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phase transformation under Continuous Cooling Conditions in Medium Carbon Microalloyed Steels

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Journal of Materials Science & Technology 2014年第5期30卷 511-516页

作者： Manuel Gomez Lucia Rancel Esther Escudero Sebastian F.Medina National Centre for Metallurgical Research CENIM-CSICAv.Gregorio del Amo 828040 MadridSpain

Several 35CrMo4 and 38MnV7 steels with different additions of Ti and V were manufactured by electroslag remelting. The influence of the alloying and microalloying elements on phase transformation at different cooling rates was studied and the continuous cooling transformation diagrams were plotted. In order to optimize the heat treatment and improve the mechanical properties, the range of cooling rates leading to a fully bainitic microstructure （without ferrite, pearlite and especially without martensite） was determined. Bainite and martensite transformation start temperatures （Bs, Ms） were also established and compared with the values predicted by empirical equations. The important role of precipitates （especially V carbonitride particles） on final microstructure and mechanical properties was assessed.

关键词： Microalloyed steel phase transformation Precipitation Dilatometry Continuous cooling transformation diagram

phase transformation at controlled locations in nanowires by in situ electron irradiation

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Nano Research 2020年第7期13卷 1912-1919页

作者： Hongtao Zhang Wen Wang Tao Xu Feng Xu Litao Sun SEU-FEI Nano-Pico Center Key Laboratory ofMEMS of Ministry of EducationSoutheast UniversityNanjing 210096China Center for Advanced Materials and Manufacture Southeast University-Monash University Joint Research InstituteSuzhou 215123China

Solid state phase transtormations have drawn great attention because they can be effectively exploited to control the microstructure and property of materials.Understanding the physics of such phase transformation processes is critical to designing materials with controlled structure and with desired properties.However,in traditional ex situ experiments,it is hard to achieve position controlled phase transformations or obtain desirable crystal phase on nanometer scale.Meanwhile the underlying mechanisms of the reaction processes are not fully understood due to the lack of direct and real-time observation.In this paper,we observe phase transformation from body-centered tetragonal PX PbTiO3 to monclinic TiO2(B)on the atomic scale by in situ electron iradiation during heat treatment in transmission electron microscope,at pre-defined locations on the sample.We demonstrate that by controlling the location of the incident electron beam,a porous TiO2(B)crystal structure can be formed at the desired area on the nanowire,which is dificult to achieve by traditional synthesis methods.Upon in situ heating,the Pb atoms in the crystal migrate out of the pristine nanowire through inelastic scattering under incident electrons while high temperature(>400℃)provides energy for the crytalization of TiO2(B)and the vlatlization of a substantial number of Pb atoms,which makes the resultingTiO2(B)nanowires to be porous.In contrast,at temperaturesphase transition from the PX-PbTiO3 to monoclinic TiO2(B),but also suggests a crystallography engineering strategy to obtain the desired crystal phase at controlled locations on the nanometer scale.

关键词： phase transformation controlled locations in situ transmission electron microscopy

phase transformation During Intercritical Tempering with High Heating Rate in a Fe-13%Cr-4%Ni-Mo Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2013年第6期26卷 669-674页

作者： Pei WANG Shenghua ZHANG Shanping LU Dianzhong LI Yiyi LI Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

The phase transformation from martensite to austenite during intercritical tempering with high heating rate in a low carbon martensitic stainless steel Fe-13%Cr-4%Ni-Mo has been investigated to clarify the microstructure evolution in some regions of the weld joint heat affected zone （HAZ）. The experimental results indicate that the start and finish temperatures of the martensite to austenite transformation keep constant when the heating rate is higher than 10 K/s, and the transformation is much faster than nickel diffusion. The mechanism of the martensite to austenite transformation changes from diffusion to diffusionless during the intercritical tempering when the heating rate is higher than 10 K/s. The diffusionless transformation and higher As temperature render it difficult for any austenite to remain at room temperature during the intercritical tempering with high heating rate that occurs in the HAZ. Adding a proper intercritical tempering with low heating rate can induce some reversed austenite in the rapid heated sample.

关键词： Martensitic stainless steel phase transformation Intercritical tempering Heating rate Microstructure

phase transformation and structural evolution in a Ti-5at.%Al alloy induced by cold-rolling

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Journal of Materials Science & Technology 2020年第14期47卷 211-223页

作者： Bingqiang Wei Song Ni Yong Liu Xiaozhou Liao Min Song State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China School of Aerospace Mechanical and Mechatronic EngineeringThe University of SydneySydneyNSW 2006Australia

The phase transformation,deformation mechanism and their correlation in a cold-rolled Ti-5 at.%Al alloy were investigated.Two types of phase transformations from a hexagonal close-packed(HCP)structure to a face-centered cubic(FCC)structure were observed:the basal-type(B-type)with an orientation relation-ship oftransformations both accommodate the strain along theaxis of the HCP matrix.With the proceeding of deformation,different deformation mechanisms were activated in the FCC and the HCP structures,respectively,which led to a faster grain refinement rate in the FCC structure than in the HCP matrix.Deformation twins with zero macroscopic strain were prevalent in the FCC domains produced by the B-type transformation,while deformation twins with macroscopic strain were normally observed in the FCC domains produced by the P-type transformation.This is in accordance with the lattice mismatches produced during phase transformation.The easy occurrence of deformation twinning in the FCC structure contributed significantly to the grain refinement process.In addition,the interaction between neighboring FCC domains produced by the two types of phase transformations also accelerated the grain refinement process.

关键词： Ti-Al alloy Deformation mechanism phase transformation Grain refinement Deformation twinning

phase transformation kinetics of Ti-1300 alloy during continuous heating

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Rare Metals 2015年第4期34卷 233-238页

作者： Ming-Pan Wan Yong-Qing Zhao Wei-Dong Zeng State Key Laboratory of Solidification Processing Northwest Polytechnical University College of Materials and Metallurgy Guizhou University Northwest Institute for Nonferrous Metal Research

Abstract The α ＋ β→β phase transformation kinetics of Ti-1300 alloy during continuous heating at different heating rates were investigated using dilatometric method. Results show that the curves of the α ＋ β→β phase transformation exhibit a typical S-shaped pattern, which indicates that the α ＋ β→β phase transformation is a nucleation-growth-controlled process. The overall activation energy of the α ＋ β→β transformation of the alloy is 797 kJ·mol^-1. The nucleation and growth mechanism of the α ＋ β→β transformation was also investigated using the non-isothermal Avrami exponent. The Avrami exponent during α ＋ β→β transformation process significantly changes with transformed volume fraction increasing, which indicates that the α ＋ β→β transformation mechanism in the Ti-1300 alloy varies at different sections.

关键词： Ti-1300 alloy phase transformation Dilatometry Kinetics

phase transformation and Thermal Stability of Aged Ti-Ni-Hf High Temperature Shape Memory Alloys

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Journal of Materials Science & Technology 2006年第5期22卷 691-695页

作者： Xianglong MENG Wei CAI K.T.Lau L.M.Zhou Liancheng ZHAO School of Materials science ＆ Engineering Harbin Institute of Technology Harbin 150001 China Department of Mechanical Engineering The Hong Kong Polytechnic umversity Hung Horn KowloonHong Kong China

The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys （SMAs） through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures （Ms） are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.

关键词： TiNiHf alloy High temperature shape memory alloy Aging phase transformation

phase transformation and Magnetic Properties of Nd_xFe_(60.5-x)Pt_(39.5)(x=0, 0.5, 1.0, 1.5) Alloys

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Journal of Rare Earths 2007年第1期25卷 84-87页

作者：成钢顾正飞周怀营王仲民袁松柳 Department of Physics Huazhong University of Science and TechnologyWuhan 430074 ChinaDepartment of Information of Materials Science and Engineering Guilin University of Electronic Technology Guilin 541004 China Department of Information of Materials Science and Engineering Guilin University of Electronic TechnologyGuilin 541004 China Department of Physics Huazhong University of Science and TechnologyWuhan 430074 China

The effect of Nd addition on the structure, phase transformation and magnetic properties of FePt based alloys was investigated. The results indicated that the transition temperature from ordered FCT to disordered FCC phase decreased with increasing Nd concentration, but for alloys quenched rapidly from the γ phase region into ice-water, it increased with increasing Nd. The Nd element not only effectively reduced the grain size of the ordered phase but also decreased the degree of the ordered phase and refined the grains of the FCC matrix phase. The remanence ratio and coereivity of the FePt based alloy as a function of the Nd content had maximum values, respectively.

关键词： Fe-Pt alloys phase transformation exchange coupling remanence ratio rare earths

phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing

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Journal of Semiconductors 2015年第3期36卷 19-22页

作者： K.Mahmood M.Asghar N.Amin Adnan Ali Department of Physics GC University Faisalabad Department of Physics The Islamia University of Bahawalpur

We have investigated the mechanism of phase transformation from ZnS to hexagonal ZnO by high- temperature thermal annealing. The ZnS thin films were grown on Si （001） substrate by thermal evaporation system using ZnS powder as source material. The grown films were annealed at different temperatures and characterized by X-ray diffraction （XRD）, photoluminescence （PL）, four-point probe, scanning electron microscope （SEM） and energy dispersive X-ray diffraction （EDX）. The results demonstrated that as-deposited ZnS film has mixed phases but high-temperature annealing leads to transition from ZnS to ZnO. The observed result can be explained as a two- step process：（1） high-energy O atoms replaced S atoms in lattice during annealing process, and （2） S atoms diffused into substrate and/or diffused out of the sample. The dissociation energy of ZnS calculated from the Arrhenius plot of 1000/T versus log （resistivity） was found to be 3.1 eV. PL spectra of as-grown sample exhibits a characteristic green emission at 2.4 eV of ZnS but annealed samples consist of band-to-band and defect emission of ZnO at 3.29 eV and 2.5 eV respectively. SEM and EDX measurements were additionally performed to strengthen the argument.

关键词： ZnS phase transformation EDX XRD PL

phase transformation and Magnetic Properties of Mechanically Alloyed PrCo5-based Magnets

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Journal of Materials Science & Technology 2006年第6期22卷 843-845页

作者： Xinguo ZHAO Zhidong ZHANG Qi YAO Jinjun LIU Weijun REN Wei LIU Dianyu GENG Shenyang National Laboratory for Materials Science International Centre for Materials Physics Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

PrCo5-based nanograin Pr=CO100-x （x=14-22） alloys with high coercivity were synthesized by mechanical alloying and subsequent annealing. The crystallization, phase components and magnetic properties of the alloys were investigated systematically. The main phase of the alloy for x=14 is Pr2CO17 with rhombohedral Th2Zn17-type. The amount of the Pr2CO17 phase decreases with increasing Pr content, and a nearly single phase PrCo5 with hexagonal CaCu5-type is formed in Pr18Co81 alloy. Further increase in the Pr content leads to the formation of another magnetically hard Pr2Co7 phase with its Curie temperature about 350℃. Remanences decrease monotonously with increasing Pr content, whereas the coercivities increase, reaching a maximum of 2040 kA/m （25.6 kOe） in Pr19CO81 powders milled for 5 h and annealed at 973 K for 2 min, and then decrease for higher Pr content. The high coercivity is attributed to the high anisotropy field of the PrCo~ phase and its nanoscale grain size.

关键词： Pr-Co magnets phase transformation Magnetic properties Mechanical alloying