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Microstructural refinement mechanism and its effect on toughness in the nugget zone of high-strength pipeline steel by friction stir welding

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Journal of Materials Science & Technology 2021年第34期93卷 221-231页

作者： R.H.Duan G.M.Xie P.Xue Z.Y.Ma Z.A.Luo C.Wang R.D.K.Misra State Key Laboratory of Rolling and Automation Northeastern UniversityNo.3 Wenhua RoadShenyang 110819China Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China School of Metallurgy Northeastern UniversityNo.3 Wenhua RoadShenyang 110819China Department of Metallurgical Materialsand Biomedical EngineeringUniversity of Texas at El PasoTX 79968USA

High-strength pipeline steel was subjected to friction stir welding(FSW)at rotation rates of 400-700 rpm,and the grain refinement mechanism of the nugget zone(NZ)was *** thermomechanical process during FSW in the NZ was simulated by multi-pass thermal compression,thereby achieving the austenitic non-recrystallization temperature(T_(nr)).The austenitic non-recrystallization in the NZ at the lowest rotation rate of 400 rpm caused a significant grain ***,the reduced rotation rate also resulted in the formation of a high ratio of island-like martensite-austenite(M-A)*** toughness of the NZs was enhanced as the rotation rate decreased,which is attributed to the fine effective grains and homogeneously distributed fine M-A constituents dramatically inhibiting crack initiation and propagation.

关键词： Pipeline steel Friction stir welding Grain refinement M-A constituent toughness

Improved toughness and Thermal Expansion of Non-stoichiometry Gd_(2-x)Zr_(2+x)O_(7+x/2) Ceramics for Thermal Barrier Coating Application

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Journal of Materials Science & Technology 2016年第1期32卷 28-33页

作者： Lei Guo Mingzhu Li Yu Zhang Fuxing Ye School of Materials Science and Engineering Tianjin UniversityTianjin 300072China Tianjin Key Laboratory of Advanced Joining Technology Tianjin UniversityTianjin 300072China Key Lab of Advanced Ceramics and Machining Technology of Ministry of Education Tianjin UniversityTianjin 300072China

Gd2Zr207 has been considered as a promising thermal barrier coating candidate, but its toughness and thermal expansion coefficient （TEC） need to be improved. In this study, Gd2-xZr2 ＋xO7 ＋χ/2 （χ = 0, 0.1, 0.3, 0.5, 0.7） compounds were produced to improve the toughness and enlarge the TEC. Gd2Zr207 and Gd1.9Zr2.1O7.05 exhibited pyrochlore structure, while Gd2-xZr2 ＋xO7 ＋χ/2 （χ = 0.3, 0.5, 0.7） consisted of pyrochlore and t＇-ZrO2 phases. With increasing ZrO2 content, the pyrochlore in the compounds had decreased lattice parameter, and its ordering degree decreased when χ 〈 0.3, then it almost kept unchanged with higher ZrO2 content. Among the Gd2-xZr2 ＋xO7 ＋χ/2 ceramics investigated, the toughness of the compounds in- creased with increasing ZrO2 content, while Gd1.7Zr23O7.15 exhibited the largest TEC. The related mechanisms were discussed in detail.

关键词： Thermal barrier coating Ceramic Phase structure toughness Thermal expansion coefficient

Effects of Microalloying and Heat-Treatment Temperature on the toughness of 26Cr–3.5Mo Super Ferritic Stainless Steels

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Acta Metallurgica Sinica(English Letters) 2014年第3期27卷 407-415页

作者： Li Ma Jian Han Junqi Shen Shengsun Hu Tianjin Key Laboratory of Advanced Joining Technology Tianjin University Baosteel Research Institute Baoshan Iron & Steel Co. Ltd School of Mechanical Materials and Mechatronic EngineeringUniversity of Wollongong

The effects of Ni content and heat-treatment process on the toughness of a super ferritic stainless steel with 26 wt% Cr and 3.5 wt% Mo were investigated. It was found that with the increase of Ni content, the Charpy impact toughness improved remarkably, and transformed from cleavage brittle fracture to the most ductile fracture. There were no obvious differences between the high- and low-Ni contents on the microstructure and mechanical properties since the addition of Ni did not influence crystal structure, phase composition, and precipitation of ultra pure ferritic stainless steels. Meanwhile, the heat-treatment process was a key point to maintain a high level of toughness by optimizing structure and removing detrimental precipitation, i.e., chi phase.

关键词： Super ferritic stainless steel Nickel Heat treatment toughness

Stereocomplexed Poly(lactide) Composites toward Engineering Plastics with Superior toughness, Heat Resistance and Anti-hydrolysis

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Chinese Journal of Polymer Science 2020年第10期38卷 1107-1116页

作者： Bao-Gou Wu Wei-Jun Yang De-Yu Niu Wei-Fu Dong Ming-Qing Chen Tian-Xi Liu Ming-Liang Du Pi-Ming Ma The Key Laboratory of Synthetic and Biological Colloids Ministry of Education Jiangnan University

Poly（lactide）,PLA,suffers from brittleness and low heat deflection temperature（HDT）,which limits its application as an engineering *** this work,poly（L-lactide）/poly（D-lactide）/ethylene-vinyl acetate-glycidyl methacrylate random copolymer（PLLA/PDLA/EVM-GMA=1/1/x） composites were prepared by melt blending,and the in situ formed EVM-g-PLA copolymers improved the compatibility between PLA and ***,the blends were subjected to a two-step annealing process during compression molding,*** annealing at 120℃ to rapidly form a certain amount of stereocomplex（sc） crystallites as nucleation sites,and then annealing at 200℃ to guide the formation of new sc *** differential scanning calorimetry（DSC） and wide angle X-ray diffraction（WAXD） measurements confirmed the formation of highly stereocomplexed PLA *** results showed that the PLLA/PDLA blend with 20 wt% of EVM-GMA had a notched impact strength up to 65 kJ/m2and an elongation at break of 48%,while maintaining a tensile strength of 40 ***,dynamic mechanical analysis（DMA） and heat deflection tests showed that the PLA composite had an HDT up to 142℃ which is 90℃ higher than that of normal PLA *** electron microscopy（SEM） confirmed the fine dispersion of EVM-GMA particles,which facilitated to understand the toughening ***,the highly stereocomplexed PLA composites simultaneously exhibited excellent chemical and hydrolysis ***,these fascinating properties may extend the application range of sc-PLA material as an engineering bioplastic.

关键词： Annealing Heat resistance PLA composites Stereocomplexation toughness

Evolution of γ’ Particles in Ni-Based Superalloy Weld Joint and Its Effect on Impact toughness During Long-Term Thermal Exposure

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Acta Metallurgica Sinica(English Letters) 2020年第4期33卷 561-572页

作者： Xian-Kai Fan Fu-Quan Li Lei Liu Hai-Chao Cui Feng-Gui Lu Xin-Hua Tang Shanghai Key Laboratory of Materials Laser Processing and Modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China State Key Lab of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150006China Shanghai Turbine Plant of Shanghai Electric Power Generation Equipment Co.Ltd Shanghai 200240China

Effects of long-term thermal exposure on γ’ particles evolution and impact toughness in the weld joint of Nimonic 263(N263)superalloy were deeply studied at 750℃.Results showed that the precipitates in the weld metal were mainly composed of fine γ’ particles,bulky MC carbides,and small M23C6 *** the thermal exposure time increasing from o to 3000 h,γ’ particles in the weld metal grew up from 19.7 nm to 90.1 nm at an extremely slow *** being exposed for 1000 h,γ’ particles coarsened and some of them transformed into acicular η *** the same time,MC carbides decomposed to form η phase and γ’ *** dynamic transition ensured the slight reduction in impact toughness of the weld metal after the thermal exposure,which indicated the stable serving performance of N263 weld joint.

关键词： Ni-based superalloy Weld joint Long-term thermal exposure γ’Phase evolution Impact toughness

Effect of Trace Element on Microstructure and Fracture toughness of Weld Metal

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Acta Metallurgica Sinica(English Letters) 2020年第3期33卷 425-436页

作者： Ke Xu Tao Fang Longfei Zhao Haichao Cui Fenggui Lu Shanghai Key Laboratory of Materials Laser Processing and Modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The microstructure and fracture toughness of weld metal under Ti-free and Ti-containing different fluxes were investigated in this *** was found that the trace element Ti of flux in submerged arc welding produced significant influence on the fracture *** addition of 60 ppm Ti induced the sharp increase in J0.2 value from 232.78 to 364.08 kJ/m^*** characterization revealed that a large number of oxide inclusions prompted the nucleation of acicular ferrites and refined grains,which improved the fracture toughness of Ti-containing weld metal ***,the crack propagation path was more tortuous and bifurcated due to the small amount of carbide precipitations along grain boundaries and blocky martensite-austenite islands for Ti-containing weld ***,the large-angle grain boundaries caused crack deflection and increased the resistance of crack propagation compared to Ti-free weld metal.

关键词： Fracture toughness Microstructure Weld metal Trace element Crack propagation

Microstructure and toughness of thick-gauge pipeline steel joint via double-sided friction stir welding combined with preheating

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International Journal of Minerals,Metallurgy and Materials 2023年第4期30卷 724-733页

作者： Guangming Xie Ruihai Duan Yuqian Wang Zong’an Luo Guodong Wang State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China

Fusion welding easily causes microstructural coarsening in the heat-affected zone(HAZ) of a thick-gauge pipeline steel joint. This is most significant in the inter-critically coarse-grained HAZ(ICCGHAZ), which considerably deteriorates the toughness of the joint. In the present work, 11-mm thick pipeline steel was joined by preheating and double-sided friction stir welding(FSW). A comparative study on the microstructure and toughness in the ICCGHAZs for FSW and gas metal arc welding(GMAW) was performed. The toughness in the ICCGHAZ for FSW was improved significantly than that in the ICCGHAZ for GMAW. Generally, the nugget zone(NZ) has a coarse microstructure in the FSW steel joint formed at the highest peak temperature. However, in the current study, the microstructure in the one-pass NZ was remarkably refined owing to the static recrystallization of ferrite. An excellent toughness was achieved in the NZ of the pipeline steel joint that employed FSW.

关键词： pipeline steel thick-gauge plate friction stir welding microstructure toughness

Elastic Modulus,Hardness,and Fracture toughness of Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12) Solid Electrolyte

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Chinese Physics Letters 2021年第9期38卷 108-116页

作者： Shan Hu Pengyu Xu Luize Scalco de Vasconcelos Lia Stanciu Hongwei Ni Kejie Zhao State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and TechnologyWuhan 430081China School of Mechanical Engineering Purdue UniversityWest LafayetteIndiana 47907USA School of Materials Engineering Purdue UniversityWest LafayetteIndiana 47907USA

Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO) is a promising inorganic solid electrolyte due to its high Li+conductivity and electrochemical stability for all-solid-state *** characterization of LLZTO is limited by the synthesis of the condensed *** we systematically measure the elastic modules,hardness,and fracture toughness of LLZTO poly crystalline pellets of different densities using the customized environmental *** LLZTO samples are sintered using the hot-pressing method with different amounts of Li2CO3 additives,resulting in the relative density of the pellets varying from 83% to 98% and the largest grain size of 13.21 ± 5.22 μ*** mechanical properties show a monotonic increase as the sintered sample densifies,elastic modulus and hardness reach 158.47± 10.10 GPa and 11.27± 1.38 GPa,respectively,for LLZTO of 98% ***,fracture toughness increases from 0.44 to 1.51 MPa·m^(1/2),showing a transition from the intergranular to transgranular fracture behavior as the pellet density *** ionic conductivity reaches 4.54 × 10^(-4 )S/cm in the condensed LLZTO which enables a stable Li plating/stripping in a symmetric solid-state cell for over 100 *** study puts forward a quantitative study of the mechanical behavior of LLZTO of different microstructures that is relevant to the mechanical stability and electrochemical performance of all-solid-state batteries.

关键词： toughness Elastic Solid

Effect of annealing and cooling rate on toughness of G115 heat-resistant steels

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Journal of Iron and Steel Research International 2022年第8期29卷 1245-1256页

作者： Zhen Liu Li Gong Chi Zhang Zheng-dong Liu Zheng-zong Chen Yun-he Yu Key Laboratory for Advanced Materials of Ministry of Education School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China Institute for Special Steels China Iron and Steel Research InstituteBeijing 100081China

The effects of annealing before normalizing and different cooling ways, i.e., air cooling, quenching, and water mist cooling after normalizing on the toughness of G115 steels were investigated. The impact tests showed that the annealed samples had better toughness compared to the unannealed samples for three cooling ways. Microstructure observations revealed that the annealed samples had a more uniform grain distribution, smaller size and area fraction of M_(23)C_(6) particles along the grain boundaries, and lower dislocation density than those in the unannealed samples, which performed together for good toughness. Among three cooling ways, air cooling gave the best toughness due to the smallest occupancy of M23C6 particles in the grain boundaries. Thus, the combination of annealing conducted before normalizing and air cooling selected after normalizing can improve the toughness a lot of G115 steels.

关键词： G115 steel Annealing M_(23)C_(6)particle Dislocation density toughness