Calculation Of Mechanical Properties And Theory Mechanisms Of TiAl Intermetallic Compounds

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.