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research plan(english version)

By Robin Gardner,2014-09-23 17:54
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research plan(english version)

    联合培养博士 研究生研修计划

    Research Plan for PhD Joint Training Program

    姓名/Name /Surname /First name:

    出生日期/Date of birth 性别/Sex (yy/mm/dd)

    在院系/School/ 所学专业/Major Department

    国内导师/ 留学国别/ Domestic supervisor Hosting country

    留学国外大学/ 留学院系/Hosting Hosting university faculty or department

    国外导师/ 研究领域/ Hosting supervisor Research area

    学习期限/Duration of study 12 months (from 2009.09 to 2010.09)

    研究课题名称/ Research title Surface plastic deformation regularity and the microstructural

    evolution of the TiAl billet

    研究背景/ Research backgroundIn the light of microstructure, directional solidification

    microstructures exhibit optimum creep resistance. Experimental results indicate that the creep rate of directionally solidified TiAl is 10 to 1000 times lower than that of the ordinary foundry alloys. Fine grained structures can improve the fatigue limit, because

    the fine grains can retard the formation of fatigue cracks and the larger number of grain boundaries associated with fine grains can impede the extension of cracks. In contrast,

    mono-microstructures can improve other properties, such as creep resistance.

    Consequently, compound microstructures are necessary to meet the dual demands of high

    creep resistance and fatigue limits. If the compound microstructures can be developed,

    it is anticipated that the mechanical properties of TiAl billets will be greatly improved.

    申请人科研准备工作概述 / Scientific preparations of the applicant In order to obtain compound microstructures in TiAl billets, namely fine recrystallized grains on the surface

    and the original directionally solidified microstructure in the center, it is necessary to introduce localized plastic deformation on the surface, while avoiding plastic deformation

    in the center. Following this surface deformation, cold deformed billets are subjected to

    vacuum heat treatment at temperatures +10?+20? above the α transus line in order

    to obtain the fine grains with the fully lamellar structures, for this kind of microstructures have optimum creep resistance and fatigue property. Three different surface plastic deformation techniques have been developed at HIT including: controlled shot peening, ball milling, and the surface extrusion milling. Equivalent strain and the Mises stress regularity were measured experimentally and simulated using FEM (with ABAQUS-6.7).

    The results indicate that the plastic deformation is localized within the depth of 0.5mm and the maximum equivalent strains of the controlled shot peening, ball milling and the

    surface extrusion milling extend up to 0.11, 0.7, 0.045respectively. And we also did

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some experiments with the transmission electronic microscopy (TEM) on the cold

    deformed samples, which shows that there are plenty of dislocation tangles on the treated surface. These results indicate that there is much distortion energy on the treated surface.

    The metallography of the cold deformed and the heat treated ball milled and surface

    extrusion milled surfaces shows that fine grains occur on the surface of the billet. The

    objective of my research is to study the microstructure evolution in shot peened of

    Ti-46Al-0.5W-0.5Si billet.

    出国学习预期目标;科研方法及时间安排/Expected goal ,research methods and arrangements

    1. To date I have processed several billets at different cold deformation parameters and

    have observed the microstructure using optical microscopy. These studies have

    examined variations in the shot peening parameters. I have also simulated the shot

    peening processes as a function of the experiment parameters with ABAQUS-6.7 to

    obtain the equivalent strain and Mises stress regularity. At MSU I plan to analyze

    the influence of the different cold deformation parameters on the lamellar and

    equiaxed grain structures with scanning electron microscopy (SEM), thereby

    developing an understanding of the correlation between the equivalent strain, Mises

    stress, and the microstructures after the cold deformation. (September 2009 to

    December 2009)

    2. Shot peening is a technique that develops very large, yet local zones of loading and

    plastic deformation. After the cold deformation, the degree of deformation in

    different zones is not identical. There is typically a deformed zone, an undeformed

    zone, and a transient zone, with significant variations in microstructure between these

    zones. At MSU I will use scanning electron microscopy (SEM) and the associated

    techniques of electron backscattered diffraction (EBSD) and electron channeling

    contrast imaging (ECCI) to study these microstructures. In particular, I will use

    EBSD to assess the crystal orientations and local crystallographic textures, while

    using ECCI to study the nature of the deformation in the grains. (January 2010 to

    March 2010)

    3. Heat treatment of heavily deformed materials typically results in the growth of new,

    defect free grains, often with crystal orientations significantly different than those of

    the deformed grains. At MSU I will study the effect of the vacuum heat treatment

    at temperature +10?+20? above the α transus line on the recrystallization and

    microstructure evolution. SEM and EBSD will be used to study the microstructure

    and grain orientation during this process. Using an in-situ heating stage available at

    MSU, I will study this microstructure evolution in real time on selected samples.

    (April 2010 to June 2010)

    4. In order to understand the correlation between the microstructures and the

    mechanical properties I carry out tensile and hardness tests on both the

    cold-deformed and the heat treated billets. (July 2010 to September 2010)

    拟留学院校在此学科领域的水平和优势/Level and advantage of the hosting institution on

    this projectIt is of critical importance in developing compound microstructures for simultaneous creep resistance and high fatigue strengths in the TiAl alloys to understand the nature of the microstructure as a function of surface heat treatment. Assessing this microstructure development requires a number of advanced characterization techniques, including SEM, EBSD, and ECCI. Michigan State University is a world leader in using

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    these techniques for assessing microstructure evolution, and one of two labs in the world (the other is in Oxford) that is capable of carrying out ECCI in a routine and flexible manner. In addition, MSU offers SEM, EBSD, and ECCI in a unique, flexible platform that allows studies to be carried out under a number of conditions, including in-situ

    heating and a variety of mechanical loads. Consequently, spending a year carrying out research at MSU offers an opportunity to explore the fundamental aspects of deformation

    development and microstructure evolution in these compound materials that cannot be carried out elsewhere.

    回国后续工作介绍/Work introduction after returning to China

    I will conclude the experiment results which I will have done at **University and

    accomplish my doctoral paper.

    国内导师签字Signature of domestic supervisor

    Date(yy/mm/dd)

    国外导师签字 Signature of hosting supervisor

    Date((yy/mm/dd)

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