researchplan(englishversion).doc

联合培养博士研究生研修计划
Research Plan for PhD Joint Training Program
姓名/Name
姓/Surname： 名/First name:
性别/Sex

出生日期/Date of birth (yy/mm/dd)

所在院系/School/
Department

所学专业/Major

国内导师/
Domestic supervisor

留学国别/
Hosting country

留学国外大学/
Hosting university

留学院系/Hosting faculty or department

国外导师/
Hosting supervisor

研究领域/
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 background：In 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, 0.045，respectively. And we also did 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 project：It 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 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：

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