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Twin boundary： Controllable interface to fatigue cracking

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Journal of Materials Science & Technology 2017年第7期33卷 603-606页

作者： Zhefeng Zhang Linlin Li Zhenjun zhang Peng zhang Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

Twin boundaries（TBs） are key factors influencing the mechanical properties of crystalline materials. We have investigated the intrinsic fatigue cracking mechanisms of TBs during the past decade. The effects of TB orientations on the fatigue cracking mechanisms were revealed via cyclic deformation of a series of grown Cu bicrystals with a sole TB. Furthermore, the combined effects of crystallographic orientation and stacking fault energy（SFE） on the fatigue cracking mechanisms were clarified through cyclic deformation of polycrystalline Cu and Cu alloys. Both developments were reviewed in this report which will provide implications to optimize the interfacial design for the improvement of fatigue performance of metallic materials.

关键词： Fatigue cracking Twin boundary Stacking fault energy Orientation

Microstructure and fatigue behavior of laser-powder bed fusion austenitic stainless steel

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Journal of Materials Science & Technology 2020年第11期42卷 191-200页

作者： Chenfan Yu Peng zhang Zhefeng Zhang Wei Liu School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Laboratory of Fatigue and Fracture For Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

The microstructures and stress-controlled fatigue behavior of austenitic stainless steel(AISI 316 L stainless steel)fabricated via laser-powder bed fusion(L-PBF)technique were investigated.For L-PBF process,zigzag laser scanning strategy(scan rotation between successive layer was 0°,ZZ sample)and crosshatching layer scanning strategy(scan rotation between successive layer was 67°,CH sample)were employed.By inducing different thermal history,it is found that the scan strategies of laser beam have a significant impact on grain size and morphology.Fatigue cracks generally initiated from persistent slip bands(PSBs)or grain boundaries(GBs).It is observed that PSBs could transfer the melt pool boundaries(MPBs)continuously.The MPBs have better strain compatibility compared with grain boundaries(GBs),thus MPBs would not be the initiation site of fatigue cracks.A higher fatigue limit strength could be achieved by employing a crosshatching scanning strategy.For the CH sample,fatigue cracks also initiated from GBs and PSBs.However,fatigue crack initiated from process-induced defects were observed in ZZ sample in high-cycle regions.Solidification microstructures and defects characteristics are important factors affecting the fatigue performance of L-PBF 316 L stainless.Process-induced defects originated from fluid instability can be effectively reduced by adjusting the laser scan strategy.

关键词： Laser-powder bed fusion Austenitic stainless steel Microstructures Fatigue crack

Fatigue cracking criterion of high-strength steels induced by inclusions under high-cycle fatigue

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Journal of Materials Science & Technology 2023年第23期154卷 114-128页

作者： Peng Wang Peng zhang Bin Wang Yankun Zhu Zikuan Xu Zhefeng Zhang Shi-changxu Innovation Center for Advanced Materials Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China School of Materials Science and Engineering University of Science and Technology of China Shenyang 110016 China

Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a large scatter of fatigue lives. In this work, four S–N curves and more than 200 fatigue fracture morphologies were comprehensively investigated with a special focus on the size and type of inclusions at the fatigue cracking origin in GCr15 steel with a wide strength range by different heat treatments after high-cycle fatigue (HCF). It is found that the percentage of fatigue failure induced by the inclusion including Al2 O3 and TiN gradually increases with increasing the UTS, while the percentage of failure at sample surfaces decreases conversely and the fatigue strength first increases and then decreases. Besides, it is interestingly noted that the inclusion sizes at the cracking origin for TiN are smaller than that for Al2 O3 because the stress concentration factor for TiN is larger than that for Al2 O3 based on the finite element simulation. For the first time, a new fatigue cracking criterion including the isometric inclusion size line in the strength-toughness coordinate system with specific physical meaning was established to reveal the relationship among the UTS, fracture toughness, and the critical inclusion size considering different types of inclusions based on the fracture mechanics. And the critical inclusion size of Al2 O3 is about 1.33 times of TiN. The fatigue cracking criterion could be used to judge whether fatigue fracture occurred at inclusions or not and provides a theoretical basis for controlling the scale of different inclusion types for high-strength steels. Our work may offer a new perspective on the critical inclusion size in terms of the inclusion types, which is of scientific interest and has great merit to industrial metallurgical control for anti-fatigue design.

关键词： High-strength steel High-cycle fatigue Critical inclusion size Inclusion types Tensile strength Fracture toughness Fatigue cracking criterion

Notch Effect of Materials: Strengthening or Weakening?

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Journal of Materials Science & Technology 2014年第6期30卷 599-608页

作者： Ruitao Qu Peng zhang Zhefeng Zhang Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

Notch is a very important geometry with widespread applications in engineering structural components. Finding a universal equation to predict the effect of notch on strength of materials is of much significance for structural design and materials selection. In the present work, we tried to find this universal equation from experimental results of metallic glasses （MGs） and other materials as well as theoretical derivations based on a universal fracture criterion （Qu and zhang, Sci. Rep. 3 （2013） 1117）. Experimental results showed that the notch effect of the studied MG was affected by the notch geometry characterized by the stress concentration factor Kt. As Kt becomes smaller, the notch strength ratio （NSR, which is the ratio of nominal ultimate tensile strength （UTS） of the notched sample to UTS of the unnotched sample） increases. By comparing MGs with other materials like brittle ceramics and ductile for ductile metals but smaller for brittle effect on strength of materials： NSR = equation was found to be consistent with crystalline metals, we find that when Kt is same, the NSR is larger ceramics. Theoretically, we derived a universal equation for notch M/Kt, where M is a constant related to materials. This universal the experimental results.

关键词： Notch Strength Metallic glass Fracture Plastic deformation

Fatigue Life Prediction of Gray Cast Iron for Cylinder Head Based on Microstructure and Machine Learning

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金属学报:英文版 2023年第9期36卷 1536-1548页

作者： Xiaoyuan Teng Jianchao Pang Feng Liu Chenglu Zou Xin Bai Shouxin Li Zhefeng Zhang School of Mechanical Engineering Liaoning Petrochemical UniversityFushun113001China Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang110016China

Conventional fatigue tests on complex components are difficult to sample,time-consuming and expensive.To avoid such problems,several popular machine learning(ML)algorithms were used and compared to predict fatigue life of gray cast iron(GCI)with the complex microstructures.The feature analysis shows that the fatigue life of GCI is mainly influenced by the external environment such as the stress amplitude,and the internal microstructure parameters such as the percentage of graphite,graphite length,stress concentration factor at the graphite tip,matrix microhardness and Brinell hardness.For simplicity,collected datasets with some of the above features were used to train ML models including back-propagation neural network(BPNN),random forest(RF)and eXtreme gradient boosting(XGBoost).The comparison results suggest that the three models could predict the fatigue lives of GCI,while the implemented RF algorithm is the best performing model.Moreover,the S–N curves fitted by the Basquin relation in the predicted data have a mean relative error of 15%compared to the measured data.The results have demonstrated the advantages of ML,which provides a generic way to predict the fatigue life of GCI for reducing time and cost.

关键词： Gray cast iron Microstructure feature Machine learning High-cycle fatigue life

Instrumented oscillographic study on impact toughness of an axle steel DZ2 with different tempering temperatures

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International Journal of Minerals,Metallurgy and Materials 2024年第7期31卷 1590-1598页

作者： Shuo Liu Peng zhang Bin Wang Kaizhong Wang Zikuan Xu Fangzhong Hu Xin Bai Qiqiang Duan Zhefeng Zhang Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China Technology Center Ma'anshan Iron and Steel Co.Ltd.Ma'anshan 243000China

Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.

关键词： axle steel DZ2 tempering process impact toughness oscillographic impact test impact crack propagation carbides

Friction and wear behavior of bioinspired composites with nacre-like lamellar and brick-and-mortar architectures against human enamel

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Journal of Materials Science & Technology 2022年第33期128卷 133-141页

作者： Kefeng Gao Jianjun Guan Hui Sun Chengwei Han Guoqi Tan Zengqian Liu Qiang Wang Zhefeng Zhang School of Mechanical Engineering Liaoning Petrochemical UniversityFushun 113001China Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Liaoning Provincial Key Laboratory of Oral Diseases School and Hospital of StomatologyChina Medical UniversityShenyang 110001China Liaoning Upcera Co. Ltd.Benxi 117004China School of Materials Science and Engineering University of Science and Technology of ChinaHefei 230026China

Friction and wear performance is critical for dental materials which are inevitably subject to reciprocating friction against opposing teeth in applications.Here in-vitro friction and wear behavior of bioinspired ceramic-polymer composites,which possess nacre-like lamellar and brick-and-mortar architectures and resemble human teeth in their stiffness and hardness,against human tooth enamel were quantitatively investigated to imitate actual service conditions in line with standardized testing configuration.The composites were revealed to exhibit different wear mechanisms and lead to differing extents of wear to the opposing tooth enamel depending on their specific architectural types and orientations.In particular,the brick-and-mortar architecture displayed much less wear than the lamellar one,without obviously roughening the contact surfaces with enamel owing to its high ceramic content,and as such did not accelerate the wear of enamel as compared to smooth ceramics.Such characteristics,combined with its unique stiffness and hardness matching those of human enamel as well as the good fracture toughness and machinability,endow the composite with a promising potential for dental applications.This work may provide an experimental basis to this end and may also give insights towards designing new bioinspired wear-resistant materials for reducing friction and wear.

关键词： Bioinspired materials Nacre-like structures Friction Wear mechanisms Orientation

Bi-continuous Mg-Ti interpenetrating-phase composite as a partially degradable and bioactive implant material

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Journal of Materials Science & Technology 2023年第15期146卷 211-220页

作者： Chenxi Dou Mingyang zhang Dechun Ren Haibin Ji Zhe Yi Shaogang Wang Zengqian Liu Qiang Wang Yufeng Zheng Zhefeng Zhang Rui Yang Liaoning Provincial Key Laboratory of Oral Diseases School and Hospital of StomatologyChina Medical UniversityShenyang 110001China Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaHefei 230026China School of Materials Science and Engineering Peking UniversityBeijing 100871China Center for Adaptive System Engineering School of Creativity and ArtShanghaiTech UniversityShanghai 201210China

Mg(and Mg alloys)and Ti(and Ti alloys)are two important classes of metallic implant materials which are respectively completely degradable and non-degradable after implantation.Making composites composed of them offers the promise for combining their property advantages for bone repair.Here,we present a Mg-Ti composite fabricated by pressureless infiltration of pure Mg melt into 3D printed Ti scaffold,and demonstrate a potential of the composite for use as new partially degradable and bioactive implant materials.The composite has such architecture that the Mg and Ti phases are topologically bicontinuous and mutually interspersed in 3D space,and exhibits several advantages over its constituents,such as higher strengths than as-cast pure Mg and Ti scaffold along with lower Young’s modulus than dense Ti.Additionally,the degradation of Mg phase may induce the formation and ingrowth of new bone tissues into the Ti scaffold to form mechanical interlocking between them;in this process,the Ti scaffold provides constant support and Young’s modulus adaptively decreases toward that of bone.Despite the accelerated corrosion than pure Mg,the composite remains non-cytotoxic and does not cause obvious adverse reactions after implantation as revealed by in vitro and in vivo experiments.This study may offer a new possibility for combining mechanical durability and bioactivity in implant materials,and allow for customized and targeted design of the implant.

关键词： Mg-Ti composite Interpenetrating-phase architecture Implant Bioactivity Degradation Strength

Relation Between Strength and Hardness of High-Entropy Alloys

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Acta Metallurgica Sinica(English Letters) 2021年第11期34卷 1461-1482页

作者： Xiaojuan Fan Ruitao Qu Zhefeng Zhang Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Nano Science and Technology Institute University of Science and Technology of ChinaSuzhou 215132China School of Materials Science and Engineering Northwestern Polytechnical UniversityXi'an 710072China

High-entropy alloys(HEAs)are composed of multiple principal elements and exhibit not only remarkable mechanical properties,but also promising potentials for developing numerous new compositions.To fully realize such potentials,highthroughput preparation and characterization technologies are especially useful;thereby,the fast evaluations of mechanical properties will be urgently required.Revealing the relation between strength and hardness is of significance for quickly predicting the strength of materials through simple hardness testing.However,up to now the strength-hardness relation for HEAs is still a puzzle.In this work,the relations between tensile or compressive strength and Vickers hardness of various HEAs with hundreds of compositions at room temperature are investigated,and finally,the solution for estimating the strengths of HEAs from their hardness values is achieved.Data for hundreds of different HEAs were extracted from studies reported in the period from 2010 to 2020.The results suggested that the well-known three-time relation(i.e.,hardness equals to three times the magnitude of strength)works for nearly all HEAs,except for a few brittle HEAs which show quite high hardness but low strength due to early fracture.However,for HEAs with different phase structures,different strengths should be applied in using the 3-time relation,i.e.,yield strength for low ductility body-centered cubic(BCC)HEAs and ultimate strength for highly plastic and work-hardenable face-centered cubic(FCC)HEAs.As for dual-phase or multi-phase HEAs,similar 3-time relations can be also found.The present approach sheds light on the mechanisms of hardness and also provides useful guidelines for quick estimation of strength from hardness for various HEAs.

关键词： High-entropy alloys Vickers hardness Strength Plasticity