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Effect of Carbon Migration on Interface Fatigue Crack Growth Behavior in 9Cr/CrMoV Dissimilar Welded Joint

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Acta Metallurgica Sinica(English Letters) 2022年第5期35卷 714-726页

作者： Qi Wang Chendong Shao Haichao Cui Yuan Gao Fenggui Lu shanghai key laboratory of materials laser Processing and modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai200240China

Fatigue crack growth(FCG)behavior of 9 Cr/CrMoV dissimilar welded joint at elevated temperature and different stress ratios was *** was paid to the region near the fusion line of 9 Cr where carbon-enriched zone(CEZ)and carbon-depleted zone(CDZ)formed due to carbon migration during the welding *** and brittle tempered martensite dominated the stress ratio-insensitive FCG behavior in the coarse grain zone(CGZ)of 9 *** crack near the CGZ-CEZ interface,crack deflection through the CEZ and into the CDZ was observed,accompanied by an accelerating FCG *** with the severe plastic deformation near the secondary crack in 9 Cr-CGZ,the electron back-scattered diffraction analysis showed less deformation and lower resistance in the direction toward the brittle CEZ,which resulted in the transverse *** spite of the plastic feature in CDZ revealed by fracture morphology,the less carbides due to carbon migration led to lower strength and weaker FCG resistance property in this *** conclusion,the plasticity deterioration in CEZ and strength loss in CDZ accounted for the FCG path deflection and FCG rate acceleration,respectively,which aggravated the worst FCG resistance property of 9 Cr-HAZ in the dissimilar welded joint.

关键词： Fatigue crack growth Dissimilar welded joint Carbon migration Crack transverse deflection Carbonenriched zone

Particles migration behavior during laser keyhole welding of ZL101/TiB_2 composites

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Acta Metallurgica Sinica(English Letters) 2012年第3期25卷 190-200页

作者： Haichao CUI Fenggui LU Xinhua TANG Shun YAO shanghai key laboratory of materials laser Processing and modification School of Materials Science andEngineeringShanghai Jiao Tong UniversityShanghai 200030China

Particle redistribution occurred with the flow of pool fluid in laser welding aluminum composites. In order to investigate particle migration behavior, a numerical model was established on laser welding of ZL101-TiB2 composite. TiB2 migration coupling with fluid was realized. The volume-of-fluid （VOF） method was employed to track free fluid surfaces. The travel heat source was realized utilizing the workpiece mo- tion in place of heat source motion, which made the heat load stable. Melting and evaporation enthalpy, recoil force, surface tension and buoyancy were considered in this model. Through the calculation it showed that the simulated weld cross section shape and particle distribution were in good agreement with experimental results.

关键词： laser welding Numerical simulation Fluid flow Particle migration

Ductility Anisotropy Induced by Ferrite in Direct laser Deposited 17-4 PH Steel: Combined Microstructure and Dislocation Density Simulation

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Acta Metallurgica Sinica(English Letters) 2021年第6期34卷 765-776页

作者： Chuanfeng Wu Junmei Chen Zhiyuan Yu Hao Lu Chun Yu Jijin Xu shanghai key laboratory of materials laser Processing and modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The anisotropic ductility of a direct laser deposited 17-4 PH cubic part was *** elongations in the specimens from varied surfaces of the part were obtained:~6.2%,~1.5%,and~4.5%in XY,YZ,and XZ samples,***,various orientations of ferrite were found in different specimens,taking the loading direction as reference.A finite element analysis depending on actual microstructures and dislocation density revealed that the orientation of ferrite caused the ductility *** orientation of ferrite affected its plastic deformability and the deformation compatibility between phases during the uniaxial *** ferrite parallel to the tensile direction in the YZ sample had the worst deformability and induced severe strain localization and stress triaxiality,which resulted in inferior *** ferrite perpendicular to the tensile direction showed the best deformability,whereas strain localization remained intense in the XZ sample owing to the unmatched deformability of *** inclined ferrite in the XY sample exhibited moderate deformability and was found to enhance the plastic flow of martensite,leading to the best deformation compatibility and ductility.

关键词： Direct laser deposition Stainless steel Ductility Anisotropy Microstructure Finite element analysis

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

Modified Gray Level Difference-Based Thresholding Segmentation and its Application in X-Ray Welding Image

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Journal of shanghai Jiaotong university(Science) 2013年第4期18卷 448-453页

作者：佟彤蔡艳孙大为吴毅雄 shanghai key laboratory of materials laser Processing and modification Shanghai Jiaotong University

Thresholding is a popular image segmentation method that often requires as a preliminary and indis- pensable stage in the computer aided image process, particularly in the analysis of X-ray welding images. In this paper, a modified gray level difference-based transition region extraction and thresholding algorithm is presented for segmentation of the images that have been corrupted by intensity inhomogeneities or noise. Classical gray level difference algorithm is improved by selective output of the result of the maximum or the minimum of the gray level with the pixels in the surrounding, and multi-structuring of neighborhood window is used to represent the essence of transition region. The proposed algorithm could robustly measure the gray level changes, and accurately extract transition region of an image. Comparisons with other approaches demonstrate the superior performance of the proposed algorithm. K

关键词： image segmentation transition region gray level difference welding image

Characterization of Multi-layer Weld Metal and Creep–Rupture Behavior of Modified 10Cr–1Mo Welded Joint

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Acta Metallurgica Sinica(English Letters) 2020年第6期33卷 808-820页

作者： Chang-Zhen Zhang Chen-Dong Shao Hai-Chao Cui Hua-Li Xu Feng-Gui Lu shanghai key laboratory of materials laser Processing and modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The rupture behavior of the modified 10Cr–1Mo steel multi-layer welded joint is determined by the fine-grain zones of the weld metal adjacent to the fusion line during the long-term creep test at 620℃. The microstructures of multi-layer weld metal before and after the creep tests were characterized in detail, and its role in creep behavior was systematically investigated. Most grain boundaries of subgrains represented the low-angle boundaries in the weld metal adjacent to the fusion line both before and after the creep test. The widths of grains in the fine-grain zones were about 0.5–1 μm. The fracture morphology appeared as "wave" structure due to the cracking initiating from multi-layer grain boundaries in the fine-grain zones. Some W elements that melted into weld metal adjacent to the fusion line altered the thermodynamic and kinetic conditions of the Laves phase formation during long-term creep exposure. Laves phase particles mainly distributed along the grain boundaries due to the faster diffusion and segregation of Mo, W, and Si elements. Moreover, higher-density grain boundaries in the fine-grain zones led to easier nucleation and growth of Laves phase particles. Compared with other areas in the welded joint, the size of Laves phase particles in the fine-grain zones of the weld metal adjacent to the fusion line was the largest ones. The interface between Laves phase particles and the matrix acted as the nucleation site of creep micro-cavities. The creep micro-cavities grew up at the expense of fine-grain boundaries and even grew across the grain boundary deeply into adjacent grains, and then developed to cracks in the fine-grain zones.

关键词： 10Cr–1Mo Welded joint Fine grains Multi-layer Creep rupture

Comparison of the Stress Corrosion Cracking Behaviour of AISI 304 Pipes Welded by TIG and LBW

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Acta Metallurgica Sinica(English Letters) 2021年第4期34卷 579-589页

作者： Ji-Jin Xu Shuai Wang Ze Chai Chun Yu Jun-Mei Chen Hao Lu shanghai key laboratory of materials laser Processing and modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai200240China

The stress corrosion cracking(SCC)behaviour of AISI 304 pipe girth welds which were welded by a single-pass laser beam welding(LBW)and a multi-pass tungsten inert gas welding(TIG),respectively,was studied by the slow strain rate tests combined with the electrochemical corrosion *** results show that fracture of both the TIG joint and LBW joint occurs in the heat-affected zone(HAZ).According to the electron-backscattered diffraction observation of the micro structures,comparison of potentiodynamic polarization curves and X-ray photoelectron spectroscopy analysis of corrosion products on HAZs of the two joints after the electrochemical tests,the LBW joint exhibits better SCC resistance than the TIG joint in corrosion environments,due to the synthetic effect of more Cr_(2)O_(3) in corrosion products,finer grains,lower residual strain and higher δ-ferrite content in its *** the TIG joint has better mechanical property,considering lower SCC susceptibility and higher production efficiency of the LBW joint,the LBW promisingly replaces the TIG for welding of AISI304 pipes in the nuclear power industry.

关键词： laser beam welding Slow strain rate test Stress corrosion cracking Tungsten inert gas welding AISI 304 stainless steel

Recent Progress in Metallurgical Bonding Mechanisms at the Liquid/Solid Interface of Dissimilar Metals Investigated via in situ X-ray Imaging Technologies

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Acta Metallurgica Sinica(English Letters) 2021年第2期34卷 145-168页

作者： Zongye Ding Naifang Zhang Liao Yu Wenquan Lu Jianguo Li Qiaodan Hu shanghai key laboratory of materials laser Processing and modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The liquid/solid(L/S)interface of dissimilar metals is critical to the microstructure,mechanical strength,and structural integrity of interconnects in many important applications such as electronics,automotive,aeronautics,and astronautics,and therefore has drawn increasing research *** design preferential microstructure and optimize mechanical properties of the interconnects,it is crucial to understand the formation and growth mechanisms of diversified structures at the L/S interface during *** situ synchrotron radiation or tube-generated X-ray radiography and tomography technologies make it possible to observe the evolution of the L/S interface directly and therefore have greatly propelled the research in this ***,we review the recent progress in understanding the L/S interface behaviors using advanced in situ X-ray imaging techniques with a particular focus on the following two issues:(1)interface behaviors in the solder joints for microelectronic packaging including the intermetallic compounds(IMCs)during refl ow,Sn dendrites,and IMCs during solidification and refl ow porosities and(2)growth characteristics and morphological transition of IMCs in the interconnect of dissimilar metals at high ***,the main achievements and future research perspectives in terms of metallurgical bonding mechanisms under complex conditions with improved X-ray sources and detectors are remarked and discussed.

关键词： Liquid/solid interface Metallurgical bonding Dissimilar interconnects In situ X-ray imaging Solidification Microelectronic packaging

Analysis of Arc Physical Property of Pulsed Tungsten Inert Gas Welding Based on Fowler-Milne Method

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Journal of shanghai Jiaotong university(Science) 2013年第3期18卷 343-347页

作者： WANG Lin HUA Xue-ming XIAO Xiao LI Fang WU Yi-xiong Welding Engineering Institute Shanghai Jiaotong University shanghai key laboratory of materials laser manufacturing and modification Shanghai 200240 China

Pulsed tungsten inert gas （TIG） welding is widely used in industry due to its superior properties, so the measurement of arc telnperature is important to analyse welding process. Arc image of spectral line in 794.8 nm is captured by high speed camera; both the Abel inversion and the Fowler-Milne method are used to calculate the temperature distribution of the pulsed TIG welding. Characteristic of transient variation in arc intensity and temperature is analyzed. When the change of current happens, intensity and temperature of arc jump as well, it costs several millisoconds. The flirther the axial position from the tungsten is, the greater the intensity jumps, and the smaller the temperature changes.

关键词： pulsed tungsten inert gas (TIG) welding Fowler-Milne method arc temperature transient variation