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Preparation of Inoculants Used in Superalloy and Analysis of the Atomic Matching Models

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Journal of Materials Science & Technology 2013年第4期29卷 387-392页

作者： fu wang jun zhang Taiwen Huang lin liu hengzhi fu State Key Laboratory of Solidification Processing Northwestern Polytechnical University

The mechanisms of grain refinement were investigated on two kinds of grain refiners used in Ni-Fe based superalloys and complete atomic matching modes were constructed in this study. It is found that there are at least three matching crystal planes having the small lattice disregistry between the refiner and the nucleated phase, which can lead to grain refinement of γ matrix. The results indicate that the （0001）, （01-10） planes of CrFeNb have a fine crystallographic matching relationship with the （111）, （110） planes of γ matrix. The disregistry of （0001）CrFeNb//（111 ）γ, （011-0）CrFeNb//（111）γ and （0110）CrFeNb//（110）γ is 3.34%, 6.60% and 5.90%, respectively. The （0001）, （0110） planes of Co3FeNb2 and （111）, （110） planes of γ matrix also have this relationship. The disregistry of （0001）Co3FeNb2//（111）γ, （0001）Co3FeNb2//（110）γ, （0110）Co3FeNb2//（111）γ and （0110）Co3FeNb2//（110）γ, is 4.45%, 9.35%, 8.38% and 6.12%, respectively.

关键词： Grain refinement Growth mechanism Superalloy Solidification

Mechanical Properties of the TaSi_2 Fibers by Nanoindentation

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Journal of Materials Science & Technology 2010年第1期26卷 65-68页

作者： Chunjuan Cui jun zhang lin liu hengzhi fu State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi an 710072 China School of Metallurgical Engineering Xi'an University of Architecture and Technology Xi'an 710055 China

The Si-TaSi2 eutectic in situ composite, which has highly-aligned and uniformly-distributed TaSi2 fibers in the Si matrix, can be obtained when the solidification rate changes from 0.3 to 9.0 mm/min. It is very interesting that one or two TaSi2 fibers are curved when the solidification rate reaches 6.0 mm/min, although it is very brittle in general. The formation mechanism of the curved fiber is discussed and mechanical properties of the TaSi2 fibers are examined by nanoindentation. It is found that the hardness and the elastic modulus of the bended TaSi2 fiber are much higher than that of the straight TaSi2 fiber. Moreover, the reasons why the mechanical properties of the straight TaSi2 fiber are different from that of the curved TaSi2 fiber are discussed. This can be ascribed to internal stress which results from mismatch of the thermal expansion coefficients of the two phases and different crystallographic orientations.

关键词： Si-TaSi2 eutectic in situ composite Directional solidification Mechanical properties Nanoindentation

Effect of Solidification Rate on Microstructure and Solid/Liquid Interface Morphology of Nie11.5 wt% Si Eutectic Alloy

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Journal of Materials Science & Technology 2015年第3期31卷 280-284页

作者： Chunjuan Cui jun zhang Tian Xue lin liu hengzhi fu School of Metallurgical Engineering Xi'an University of Architecture and Technology State Key Laboratory of Solidification Processing Northwestern Polytechnical University

In this study NieN i3 Si eutectic in situ composites are obtained by Bridgman directional solidification technique when the solidification rate varies from 6.0 mm/s to 40.0 mm/s. At the low solidification rates the lamellar spacing is decreased with increasing the solidification rate. When the solidification rate is higher than 25 mm/s, the lamellar spacing tends to be increased, because the higher undercooling makes the mass transport less effective. The adjustments of lamellar spacing are also observed during the directional solidification process, which is consistent with the minimum undercooling criterion. Moreover, the transitions from planar interface to cellular, then to dendritic interface, and finally to cellular interface morphologies with increasing velocity are observed by sudden quenching when the crystal growth tends to be stable.

关键词： Directional solidification Eutectic in situ compos

Coarsening kinetics of γ' precipitates in a Re-containing Ni-based single crystal superalloy during long-term aging

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Journal of Materials Science & Technology 2021年第3期62卷 1-10页

作者： Jiachen zhang lin liu Taiwen Huang Jia Chen Kaili Cao Xinxin liu jun zhang hengzhi fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China

The morphological evolution and coarsening kinetics ofγ'precipitates in a Re-containing Ni-based single crystal superalloy were investigated during isothermal aging at 900,950 and 1000℃.After heat treatment,well-defined cuboidalγ'precipitates with low misfit was obtained within the experimental *** coarsening rate constants and particle size distribution(PSD)ofγ'phases were calculated and specified based on the measured precipitate sizes for va rying periods of aging times from 100 to 2000 *** aging for 2000 h,γ'precipitates maintained cubical shape at 900℃,while exhibited sphere at 950 and 1000℃.Coarsening models based on diffusion-controlled process with a functional relationship of r^(3) vs.t(classic Lifshitz-Slyozov-Wagner coarsening model)and interface-controlled model with a function of r^(2) vs.t(trans-interface diffusion-controlled coarsening model)were investigated to fit between the experimental results and theoretical *** was found that Re as the slowest diffusing solute in the alloy constituted the rate-limited step for coarsening based on LSW model,while the process limiting coarsening as governed by an interface diffusion process could possibly be related to the Al diffusion through theγ/γ'*** PSDs and coarsening exponent were discussed by comparing the experimental data with predictions of LSW and TIDC ***,coarsening mechanism could be divided into four regimes:(i)coarsening by diffusion-controlled;(ii)coarsening by diffusion and interface cocontrolled;(iii)coarsening by interface-controlled;(iv)coarsening by interface-controlled accompanied withγ'coalescence.

关键词： Precipitate coarsening Three-dimensional atom probe(3DAP) Interfacial energy Diffusion Particle size distribution Ni-base single crystal superalloys

Phase growth patterns for Al_(2)O_(3)/GdAlO_(3)eutectics over wide ranges of compositions and solidification rates

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Journal of Materials Science & Technology 2021年第6期65卷 89-98页

作者： Weidan Ma jun zhang Haijun Su Guangrao Fan Min Guo lin liu hengzhi fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi'an 710072China

Phase selection and growth characteristics of directionally solidified Al_(2)O_(3)/GdAlO_3(GAP)faceted eutectic ce ramics are investigated over wide ranges of compositions and solidification rates to explore the eutectic coupled *** the obse rvation of the quenched solid-liquid interface,the competitive growth of primary faceted Al_(2)O_(3)phase,prima ry non-faceted GAP phase and Al_(2)O_(3)/GAP eutectic with diffe rent morphologies is *** transitions from wholly eutectic to primary Al_(2)O_(3)(GAP)dendrite plus eutectic and then to wholly eutectic are found in Al_(2)O_(3)-2 O mol%Gd_(2)O_(3)hypoeutectic(Al_(2)O_(3)-26 mol%Gd_(2)O_(3)hypereutectic)ceramics with the increase of solidification *** dendrite growth of faceted Al_(2)O_(3)and non-faceted GAP phases are well predicted by KGT model,which have introduced appro p riate dimensionless supersaturationΩto characterize the anisotropic growth of *** on the maximum interface temperature criterion,the competitive growth of primary phase and eutectic is analyzed theoretically and the predicted coupled zone of Al_(2)O_(3)/GAP eutectic ceramics is in good agreement with the experimental ***,the influence of microstructure with these different morphologies on the flexural strength of Al_(2)O_(3)/GAP eutectic ceramics is studied.

关键词： Directional solidification Competitive growth Flexural strength Laser floating zone melting

Unique strength-ductility balance of AlCoCrFeNi_(2.1)eutectic high entropy alloy with ultra-fine duplex microstructure prepared by selective laser melting

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Journal of Materials Science & Technology 2022年第16期111卷 298-306页

作者： Yinuo Guo Haijun Su Haotian Zhou Zhonglin Shen Yuan liu jun zhang lin liu hengzhi fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Research and Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China

As a typical dual-phase eutectic high entropy alloy(EHEA),AlCoCrFeNi_(2.1)can achieve the fair matching of strength and ductility,which has attracted wide ***,the engineering applications of as-cast AlCoCrFeNi_(2.1)EHEAs still face challenges,such as coarse grain and low yield strength resulting from low solidification rate and temperature *** this study,selective laser melting(SLM)was introduced into the preparation of AlCoCrFeNi_(2.1)EHEA to realize unique strength-ductility balance,with emphasis on investigating the effects of processing parameters on its eutectic microstructure and *** results show that the SLM-ed samples exhibit a completely eutectic structure consisting of ultra-fine face-centered cubic(FCC)and ordered body-centered cubic(B2)phases,and the duplex microstructure undergoes a morphological evolution from lamellar structure to cellular structure as laser energy input *** SLM-ed AlCoCrFeNi_(2.1)EHEA presents an excellent match of high tensile strength(1271 MPa),yield strength(966 MPa),and good ductility(22.5%)at room temperature,which are significantly enhanced by the ultra-fine grains and heterogeneous structure due to rapid solidification rate and high temperature gradient during ***,the yield strength increment of~50%is realized with no loss in ductility as compared with the as-cast samples with the same *** this basis,the precise complex component with excellent mechanical properties is well *** work paves the way for the performance improvement and complex parts preparation of EHEA by microstructural design using laser additive manufacturing.

关键词： Selective laser melting High-entropy alloy Eutectic structure Rapid solidification Tensile properties

Effect of solidification parameters on the microstructures of a single crystal Ni-based superalloy AM3

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China Foundry 2010年第3期7卷 217-223页

作者： Yu Zhuhuan liu lin Zhao Xinbao zhang Weiguo zhang jun fu hengzhi State Key Laboratory of Solidification Processing Northwestern Polytechnic University Xi＇ an 7100721 China Materials Science and Engineering Department Xi＇an University of Science and Technology Xi＇an 710054 China

A single crystal Ni-based superalloy AM3 was processed at withdraw rates of 3.5, 10, 50, 100, 200, and 500 μm·s-1, *** as-cast microstructures and solidification segregation ratio were characterized with various withdraw *** shape and size of carbide microstructures were *** expected, the primary and secondary dendrite arm spacings (PDAS and SDAS) decrease with the increase of withdraw *** highest volume fraction of eutectic γ/γ' is observed at the 100 μm·s-1 withdraw *** volume fraction of eutectic γ/γ' does not appear to be a strong function of the withdraw *** increasing withdraw rate, interface morphologies change in the sequence of planar, cellular, and *** is a general refinement of the microstructure as the withdraw rate *** analysis showed that withdraw rate does not have obvious influence on the segregation of elements.

关键词： Ni-based superalloy single crystal withdraw rate solidi fi cation PDAS SDAS

Superb cryogenic strength of equiatomic CrCoNi derived from gradient hierarchical microstructure

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Journal of Materials Science & Technology 2019年第6期35卷 957-961页

作者： Bin Gan Jeffrey M. Wheeler Zhongnan Bi lin liu jun zhang hengzhi fu School of Materials Science and Engineering Northwestern Polytechnical University Xi'an 710072 China Laboratory for Nanometallurgy Department of Materials Science ETH Zurich Vladimir-Prelog-Weg 5 Zurich CH-8093 Switzerland Central Iron and Steel Research Institute No. 76 Xueyuannan Road Beijing 100081 China

This work demonstrates the effectiveness of a cryogenic torsional pre-straining for significantly improving the cryogenic strength of an equiatomic CrCoNi alloy. The origin of this phenomenon is elucidated by various microstructural characterization tools, which shows that the sequential torsion and tension tests lead to the observed hierarchical microstructure through the activation of different twinning systems and stacking faults. This gives rise to the significant increase in the yield strength from 600 MPa to 1215 MPa,while the fracture strain changes from 68% to 48%. The current study reveals that the incorporation of nanotwins architecture by shear deformation may constitute a viable strategy to tune the mechanical performance and, in particular, to dramatically increase the strength while keeping a good ductility.

关键词： Medium entropy alloy CrCoNi Torsion Hierarchical microstructure Strengthening

Unveiling the dynamic instability mechanism of microstructure transformation in faceted oxide eutectic composite ceramics

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Journal of Materials Science & Technology 2023年第13期144卷 224-234页

作者： Haijun Su Yuan liu Qun Ren Zhonglin Shen Min Guo Xi Li jun zhang lin liu hengzhi fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China Department of Material Science and Engineering Shanghai UniversityShanghai 200072China

Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification ***,the microstructure trans-formation of faceted Al_(2)O_(3)/Er_(3)Al_(5)O_(12) thermal emission eutectic composite ceramics is explored over wide ranges of compositions(13.5 mol%-22.5 mol%Er_(2)O_(3))and solidification rates(2-200μm/s).Entirely cou-pled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%-22.5 mol%Er_(2)O_(3) at low solidification *** competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature *** ad-dition,the mechanisms of irregular eutectic spacing selection and adjustment under different solidifi-cation rates are revealed based on Magnin-Kurz model.A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface *** to the well mi-crostructure tailoring,the flexural strength of Al_(2)O_(3)/Er_(3)Al_(5)O_(12) eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low *** eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refin-ing *** as-designed Al_(2)O_(3)/Er_(3)Al_(5)O_(12) composites with microstructural tailoring have great potential as integrations of structural and functional materials.

关键词： Directional solidification Laser floating zone melting Al_(2)O_(3)/Er_(3)Al_(5)O_(12)eutectic composite ceramics Eutectic growth mechanism Microstructure transformation