TiN晶体尺寸与其力学性能的第一性原理研究

Grain Size Effect on the Mechanical Properties of TiN:First-Principle Studies

纳米多晶体材料因其独特的力学性能而成为当前材料科学领域的研究热点之一,尤其是晶粒尺寸对其力学性能的影响倍受关注。本文采用基于密度泛函理论的第一性原理方法,模拟计算了晶粒尺寸为0.6387—2.332nm的TiN的力学性能,得到应力应变关系及屈服强度。计算结果表明,随着晶粒尺寸的增加,TiN的屈服强度降低,晶粒呈现软化趋势。通过对应力-应变曲线分析可知:TiN在应变5%处开始屈服,其屈服强度大约为21.5GPa;抗拉强度发生在应变约为15%时,且随着晶粒尺寸的增加,抗拉强度降低。本文对照了屈服极限的计算值和有限元方法的拟合值,讨论了实验中TiN表面的微观结构与硬度、弹性模量的关系。研究表明,TiN试样中的缺陷对其硬度和强度有很大影响。

Nanoscale polycrystalline materials with unique mechanical properties become now a hot issue in the field of materials science. One of the research focuses is the grain size effect on the material mechanical properties. In this paper, the grain size effect of TiN nanocrystals is studied with the first principle method based on the density functional theory. The total energies of a series of TiN crystals with different grain sizes ranging from 0.6387nm to 2.332nm are calculated by means of the first principle method to reveal their mechanical properties in the case of simple tension. The calculation results include the strain-stress relationships and the related yield strength. The strain-stress curves show that the yield strength of TiN crystal decreases with the increase of the grain size. That means that the TiN crystal trends to softening as the result of the increase of the grain size. The stress-strain curve indicates also that TiN crystal begins to yield at the tensile strain of 5%, and the yield strength is about 21.5GPa. The TiN crystal has the highest tensile strength at approximately 15% of the tensile strain. As the grain size increases, the tensile strength of TiN decreases. The correlation between the microstructure of TiN and their hardness and elastic properties is discussed, which indicates that besides the grain size effect, the defects in the TiN film is a crucial factor that affects their hardness and strength.