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Formation mechanism of partial stacking faults by incompletemixed-mode phase transformation: A case study of Fe-Ga alloys

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Journal of materials Science & Technology 2022年第22期117卷 59-64页

作者： Tianzi Yang tianyu ma Feng Liu Xiaobing Ren Frontier Institute of Science and Technology State Key Laboratory for Mechanical Behavior of Materialsand MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed MatterXi’an Jiaotong UniversityXi’an 710049China State Key Laboratory of Solidification Processing and Analytical and Testing Center Northwestern Polytechnical UniversityXi’an 710072China Center for Functional materials National Institute for Materials ScienceTsukuba 305-0047IbarakiJapan

Partial stacking faults(PSFs) formed by incomplete mixed-mode phase transformation have been found to exhibit unfixed slip distance of closely-packed planes unlike those of the deformation-induced stacking faults(SFs) with fixed distance. Though engineering PSFs can yield appealing properties, such as the enhanced damping capacity, understanding of the interaction between lattice distortion and atomic diffusion and their influences on forming PSFs is still far from being clear. Herein we performed a case study on aged Fe-Ga alloy that undergoes a mixed-mode phase transformation from body-centered cubic(BCC)to ordered face-centered cubic(FCC). The TEM investigations showed that the faulted {111}-FCC distance of the PSFs is shorter than a/6 of the typical {111}- SFs in deformed FCC materials and the PSFs have disordered Fe and Ga arrangements. Further studies revealed that such PSFs will not be completely dissociated at FCC twin boundaries(TBs) even after long term isothermal aging. Consequently,the formation of PSFs can be ascribed to the transformation-dependent atomic ordering and lattice shear strain of the parent BCC lattice, where the diffusion-controlled glides of the PSFs-associated dislocations will accelerate atomic diffusions due to the dislocation-pipe effect along -FCC direction, but may hinder the atomic diffusions across the {111}-FCC TBs due to the retarding effect. This study may add important insight into the defects process during mixed-mode phase transformation and broaden the knowledge of the interaction between concurrently-happened lattice distortion and atomic diffusion.

关键词： Stacking faults Mixed-mode phase transformation Diffusion Lattice distortion Fe-Ga alloy

Stabilities,mechanical and thermodynamic properties of Al-RE intermetallics:A first-principles study

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Journal of Rare Earths 2022年第2期40卷 345-352,I0006页

作者： Tongyu Liu tianyu ma Yingmin Li Yuyan Ren Weihua Liu School of materials Science and Engineering Shenyang University of TechnologyShenyang 110870China School of Mechanical Engineering Weifang University of Science and Technology Weifang 262700China

Stabilities,mechanical and thermodynamic properties of 87 intermetallics in Al-RE binary system were studied by first-principles based on density functional theory(DFT).The results show that the calculated stabilities at T=0 K are in good agreement with experimental values.Al2 RE intermetallics exhibit the best stability in Al-RE binary compounds;and the stabilities in descending order are Al2 RE,Al3 RE,AlRE,Al11RE_(3),AlRE2 and AlRE_(3).The calculated Al-RE intermetallics possess mechanical stabilities.The hardness and strength of the most Al-RE intermetallics are greater than pure aluminum except AlCe,AlPr,AlEu and AlYb.The hardness and strength in descending order are Al11RE_(3),Al3 RE,Al2 RE and AIRE.Part of AlRE intermetallics exhibit ductility;the others are brittle.The heat capacities of Al-RE intermetallics in ascending order are Al-Sc,Al-Y,Al-lanthanides.On the contrary,the coefficient of thermal expansion(CTE)in ascending order is Al-lanthanides,Al-Y and Al-Sc.

关键词： Rare earth First-principles Stability Mechanical modulus Heat capacity

Effects of pre-aging on defects evolution and magnetic properties of Sm-Co-Fe-Cu-Zr magnets

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Journal of Rare Earths 2022年第12期40卷 1878-1884,I0003页

作者： Munzali Musa Xin Song Yao Liu Fang Wang Jiuping Fan tianyu ma Xiaobing Ren Frontier Institute of Science and Technology State Key Laboratory for Mechanical Behavior of MaterialsMOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed MatterXi'an Jiaotong UniversityXi'an 710049China Nigeria Police Academy Faculty of ScienceDepartment of PhysicsP.O.Box 14830Kano StateNigeria Key Laboratory of magnetic Molecules and magnetic Information materials of Ministry of Education Shanxi Normal UniversityLinfen 041004China National Institute for materials Science TsukubaIbaraki305-0047Japan

The heterogeneous precipitation in the 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets has been found to contain complex formation and dissociation of defects.Though low-temperature pre-aging has been utilized to promote the precipitate nucleation by the enlarged chemical driving force,how the defects evolve after pre-aging and how the possibly changed defects state affects the subsequent precipitation behavior remain unclear.In this work,a model magnet Sm25Co47.9Fe18.5Cu5.6Zr3.0(wt%)was selected to study.Through comparison with the as-solution-treated state,it is found that pre-aging for 2 h at 550℃reduces the defects density,which was characterized by less cell boundaries(i.e.,larger cell size)and less basal stacking faults inside the cells(i.e.,higher 2:17 R ordering degree).Further studies reveal that after aging for the same time(10 h)at the same temperature(830℃),the reduced density of defects by preaging also leads to slower precipitation/phase transformation kinetics when co mpared with the non-preaged one,which was characterized by the lower 2:17 R ordering degree and smaller coercivity for the former.These findings suggest that pre-aging has a strong influence on the density of defects and their evolution during subsequent isothermal aging process,which should be carefully considered to tailor the microstructure and magnetic properties of Sm-Co-Fe-Cu-Zr magnets.

关键词： Rare earths Sm-Co magnet magnetic properties Precipitates Defects

Exchange interaction and demagnetization process of high-abundance rare-earth magnets sintered using dual alloy method

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Science China(Physics,Mechanics & Astronomy) 2022年第4期65卷 104-111页

作者： Dan Liu Tongyun Zhao Jiaying Jin tianyu ma Jiefu Xiong Baogen Shen Fengxia Hu Jirong Sun Department of Physics School of Artificial IntelligenceBeijing Technology and Business UniversityBeijing 100048China Ganjiang Innovation Academy Chinese Academy of SciencesGanzhou 341000China State Key Laboratory of magnetism Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of materials Science and Engineering Zhejiang UniversityHangzhou 310027China

The 2:14:1-type rare-earth(RE)-Fe-B permanent magnets prepared by the dual alloy method have been found to possess much superior magnetic properties to those prepared by the single alloy method,providing an appealing route to promote the utilization of high-abundance RE elements Ce and La and balance the use of the RE source.However,the relationship between magnetic interactions among different 2:14:1 main phases and superior magnetic properties is still unclear.In this study,we investigated the magnetic interactions and reversal field distribution in these magnets using first-order reversal curve(FORC)images.The FORC images showed that(Nd,Pr)27.8(La,Ce)2.7FebalM1.4B1.0(S-9)and(Nd,Pr)19.5(La,Ce)11.0FebalM1.4B1.0(S-36)have the characteristics of multiple main phases.The reverse magnetic fields corresponding to the soft and hard main phases,as well as the associated exchange coupling,were highly dependent on the La Ce content.The higher the La Ce content,the weaker the exchange coupling and the more asynchronous the demagnetization process.In addition,the FORC images indicated that the magnetization reversal process also varies with La Ce content,where the nucleation and propagation of reversed domains dominant in the S-9 magnet,while the domain propagation in the S-36 magnet is considerably suppressed.Additional micromagnetic simulations also revealed that the coercivity and exchange coupling of multi-main-phase magnets decrease with increasing La Ce content,correlating well with the experimental results.These findings may not only contribute to a better understanding of the complex magnetic interactions between the soft and hard phases and how they affect macroscopic magnetic properties but also help in improving the magnetic performance of the RE-Fe-B magnets with high La Ce content.

关键词： permanent magnets exchange interaction first-order reversal curve micromagnetism high abundance rare-earth magnets

Enhanced magnetostriction of a Narrow Hysteresis Tb_(0.26)Dy_(0.54)Ho_(0.20)Fe_2 Alloy

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Acta Metallurgica Sinica(English Letters) 2013年第4期26卷 461-466页

作者： Xingwen PAN Changsheng ZHANG tianyu ma Mi YAN Jing LI State Key Laboratory of Silicon materials Department of Materials Science and EngineeringCyrus Tang Center for Sensor Materials and ApplicationsZhejiang University

In this work, a magnetic annealing method used to enhance the magnetostrictive property of a narrow hysteresis alloy Tb0.26Dyo.saHo0.20Fe2 is reported. Cylindrical-rod shaped specimen with 〈110〉 crystal orientation was fabricated using zone-melting unidirectional solidification technique, followed by annealing in a transverse magnetic field of 366 kA/m. The crystal orientation and bi-phase solidified morphology can be retained after magnetic annealing. A high magnetostriction of 1.508×10^-3 was obtained in the magnetically annealed specimen, which is 25.2% larger than the untreated one. Simultaneously, the magnetostriction hysteresis width is slightly enlarged from 4.45 to 6.36 kA/m, which is still much lower than that of the Ho-free Tbo.3Dy0.TFe2 alloy. The additional anisotropy which is induced by magnetic annealing, as reflected by the magnetic hysteresis loops, is responsible for the enhancement of magnetostrictive performance.

关键词： magnetostriction magnetostriction hysteresis Induced anisotropy

Promoting the La solution in 2:14:1-type compound:Resultant chemical deviation and microstructural nanoheterogeneity

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Journal of materials Science & Technology 2021年第3期62卷 195-202页

作者： Yongsheng Liu Jiaying Jin tianyu ma Baixing Peng Xinhua Wang Mi Yan School of materials Science and Engineering State Key Laboratory of Silicon materialsKey Laboratory of Novel Materials for Information Technology of Zhejiang ProvinceZhejiang UniversityHangzhou310027China

RE_(2)Fe_(14)B-based(RE,rare earth)permanent magnets containing abundant and cheap La/Ce have attracted intense attention recently.In comparison with Ce that can fully replace Nd in the 2:14:1 lattice,La substitution for Nd has long been limited at a low level.Here we present that through doping La35 Ce65 alloy with the La/Ce ratio in natural mineral,stable 2:14:1 phase can be maintained at 1273 K within the entire substitution range of[(La_(35)Ce_(65))、(Pr_(20)Nd_(80))_(1-x)]_(2.14)Fe_(14)B(0.6≤x≤1.0,at.%),as verified by composition analysis,microstructural characterization and magnetic measurements.Interestingly,the promoted La solution in 2:14:1 phase induces two unique findings upon coexisting La-Ce-Pr-Nd:i)Compared to Ce that fits well with the nominal concentration,La deviates noticeably from the nominal one;ii)Nanoscale spinodal-decomposition-like phase separation is observed due to different solubilities of La-Ce-Pr-Nd elements in 2:14:1 phase.Above joint effects induce higher Curie temperature than estimation based on the rule of mixture,which delights the prospect of La_(35)Ce_(65)alloy in developing low-cost permanent materials.

关键词： La-Ce Permanent magnets Nd-Fe-B Microstructure

Enhanced magnetic properties in chemically inhomogeneous Nd-Dy-Fe-B sintered magnets by multi-main-phase process

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Journal of Rare Earths 2021年第5期39卷 558-564页

作者： Xiaolian Liu Mengjie Pan Pei Zhang tianyu ma Lizhong Zhao Lingwei Li College of materials&Environmental Engineering Hangzhou Dianzi UniversityHangzhou 310018China State Key Laboratory of Silicon materials Key Laboratory of Novel Materials for Information Technology of Zhejiang ProvinceDepartment of Materials Science and EngineeringZhejiang UniversityHangzhou 310027China

Homogeneous substitution of Dy for Nd in the hard magnetic 2:14:1 phase can effectively enhance coercivity to ensure the high temperature operation,however,inevitably deteriorate remanence at expense.In this work,we performed a comparative investigation of the two magnets prepared by multimain-phase(co-sintering Nd_(2)Fe_(14)B and(Nd,Dy)_(2)Fe_(14)B powders)and single-main-phase(sintering(Nd,Dy)_(2)Fe_(14)B powders)approaches.The comparative investigation reveals that at the same Dy substitution level(2.16 wt%),such chemically inhomogeneous multi-main-phase magnet possesses better roomtemperature magnetic properties as well as thermal stability than those of the single-main-phase one with homogenous Dy distribution in the matrix grains.Room-temperature magnetic properties H_(Cj)=1664 kA/m,B_(r)=1.33 T and(BH)_(max)=350.4 kJ/m^(3)for the multi-main-phase magnet are all better than those for the single-main-phase magnet with H_(Cj)=1536 kA/m,B_(r)=1.29 T and(BH)_(max)=318.4 kj/m^(3).In addition,over the temperature range from 295 to 423 K,both the temperature coefficients of coercivity and remanence for the multi-main-phase magnet are also lower than that for the single-main-phase magnet.Such superior magnetic performance is attributed to the short-range magnetic interactions inside individual 2:14:1 phase grains and the long-range magnetostatic interactions between adjacent grains with inhomogeneous Dy distribution.Our work provides a feasible approach of enhancing coercivity and retaining energy product simultaneously in the Nd-Dy-Fe-B permanent magnets.

关键词： Permanent magnet Nd-Fe-B magnet Multi-main-phase magnetic properties Thermal stability Microstructure

Enhanced damping capacity of ferromagnetic Fe-Ga alloys by introducing structural defects

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Journal of materials Science & Technology 2021年第25期84卷 173-181页

作者： Ruihua Qiao Junming Gou Tianzi Yang Yiqun Zhang Feng Liu Shanshan Hu tianyu ma Frontier Institute of Science and Technology State Key Laboratory for Mechanical Behavior of Materialsand MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed MatterXi’an Jiaotong UniversityXi’an710049China State Key Laboratory of Solidification Processing and Analytical&Testing Center Northwestern Polytechnical UniversityXi'an710072China School of materials Science and Engineering Zhejiang UniversityHangzhou310027China

The irreversible motion of magnetic domain walls in ferromagnets can dissipate a large portion of the elastic energy,and the associated damping capacity is proportional to the magnetostriction constant.In contrast,here we found that the damping capacity of the large magnetostriction Fe-Ga alloys can be enhanced by 2-3 times through introducing structural defects including interfacial dislocations and stacking faults,despite that these defects deteriorate the magnetostriction.These structural defects were introduced by aging the BCC(body-centered-cubic)solution-treated precursor,for which the formation of mechanically harder FCT(face-centered-tetragonal)and/or FCC(face-centered-cubic)phases can result in high-density partial dislocations at the semi-coherent phase interfaces and quasi-periodically stacked nano-layer substructure inside the FCC variants.The structural defects act as extra damping sources besides the magnetic domain walls because the structural accommodation of the semi-coherent phase interfaces between BCC and FCT/FCC nanoprecipitates with different elastic moduli and the nano-layer substructure towards long-range ordered periodical stacking can dissipate a large portion of mechanical energy.These findings suggest that introducing structural defects provides fresh freedom to design high damping ferromagnetic materials.

关键词： Ferromagnets Damping capacity Defects magnetostriction Fe-Ga alloy

Role of primary Zr-rich particles on microstructure and magnetic properties of 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets

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Journal of materials Science & Technology 2020年第18期52卷 73-81页

作者： Tao Yuan Xin Song Xianglong Zhou Wentao Jia Munzali Musa Jingdong Wang tianyu ma Frontier Institute of Science and Technology State Key Laboratory for Mechanical Behavior of Materialsand MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed MatterXi'an Jiaotong UniversityXi'an710049China The Southwest Applied magnetism Research Institute Mianyang621000China

Trace Zr addition is essential for achieving desired cellular nanostructure and large coercivity in the pinning-controlled 2:17-type Sm-Co-Fe-Cu-Zr magnets that have served as the strongest high temperature permanent magnets for over 40 years.However,accompanying this is the formation of Zr-rich particles that may deteriorate the hard magnetic properties.Besides the formerly-reported 1:3R Zr-rich platelets,in this work,1–2μm sized Zr6(Co,Fe)23(6:23)particles(Fm 3 m)and 100–200 nm sized 1:3R Zr-rich particles were also found based on combined structural identifications and element mapping analysis.Around such particles,the desired 1:5H cell wall precipitates that provide the strongest pinning force of magnetic domain wall motions are rare,forming the precipitate-free-zones(PFZs).The 1:5H-PFZs and the soft magnetism of both 6:23 and 1:3R Zr-rich particles act as local weak pinning points,which are unfavorable to retain the large magnetization in strong opposite fields and lead to poor squareness.As observed in a Sm25Co45.9Fe19.5Cu5.6Zr4.0(wt.%)magnet,the co-existence of such Zr-rich particles and the associated 1:5H-PFZs leads to a pretty low squareness factor of only 52.89%given the large coercivity of 29.04 kOe.Our findings suggest that careful controlling the Zr content and avoiding its aggregation to form harmful 6:23 and 1:3R Zr-rich particles are essential for achieving high squareness as well as large energy product in the Sm-Co-Fe-Cu-Zr permanent magnets.

关键词： Permanent magnets Sm-Co alloys Microstructure Precipitates