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Segregation enabled outstanding combination of mechanical and corrosion properties in a FeCrNi medium entropy alloy manufactured by selective laser melting

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Journal of Materials Science & Technology 2022年第4期99卷 207-214页

作者： Heng Duan Bin Liu Ao Fu Junyang He Tao Yang C.T.Liu Yong Liu State Key Lab of Powder Metallurgy Central South UniversityChangsha 410083China Max-Planck-Institut für Eisenforschung Max-Planck-βe 1Düsseldorf 40237Germany Department of Materials Science and Engineering City University of Hong KongHong KongChina Department of Mechanical Engineering City University of Hong KongHong KongChina

Selective laser melting(SLM)has the advantage in preparing supersaturated solid solutions due to its unique thermal field and high solidification rate.In this study,a face-centered cubic single-phase FeCrNi medium entropy alloy(MEA)with an ultrahigh Cr content(~35 at.%)was additively manufactured by SLM.The as-built MEA shows a hierarchical microstructure of coarse columnar grains and submicron dislocation cell structures,where the cell boundaries are probed segregated with Cr and C and decorated with nano carbides.The appearance of these dislocation barriers results in an excellent combination of strength(σ_(0.2)=745 MPa,σ_(UTS)=1007 MPa)and ductility(ε_(f)=31%).The current MEA also shows a superb corrosion resistance with a corrosion current density of 0.06μA cm^(−2) in 3.5 wt.%NaCl solution,which is far lower than that of 316 L.The high content of solutioned Cr in the MEA ensures sufficient Cr supply to form an integrated Cr_(2)O_(3) passive film,and the large number of cell boundaries acting as the diffusion channels lead to the fast formation of a stable passive film over the alloy surface.

关键词： Selective laser melting microsegregation Strength Ductility Corrosion resistance

Effect of melting rate on microsegregation and primary MC carbides in M2 high-speed steel during electroslag remelting

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China Foundry 2021年第3期18卷 163-169页

作者： Fu-xing Yin Ming Su Fa Ji Qing-chao Tian Ya-guan Bai Jian-hang Feng Zhi-xia Xiao School of Materials Science and Engineering Hebei University of TechnologyTianjin 300130China Tianjin Key Laboratory of Layered Composite Materials Tianjin 300130China State Key Laboratory of Advanced Special Steel Shanghai Key Laboratory of Advanced FerrometallurgySchool of Materials Science and EngineeringShanghai UniversityShanghai 200444China Tianjin Heavy Industries Research and Development Co. Ltd.Tianjin 300457China

Large-size primary MC carbides can significantly reduce the performance of M2 high-speed steel.To better control the morphology and size of primary MC carbides,the effect of melting rate on microsegregation and primary MC carbides of M2 steel during electroslag remelting was investigated.When the melting rate is decreased from 2 kg·min^(-1) to 0.8 kg·min^(-1),the columnar dendrites are gradually coarsened,and the extent of segregation of Mo and V is alleviated,while the segregation of Cr becomes severe.At 2 kg·min^(-1),the number of primary MC carbides per unit area with the sizes in the range of 2 μm to 6 μm accounts for about 75% of all MC carbides,while the carbides are mainly concentrated on the size larger than 8 μm at 0.8 kg·min^(-1).Thermodynamic calculations based on the Clyne-Kurz (simplified to C-K) model shows that MC carbide can be precipitated in the final solidification stage and a smaller secondary dendrite arm spacing caused by higher melting rate (2 kg·min^(-1) in this experiment) facilitates the refinement of primary MC carbides.

关键词： high-speed steel MC carbide melting rate electroslag remelting microsegregation

Numerical simulation of microstructure evolution and microsegregation of U-Nb alloy during solidification process

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China Foundry 2017年第5期14卷 412-415页

作者： Bin Su Zhi-qiang Han Hong-zhang Deng Rong Ma Dong Chen Jun Wu Zhen-hong Wang Institute of Materials China Academy of Engineering Physics Key Laboratory for Advanced Materials Processing Technology(Ministry of Education) School of Materials Science and EngineeringTsinghua University

In this work, a cellular automaton model has been developed to simulate the microstructure evolution of U-Nb alloy during the solidification process. The preferential growth orientation, solute redistribution in both liquid and solid, solid/liquid interface solute conservation, interface curvature and the growth anisotropy were considered in the model. The model was applied to simulate the dendrite growth and Nb microsegregation behavior of U-5.5 Nb alloy during solidification, and the predicted results showed a reasonable agreement with the experimental results. The effects of cooling rates on the solidification microstructure and composition distribution of U-5.5 Nb were investigated by using the developed model. The results show that with the increase of the cooling rate, the average grain size decreases and the Nb microsegregation increases.

关键词： U-Nb 合金 microsegregation 微观结构细胞的自动机数字模拟 TP391.99 一

SOLIDIFICATION AND microsegregation BEHAVIORS OF NICKEL-BASE SINGLE CRYSTAL SUPERALLOY SOLIDIFIED AT MEDIUM COOLING RATE

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中国有色金属学会会刊：英文版 1998年第1期8卷 84-88页

作者： Du Wei, Li Jianguo and Fu HengzhiState Key Laboratory of Solidification Processing,Northwestern Polytechnical University, Xi′an 710072, P. R. China

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关键词： single crystal superalloy cooling rate microstructure microsegregation

Nature of large (Ti, Nb)(C, N) particles precipitated during the solidification of Ti, Nb HSLA steel

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Journal of University of Science and Technology Beijing 2007年第2期14卷 112-117页

作者： Xiaojun Zhuo Xinhua Wang Wanjun Wang Hae-Geon Lee Metallurgical and Ecological Engineering School University of Science and Technology Beijing Beijing 100083 China Graduate Institute of Ferrous Technology Pohang University of Science and Technology Pohang 790-784 South Korea

To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.

关键词： carbonitride microsegregation dendritic region unidirectional solidification cooling rate

Coalescence-dominated microstructure evolution during solidification of 20SiMn steel

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Journal of Iron and Steel Research(International) 2020年第5期27卷 506-516页

作者： Xiao-ping Ma Dian-zhong Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016LiaoningChina

The evolution of microstructures during the solidification of 20SiMn steel was investigated.The dominant role of coalescence was revealed by analyzing the quenched microstructures and the solute distribution.In the parameter range investigated,including the slow solidification,the fast solidification and the directional solidification,the coalescence can happen at multiple solidification stages and on multi-scales.During the directional solidification,the ternary and fourth dendritic arms coalesce into the secondary dendritic arms,and the secondary dendritic arms further coalesce to produce the cellular crystals.The cellular crystals become coarse through further coalescence.During the non-directional solidification,the initial microstructures are discrete crystals without the dendritic pattern.Both the dendritic arms and dendritic stems appearing in the later solidification stage are produced by the coalescence on multi-scales.The coalescence is more significant in the later solidification stage.The mechanism of coalescence is attributed to different melt compositions in different local domains and the reduction of the interface energy.

关键词： Solidification Microstructure Coalescence Steel microsegregation

Development of gas tungsten arc welding using current pulsing technique to preclude chromium carbide precipitation in aerospace-grade alloy 80A

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International Journal of Minerals,Metallurgy and Materials 2019年第2期26卷 210-221页

作者： P.Subramani M.Manikandan School of Mechanical Engineering Vellore Institute of Technology

Weldments were produced using gas tungsten arc welding(GTAW) and pulsed current gas tungsten arc welding(PCGTAW) techniques with ERNiCr-3 filler wire. Macro examination revealed that the resultant weldments were free from defects. A refined microstructure was observed in the weldment fabricated through PCGTAW. Scanning electron microscopy(SEM) analysis revealed secondary phases in the grain boundaries. Energy-dispersive X-ray spectroscopy(EDS) analysis revealed that microsegregation of Cr carbide precipitates was completely eradicated through PCGTAW. The microsegregation of Nb precipitates was observed in the GTA and PCGTA weldments. X-ray diffraction(XRD) analysis revealed the existence of M_(23)C?_6 Cr-rich carbide and Ni_8Nb phases in the GTA weldments. By contrast, in the PCGTA weldments, the Ni_8Nb phase was observed. The Cr_2Ti phase was observed in both the GTA and the PCGTA weldments. Tensile tests showed that the strength and ductility of the PCGTA weldments were slightly higher than those of the GTA weldments.

关键词： Ni-based superalloy welding pulse current microsegregation chromium carbide

Effect of Heat Input on the Microstructure and Properties of Dissimilar Weld Joint Between Incoloy 28 and Superaustenitic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2014年第2期27卷 259-266页

作者： M.S.Abdel Rahman N.A.Abdel Raheem M.R.El Koussy Department of Metallurgy Faculty of EngineeringCairo University

Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between superaustenitic stainless steel （UNS S31254） and Incoloy 28 （UNS N08028）. The two materials were butt-welded with ER NiCrMo3. The metallurgical changes associated with welding of SASS and Incoloy 28 were studied using optical microscope, SEM, and EDX. The mechanical and corrosion properties were investigated using tensile test, Vickers hardness test, and pitting and crevice corrosion tests. The weld metal microstructure showed precipitates with needle-like shape at 3 and 5 kJ/mm. Also, the microstructure showed unmixed zone （UMZ） at the fusion line of both SASS and Incoloy 28 sides at all the investigated heat inputs. The Mo microsegregation within UMZ at Incoloy 28 side increased as the heat input increased from 1 to 5 k J/ram but that in SASS increased with increasing heat input from 1 to 3 kJ/mm and then decreased with increasing from 3 to 5 kJ/mm. The ultimate tensile strengths for all specimens at all the investigated heat inputs are acceptable. The average hardness noticeably changed in weld metal as the heat input increased from 1 to 5 kJ/mm. Other zones such as HAZ or UMZ did not demonstrate marked changes in the average hardness. The pitting and crevice corrosion rates of the weld joint were found significant at l and 3 kJ/mm but insignificant at 5 kJ/mm according to ASTM G48.

关键词： Superaustenitic Incoloy 28 Welding Heat input Unmixed zone microsegregation Corrosion

Advances in phase relationship for high Nb-containing TiAl alloys

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Rare Metals 2016年第1期35卷 15-25页

作者： Yong-Feng Liang Xiang-Jun Xu Jun-Pin Lin State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Materials and Chemistry School Zhongyuan University of Technology

γ-TiAl alloys,including two categories（the conventional TiAl and the high Nb-containing TiAl（high Nb-TiAl））,are technologically intriguing because of their applications at high temperatures.Specifically,the service temperature of the high Nb-TiAl alloys is 60-100℃higher than that of conventional TiAl alloys.Recently developed TiAl alloys,for example TNB,TNM,β-γ alloys,belong to the high Nb-TiAl alloys,displaying similar behavior in phase transformation,strengthening,oxidation at high temperatures,and relationships between composition,microstructure,and mechanical properties.This work presents an in-depth review of the high Nb-TiAl alloys regarding the advances in phase diagram,formation mechanism of the new γ_1 phase,microsegregation induced by adding a high content of alloying element Nb,and the mechanism of the B2/ω phase formation.Some challenges in developing the high Nb-TiAl alloys are also discussed.

关键词： TiAl alloy Nb addition Phase diagram microsegregation Microstructure