Magnesia-calcia refractories are widely used in the production process of clean steel due to their excellent high-tem-perature stability,slag resistance and ability to purify molten steel.However,there are still probl...Magnesia-calcia refractories are widely used in the production process of clean steel due to their excellent high-tem-perature stability,slag resistance and ability to purify molten steel.However,there are still problems such as difficult sintering and easy hydration.Magnesia-calcia materials with various calcium oxide contents were prepared by using induction sintering,and the sintering property combined with the hydration resistance of the materials was investigated.The experimental results showed that the magnesia-calcia materials prepared under induction field had higher density,microhardness and hydration resistance.In particular,the relative density of induction sintered magnesia-calcia materials with 50 mo1%CaO was greater than 98%,and the average grain size of CaO was 4.56μm,which was much larger than that of traditional sintered materials.In order to clarify the densification and microstructure evolution mechanism of the magnesia-calcia materials,the changes in temperature and magnetic field throughout the sintering process were analyzed by using finite element simulation.The results showed that the larger heating rate and higher sintering temperature under the induction sintering mode were beneficial to the rapid densification.In addition,the hot spots generated within the material due to the difference in high-temperature electric conductivity between MgO and CaO were the critical factor to realize selective sintering in MgO-CaO system,which provides a novel pathway to solve the problem of difficult sintering and control the microstructure of high-temperature composite material used in the field of high-purity steel smelting.展开更多
Micropores are decisive to mechanical properties and thermal deformation capabilities of powder met-allurgy(P/M)Ti alloys sintered compacts.As a result,achieving express densification is of prime im-portance and has a...Micropores are decisive to mechanical properties and thermal deformation capabilities of powder met-allurgy(P/M)Ti alloys sintered compacts.As a result,achieving express densification is of prime im-portance and has attracted increasing attention recently.Induction heating owns the merits of high effi-ciency,short process,and low cost,and thus has huge potential to be used as a sintering approach for the fabrication of P/M Ti alloys.Nevertheless,the facilitated densification behavior associated with induction heating sintering remains unclear so far.To address it,powder metallurgy Ti6Al4V is manufactured via induction heating sintering with which the underlying sintering mechanism is investigated in-depth.It is found that induction heating could generate a fully densified compact in a remarkably shortened time,demonstrating its superior sintering efficiency as compared with conventional resistance furnace heat-ing.COMSOL finite element analysis reveals that the maximum current density during induction heating can reach 10^(6)A m^(–2)though the magnetic field strength is solely 0.02 T,leading to a slight tempera-ture difference of approximately 30℃between the interior and exterior of the billet.Furthermore,the rapid heating essentially starts at sharp corners of particles due to the potent current concentration ef-fect,which facilitates the cracking of the particle surface oxide film and thus enhances the direct contact between them.Moreover,the electromigration effect caused by induction current promotes the diffusion capability of elements,giving rise to expedited densification,alloying,and chemical homogenization.This work provides not only critical insight into the sintering mechanism of induction heating sintering but also significant guidance for low-cost powder metallurgy materials preparation.展开更多
MgO–CaO refractories have attracted much attention in the field of clean steel due to the ability of their internal CaO to adsorb elements such as S and P in molten steel.However,there are still some problems such as...MgO–CaO refractories have attracted much attention in the field of clean steel due to the ability of their internal CaO to adsorb elements such as S and P in molten steel.However,there are still some problems such as difficult sintering and insufficient corrosion resistance existing in this system.Different contents of Y_(2)O_(3) were introduced into MgO–CaO system to prepare MgO–CaO–Y_(2)O_(3) ternary refractories via traditional and induction sintering methods.The influence of microstructural regulation on the slag-resistant properties of the refractories was investigated.The results show that the introduction of Y_(2)O_(3) in the MgO–CaO refractories prepared via the two sintering methods leads to the grain boundary reconstruction effect.Under the condition of traditional sintering,when a smaller amount of Y_(2)O_(3) is introduced into the MgO–CaO refractories,Y_(2)O_(3) is able to activate the lattice,promote sintering,and improve the densification of the refractories.However,when more Y_(2)O_(3) is introduced,the excess Y_(2)O_(3) hinders the sintering densification process.Combined with lamellar intergranular phase generated in the refractories,Y_(2)O_(3)-based solid solution can react with the slag,increase the slag viscosity and inhibit the penetration of the slag into the refractories.Under the condition of induction sintering,the solid solution of yttrium ions in CaO is increased by using the coupling of electromagnetic and thermal fields.Compared with the MgO–CaO refractories with high Y_(2)O_(3) content prepared by traditional sintering,the induction sintered refractories have higher densification,which further increases the corrosion resistance.The results provide a new path for developing long-life MgO–CaO based refractories.展开更多
The effect of incorporating limited-diffusivity elements such as Fe and Ti on thermal stability of the nanocrystalline Al alloy was investigated.Al−10wt.%Fe and Al−10wt.%Fe−5wt.%Ti alloys were fabricated.The initial m...The effect of incorporating limited-diffusivity elements such as Fe and Ti on thermal stability of the nanocrystalline Al alloy was investigated.Al−10wt.%Fe and Al−10wt.%Fe−5wt.%Ti alloys were fabricated.The initial mixtures of powders were milled for 100 h in vacuum.The bulk samples were fabricated from the milled powders in a high frequency induction heat sintering(HFIHS)system.The milled powders and the bulk sintered samples were characterized by X-ray diffraction(XRD),Vickers microhardness,field emission scanning electron microscopy(FESEM-EDS)and transmission electron microscopy(TEM).The observations indicated that Fe and Ti were completely dispersed in the matrix to form a supersaturated solid solution(SSSS)with Al.Additionally,the inclusion of alloying elements led to an increase in hardness and yield strength of the alloy by 127%and 152%,respectively.The elevated temperature compression tests were carried out to evaluate the thermal stability of the alloys.The Al−10wt.%Fe−5wt.%Ti alloy revealed the optimum thermally stable behavior of the three alloys studied.The incorporation of Fe and Ti improved the thermal stability of the developed alloys through inhibiting the grain growth,hindering dissolution and growth of second phases(such as Al13Fe4 and Al13Ti),and forming a stable solid solution.展开更多
基金The authors would like to express the gratitude for the financial support from the National Natural Science Foundation of China(U20A20239).
文摘Magnesia-calcia refractories are widely used in the production process of clean steel due to their excellent high-tem-perature stability,slag resistance and ability to purify molten steel.However,there are still problems such as difficult sintering and easy hydration.Magnesia-calcia materials with various calcium oxide contents were prepared by using induction sintering,and the sintering property combined with the hydration resistance of the materials was investigated.The experimental results showed that the magnesia-calcia materials prepared under induction field had higher density,microhardness and hydration resistance.In particular,the relative density of induction sintered magnesia-calcia materials with 50 mo1%CaO was greater than 98%,and the average grain size of CaO was 4.56μm,which was much larger than that of traditional sintered materials.In order to clarify the densification and microstructure evolution mechanism of the magnesia-calcia materials,the changes in temperature and magnetic field throughout the sintering process were analyzed by using finite element simulation.The results showed that the larger heating rate and higher sintering temperature under the induction sintering mode were beneficial to the rapid densification.In addition,the hot spots generated within the material due to the difference in high-temperature electric conductivity between MgO and CaO were the critical factor to realize selective sintering in MgO-CaO system,which provides a novel pathway to solve the problem of difficult sintering and control the microstructure of high-temperature composite material used in the field of high-purity steel smelting.
基金supported by the National Key Research and Development Program of China(No.2020YFB2008300)the National Natural Science Foundation of China(Nos.51971097 and 52301147)+2 种基金the Young Elite Scientist Sponsorship Program by China Association for Science and Technology(No.YESS20210054)the Hubei Province Natural Science Foundation(No.ZRMS2022000863)the Fundamental Research Funds for the Central Universities of Huazhong University of Science and Technology(No.2172021XXJS010)and the project supported by State Key Laboratory of Powder Metallurgy,Central South University,Changsha,China.
文摘Micropores are decisive to mechanical properties and thermal deformation capabilities of powder met-allurgy(P/M)Ti alloys sintered compacts.As a result,achieving express densification is of prime im-portance and has attracted increasing attention recently.Induction heating owns the merits of high effi-ciency,short process,and low cost,and thus has huge potential to be used as a sintering approach for the fabrication of P/M Ti alloys.Nevertheless,the facilitated densification behavior associated with induction heating sintering remains unclear so far.To address it,powder metallurgy Ti6Al4V is manufactured via induction heating sintering with which the underlying sintering mechanism is investigated in-depth.It is found that induction heating could generate a fully densified compact in a remarkably shortened time,demonstrating its superior sintering efficiency as compared with conventional resistance furnace heat-ing.COMSOL finite element analysis reveals that the maximum current density during induction heating can reach 10^(6)A m^(–2)though the magnetic field strength is solely 0.02 T,leading to a slight tempera-ture difference of approximately 30℃between the interior and exterior of the billet.Furthermore,the rapid heating essentially starts at sharp corners of particles due to the potent current concentration ef-fect,which facilitates the cracking of the particle surface oxide film and thus enhances the direct contact between them.Moreover,the electromigration effect caused by induction current promotes the diffusion capability of elements,giving rise to expedited densification,alloying,and chemical homogenization.This work provides not only critical insight into the sintering mechanism of induction heating sintering but also significant guidance for low-cost powder metallurgy materials preparation.
基金financially supported by the National Natural Science Foundation of China(Nos.U20A20239 and U21A2057)the Key Research and Development Project of Hubei Province,China(No.2023BEB017)2023 Longzhong Talent Support Plan(23).
文摘MgO–CaO refractories have attracted much attention in the field of clean steel due to the ability of their internal CaO to adsorb elements such as S and P in molten steel.However,there are still some problems such as difficult sintering and insufficient corrosion resistance existing in this system.Different contents of Y_(2)O_(3) were introduced into MgO–CaO system to prepare MgO–CaO–Y_(2)O_(3) ternary refractories via traditional and induction sintering methods.The influence of microstructural regulation on the slag-resistant properties of the refractories was investigated.The results show that the introduction of Y_(2)O_(3) in the MgO–CaO refractories prepared via the two sintering methods leads to the grain boundary reconstruction effect.Under the condition of traditional sintering,when a smaller amount of Y_(2)O_(3) is introduced into the MgO–CaO refractories,Y_(2)O_(3) is able to activate the lattice,promote sintering,and improve the densification of the refractories.However,when more Y_(2)O_(3) is introduced,the excess Y_(2)O_(3) hinders the sintering densification process.Combined with lamellar intergranular phase generated in the refractories,Y_(2)O_(3)-based solid solution can react with the slag,increase the slag viscosity and inhibit the penetration of the slag into the refractories.Under the condition of induction sintering,the solid solution of yttrium ions in CaO is increased by using the coupling of electromagnetic and thermal fields.Compared with the MgO–CaO refractories with high Y_(2)O_(3) content prepared by traditional sintering,the induction sintered refractories have higher densification,which further increases the corrosion resistance.The results provide a new path for developing long-life MgO–CaO based refractories.
文摘The effect of incorporating limited-diffusivity elements such as Fe and Ti on thermal stability of the nanocrystalline Al alloy was investigated.Al−10wt.%Fe and Al−10wt.%Fe−5wt.%Ti alloys were fabricated.The initial mixtures of powders were milled for 100 h in vacuum.The bulk samples were fabricated from the milled powders in a high frequency induction heat sintering(HFIHS)system.The milled powders and the bulk sintered samples were characterized by X-ray diffraction(XRD),Vickers microhardness,field emission scanning electron microscopy(FESEM-EDS)and transmission electron microscopy(TEM).The observations indicated that Fe and Ti were completely dispersed in the matrix to form a supersaturated solid solution(SSSS)with Al.Additionally,the inclusion of alloying elements led to an increase in hardness and yield strength of the alloy by 127%and 152%,respectively.The elevated temperature compression tests were carried out to evaluate the thermal stability of the alloys.The Al−10wt.%Fe−5wt.%Ti alloy revealed the optimum thermally stable behavior of the three alloys studied.The incorporation of Fe and Ti improved the thermal stability of the developed alloys through inhibiting the grain growth,hindering dissolution and growth of second phases(such as Al13Fe4 and Al13Ti),and forming a stable solid solution.
