Si在TiAl_3中取代行为的第一性原理研究

First principles study on substitution behaviour of Si in TiAl_3

采用基于密度泛函理论的第一性原理方法,研究了Si原子在TiAl3中的格点取代行为.通过对不同原子被置换后的c/a值、形成能以及电子态密度的计算和比较,发现Si原子倾向于取代TiAl3中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Si原子的取代行为,对Si原子占据的格点以松散或紧凑分布下体系的总能、形成能以及电子态密度进行了计算,结果表明Si原子倾向于取代TiAl3中松散分布的Al(2)原子.对c/a值的计算表明,随Al(2)格点Si原子浓度的增加,c/a值逐渐增大;而当Si取代Al(1)格点时,c/a值随Si原子浓度的增加而减小.研究表明,Si在TiAl3中的极限固溶度介于12.5at%—18.75at%之间.

The site preference of Si in TiAl3 is calculated by using a first principles method based on density functional theory. The analyses of the c/a value, the formation energy and density of states of systems with different substitution behaviours show that Si prefers to occupy the AI site. The site preference is primarily determined by the electronic structure, and the calculated result is in good agreement with the experimental result. In order to further study the site preference, the occupied sites are divided into two different distributions, the loose distribution and the compact distribution. The calculations of total energy, the formation energy and density of states of systems indicate that Si has a preference for Al（2） sites with a loose distribution. When the systems with Al（2） sites are substituted, the value of c/a increases with doped Si concentration increasing, which is opposite to the case where Al（ 1 ） sites are substituted. The study also indicates that the limited solubility of Si in TiAl3 lies between 12.5at% and 18.75at%.