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Solute drag-controlled grain growth in magnesium investigated by quasi in-situ orientation mapping and level-set simulations

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镁合金学报(英文) 2023年第7期11卷 2312-2325页

作者： Risheng Pei Yujun Zhao Muhammad Zubair Sangbong Yi Talal Al-Samman Institut für Metallkunde und Materialphysik RWTH Aachen University52056 AachenGermany Institute of Materials and Process Design Helmholtz-Zentrum Hereon21502 GeesthachtGermany Department of Metallurgical and Materials Engineering Faculty of ChemicalMetallurgical&Polymer EngineeringUniversity of Engineering&Technology(UET)LahorePakistan Institute for Materials Ruhr-Universität Bochum44801 BochumGermany

Critical properties of metallic materials,such as the yield stress,corrosion resistance and ductility depend on the microstructure and its grain size and size distribution.Solute atoms that favorably segregate to grain boundaries produce a pinning atmosphere that exerts a drag pressure on the boundary motion,which strongly affects the grain growth behavior during annealing.In the current work,the characteristics of grain growth in an annealed Mg-1 wt.%Mn-1 wt.%Nd magnesium alloy were investigated by advanced experimental and modeling techniques.Systematic quasi in-situ orientation mappings with a scanning electron microscope were performed to track the evolution of local and global microstructural characteristics as a function of annealing time.Solute segregation at targeted grain boundaries was measured using three-dimensional atom probe tomography.Level-set computer simulations were carried with different setups of driving forces to explore their contribution to the microstructure development with and without solute drag.The results showed that the favorable growth advantage for some grains leading to a transient stage of abnormal grain growth is controlled by several drivers with varying importance at different stages of annealing.For longer annealing times,residual dislocation density gradients between large and smaller grains are no longer important,which leads to microstructure stability due to predominant solute drag.Local fluctuations in residual dislocation energy and solute concentration near grain boundaries cause different boundary segments to migrate at different rates,which affects the average growth rate of large grains and their evolved shape.

关键词： Magnesium alloys Grain growth Quasi in-situ EBSD Level-set simulation Solute drag dislocation density gradient

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Normal and abnormal grain growth in magnesium:Experimental observations and simulations

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Journal of Materials Science & Technology 2020年第15期47卷 257-270页

作者： Risheng Pei Sandra Korte-Kerzel Talal Al-Samman Institut fur Metallkunde und Materialphysik RWTH Aachen UniversityD-52056AachenGermany

Commercial purity as-cast magnesium was hot rolled and subsequently annealed at different temperatures in order to investigate its grain growth behavior and link it to the texture evolution.Annealing at an intermediate temperature of 220℃ gave rise to abnormal grain growth with a few grains reaching a grain diameter 10 times larger than the mean.Increasing the annealing temperature to 350℃ yielded normal grain growth.Both types of grain growth revealed a strengthening of the(0001) texture component.It is hypothesized that a dislocation density gradient after recrystallization grants(0001) grains a size advantage during early stages of growth.The type of growth will be,however,determined by the mobility of the present grain boundaries and triple junction drag,which are strongly dependent on the annealing temperature.The above hypothesis of the interplay between these parameters was explored through curvature-and re sidual dislocation-density-gradient-driven grain growth simulations using a formerly developed level-set approach.The simulation outcome suggests that application of such a modeling approach in microstructure studies of magnesium can provide valuable new insights into the problem of grain growth and associated texture evolutio n.

关键词： Pure magnesium Grain growth Texture dislocation density gradient Level-set modeling

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Effect of dislocation Mechanism on Elastoplastic Behavior of Crystals with Heterogeneous dislocation Distribution

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Acta Mechanica Solida Sinica 2020年第4期33卷 487-495页

作者： Songjiang Lu Jian Xiong Dean Wei Yifan Ding Bo Zhang Ronghai Wu Xu Zhang Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province School of Mechanics and EngineeringSouthwest Jiaotong UniversityChengdu 610031China School of Mechanics Civil Engineering and ArchitectureNorthwestern Poly technical UniversityX i’an 710129China

gradient structures have excellent mechanical properties,such as synergetic strength and ductility.It is desirable to reveal the connection between the gradient structure and mechanical properties.However,few studies have been conducted for materials with heterogeneous dislocation distribution.In the present study,we use the discrete dislocation dynamics(DDD)method to investigate the effect of dislocation density gradient on the elastoplastic behavior of single crystals controlled by source activation.In contrast to the intuitive expectation that gradient structure affects the mechanical properties,the DDD simulations show that the elastic moduli and yield stresses of three gradient samples(i.e.,no gradient,low gradient,and high gradient)are almost identical.Different from the progressive elastic-plastic transition in the samples controlled by Taylor hardening(i.e.,the mutual interaction of dislocation segments),the flow stresses of source activation ones enter into a stage of nearly ideal plasticity(serrated flow)immediately after yielding.The microstructure evolution demonstrates that the mean dislocation spacing is relatively large.Thus,there are only a few or even one dislocation source activated during the plastic flow.The intermittent operation of sources leads to intensive fluctuation of stress and dislocation density,as well as a stair-like evolution of plastic strain.The present work reveals that the effect of dislocation density gradient on the mechanical response of crystals depends on the underlying dislocation mechanisms controlling the plastic deformation of materials.

关键词： dislocation dynamics Microplasticity dislocation mechanism dislocation density gradient

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