Mg-Al-Y合金中Al-Y金属间化合物的相稳定性、弹性和热力学性质的第一原理计算

来源期刊:中国有色金属学报2015年第12期

论文作者:陈红蕾 林立 毛萍莉 刘正

文章页码:3319 - 3327

关键词:Mg-Al-Y合金;第一原理计算;相稳定性;电子结构;弹性;热力学性质

Key words:Mg-Al-Y alloy; first principles calculation; phase stability; electronic structure; elastic property; thermodynamic property

摘    要:通过基于密度泛函理论的第一原理计算方法,对Mg-Al-Y合金中的主要强化相,即Al2Y和Al3Y的相稳定性、电子结构、弹性性质以及热力学性质进行计算。相生成热的计算结果表明:Al2Y和Al3Y均可稳定存在,Al2Y的结构稳定性更强,因此,在合金的凝固过程中,Al2Y优先析出。Al2Y和Al3Y的电子态密度(DOS)和差分电荷密度计算的结果表明:Al2Y和Al3Y两相可以稳定存在的内在本质在于Al原子与Y原子的价电子轨道发生强烈的相互作用,形成了spd杂化。两相内的原子成键均为共价键、离子键和金属键。体模量B、剪切模量G、弹性模量E、泊松比ν和各向异性因子A等力学性质参数的计算结果表明:这两种相为强硬的脆性相并都为各向同性,因此,具有相似的强化效果。两相熔点较高表明其具有很好的热稳定性,能够提高合金的高温性能。声子谱和声子态密度计算以及德拜温度的计算结果进一步验证了两相具有结构稳定性较高。两相的热力学性质符合一般热力学规律,其中自由能的计算结果表明:两相的稳定性顺序没有发生变化。随着温度的升高,Al2Y的结构稳定性仍强于Al3Y的。

Abstract: Phase stability, electronic structure, elastic and thermodynamic properties of Al2Y and Al3Y phases were investigated by means of first–principles calculations based on density functional theory (DFT). The results of formation enthalpy show that both two phases can stay stably, and Al2Y is more stable than Al3Y. Therefore, Al2Y has the priority to precipitate in the process of alloy solidification. The calculated density of state (DOS) and the electron density difference indicate that the phase stability of Al2Y and Al3Y is due to the strong interaction between valence electron orbits of Al and Y atoms, forming the spd hybridization. The bonding characteristics of Al2Y and Al3Y phases are all covalent bond, ionic bond and metallic bond. The calculated results of bulk modulus (B), shear modulus (G), elastic modulus (E), Poisson’s ratio ( ) and anisotropic coefficient (A) show that Al2Y and Al3Y phases are strong, hard and isotropic. Their similar mechanical properties contribute to their similar performance in Mg-Al-Y alloy. The phonon spectrum, phonon density of states and Debye temperature show their good structural stability as before. High melting points of Al2Y and Al3Y show that their strong thermal stability can improve the mechanical properties of alloy at high temperature. The thermodynamic properties of the two phases conform to the general laws, and the calculated free energy shows that the stability sequence of the two phases has not changed. With the increase of temperature, the structure stability of Al2Y is still better than that of Al3Y.

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