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Unusual He-ion irradiation strengthening and inverse layer thickness-dependent strain rate sensitivity in transformable high-entropy alloy/metal nanolaminates:A comparison of fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu vs fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu

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Journal of materials Science & Technology 2022年第21期116卷 199-213页

作者： Y.f.Zhao H.H.Chen D.D.Zhang J.Y.Zhang Y.Q.Wang K.Wu G.Liu J.Sun state key laboratory for mechanical behavior of materials Xi’an Jiaotong UniversityXi’an 710049China

In this work,we prepare transformable HEA/Cu nanolaminates(NLs)with equal individual layer thick-ness(h)by the magnetron sputtering technique,i.e.,fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu and fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu,and comparatively study He-ion irradiation effects on their microstructure and mechanical properties.It ap-pears that the as-deposited HEA/Cu NLs manifest two size h-dependent hardness regimes(i.e.,increased hardness at small h and hardness plateau at large h),while the He-implanted ones exhibit monotonically increased hardness.Contrary to the fashion that smaller h renders less irradiation hardening in bimetal NLs,the fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs manifest the trend that smaller h leads to greater irradiation hard-ening.By contrast,the fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs exhibit the maximum irradiation hardening at a critical h=50 nm.Below this critical size,smaller h results in lower radiation hardening(similar to bimetal NLs),while above this size,smaller h results in greater radiation hardening(similar to fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs).Moreover,these transformable HEA/Cu NLs display inverse h-dependent strain rate sensitivity(SRS m)before and after He-ion irradiation.Nevertheless,compared with as-deposited samples,the irradi-ated fe_(50)Mn_(30)Co_(10)Cr_(10)/Cu NLs display reduced SRS,while the irradiated fe_(50)Mn_(30)Co_(10)Ni_(10)/Cu NLs dis-play enhanced SRS.Such unusual size-dependent irradiation strengthening and inverse h effect on SRS in irradiated samples were rationalized by considering the blocking effects of He bubbles on dislocation nucleation and motion,i.e.,dislocations shearing or bypassing He bubbles.

关键词： High entropy alloy/metal nanolaminates Interfaces Irradiation hardening Strain rate sensitivity Size effects

High-entropy Sm_(2)B_(2)o_(7)(B=Ti,Zr,Sn,Hf,Y,Yb,Nb,and Ta) oxides with highly disordered B-site cations for ultralow thermal conductivity

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Journal of materials Science & Technology 2022年第24期119卷 182-189页

作者： Liang Xu Lei Su Hongjie Wang Hongfei Gao Pengfei Guo Min Niu Kang Peng Lei Zhuang Zhiwei Dai state key laboratory for mechanical behavior of materials Xi’an Jiaotong UniversityXi’an 710049China

materials with ultralow thermal conductivity and good thermal stability are of great interest in numerous applications such as energy storage and conversion devices,and thermal insulation components.In this work,a family of high-entropy Sm_(2)B_(2)o_(7)(B=Ti,Zr,Sn,Hf,Y,Yb,Nb,and Ta) oxides with highly disordered cations on the B-site has been synthesized by introducing large atomic-size mismatch,mass and charge disorder.Through tuning the composition,the high-entropy Sm_(2)B_(2)o_(7) oxides can be engineered from pyrochlore to fluorite structure,accompanied with an order-disorder transition.The pyrochlore Sm_(2)(Nb_(0.2)Sn_(0.2)Ti_(0.2)Y_(0.2)Zr_(0.2))_(2)o_(7) and fluorite Sm_(2)(Nb_(0.2)Ta_(0.2)Y_(0.2)Yb_(0.2)Zr_(0.2))_(2)o_(7) exhibit low thermal conductivities of 1.35 W·m^(-1)·K^(-1) and 1.23 W·m^(-1)·K^(-1),respectively,indicating their good thermal insulation.In addition,the high-entropy fluorite Sm_(2)(Nb_(0.2)Ta_(0.2)Y_(0.2)Yb_(0.2)Zr_(0.2))_(2)o_(7) also shows average thermal expansion coefficient of 10.2 × 10^(-6)℃^(-1) and high-temperature stability even after thermal exposure at 1600 °C in air for 30 h.These results indicate that the high-entropy Sm_(2)B_(2)o_(7)(B=Ti,Zr,Sn,Hf,Y,Yb,Nb,and Ta) can be promising candidates for thermal barrier coatings and thermally insulators.

关键词： High-entropy oxides Atomic sizes mismatch Mass and charge disorder Thermal conductivity Thermal barrier coatings materials

Migration of weakly bonded oxygen atoms in a-IGZo thin films and the positive shift of threshold voltage in TfTs

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Chinese Physics B 2022年第9期31卷 397-403页

作者：王琛路文墨李奉南罗巧梅马飞 state key laboratory for mechanical behavior of materials Xi'an Jiaotong UniversityXi'an 710049China

Amorphous indium-gallium-zinc oxide(a-IGZo)thin films are prepared by pulsed laser deposition and fabricated into thin-film transistor(TfT)devices.In-situ x-ray photoelectron spectroscopy(XPS)illustrates that weakly bonded oxygen(o)atoms exist in a-IGZo thin films deposited at high o_(2) pressures,but these can be eliminated by vacuum annealing.The threshold voltage(V_(th))of the a-IGZo TfTs is shifted under positive gate bias,and the Vth shift is positively related to the deposition pressure.A temperature variation experiment in the range of 20 K-300 K demonstrates that an activation energy of 144 meV is required for the Vth shift,which is close to the activation energy required for the migration of weakly bonded o atoms in a-IGZo thin films.Accordingly,the Vth shift is attributed to the acceptor-like states induced by the accumulation of weakly bonded o atoms at the a-IGZo/Sio_(2) interface under positive gate bias.These results provide an insight into the mechanism responsible for the Vth shift of the a-IGZo TfTs and help in the production of reliable designs.

关键词： a-IGZo thin films weakly bonded o atoms threshold voltage shift

Critical scale grain size for optimal lifetime of TBCs

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Journal of materials Science & Technology 2022年第20期115卷 241-250页

作者： Lin Chen Guo-Hui Meng Chang-Jiu Li Guan-Jun Yang state key laboratory for mechanical behavior of materials School of Materials Science and EngineeringXi’an Jiaotong UniversityXi’an 710049China

Thermal barrier coatings(TBCs)suffer from spalling failure resulting from the rapid growth of thermally grown oxides(TGo)on the metallic bond coat.In this study,to achieve the optimal lifetime of TBCs,a lifetime phase diagram was constructed for the entire service of TBCs.Herein,both the thermal mismatch stress during thermal cycling and the TGo growth stress during thermal exposure were considered.first,thickening behavior of the Al_(2)o_(3) scale related to grain size was investigated.Second,transverse delamination failure due to the thermal mismatch stress was analyzed.Third,vertical cracking failure related to early scale growth was explored.finally,a critical scale grain size of~2.5μm was identified for achieving the optimal lifetime of TBCs.It was experimentally proved that vertical cracking of the Al_(2)o_(3) scale occurred during early oxidation as the scale grain size was larger than~4μm after pre-oxidation.The proposed lifetime phase diagram and critical scale grain size effect serve as novel criteria for the design of next-generation durable TBCs.

关键词： TGo growth Grain size Grain boundaries Channel cracking Service lifetime

Enhancing the high-temperature creep properties of Mo alloys via nanosized La_(2)o_(3) particle addition

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Journal of materials Science & Technology 2022年第35期130卷 53-63页

作者： P.M.Cheng C.Yang P.Zhang J.Y.Zhang H.Wang J.Kuang G.Liu J.Sun state key laboratory for mechanical behavior of materials Xi’an Jiaotong UniversityXi’an 710049China School of mechanical Engineering Chengdu UniversityChengdu 610106China

Molybdenum(Mo) alloys with different La_(2)o_(3)particle additions(0.6,0.9,1.5 wt.%) were prepared by powder metallurgy to investigate the effect of La_(2)o_(3)particles on microstructural evolution and creep behavior of the alloy.Pure Mo,annealed at 1500℃ for 1 h,presented a fully recrystallized microstructure characterized by equiaxed grains.The alloys doped with La_(2)o_(3)particles(Mo-La_(2)o_(3)alloys),on the other hand,exhibited fibrous grains elongated in the rolling direction of the plate.In contrast to the shape of the grains,the average grain size of the alloys was found to be insensitive to the addition of La_(2)o_(3)particles.Nanosized La_(2)o_(3)particles with diameters ranging from 65 to 75 nm were distributed within the grain interior.Tensile creep tests showed that dislocation creep was the predominant deformation mode at intermediate creep rate(10^(-7)s^(-1)-10^(-4)s^(-1)) in the present alloys.The creep stress exponent and activation energy were found to decrease with increasing temperature,particularly within the low creep rate regime(o-La_(2)o_(3)alloys exhibited remarkably greater apparent stress exponent and activation energy than pure Mo.A creep constitutive model based on the interaction between particles and dislocations was utilized to rationalize the nanoparticle-improved creep behavior.It was demonstrated that low relaxed efficiency of dislocation line energy,which is responsible for an enhanced climb resistance of dislocations,is the major creep strengthening mechanism in the Mo-La_(2)o_(3)alloys.In addition,the area reduction and creep fracture mode of the Mo-La_(2)o_(3)alloys were found to be a function of the creep rate and temperature,which can be explained by the effect of the two parameters on the creep and fracture mechanisms.

关键词： Mo alloys Nanosized particles Creep strength Deformation and fracture

Epitaxial growth and cracking of highly tough 7YSZ splats by thermal spray technology

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Journal of Advanced Ceramics 2018年第1期7卷 17-29页

作者： Lin CHEN Guan-Jun YANG state key laboratory for mechanical behavior of materials School of Materials Science and Engineering Xi'an Jiaotong University

Thermally sprayed coatings are essentially layered materials and contain large numbers of lamellar pores. It is thus quite necessary to clarify the formation mechanism of lamellar pores which significantly influence coating performances. In the present study, to elaborate the formation mechanism of lamellar pores, the yttria-stabilized zirconia(Zro_2–7 wt% Y_2o_3, 7YSZ) splats, which have high fracture toughness and tetragonal phase stability, were employed. Interestingly, anomalous epitaxial growth occurred for all deposition temperatures in spite of the extremely high cooling rate,which clearly indicated chemical bonding and complete contact at splat/substrate interface before splat cooling. However, transverse spallation substantially occurred for all deposition temperatures in spite of the high fracture toughness of 7YSZ, which revealed that the lamellar pores were from transverse cracking/spallation due to the large stress during splat cooling. Additionally, fracture mechanics analysis was carried out, and it was found that the stress arose from the constraint effect of the shrinkage of the splat by locally heated substrate with the value about 1.97 GPa. This clearly demonstrated that the stress was indeed large enough to drive transverse cracking/spallation forming lamellar pores during splat cooling. All of these contribute to understanding the essential features of lamellar bonding and further tailoring the coating structures and performance.

关键词： epitaxial growth crack patterns transverse cracking/spallation stress locally heated substrate

Crystallization kinetic characteristics of oxygen-induced I-phase and Zr_2Cu phase in Zr_(65)Cu_(27.5)Al_(7.5) glassy alloy

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中国有色金属学会会刊：英文版 2008年第3期18卷 610-616页

作者：贺林韩振华江峰孙军 state key laboratory for mechanical behavior of materials Xi'an Jiaotong University state key laboratory for mechanical behavior of materials Xi’an Jiaotong University

Based on the construction of TTT diagrams by isothermal DSC measurements, the thermal stabilities of Zr65Cu27.5Al7.5 glassy alloys containing 0.68% and 0.06% [o] (molar fraction) were compared. The changing tendencies of the thermal stabilities reflected in the TTT-diagrams were validated by XRD analyses and TEM observations. The crystallization kinetic characteristics of oxygen-induced I-phase and Zr2Cu phase in Zr65Cu27.5Al7.5 glassy alloy were discussed. It is found that oxygen promotes the precipitation of I-phase and retards the formation of Zr2Cu phase. If the pre-crystallization event for oxygen-induced I-phase is permitted and the main-crystallization event for Zr2Cu phase is taken as the thermal stability criterion, the alloy with higher oxygen content has longer onset time for crystallization within a rather large supercooling temperature range. The possibility for the preparation of Zr65Cu27.5Al7.5 glassy alloy-based composite containing oxygen-induced I-phase was also forecasted.

关键词：金属性玻璃热力学研究相位转换杂质氧化

one-step multi-compositional oxidation of YSi alloy:Experiments and ab initio computation

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Journal of materials Science & Technology 2023年第27期158卷 253-262页

作者： W.J.Wang J.C.Luo L.Chen G.J.Yang state key laboratory for mechanical behavior of materials School of Materials Science and EngineeringXi’an Jiaotong UniversityXi’an 710049China Xi’an Jiaotong University Suzhou Institute Suzhou 215123China

YSi alloy is a promising candidate as oxidation resistant coatings for both the bond coat of environmental barrier coatings(EBCs)and anti-ablation coatings at a high temperature of∼1300℃.In this study,a one-step multi-compositional oxidation by rapid heating oxidation mode is proposed to reduce the oxidation rate by 3.6 times compared to conventional slow heating oxidation mode.Results show that preferentially formed Y_(2)o_(3) oxide initiates a multi-step oxidation,produces a cracking and porous oxides,and thereby resulting in a fast oxidation with pesting.The one-step multi-compositional oxidation with a compact and dense Y_(2)Si_(2)o_(7)scale contributes to the much better oxidation resistance for rapid heating oxidation mode of YSi alloy.The stable formation of Y_(2)Si_(2)o_(7)scale is comprehensively understood by the energy barrier,charge density and electronic level based on density functional theory.This study demonstrates a promising application of YSi alloy by rapid heating oxidation mode.

关键词： YSi alloy one-step oxidation Multi-compositional scale Y_(2)Si_(2)o_(7) Energy barrier

Multiscale Structure Engineering for High-Performance Pb-free Piezoceramics

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Accounts of materials Research 2022年第4期3卷 461-471页

作者： Xiang Lv Ting Zheng Chunlin Zhao Jie Yin Haijun Wu Jiagang Wu Department of materials Science Sichuan UniversityChengdu 610064China state key laboratory for mechanical behavior of materials Xi’an Jiaotong UniversityXi’an 710049China

CoNSPECTUS:The increasing world energy crisis drives humans to harvest the energy in nature as much as possible without heavily damaging the environment.However,most of the energy in nature cannot be used directly.Therefore,pursuing technologies or matter that can directly interconvert different energies has been one of the most cutting-edge fields in science and technology.Such a magic ability exists in true-life piezoelectric materials that generate charge when being given a force and vice versa,rendering them highly promising for energy harvesting and conversion because of the tremendous mechanical energy on the earth,such as tide energy.Thus,piezoelectric materials,represented by the lead zirconate titanate(Pb(Zr,Ti)o_(3),PZT)family,have been largely used in various traditional and burgeoning fields,such as electronic information,biomedical treatment,and wearable flexible electronic devices,and are one of the most important favorites in multidisciplinary fields.However,Pb is highly toxic.Driven by environmental protection and concern for human health,Pb-free piezoceramics are rapidly being developed to hopefully replace Pb-based ones.In particular,the renewal of Restriction of the use of certain Hazardous Substances(e.g.,RoHS 2),issued by the European Union,declared that replacement of PZT“...may be scientif ically and technologically practical to a certain degree...”.Therefore,developing high-performance Pb-free piezoceramics has become more urgent than ever.In this context,some Pb-free piezoceramics,represented by potassium sodium niobate((K,Na)Nbo_(3),KNN),barium titanate(BaTio_(3),BT),bismuth barium titanate((Bi,Na)Tio_(3),BNT),and bismuth ferrite(Bifeo_(3),Bfo),stand out because of their unique or similar traits.However,several key challenges,including an inferior overall performance compared to Pb-based counterparts and an unclear structure−property relationship from multiscale viewpoints,have severely hindered the development of Pb-free piezoceramics for a long time.Pb-based piezoceramics possess decen

关键词： ceramics piezoelectric bismuth