Fe-Mn-Al-C κ型碳化物中无序和非化学计量的从头算解释
Ab initio explanation of disorder and off-stoichiometry in Fe-Mn-Al-C kappa carbides
摘要：
碳化物在许多材料的强度和延展性中起着核心作用。模拟这些沉淀物对机械性能的影响需要了解它们的原子构型。特别地，经常观察到C含量基本上偏离理想的化学计量组成。在目前的工作中，我们专注于Fe-Mn-Al-C钢，为此，我们确定了纳米级卡帕碳化物（Fe，Mn）3AlC的原子探针层析成像（APT）的组成相比，位于晶界的较大的沉淀物。结合密度泛函理论和热力学概念，我们首先确定了这些碳化物中存在化学和磁性无序的临界温度。其次，实验观察到的C含量的减少被解释为分配过程中的化学能的增益和出现在连贯的微观结构中的弹性应变之间的折衷。
英文摘要：
Carbides play a central role for the strength and ductility in many materials. Simulating the impact of these precipitates on the mechanical performance requires the knowledge about their atomic configuration. In particular, the C content is often observed to substantially deviate from the ideal stoichiometric composition. In the present work, we focus on Fe-Mn-Al-C steels, for which we determined the composition of the nano-sized kappa carbides (Fe,Mn)3AlC by atom probe tomography (APT) in comparison to larger precipitates located in grain boundaries. Combining density functional theory with thermodynamic concepts, we first determine the critical temperatures for the presence of chemical and magentic disorder in these carbides. Secondly, the experimentally observed reduction of the C content is explained as a compromise between the gain in chemical energy during partitioning and the elastic strains emerging in coherent microstructures.
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