多
基金financially supported by National Natural Science Foundation of China(Nos.U1908223 and U1960203)Fundamental Research Funds for the Central Universities(Grant No.N2125017)Talent Project of Revitalizing Liaoning(Grant No.XLYC1902046).
文摘A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulated by dynamic mesh techniques.The results show that as the ingot grows,the molten pool profile changes from shallow and flat to V-shaped,and both the molten pool depth and the mushy width increase.Meanwhile,the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis.As melt rate increases,both the molten pool depth and the mushy width increase.It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold.The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width.In addition,as melt rate increases,the local solidification time(LST)of ingot decreases obviously at first and then increases.When melt rate is controlled in a suitable range,LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest,which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.
文摘A new technique IMS (Incremental Melting and Solidification Process) has been introduced. A kind of cast steel high Mn foundry alloy gradient rnalerial was produced by this process. The microstructure and mechanical properties of the alloy were tested. Fe and Mn in the samples were measured by EPMA. The experimental results show that the content and hardness of Fe-Mn alloy vary continuously and the IMS process is an alternative way in producing metal matrix gradient material. It is possible for these materials to be made into some parts such as camshaft.
文摘A mathematical formulation is applied to represent the phenomena in theincremental melting and solidification process (IMSP), and the temperature and electromagneticfields and the depth of steel liquid phase are calculated by a finite difference technique using thecontrol volume method. The result shows that the predicted values are in good agreement with theobservations. In accordance with the calculated values for different kinds of materials anddifferent size of molds, the technological parameter of the IMS process such as the power supply andthe descending speed rate can be determined.
基金supported by the National Natural Science Foundation of China (Grant No.52376181)。
文摘The melting process of a phase change material(PCM) inside a capsule can be promising in the thermal management of spacecraft. Such spacecraft operate under various gravity conditions, but previous studies have mostly considered the influence of gravity conditions on the constrained melting process of a PCM and not on its unconstrained melting process. In this study, a numerical model was constructed to comprehensively analyze the constrained and unconstrained melting processes of a PCM inside a spherical capsule under low-gravity conditions. After validation, the model was then applied to investigating the effects of low-gravity conditions on the evolution of velocity, temperature, melt layer thickness, heat transfer, liquid fraction, and total melting time. For the unconstrained melting process, low-gravity conditions weaken buoyancy-driven natural convection and slow down the solid PCM downward trend, thereby limiting the melting rate. In addition, the melt layer thickness does not increase linearly with decreasing gravity. Specifically, the increase in melt layer thickness is smaller by about 1.06 mm when the gravity drops from 0.4g to 0.2g compared to when it drops from 0.2g to 0.1g. The local heat flux in the contact melting area gradually decreases with the reduction of gravity during the unconstrained melting process. During the constrained melting process, notable oscillations in the local heat flux were observed. Decreasing the gravity from g to 0g increased the total melting times of the constrained and unconstrained melting processes by 417% and 621%, respectively.
文摘The purpose of this paper is to study large-sized copper billets refined with 5N ultrahigh purity after vacuum melting and directional solidifi-cation （VMDS）. The precise impurity analysis of copper billets was carried out with a glow discharge mass spectrometer （GDMS）. The re-sults demonstrate that the total concentration of twenty-two impurities is decreased by 63.1wt.%-66.5 wt.%. Ag, P, S, Na, Mg, Se, Zn, In and Bi are easy to be removed due to lgPimp - lgPCu 1.5, and they can be removed effectively under the vacuum condition of 1650-1700 K for 30 min. The electrical conductivity of 5N copper is higher than that of the raw material as the impurity concentrations decrease. The segrega-tion effect in directional solidification can be remarkable when the equilibrium distribution coefficient （k0） value is less than 0.65 due to the strong affinity of Cu for some metallic and non-metallic impurities.
基金financially supported by the Natural Science Foundation Joint Fund of Liaoning Province,China(No.2023-MSLH-342).
文摘The effect of melt superheating treatment on the solidification microstructure and mechanical properties of theγ'phase precipitation-strengthened K424 superalloy was investigated.Differential scanning calorimetry(DSC)experiments were conducted to explore the influence of melt treatment temperature on the undercooling of the superalloy.Additionally,pouring experiments were carried out to assess how alterations in both the temperature and duration of melt treatment impacted the grain size,secondary dendrite arm spacing(SDAS),elemental segregation,and mechanical properties of the alloy.Metallographic analysis,scanning electron microscopy,energy dispersive spectroscopy(EDS)and Thermo-Calc software were employed for microstructure characterization.The test specimens were subjected to tensile testing at room temperature and stress rupture testing at 975℃ under 196 MPa.The findings reveal that appropriate melt treatment conditions result in decreased grain size,refined SDAS,minimized elemental segregation,and significant improvements in mechanical properties.Specifically,the study demonstrates that a melt treatment at 1,650℃ for 5 min results in the smallest average grain size of 949μm and the smallest SDAS of 25.38μm.Furthermore,the room temperature tensile properties and creep resistance are notably affected by the melt treatment parameters.It is shown that specific melt treatment conditions,such as holding at 1,650℃ for 5 min,result in superior room temperature strength and extended stress rupture life of the K424 superalloy,while a balance between strength and stability is achieved at 1,600℃ with a holding time of 10 min.These findings offer guidance for optimizing the melt treatment parameters for the K424 superalloy,laying a foundation for further investigations.
基金supported by the National Natural Science Foundation of China(U1908225)the Fundamental Research Funds for Central Universities(N2225012 and N232405-06).
文摘In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were investigated using kinetic empirical equation by fitting and combining with X-ray diffraction,X-ray fluorescence,scanning electron microscopy,energy-dispersive spectrometry,and optical microscopy.The results show that iron reduction is controlled by the mass transfer process of(FeOx)in the slag,while vanadium reduction is controlled by both the mass transfer of(VOx)in the slag and the mass transfer of[V]in the molten iron,and the slag–metal interfacial reaction is the only pathway for vanadium reduction.The reduction of iron and vanadium is an obvious first-order reaction,with activation energy of 101.6051 and 197.416 kJ mol^(−1),respectively.Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency.The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe_(2)O_(3)→Fe_(3)O_(4)/FeV_(2)O_(4)→FeTiO_(3) and FeV_(2)O_(4)→MgV_(2)O_(5);titanium in slag is mainly in the form of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and CaTiO_(3).As the reaction time went on,the molar ratio(nTi/nMg)in Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and the Ti2O_(3) content in the slag gradually went up,while the area proportion of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)went up and then down,and the porosity of the slag and the grain size of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)got smaller.
基金supported by the National Natural Science Foundations of China Nos.51271149 and 50901060)the National Basic Research Program of China(No.2011CB610404)+3 种基金the National Aerospace Science Foundation of China(No.2010ZF53059)the NPU Foundations for Fundamental Research(No.NPUJC20110279)the Fund of the Innovation Base of Graduate Students of NPUsupported partly by the National Research Foundation of Korea(No.2012-0009451)
文摘Rapid solidification of Ti-50 at.%Al peritectic alloy is realized by laser melting technique at diferent conditions of laser power and scanning speed. The temperature field and the cooling rate under the corresponding conditions are derived from the finite element simulation.℃omparing the measured pool size with the simulated result, the laser absorptivity of Ti-50 at.%Al peritectic alloy at diferent conditions can be deduced to establish the relationships between the laser absorptivity, the laser power and the scanning speed. The morphology evolution and the phase selection of Ti-50 at.%Al peritectic alloy are described by the temperature gradient and the cooling rate. With the increase of temperature gradient and cooling rate, β phase replaces α phase to become the leading growth phase. And the growth of α phase experiences the transition from facet to non-facet manner, while β phase is refined. To understand the underlying mechanism of the competition growth can bring benefit to the industrial application of Ti-Al alloy.
基金supported by the National Natural Science Foundation of China(Nos.52401178 and U24A20713)the IMR Innovation Fund(No.2024-PY06)the CAS-WEGO Research and Development Plan Project.
文摘Ti-Zr-Cu alloy has garnered signifcant attention in the feld of dental implants due to its excellent biocompatibility,antibacterial properties,and potentially controllable mechanical properties.However,two critical challenges remain in the selective laser melting(SLM)fabrication of Ti-Zr-Cu alloy:First,the high thermal conductivity of the Cu element tends to destabilize the solidifcation behavior of the molten pool,leading to uncontrollable pore defect evolution;Second,the infuence of process parameters on the synergistic efects of zirconium solution strengthening and copper precipitation strengthening is not well understood,hindering precise control over the material's mechanical properties.To address these issues,this study systematically elucidates the quantitative impact of energy input on the defect formation mechanisms and strengthening efects in the SLM processing of Ti15Zr5Cu alloy.By optimizing laser power(120–200 W)and scanning speed(450–1200 mm/s)through a full-factor experimental design,we comprehensively analyze the efects of energy input on defect morphology,microstructure evolution,and mechanical performance.The results demonstrate that as energy density decreases,defect types transition from spherical pores to irregular pores,signifcantly infuencing mechanical properties.Based on the defect evolution trends,three distinct energy density regions are identifed:the high-energy region,the lowenergy region,and the transition region.Under the optimal processing conditions of a laser power of 180 W and a scanning speed of 1200 mm/s,the Ti15Zr5Cu alloy exhibits a relative density of 99.998%,a tensile strength of 1490±11 MPa,and an elongation at break of 6.0%±0.5%.These properties ensure that the material satisfes the stringent requirements for high strength in narrow-diameter implants used in the maxilloanterior region.This study provides theoretical and experimental support for the process-property optimization of Ti-Zr-Cu alloys in additive manufacturing and promotes their application in the fabrication of high-performance,antibacterial dental implants.
文摘The impact and solidification processes of single melting tin dust at the micron scale on a spherical bead were numerically studied with hot flue gas flow. The geometrical evolution of dust impacting on hot bead and spreading without solidification involved initial spreading, retraction and oscillation, and stabilizing. The increased impact angle was found to reduce maximum spread area, weaken retraction and oscillation, and raise steady spread area. Dust impacting on cold bead completely solidified after liquid spreading and solidification without retraction and oscillation. Increased impact angle raised solidification sliding distance, whereas it reduced solidification spread area. Then, the effects of bead temperature, dust inlet velocity and size on the sliding and spreading of dust were studied, and the results indicated that increasing bead temperature, dust inlet velocity and size could raise solidification sliding distance and solidification spread area. With the dusts continually impacting on the bed, a dust layer forms at the front of bead, being different from that of solid dust, which becomes thick firstly, and then spreads from bead front to sides.
基金supported by the National Natural Science Foundation of China(Grant Nos.52274339,52174321,52074186,and 52104337)Natural Science Foundation of Jiangsu Province(Grant No.BK20231317)China Baowu Low-Carbon Metallurgy Innovation Fund(Grant No.BWLCF202108).
文摘To investigate the nucleation behavior during the single-phased metallic solidification process,the commercial ultrapure ferritic stainless steels with no(Initial steel)and various melt treatments(R1,MR1,Y2,MY1,and M1 steels)were used to carry out the differential scanning colorimetry(DSC)and high-temperature confocal laser scanning microscope(HT-CLSM)experiments.Based on the results of DSC experiments,the equilibrium solidification process as well as the relationship among the critical undercooling degree(△T_(c)^(DSC)),latent heat of fusion/crystallization(△H_(f)/△H_(c)),equiaxed grain ratio(ER),and average grain size(△_(ave)^(ingot))was revealed.ER is increased with the decreasing△T_(c)^(DSC)and increasing△H_(f)/△H_(c);however,△_(ave)^(ingot)is decreased with them.Referring to the results of HT-CLSM experiments,the average sizes of micro-/macrostructures(d_(ave)/D_(ave)/)are decreased with the increasing cooling rate,as well as the difference between and apparent critical undercooling degree(△T_(c)^(CLSM))was revealed.The heterogeneous nucleation of the crystal nuclei occurs only if△T_(c)^(CLSM)>△T_(c)^(DSC).Combining with the interfacial wetting-lattice mismatch heterogeneous nucleation model,the dynamic mechanism of the metallic solidification was revealed.The as-cast grains of the melt-treated samples were obviously refined,owing to the much higher actual heterogeneous nucleation rates(I_(heter.,i))obtained through melt treatments,and the heterogeneous nucleation rates(I_(heter.,ij))for all samples are increased with the cooling rates,firmly confirming that the as-cast grains of each sample could be refined by the increasing cooling rates.
基金financially supported by the Joint Fund Project of Equipment Pre-research of Education Ministry(Grant No.6141A02033230)。
文摘The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical issue, in this study, Si is employed to assist the SLM printing of high-strength Al7075. The laser energy density during SLM is optimized, and the eff ects of Si element on solidification path, relative density, microstructure and mechanical properties of Al7075 alloy are studied systematically. With the modified solidification path, laser energy density, and the dense microstructure with refined grain size and semi-continuous precipitates network at grain boundaries, which consists of fine Si, β-MgSi, Q-phase and θ-AlCu, the hot cracking phenomenon and mechanical properties are eff ectively improved. As a result, the tensile strength of the SLM-processed Si-modified Al7075 can reach 486 ± 3 MPa, with a high relative density of ~ 99.4%, a yield strength of 291 ± 8 MPa, fracture elongation of(6.4 ± 0.4)% and hardness of 162 ± 2(HV) at the laser energy density of 112.5 J/mm~3. The main strengthening mechanism with Si modification is demonstrated to be the synergetic enhancement of grain refinement, solution strengthening, load transfer, and dislocation strengthening. This work will inspire more new design of high-strength alloys through SLM.
基金Funded by the National Natural Science Foundation of China(Nos.51202222,51002110)the State Key Laboratory of Silicate Materials for Architectures(Wuhan University of Technology)(No.SYSJJ2013-07)
文摘The relationships between microstructure and melting temperature of slag containing different heavy metals （Zn, Cu, Pb and Cr） were studied. Furthermore, the corresponding solidification mechanism and rule of heavy metals were analyzed by microscopic tests during melting and reconstructing process. Based on preliminary results, three conclusions were derived. Firstly, pure slag would begin to melt when the temperature reached 1 180℃; however, Zn did not play any fluxing action. Secondly, upon adding Cu and Pb, the initial melting temperature of slag decreased by 5-8℃ and their fluxing effect was observed. Thirdly, the initial melting temperature and the reaction time for slag decreased by 22℃ and 6 s respectively after adding Cr; the fluxing action was significant under Cr. The results of X-ray diffraction （XRD） and Fourier transform infrared spectroscope （FTIR） analyses showed that the above heavy metals had little influence on the reconstruction of slag. Toxicity characteristic leaching procedure （TCLP） leaching tests showed a good solidification effect of the heavy metals with melting slag, fixation rate of Zn, Cu, Pb and Cr was 36.3%, 24.6%, 9.2% and 93.2%, respectively. The leaching toxicity of the heavy metals met the requirements for environmental emission after solidification treatment.
基金This work was supported by the National Science Foundation under award No.CTS-9876198MRSEC program under award No.DMR-00800221.
文摘A good understanding of melting and resolidification of the substrate will help us to achieve better bonding.Anumerical model is developed to investigate the solidification of the droplet,and melting and resolidification of thesubstrate.The molybdenum powder spraying onto three different substrates:a stainless steel,brass(70%Cu)andaluminum by atmospheric plasma spraying has been investigated.The maximum melting depth of the substrate hasbeen measured and compared with the numerical prediction.Experimental results show that the material propertiesof the splat and substrate and melting temperature of the substrate play the important roles on substrate melting.A dimensionless parameter,temperature factor,has been proposed and served as an indicator for substrate melting.
基金This work was supported by the Guangdong YangFan Innovative&Entrepreneurial Research Team Program(Grant No.2016YT03C071)the Guangdong Science and Technology Special Fund Project(Grant No.SDZX202005).
文摘The effect of melting rate on the temperature distribution,velocity field,macrosegregation and dendrite arm spacing during electroslag remelting continuous directional solidification process with a mould of 160 mm in diameter was investigated.The mechanism of solute transport and dendrite growth of austenitic hot-work die steel during electroslag remelting process was proposed.The results showed that a lower melting rate contributed to a higher temperature gradient as well as a shallower liquid metal molten pool.With the increase in the melting rate,the central counterclockwise vortex in the slag and clockwise vortex in the liquid metal molten pool grew,whereas the marginal clockwise vortex in the slag reduced.With increasing melting rate,the macrosegregation of carbon became more serious,whereas the average value of secondary dendrite arm spacing first decreased and then increased.The secondary dendrite arm spacing reached a minimum value at melting rate of 98 kg/h,which indicated that 98 kg/h was a proper melting rate for electroslag remelting continuous directional solidification process with a mould of 160 mm in diameter.
文摘During the welding of AZ91 cast alloy,the presence of eutectic β-Mg17Al12 phase results in constitutional liquation in the original interdendritic regions and in the formation of a partially melted zone(PMZ). In this study,gas tungsten arc welding(GTAW) and partial melting(simulated using furnace,salt bath and Gleeble) experiments were conducted. The results show that practically there would not be a critical heating rate during the welding to prevent constitutional liquation. The gradual change of the re-solidification microstructure within PMZ from base metal side to weld metal side was characterized. A sharp transition from base metal to PMZ has been observed. It is found that the original partially divorced eutectic has become a more regular eutectic in most of the PMZ,although close to the fusion boundary the re-solidified eutectic is again a more divorced one. Proceeding the eutectic re-solidification,α-Mg re-solidified with a cellular growth resulting in a serrated interface. The morphological change affected by the peak temperature and cooling rate will be presented and explained.
文摘A heat and mass transfer modelling containing phase transformation dynamics is made for pure metals and binary alloys under pulsed laser processing. The nonequilibrium effects of processing parameters and physical properties are evaluated on the melting and solidification of pure metals (Al, Cu, Fe and Ni) and Al Cu alloys. It is shown that the energy intensity of laser beam and physical properties of metals and the solute concentration of alloys have important effect on the interface temperature, melting and solidification velocity, melting depth and non equilibrium partition coefficient. This situation is resulted from the interaction of heat transfer, redistribution of solute, solute trapping and growth kinetics.
基金Project(51174187) supported by the National Natural Science Foundation of ChinaProject(2011BAE03B01) supported by the National Technology R & D Program of China
文摘The investigation on purification of metallurgical grade silicon by solidification of hypereutectic Al-Si melt with super gravity as an intensified separation way was carried out.The results indicate that the refined silicon grains are successfully enriched at the bottom of the Al-Si alloy along the direction of super gravity.Then the refined silicon was collected by aqua regia leaching.The purity of the collected silicon is analyzed as 99.92%,which is obviously improved compared with the purity of the metallurgical grade silicon of 99.59%,proving the feasibility of this purification method.Furthermore,the mass fraction of B is reduced from 8.33×10-6 to 5.25×10-6 and that of P from 33.65×10-6 to13.50×10-6.
基金Project(SELF-2011-01)supported by the Open Project of Shanghai Key Laboratory of Modern Metallurgy and Materials Processing,ChinaProjects(51204109,51035004)supported by the National Natural Science Foundation of China
文摘A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards and distribute randomly inside the Al melt, which induces more nucleation sites resulting in grain refinement. At the same time, the effect of nuclei size on the nuclei distribution and refinement employing electric current pulse （ECP） was also investigated. The smaller nuclei migrate a short distance with the Al melt at lower speed. But for the larger nuclei, the migration downwards with higher speed benefits the refinement of interior grains of the melt. The research results help to better understand the refinement process and provide a more reasonable explanation of the grain refinement mechanism using ECP.
基金Project(12511075)supported by the Foundation of Heilongjiang Education Committee,China
文摘To improve the poor stability of casting process of Al alloy with high Mg content, which leads to poor final product quality, the melting purification process and the influences of the refiner on the microstructure and defect of 5083 alloy were studied. The results show that the optimized process for the rotary impeller degassing of 5083 alloy is as follows： a rotary speed of 250-400 r/min; a gas flow of 1.2-2.0 L/s, a refining time of 10-15 min. This optimized process can reduce the gas content in the solid alloy to 2× 10^-3 mL/g or lower. Due to the addition of grain refiner, the cast microstructure of 5083 alloy is refined. The Al-5Ti-IB wire shows the best refining effect among all the refiners. The refining effect is improved with the increase of grain refiner addition amount. And the refinement effects become stable when Ti content reaches 0.1% or higher. The surface crinkling defect of the billet can be easily found in the alloy refined with Al-5Ti-IB wire compared with the alloys refined with other refiners.
