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The simultaneous improvements of strength and ductility in additive manufactured Ni-based superalloy via controlling cellular subgrain microstructure

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Journal of materials Science & Technology 2021年第9期68卷 184-190页

作者： Yanan Zhao zongqing ma Liming Yu Ji Dong Yongchang Liu State Key Lab of Hydraulic Engineering Simulation and Safety.School of materials Science and Engineering Tianjin UniversityTianjin 300072China Tianjin Sino-German University of Applied Sciences TianjinChina

Fine cellular subgrain structure was formed in the Selective Laser Melting(SLM) manu factured IN718 alloy via optimizing the processing *** the subsequent homogenization heat treatment process,the Laves phase dispersed at the subgrain boundaries can be eliminated while the cellular subgrain structure is reserved in the printed samples after holding at 1080℃ for 50 *** the prolongation of the holding time,the subgrain boundaries undergo low angle rotation via the motion ofdislocation,which leads to the annihilation of the cellular subgrain ***,during the subsequent double aging heat treatment process,the reserved cellular subgrain structure in the homogenized samples promotes the precipitation of γ" second phase nanoparticles,and these precipitated γ" phase nanoparticles prefer to distribute at subgrain *** was found that these unique subgrain boundaries with γ" phase precipitates can hinder but not fully terminate the motion of dislocation during the plastic deformation process,which contributes to increasing the strength as well as holding the stable plastic ***,the strength and ductility of final prepared IN718 alloy with cellular subgrain microstructure were improved simultaneously compared to the prepared alloy without cellular subgrain structure,which even exceed the mechanical properties standards(AMS 5662) of wrought IN718 *** results in our work suggest that controlling the subgrain structure is a promising effective strategy to improve the mechanical properties of SLM manu factured nickel-based superalloy.

关键词： Selective laser melting Superalloy Subgrain structure Strengthening and toughening

Synthesis of W-Y2O3 alloys by freeze-drying and subsequent low temperature sintering:Microstructure refinement and second phase particles regulation

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Journal of materials Science & Technology 2020年第1期36卷 84-90页

作者： Weiqiang Hu Zhi Dong Liming Yu zongqing ma Yongchang Liu State Key Lab of Hydraulic Engineering Simulation and Safety School of Materials Science and EngineeringTianjin UniversityTianjin 300072China

In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature *** average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 *** low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(many Y6 WO12(mation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase *** combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 *** work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys.

关键词： W-Y2O3 alloys Freeze-drying Low temperature sintering Ultrafine grains

Influence of Yttrium Addition on the Reduction Property of Tungsten Oxide Prepared via Wet Chemical Method

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Acta Metallurgica Sinica(English Letters) 2020年第2期33卷 275-280页

作者： Nan Liu Zhi Dong zongqing ma Zhu Qian Lei ma Liming Yu Yongchang Liu State Key Lab of Hydraulic Engineering Simulation and Safety School of Materials Science and EngineeringTianjin UniversityTianjin 300072China Tianjin Zhujin Technology Development Corporation Tianjin 300400China

W-Y2O3 composite nanopowders prepared via wet chemical method exhibit unique morphologies and micro *** yttrium addition during chemical reaction process affects not only the composition of tungsten acid hydrate precursors,but also the reduction property of tungsten oxide transformed from *** this study,the morphology evolution of the samples with and without yttrium during reduction process has been studied,and it is found that the addition of yttrium can exert a strong influence on the reduction route of tungsten oxide and the final morphology of tungsten *** cause of the difference of reduction route and tungsten particle morphology is also *** is suggested that the composition of the samples with yttrium at the beginning of reduction is pure cubic system WO3(c-WO3),and the c-WO3 particles have c-WO3 whiskers attached to the *** kind of whiskers is essential for c-WO3 to be reduced directly to tungsten and also helpful to obtain W-Y2O3 powders with small size and good uniformity.

关键词： W–Y2O3 nanopowders Wet chemical method Reduction property

Refined microstructure and enhanced mechanical properties in Mo-Y_(2)O_(3)alloys prepared by freeze-drying method and subsequent low temperature sintering

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Journal of materials Science & Technology 2021年第29期88卷 36-44页

作者： Weiqiang Hu Tao Sun Chenxi Liu Liming Yu Tansir Ahamad zongqing ma Tianjin Key Laboratory of Composite and Functional materials School of Materials Science and EngineeringTianjin UniversityTianjin300072China Key Laboratory of Mechanism Theory and Equipment Design of Ministry of Education Tianjin UniversityTianjin300350China Department of Chemistry College of ScienceKing Saud UniversityP.O.Box 2455Riyadh11451Saudi Arabia

The ultrafine Mo-Y_(2)O_(3)composite powders were successfully synthesized by innovative freeze-drying ***,the freeze-dried Mo-Y_(2)O_(3)composite powders with high sintering activities possess an average grain size of 54 *** low temperature sintering at 1600°C,the Mo-Y_(2)O_(3)alloys maintaining a high density(99.6%)have the finest grain size(620 nm)comparing with available literature about oxide dispersion strengthened molybdenum alloy(ODS-Mo).The oxide particles remain their small size(mainlymatrix,and its formation can absorb nearby oxygen impurities,which involves the purification of Mo *** mechanical properties show that Mo-Y_(2)O_(3)alloy possess a high hardness of 487±28 HV_(0.2),a high yield strength of 902 MPa,a high compressive strength of1110 MPa,*** work suggests that freeze-drying and subsequent low temperature sintering can shed light on the preparation of ultrafine ODS-Mo alloys with high performance.

关键词： Mo-Y_(2)O_(3) Freeze-drying Low temperature sintering Ultrafine grains Y_(5)MO_(2)O_(12)particles

Tailoring the secondary phases and mechanical properties of ODS steel by heat treatment

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Journal of materials Science & Technology 2019年第6期35卷 1064-1073页

作者： Qian Zhao zongqing ma Liming Yu Huijun Li Chenxi Liu Chong Li Yongchang Liu State Key Lab of Hydraulic Engineering Simulation and Safety School of Materials Science & EngineeringTianjin University

The oxide dispersion strengthened(ODS) steel with the nominal composition of Fe–14 Cr–2 W–0.3 Ti–0.2 V–0.07 Ta–0.3 Y2O3(wt%) was fabricated by mechanical alloying and hot isostatic pressing(HIP). In order to optimize the relative volume fraction of secondary phases, the as-HIPed ODS steel was annealed at 800°C, 1000°C, 1200°C for 5 h, respectively. The microstructures and different secondary phases of the as-HIPed and annealed ODS samples were identified by scanning electron microscopy(SEM), transmission electron microscopy(TEM), and X-ray diffraction(XRD). The tensile properties of all the ODS steels at room temperature were also investigated. The results indicate that annealing is an effective way to control the microstructure and the integral secondary phases. The annealing process promotes the dissolution of M23C6 particles, thus promoting the precipitation of *** obvious coarsening of Y2Ti2O7 nanoparticles can be observed during annealing. The tensile results indicate that the annealed ODS sample with the optimized secondary phases and high density possesses the best mechanical properties.

关键词： ODS steel Annealing Secondary phase Mechanical property

Ultra-fine W-Y_(2)O_(3)composite powders prepared by an improved chemical co-precipitation method and its interface structure after spark plasma sintering

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Tungsten 2019年第3期1卷 220-228页

作者： Weiqiang Hu Qingshuang ma zongqing ma Yuan Huang Zumin Wang Yongchang Liu Tianjin Key Laboratory of Composite and Functional materials School of Materials Science and EngineeringTianjin UniversityTianjin 300072China

Y_(2)O_(3)-doped tungsten(W-Y_(2)O_(3))composite powders prepared by a traditional chemical co-precipitation method possess obvious bimodal distribution in size,which would deteriorate their sintering *** bimodal distribution can be effectively eliminated by an improved chemical co-precipitation method,in which the cationic surfactant cetyltrimethyl-ammonium bromide(CTAB)was innovatively *** reduced powders with excellent uniformity have an average grain size of only~31.5 *** is noteworthy that Y_(2)O_(3)particles would fuse and grow with the growth of W grains during subsequent spark plasma sintering(SPS)process,which was rarely reported in relevant literature *** top of that,phase interfaces of sintered W-Y_(2)O_(3)alloys were systematically *** to the intracrystalline oxygen content,the oxygen content at W/Y_(2)O_(3)phase boundaries is relatively *** can be found that the(110)crystal planes of W form coherent,semi-coherent,and non-coherent interfaces with different crystal planes of Y_(2)O_(3).The weak interfacial bonding strength between W and Y_(2)O_(3)phases results from relatively more oxygen impurities as well as more semi-coherent/non-coherent interfaces at phase boundaries compared with the inner W grains.

关键词： Y_(2)O_(3)-doped tungsten Chemical co-precipitation method CTAB SPS Phase boundary

Microstructure refinement and second phase particle regulation of Mo-Y_(2)O_(3) alloys by minor TiC additive

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International Journal of Minerals,Metallurgy and materials 2022年第11期29卷 2012-2019页

作者： Weiqiang Hu Fengming Gong Shaocun Liu Jing Tan Songhua Chen Hui Wang zongqing ma Tianjin Key Laboratory of Composite and Functional materials School of Materials Science and EngineeringTianjin UniversityTianjin 300072China CNPC Project management Company Tianjin Design Institute Tianjin 300072China College of Chemistry and material Science Longyan UniversityLongyan 364012China School of Mechanical Engineering Chengdu UniversityChengdu 610106China

The oxide dispersion strengthened Mo alloys(ODS-Mo)prepared by traditional ball milling and subsequent sintering technique generally possess comparatively coarse Mo grains and large oxide particles at Mo grain boundaries(GBs),which obviously suppress the corresponding strengthening effect of oxide *** this work,the Y_(2)O_(3) and TiC particles were simultaneously doped into Mo alloys using ball-milling and subsequent low temperature *** by TiC addition,the Mo-Y_(2)O_(3) grains are sharply refined from 3.12 to 1.36μ*** particular,Y_(2)O_(3) and TiC can form smaller Y-Ti-O-C quaternary phase particles(~230 nm)at Mo GBs compared to single Y_(2)O_(3) particles(~420 nm),so as to these new formed Y-Ti-O-C particles can more effectively pin and hinder GBs *** addition to Y-Ti-O-C particles at GBs,Y_(2)O_(3),TiOx,and TiCx nanoparticles(matrix to form a new strengthening phase,thus strengthening and purifying Mo ***,the pure Mo,Mo-Y_(2)O_(3),and Mo-Y_(2)O_(3)-TiC alloys have similar relative densities(97.4%-98.0%).More importantly,the Mo-Y_(2)O_(3)-TiC alloys exhibit higher hardness(HV0.2(425±25))compared to Mo-Y_(2)O_(3) alloys(HV0.2(370±25)).This work could provide a relevant strategy for the preparation of ultrafine Mo alloys by facile ball-milling.

关键词： Mo-Y_(2)O_(3)-TiC alloys ball-milling low temperature sintering ultrafine grains high hardness

Effect of W addition on phase transformation and microstructure of powder metallurgic Ti-22Al-25Nb alloys during quenching and furnace cooling

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Chinese Journal of Aeronautics 2019年第5期32卷 1343-1351页

作者： Junpeng YANG Qi CAI zongqing ma Yuan HUANG Liming YU Huijun LI Yongchang LIU State Key Lab of Hydraulic Engineering Simulation and Safety School of Materials Science & Engineering Tianjin University materials Genome Institute Shanghai University

Powder metallurgic Ti2 AlNb alloys with W addition are sintered at 900, 1000, 1070 °C,and 1150 °C(i.e., in the O + B2, a_2+ B2 + O, a_2+ B2, and single B2 phase regions, respectively)for 12 h, followed by water quenching and furnace cooling. Comparisons of phase and microstructure between quenched and furnace-cooled W-modified alloys are carried out to illustrate the phase transformation and microstructure evolution during the cooling process. Furthermore, a comparison is also made between W-modified and W-free alloys, to reveal the function of the W alloying.W addition accelerates the solutions of a_2 and O phases during the high-temperature holding, and a Widmannsta¨tten B2 + O structure, which contributes to the properties, is induced by furnace cooling from all the phase regions. The Widmannsta¨tten structure includes a B2 matrix, primary O, and secondary O precipitates. However, W alloying refines the Widmannsta¨tten structure only when the alloys are solution-treated and then cooled from the single B2 phase. Although the hardness of the W-modified alloys is lower than that of the W-free alloys sintered in the same phase region, an enhancement of hardness, 489 ± 18 HV, is obtained in the alloy solution-treated in the single B2 phase region for only 0.5 h.

关键词： Hardness Phase formation Ti2AlNb-based alloy W addition Widmannsta¨tten microstructure

Controlled synthesis of high-quality W-Y2O3 composite powder precursor by ascertaining the synthesis mechanism behind the wet chemical method

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Journal of materials Science & Technology 2020年第1期36卷 118-127页

作者： Zhi Dong Nan Liu Weiqiang Hu zongqing ma Chong Li Chenxi Liu Qianying Guo Yongchang Liu State Key Lab.of Hydraulic Engineering Simulation and Safety School of Materials Science and EngineeringTianjin UniversityTianjin300072China

As an emerging preparation technology,wet chemical method has been employed widely to produce lots of alloy materials such as W and Mo based alloys,owing to its unique technical *** the synthesis mechanism behind wet chemical method is indispensable for controlled synthesis of highquality W-Y2 O3 composite powder *** co-deposition mechanism of yttrium and tungsten component behind the wet chemical method of preparing yttrium-doped tungsten composite nanopowder was investigated systematically in this work.A series of co-deposited composite powders fabricated under different acidity conditions were used as research targets for investigating the effect of surface composition and structure on co-deposition *** was found that white tungstic acid has more W-OH bonds and much higher co-deposition efficiency with Y^3+ions than yellow tungstic *** is illustrated that the coordination reaction between W-OH bonds on tungstic acid particles and Y^3+ions brings the co-deposition of yttrium and tungsten component into *** displacing H^+ions in W-OH bonds,Y^3+ions can be adsorbed on the surface of or incorporated into tungstic acid particles in form of ***,to control and regulate Y2 O3 content in powder precursor accurately,H^+ion concentration in wet chemical reaction should be in range of 0.55-2.82 mol L^-1 to obtain white tungstic ***,H^+ion concentration also has prominent effect on the grain size and morphology of reduced powder *** optimal value should be around 1.58 mol L^-1,which can lead to minimum W grain size(about 17 nm) without bimodal *** chemical mechanism proposed in this work could produce great sense to preparation of high-quality precursor for sintering high-performance Y2 O3 dispersion strengthened W based *** work may also shed light on the approach to exploit analogous synthesis mechanism in other alloy systems.

关键词： W-Y2O3 Wet chemical method W-OH bond Ligand Co-deposition mechanism