【作者】 高丽洁；

【导师】 周惦武；

【作者基本信息】 湖南大学 ， 机械制造及其自动化， 2010， 硕士

【摘要】 TiAl合金由于具有密度小,高温性能好等诸多优点,在航天、航空等行业深受青睐,然而力学性质尤其脆性大限制了其广泛应用。为致力将TiAl合金发展成实际应用的航空、航天材料,目前国内外科研工作者在采用合金化及热加工等手段来改善其脆性等方面开展了大量工作,本论文选取TiAl合金作为研究对象,依托改善TiAl合金力学性质的部分实验结果为背景,建立合金形成热、弹性常数等微观物理量与合金体系相结构稳定性、力学性质等宏观性能的对应关系,通过第一性原理的计算方法获得TiAl合金的微观物理特征量及各种电子结构信息,在研究TiAl合金基本物理性质的基础上,以Zn、Co、Fe、Sc、Nb、V、Cu、Cr原子置换TiAl中的Al来考查合金化效应对体系结构稳定性与力学性质的影响,基于电子机制的分析,探讨合金化提高TiAl体系力学性质的理论机制。计算了富Al和富Ti两种TiAl合金体系的平衡晶格常数、合金形成热、态密度和能带,发现平衡晶格常数计算值与实验值和他人计算值基本吻合；富Al的TiAl合金的结构稳定性优于富Ti的TiAl合金；富Al的TiAl合金的结构稳定性优于富Ti的TiAl合金的主要原因在于富Al的TiAl合金在费米能级上的成键电子数少于富Ti的TiAl合金。计算了Zn、Co、Fe、Sc、Nb、V、Cu、Cr合金化富Al的TiAl合金体系的合金形成热与态密度,发现合金化原子置换TiAl中的Al后,体系的合金形成热均为负值,合金化后TiAl体系均能形成稳定结构；合金化原子占据TiAl中的Al原子的能力由强到弱的次序依次是Zn、Co、Fe、Sc、Nb、V、Cu、Cr;合金化后结构的稳定性由好到差依次是Zn、Co、Fe、Sc、Nb、V、Cu、Cr;合金化后结构稳定性的强弱主要取决于费米能级附近电子杂化成键作用的强弱。计算了Zn、Co、Fe、Sc、Nb、V、Cu、Cr合金化富Al的TiAl合金体系的弹性常数、杨氏模量E、剪切模量G、体模量B、泊松比v和电子密度,发现合金化后使TiAl合金的硬度降低,硬度高低次序为：V-TiAl>Nb-TiAl> Cr-TiAl> Sc-TiAl>Co-TiAl> Zn-TiAl>TiAl>Fe-TiAl>Cu-TiAl;以G/B衡量,合金化体系延性逐渐变差顺序为：Fe-TiAl> Cr-TiAl> Co-TiAl> TiAl>V-TiAl> Nb-TiAl >Cu-TiAl> Zn-TiAl> Sc-TiAl;以C12-C44衡量,合金化体系延性逐渐变差顺序为：Fe-TiAl> Cr-TiAl> Co-TiAl> Cu-TiAl>V-TiAl> Nb-TiAl>Zn-TiAl> Sc-TiAl> TiAl; Fe、Cr、Co合金化均能都提高TiAl合金的延性；合金化后TiAl合金的原子平均价键强度由大到小的次序为：Fe-TiAl>Cr-TiAl>Co-TiAl> V-TiAl> TiAl>Nb-TiAl>Zn-TiAl>Cu-TiAl>Sc-TiAl;电子密度的分析结果较好解释了Fe、Cr.Co合金化后能提高TiAl的延性的原因。更多还原

【Abstract】 TiAl alloy has been wildly used in aeronautics,astronautics and many other industries due to the advantages of low density and good high temperature performance,However, its further applications has been limited by some mechanical properties,especially brittleness.At present,the researchers of domestic and foreign have done many works to improve the brittleness by alloying,hot-working and other means in order to develop the TiAl alloy to aeronautics and astronautics materials in the practical application.This thesis take the TiAl alloying as the research object,improve the properties based on some results of experiments,establish the corresponding relationships between the micro-physical of alloy heat of formation and elastic constant and macro-properties of phase structure stability and the mechanical propertie,investigate the alloying effects to the influence of the stability of architecture and mechanical properties by putting Zn,Co,Fe,Sc,Nb,V,Cu,the Cr atom into the TiAl to replace the Al atoms,which based on the basic physical properties of TiAl alloys(micro-physical characteristics and electronic structure information)by the calculations of first principle,and probe the alloying theory mechanism of improving the mechanical properties of TiAl from the analysis of electronic mechanisms.The calculate results of the lattice constant,heat of formation,electronic density of state and energy band of Al-rich and TiAl-rich are fairly good agreement between theoretied and experimental results showed by the previous researches,and the structure of Ti-Al of Al-rich is more stable than Ti-rich,mainly because the number of the bonding electrons is less in fermi level.According to the results of the heat of formation and density of state by replacing the Zn,Co,Fe,Sc,Nb,V,Cu,Cr into the Al,the TiAl alloying system is a stable structure due to the heat of formation is negative,the descending order of capability of the above atoms to replace Al is Zn,Co,Fe,Sc,Nb,V,Cu,Cr,and the structural stability of alloy from good to bad followed by Zn,Co,Fe,Sc,Nb,V,Cu,Cr,which depends on the bonding strength near the fermi level.According to the results of Eonstants modulus (E),Young’s modulus(Y),Shear modulus(G),Bulk modulus(B),Poisson’s ratio and the velectron density of the above alloy-system.We learn that alloying can reduce the hardness of TiAl alloy,the descending order of hardness is V-TiAl> Nb-TiAl> Cr-TiAl> Sc-TiAl> Co-TiAl> Zn-TiAl> TiAl> Fe-TiAl> Cu-TiAl,the ductility of alloyed system gradually deteriorated in the order of Fe-TiAl> Cr-TiAl> Co-TiAl> TiAl> V-TiAl> Nb-TiAl > Cu-TiAl> Zn-TiAl> Sc-TiAl measured by G/E and Fe-TiAl> Cr-TiAl> Co-TiAl> TiAl> V-TiAl> Nb-TiAl> Cu-TiAl> Zn-TiAl> Sc-TiAl measured by C12-C44,the descending order of average bond strength is Fe-TiAl> Cr-TiAl> Co-TiAl> V-TiAl> TiAl> Nb-TiAl> Zn-TiAl> Cu-TiAl> Sc-TiAl and the alloying of Fe,Cr,Co can improve the ductility form the results of the electron density.更多还原