Laser powder bed fusion(LPBF)is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry.Whereas it inevitably introduces specific microstructures and pore defects,...Laser powder bed fusion(LPBF)is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry.Whereas it inevitably introduces specific microstructures and pore defects,which will further influence the mechanical properties.Hence,aiming at exploring the LPBF process-related microstructures and pore defects,and especially their influences on the damage mechanism and mechanical properties,Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds.The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density,while lower scanning speeds result in elongated columnar grains with lower dislocation density.The pore defects analyzed by X-ray computed tomography(XCT)suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion(LOF)pores,and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity.Moreover,the insitu XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism.Specifically,high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scan-ning direction.Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces,while metallurgical and keyhole pores have little impact on damage evolution.Eventually,the process-structure-property correlation is established.The presence of high volume fraction of lamel-lar LOF pores,resulting from high scanning speed,leads to inferior yield strength and ductility.Besides,specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds,slightly reducing yield strength while slightly enhancing ductility.This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.展开更多
The Fe-Ni36 alloy was prepared via the one-step electrolysis of a mixed oxides precursor in a molten Na2CO3-K2CO3 eutectic melt at 750℃,where porous Fe_(2)O_(3)-NiO pellets served as the cathode and the Ni10 Cu11 Fe ...The Fe-Ni36 alloy was prepared via the one-step electrolysis of a mixed oxides precursor in a molten Na2CO3-K2CO3 eutectic melt at 750℃,where porous Fe_(2)O_(3)-NiO pellets served as the cathode and the Ni10 Cu11 Fe alloy was an inert anode.During the electrolysis,Ni O was preferentially electro-reduced to Ni,then Fe_(2)O_(3)was reduced and simultaneously alloyed with nickel to form the Fe-Ni36 alloy.Different cell voltages were applied to optimize the electrolytic conditions,and a relatively low energy consumption of 2.48 k W·h·kg^(-1) for production of Fe Ni36 alloy was achieved under 1.9 V with a high current efficiency of 94.6%.The particle size of the alloy was found to be much smaller than that of the individual metal.This process provides a low-carbon technology for preparing the Fe-Ni36 alloy via molten carbonates electrolysis.展开更多
In this work,the Invar 36 alloys were manufactured using cold spray(CS)additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical propert...In this work,the Invar 36 alloys were manufactured using cold spray(CS)additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical properties under as-sprayed(AS)and heat-treated(HT)conditions.XRD(X-ray diffraction)and ICP-AES(inductively coupled plasma atomic emission spectroscopy)analyses show that no phase transformation,oxidation,nor element content change have occurred.The X-ray computed tomography(XCT)exhibited a near fully dense structure with a porosity of 0.025%in the helium-produced sample under as-sprayed condition,whereas the nitrogen-produced samples produced at 5 MPa and 800℃show more irregular pore defects.He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation.The post heat-treatment exhibited a promoted grain growth,inter-particle diffusion,as well as the formation of annealing twins.Between25℃and 200℃,the nitrogen samples possessed lower CTE(coefficient of thermal expansion)values(1.53×10^(-6)/℃)compared with those produced by casting and laser additive manufacturing.The He-AS samples exhibited a noticeable negative CTE value between 25℃and 200℃,which may due to the significant compressive residual stress(-272 MPa)compensating its displacement with temperature increase during CTE test.The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility.In conclusion,the CS technique can be considered as a potential method to produce the Invar36 component with high thermal and mechanical performance.展开更多
Effects of Ti-Ce refiners on the solidification structure and the hot ductility of Fe-36Ni invar alloy were investigated, the corresponding mechanisms were also discussed. The results showed that the solidification of...Effects of Ti-Ce refiners on the solidification structure and the hot ductility of Fe-36Ni invar alloy were investigated, the corresponding mechanisms were also discussed. The results showed that the solidification of the alloy was remarkably refined with the addition of 0.05%Ti-0.01%Ce refiners. Not only did the columnar grains become shorter and thinner, but the growth pattern of them changed into staggered growth from linear growth. The alloy had a bad hot ductility below 1050 °C, which was mainly attrib-uted to weaker boundaries and the presence of grain boundary sliding. However, the hot ductility of the alloy was highly enhanced at 850-1000 °C as the addition of 0.05%Ti-0.01%Ce refiners could refine grain sizes, thus hinder grain boundary sliding, strengthen the grain boundary and promote the grain boundary movement. The alloy had a good hot ductility over 1050 °C, dynamic recrys-tallization occurred and was found to be responsible for the better hot ductility. In addition, the average coefficient of thermal ex-pansion of the alloy decreased a little with the addition of 0.05%Ti-0.01%Ce refiners, which met the requirement of material prop-erties.展开更多
The hot ductility of Fe-36Ni invar alloy with different additions of the element cerium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850 - 1 050℃, and the improvement ...The hot ductility of Fe-36Ni invar alloy with different additions of the element cerium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850 - 1 050℃, and the improvement mechanism of the hot ductility was analyzed using a combination of SEM, EDS, and OM. The results indicated that Fe-36Ni invar alloy exhibited poor hot ductility below 1 050℃, which was mainly attributed to weak grain boundaries and the action of grain boundary sliding. However, the alloys with cerium contents of 0. 016% and 0.024% both demonstrated substantial improvement in the hot ductility over the entire testing temperature range. The observed improvement of the hot ductility of the alloy with 0. 016% cerium at 950 ~C and the alloy with 0.024% cerium at 900℃ was associated mainly with the grain boundary strengthening and the restriction of the grain boundary sliding because the addition of cerium reduced the segregation of sulfur at grain boundaries and refined the grain structure. The occurrence and acceleration of dynamic recrystallization were found to be responsible for the high hot ductility of the alloy with 0.016% cerium at 1 000℃ and the alloy with 0. 024% cerium at 950 - 1 000℃ as a result of the refinement of the grain structure by addition of cerium.展开更多
The effect of Ce, La and mischmetal on the solidification structure of Fe-36Ni invar alloy was investigated. The results show that great amounts of high-melting point compounds （ Ce2O3, La202S and （ Ce, La）2O2S ） ...The effect of Ce, La and mischmetal on the solidification structure of Fe-36Ni invar alloy was investigated. The results show that great amounts of high-melting point compounds （ Ce2O3, La202S and （ Ce, La）2O2S ） respectively formed in the alloy with the addition of Ce, La or mischmetal. Based on the theory of lattice misfit, the lattice misfit between the （0001） surfaces of Ce2O3,Ce2O2S and La2O2S and （100） surface of Fe-36Ni invar alloy were 6.21%, 5.77 % and 5.42 %, respectively, which are relatively low. Therefore, Ce2 O3, La2 O2 S and （ Ce, La） 2 O2 S could serve as the core of heterogeneous nucleation, improve the equiaxed grain ratio, reduce the equiaxed grain size and refine the solidification structure of alloy.展开更多
Invar steels possess excellent thermal expansion properties,making them suitable as materials for manufacturing precision instruments.However,conventional invar steels lack sufficient strength for engineering applicat...Invar steels possess excellent thermal expansion properties,making them suitable as materials for manufacturing precision instruments.However,conventional invar steels lack sufficient strength for engineering applications,and various strengthening methods are urgently needed to enhance their strength.In this work,the possibility of enhancing the strength and maintaining low coefficient of thermal expansion(CTE)of the steel through mechanical heat treatment and the introduction of vanadium carbonitride is demonstrated.V-N microalloying and various heat treatment processes enable invar steel to enhance its strength while maintaining low thermal expansion properties.The strength of low-nitrogen addition invar steel measured 593 MPa during direct aging,representing a 44.6% increase compared to invar steel.After undergoing cold-deformation aging,the strength of low-nitrogen invar steel increased to 790 MPa,indicating a substantial improvement in strength relative to the direct aging condition.Notably,the coefficient of thermal expansion remained at 0.98×10^(-6)℃^(-1).By further increasing N content to introduce more vanadium carbonitride,the strength of high-nitrogen invar steel reached 927 MPa under cold-deformation process while maintaining a low CTE value of 1.02×10^(-6)℃^(-1).This achieved an extraordinary balance of high strength and low CTE,which is due to a well combination of various strengthening mechanisms,especially the Orowan strengthening where dislocations continuously bypass vanadium carbonitride to achieve the strengthening effect.The resulting findings are important for future preparation of excellent properties invar steel in industrial applications.展开更多
基金support of the National Natural Science Foundation of China(Grant Nos.12372133 and 12027901)supported by the Natural Science Foun-dation of Hunan Province(Grant No.2021JJ30085)+2 种基金the Science and Technology Innovation Program of Hunan Province(Grant No.2021RC30306)Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University(Grant No.Kfkt2021-01)the Fund of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body(Grant No.52175012).
文摘Laser powder bed fusion(LPBF)is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry.Whereas it inevitably introduces specific microstructures and pore defects,which will further influence the mechanical properties.Hence,aiming at exploring the LPBF process-related microstructures and pore defects,and especially their influences on the damage mechanism and mechanical properties,Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds.The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density,while lower scanning speeds result in elongated columnar grains with lower dislocation density.The pore defects analyzed by X-ray computed tomography(XCT)suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion(LOF)pores,and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity.Moreover,the insitu XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism.Specifically,high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scan-ning direction.Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces,while metallurgical and keyhole pores have little impact on damage evolution.Eventually,the process-structure-property correlation is established.The presence of high volume fraction of lamel-lar LOF pores,resulting from high scanning speed,leads to inferior yield strength and ductility.Besides,specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds,slightly reducing yield strength while slightly enhancing ductility.This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.
基金the National Natural Science Foundation of China(Nos.51874211 and 51325102)。
文摘The Fe-Ni36 alloy was prepared via the one-step electrolysis of a mixed oxides precursor in a molten Na2CO3-K2CO3 eutectic melt at 750℃,where porous Fe_(2)O_(3)-NiO pellets served as the cathode and the Ni10 Cu11 Fe alloy was an inert anode.During the electrolysis,Ni O was preferentially electro-reduced to Ni,then Fe_(2)O_(3)was reduced and simultaneously alloyed with nickel to form the Fe-Ni36 alloy.Different cell voltages were applied to optimize the electrolytic conditions,and a relatively low energy consumption of 2.48 k W·h·kg^(-1) for production of Fe Ni36 alloy was achieved under 1.9 V with a high current efficiency of 94.6%.The particle size of the alloy was found to be much smaller than that of the individual metal.This process provides a low-carbon technology for preparing the Fe-Ni36 alloy via molten carbonates electrolysis.
基金supported financially by the National Key Research and Development Program of China(No.2019YFA0705300)the Guangdong Special Support Program(No.2019BT02C629)+6 种基金the National Natural Science Foundation of China(No.51690160)the Shanghai Science and Technology Committee(No.19DZ1100704)the Shanghai Sailing Program(No.19YF1415900)Golden Apple Project of Baosteel Co.,Ltd(No.A19EC13500)the Guangdong Basic and Applied Basic Research Foundation(No.2019B1515120016)the Guangzhou Science and Technology Program(Nos.202002030290 and 202007020008)the GDAS’Project of Science and Technology Development(Nos.2019GDASYL-0503006 and 2020GDASYL-20200302011)。
文摘In this work,the Invar 36 alloys were manufactured using cold spray(CS)additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical properties under as-sprayed(AS)and heat-treated(HT)conditions.XRD(X-ray diffraction)and ICP-AES(inductively coupled plasma atomic emission spectroscopy)analyses show that no phase transformation,oxidation,nor element content change have occurred.The X-ray computed tomography(XCT)exhibited a near fully dense structure with a porosity of 0.025%in the helium-produced sample under as-sprayed condition,whereas the nitrogen-produced samples produced at 5 MPa and 800℃show more irregular pore defects.He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation.The post heat-treatment exhibited a promoted grain growth,inter-particle diffusion,as well as the formation of annealing twins.Between25℃and 200℃,the nitrogen samples possessed lower CTE(coefficient of thermal expansion)values(1.53×10^(-6)/℃)compared with those produced by casting and laser additive manufacturing.The He-AS samples exhibited a noticeable negative CTE value between 25℃and 200℃,which may due to the significant compressive residual stress(-272 MPa)compensating its displacement with temperature increase during CTE test.The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility.In conclusion,the CS technique can be considered as a potential method to produce the Invar36 component with high thermal and mechanical performance.
文摘Effects of Ti-Ce refiners on the solidification structure and the hot ductility of Fe-36Ni invar alloy were investigated, the corresponding mechanisms were also discussed. The results showed that the solidification of the alloy was remarkably refined with the addition of 0.05%Ti-0.01%Ce refiners. Not only did the columnar grains become shorter and thinner, but the growth pattern of them changed into staggered growth from linear growth. The alloy had a bad hot ductility below 1050 °C, which was mainly attrib-uted to weaker boundaries and the presence of grain boundary sliding. However, the hot ductility of the alloy was highly enhanced at 850-1000 °C as the addition of 0.05%Ti-0.01%Ce refiners could refine grain sizes, thus hinder grain boundary sliding, strengthen the grain boundary and promote the grain boundary movement. The alloy had a good hot ductility over 1050 °C, dynamic recrys-tallization occurred and was found to be responsible for the better hot ductility. In addition, the average coefficient of thermal ex-pansion of the alloy decreased a little with the addition of 0.05%Ti-0.01%Ce refiners, which met the requirement of material prop-erties.
文摘The hot ductility of Fe-36Ni invar alloy with different additions of the element cerium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850 - 1 050℃, and the improvement mechanism of the hot ductility was analyzed using a combination of SEM, EDS, and OM. The results indicated that Fe-36Ni invar alloy exhibited poor hot ductility below 1 050℃, which was mainly attributed to weak grain boundaries and the action of grain boundary sliding. However, the alloys with cerium contents of 0. 016% and 0.024% both demonstrated substantial improvement in the hot ductility over the entire testing temperature range. The observed improvement of the hot ductility of the alloy with 0. 016% cerium at 950 ~C and the alloy with 0.024% cerium at 900℃ was associated mainly with the grain boundary strengthening and the restriction of the grain boundary sliding because the addition of cerium reduced the segregation of sulfur at grain boundaries and refined the grain structure. The occurrence and acceleration of dynamic recrystallization were found to be responsible for the high hot ductility of the alloy with 0.016% cerium at 1 000℃ and the alloy with 0. 024% cerium at 950 - 1 000℃ as a result of the refinement of the grain structure by addition of cerium.
文摘The effect of Ce, La and mischmetal on the solidification structure of Fe-36Ni invar alloy was investigated. The results show that great amounts of high-melting point compounds （ Ce2O3, La202S and （ Ce, La）2O2S ） respectively formed in the alloy with the addition of Ce, La or mischmetal. Based on the theory of lattice misfit, the lattice misfit between the （0001） surfaces of Ce2O3,Ce2O2S and La2O2S and （100） surface of Fe-36Ni invar alloy were 6.21%, 5.77 % and 5.42 %, respectively, which are relatively low. Therefore, Ce2 O3, La2 O2 S and （ Ce, La） 2 O2 S could serve as the core of heterogeneous nucleation, improve the equiaxed grain ratio, reduce the equiaxed grain size and refine the solidification structure of alloy.
基金supported by the Shanxi Provincial Basic Research Program(No.202403021221046)the National Natural Science Foundation of China(Nos.52004180 and 52204350)+5 种基金the China Postdoctoral Science Foundation(No.2020M683706XB)the Research Project Supported by Shanxi Scholarship Council of China(No.2023-080)the Fund Projects for the Central Government to Guide the Development of Local Science and Technology(No.236Z1023G)the Hebei Province High-level Talent Funding Project(No.B20231016)the National College Student Innovation and Entrepreneurship Training Program(No.202410112116)the Graduate Student Scientific Research Innovation Program(No.2024KY278).
文摘Invar steels possess excellent thermal expansion properties,making them suitable as materials for manufacturing precision instruments.However,conventional invar steels lack sufficient strength for engineering applications,and various strengthening methods are urgently needed to enhance their strength.In this work,the possibility of enhancing the strength and maintaining low coefficient of thermal expansion(CTE)of the steel through mechanical heat treatment and the introduction of vanadium carbonitride is demonstrated.V-N microalloying and various heat treatment processes enable invar steel to enhance its strength while maintaining low thermal expansion properties.The strength of low-nitrogen addition invar steel measured 593 MPa during direct aging,representing a 44.6% increase compared to invar steel.After undergoing cold-deformation aging,the strength of low-nitrogen invar steel increased to 790 MPa,indicating a substantial improvement in strength relative to the direct aging condition.Notably,the coefficient of thermal expansion remained at 0.98×10^(-6)℃^(-1).By further increasing N content to introduce more vanadium carbonitride,the strength of high-nitrogen invar steel reached 927 MPa under cold-deformation process while maintaining a low CTE value of 1.02×10^(-6)℃^(-1).This achieved an extraordinary balance of high strength and low CTE,which is due to a well combination of various strengthening mechanisms,especially the Orowan strengthening where dislocations continuously bypass vanadium carbonitride to achieve the strengthening effect.The resulting findings are important for future preparation of excellent properties invar steel in industrial applications.
