分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2020-08-23
摘要： 实验测量表明体心立方固溶体 约在 2.0 at.% Mn发生相变，但这一相变的机制，相变前后铁锰体系的物理性质变化至今仍不清楚。本文通过密度泛函计算，揭示了这一相变是一种同构相变，并阐明了相变机制和相变前后物理性质的变化。
分类： 材料科学 >> 金属与冶金 提交时间： 2018-09-14
摘要： 理解合金元素如何调制金属材料的弹性模量在固体物理理论及金属材料的机械性能的工程设计领域都很重要。本文采用第一性原理方法计在合金原子浓度在 0.4 到 1.85 at% 范围内 12 种铁基固溶体的弹性模量并研究合金元素对 bcc 铁基体弹性模量的机制。
分类： 材料科学 >> 金属与冶金 提交时间： 2017-08-23
摘要： Nonuniform strain fields might induce the segregation of alloying solutes and ultimately lead to the mechanical performance degradation of body-centered-cubic (bcc) Fe based steels serving in extreme environments, which is worthy of investigation. In this paper, two typical volume conserving strains, shear strain (SS) and normal strain (NS), are proposed to investigate the strain effects on solute stabilities in bcc iron by first-principles calculations. For solutes in each transition metal group, the calculated substitution energy change due to SS exhibits a linear dependence on the valence d radius of the solutes, and the slope decreases in an exponential manner as a function of the absolute difference between the Watson’s electronegativity of iron and the averaged value of each transition metal group. This regularity is attributed to the Pauli repulsion between the solutes and the nearest neighboring Fe ions modulated by the hybridization of valence d bands and concluded to be originated from the characteristics of valence d bonding between the transition-metal solutes and Fe ions under SS. For main-group and post transition-metal solutes, the considerable drop of substitution energy change due to NS is concluded to be originated from the low-energy side shift of the widened valence s and p bands of the solutes. Our results indicate that the stabilities of substitutional solutes in iron under volume-conserving strain directly correlate with the intrinsic properties of the alloying elements, such as the valence d radius and occupancy, having or not having valence s and p bands.
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