Entropy: A controversy between experiment and calculations in grain boundary segregation

IF 33.6 1区材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY

Progress in Materials Science Pub Date : 2025-01-17 DOI:10.1016/j.pmatsci.2025.101431

Pavel Lejček, Mojmír Šob

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Abstract

Grain boundary segregation is one of the crucial phenomena affecting the properties of the materials and their technological applications. However, 50 years since starting its intensive study, there still remain open questions and controversies related to this phenomenon. Probably, the most serious uncertainty consists in understanding the segregation entropy. While this term seems to result directly from experimental studies of temperature dependence of chemical composition of grain boundaries, it is mostly neglected in theoretical calculations. This negligence arises from the fact that most of the first-principles calculations are performed at the temperature of 0 K and, therefore, the segregation entropy is usually not evaluated. Consequently, it is supposed that its contribution at enhanced temperatures is negligible which is supported by scarce calculations of the vibrational entropy of grain boundary segregation. Another question discussed presently between theoreticians on one hand and experimenters on the other hand deals with physical meaning of the values of the thermodynamic quantities determined from the average grain boundary concentration.This paper summarizes the present knowledge on the segregation entropy in metallic hosts and documents some issues in which the segregation entropy plays important and irreplaceable role. These issues are represented by the enthalpy–entropy compensation effect, by the method of prediction of grain boundary segregation and by comparison of calculated results and experimental or predicted data. The role of the entropy is also crucial in the recently discussed cases of the entropy-dominated and entropy-driven grain boundary segregation. Finally, collective processes related to grain boundaries – grain boundary migration and intergranular fracture – are discussed suggesting that these processes, based on coordinated behavior of numerous neighbor atoms in the grain boundary core, will be better characterized by average values of characteristic quantities rather than by the values of these quantities for individual sites.

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熵：晶界偏析的实验与计算之争

晶界偏析是影响材料性能和工艺应用的重要现象之一。然而，在对这一现象进行深入研究50 年后，仍然存在着一些悬而未决的问题和争议。也许，最严重的不确定性在于对隔离熵的理解。虽然这一术语似乎是直接从晶界化学成分温度依赖性的实验研究中得出的，但它在理论计算中大多被忽视。这种疏忽是由于大多数第一性原理计算是在0 K的温度下进行的，因此，通常不计算偏析熵。因此，假定它在提高温度下的贡献可以忽略不计，这是由晶界偏析的振动熵的稀缺计算支持的。目前理论家和实验人员讨论的另一个问题是由平均晶界浓度确定的热力学量的物理意义。本文综述了金属基体中偏析熵的现有知识，并列举了偏析熵在金属基体中发挥不可替代的重要作用的一些问题。这些问题由焓熵补偿效应、晶界偏析预测方法以及计算结果与实验或预测数据的比较来表示。熵的作用在最近讨论的熵主导和熵驱动的晶界偏析中也是至关重要的。最后，讨论了与晶界相关的集体过程-晶界迁移和晶间断裂-表明这些过程基于晶界核心中众多相邻原子的协调行为，将更好地表征特征量的平均值，而不是单个位点的这些量的值。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Progress in Materials Science 工程技术-材料科学：综合

CiteScore

59.60

自引率

0.80%

发文量

101

审稿时长

11.4 months

期刊介绍： Progress in Materials Science is a journal that publishes authoritative and critical reviews of recent advances in the science of materials. The focus of the journal is on the fundamental aspects of materials science, particularly those concerning microstructure and nanostructure and their relationship to properties. Emphasis is also placed on the thermodynamics, kinetics, mechanisms, and modeling of processes within materials, as well as the understanding of material properties in engineering and other applications. The journal welcomes reviews from authors who are active leaders in the field of materials science and have a strong scientific track record. Materials of interest include metallic, ceramic, polymeric, biological, medical, and composite materials in all forms. Manuscripts submitted to Progress in Materials Science are generally longer than those found in other research journals. While the focus is on invited reviews, interested authors may submit a proposal for consideration. Non-invited manuscripts are required to be preceded by the submission of a proposal. Authors publishing in Progress in Materials Science have the option to publish their research via subscription or open access. Open access publication requires the author or research funder to meet a publication fee (APC). Abstracting and indexing services for Progress in Materials Science include Current Contents, Science Citation Index Expanded, Materials Science Citation Index, Chemical Abstracts, Engineering Index, INSPEC, and Scopus.