采用Wagner-Schottky点缺陷热力学模型和第一性原理平面波赝势方法,计算研究了D019-Ti3Al金属间化合物中空位和反位2种类型点缺陷的形成焓、平衡浓度及相互作用.结果表明,这些缺陷的平衡浓度均随温度升高而增大,反位缺陷浓度均高于空位缺陷,Ti原子空位的浓度高于Al原子空位.在理想化学计量比成分下,Ti原子反位与Al原子反位缺陷浓度基本相当;在略偏离计量比的富Ti成分端,Ti原子的反位缺陷浓度高于Al原子;在富Al成分端则情形相反.计算结果表明,3种点缺陷对(AlTi-TiAl、TiAl-TiAl、VAl-AlTi)在基体中具有较强的聚集趋势,而其它类型的点缺陷对则有向基体扩散的趋势.
The intermetallics D019-Ti3Al has low specific density and high thermal resistance for both bulk and coating applications in engineering area.The point defects such as thermal vacancy,compostion vacancy and antisite defect have great influence on the properties of D019-Ti3Al,but are usally neglected.According to available research data from both theory and experiment,it is commonly considered that the thermal vacancies in D019-Ti3Al provide paths for atomic migration and diffusion,the antisite defects play an important role in the disordering of D019-Ti3Al,and the interaction between composition vacancy and antisite defect may have important influence on atomic diffusion and dislocation movement.So it is necessary to explore the mechanism of interaction between composition vacancy and antisite defect for more accurate understanding of the atomic diffusion,dislocation movement and plastic deform in D019-Ti3Al.In this work,the formation enthalpy,equilibrium concentration,and binding energy of composition vacancyand antisite defect in D019-Ti3Al intermetallics were calculated by using both the Wagner-Schottky model of point defect thermodynamics and the plane wave pseudopotential method in first-principles.Results suggest that,in the whole composition range of interest,the point defect concentrations increase with the increase of temperature.In particular,the concentrations of antisite defects are higher than those of vacancies,and the vacancy concentration of Ti is higher than that of Al.At the stoichiometric composition,the concentrations of antisite defects of Ti and Al are very close.At the Ti-rich side of component,the antisite defect of Ti dominates in concentration,while at the Al-rich side,that of Al dominates in concentration.For the calculated results of 3 types of point defect pairs,AlTi-TiAl,TiAl-TiAl and VAl-AlTi,they may have the strong trend to aggregate,while others may show the tend to diffuse into the matrix.
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