Heterogeneous Nucleation and Microstructure Formation: From a Model Systems to Applied Metal Physics
Heterogeneous Nucleation and Microstructure Formation: From a Model Systems to Applied Metal Physics
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异质成核和微观结构形成：从模型系统到应用金属物理学
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发表时间：
2014
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通讯作者：
H. Emmerich
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作者：
H. Emmerich
金属合金的大多数物理和化学性能在很大程度上取决于其微观组织形态。一个例子是铁素体钢和奥氏体钢的晶体结构，其中所需的机械、电和磁性能与钢的同样所需的特定微观结构密切相关。由于许多当今工业相关的金属合金系统是从熔融状态加工的，因此对作为基本的主要加工步骤的固化的最定量的理解是对这种期望的微结构进行最定量的定制的前提。尽管如此，作为初始凝固步骤的异质形核和连续的微观结构形成仍然远未被全面理解。然而，现有的先进模型和最近的实验结果的比较带来了有争议的结论。为了推进这些科学讨论，从2007年到2013年，德国研究基金会（DFG）资助了与异质成核和初始微观结构形成相关的科学优先计划1296，旨在从根本上理解异质成核的基本机制以及随后核发展为特定的异质微观结构。为此，开发了一种跨越系统和方法的科学方法，其中以比较的方式研究了最简单类型的模型系统，用于异质晶体顺序，纯金属，二元金属合金和胶体。此外，还使用从原子到微观尺度的补充实验和模拟技术对它们进行了评估，以获得所有相关时间和长度尺度的全面视图，如图1所示。在优先计划的背景下详细探讨的一些问题如下：关于异质成核，临界成核晶粒是什么样子的？接触角的经典概念对异质成核有意义吗？关于异质成核的成核势垒的主要贡献的声明，例如它们可以从分子模拟中获得，可以与通过相场方法获得的数据相一致吗？关于从晶核到显微组织的转变，根据相图中的精确参考点，在结晶和偏析之间的相互作用中，显微组织如何从晶核发展？相对于该参考点的变化，这些情景的稳定性如何？关于微观结构的发展，什么样的结果来自于对微观结构初始发展的成核的新理解，例如，新的动力学比例定律凝固组织的初始生长遵循什么样的动力学规律？参考文献5最近概述了该优先计划的最重要成果。在JOM的这一部分中，我们更进一步，介绍了优先计划中获得的一些更实用的最新成果，这些成果建立了从模型系统的基础研究到工业上更相关的多组分和多相金属系统的桥梁。在这里讨论的与这种系统中的非均质成核和初始微观结构形成相关的更应用的具体问题的范围从识别接种工艺参数对可实现的晶粒细化量的定量影响，到对四相包晶反应中的动力学的综合评估，指出不同类型的包晶的差异，基于新建立的模拟方法，定量评估固-固体系中的成核能。Heike Emmerich是TMS材料加工与制造部门相变委员会的客座编辑，也是本期异质成核和初始微观结构形成主题的协调员。JOM，2014年第66卷第8期
Most physical and chemical properties of metallic alloys are determined to a large degree via their microstructure morphology. One example is the crystal structure of a ferritic and an austinitic steel, respectively, in which the desired mechanical, electrical, and magnetic properties are strongly tied to a likewise desired specific microstructure of the steel. As many of today’s industrial relevant metallic alloy systems are processed from the molten state, a most quantitative understanding of solidification as an essential primary processing step is a premise for a most quantitative tailoring of such desired microstructures. Nonetheless, heterogeneous nucleation and successive microstructure formation as initial solidification steps are still far from being comprehensively understood. However, the comparison of available advanced models and recent experimental results brings about controversial conclusions. To progress these scientific discussions, from 2007 to 2013, the German Research Foundation (DFG) funded the scientific priority program 1296 related to the heterogeneous nucleation and initial microstructure formation, aiming at a fundamental understanding of the basic mechanisms underlying heterogeneous nucleation as well as the subsequent development of the nucleus into a specific heterogeneous microstructure. To that end, a systemand method-spanning scientific approach was developed, in which the simplest types of model systems for heterogeneous crystalline orders, pure metals, binary metal alloys, and colloids were investigated in a comparative manner. Moreover, they were assessed with complementary experimental as well as simulation techniques from the atomic to the microscale to obtain a comprehensive view across all relevant time and length scales, as depicted in Fig. 1. Some questions explored in detail in the context of the priority program were as follows: With respect to heterogeneous nucleation, what does a critical nucleation grain look like? Does the classic concept of a contact angle make sense for heterogeneous nucleation? Can claims made about the dominant contributions to the nucleation barrier for heterogeneous nucleation, such as they can be obtained from molecular simulations, be reconciled with data gained via the phase-field method? With respect to transition from nucleus to microstructure, how does a microstructure develop from a nucleus in the interplay between crystallization and segregation depending on the precise reference point in the phase diagram? How stable are those scenarios with respect to changes of that reference point? With respect to microstructure development, what kind of consequence results from the new understanding of nucleation for the initial development of the microstructure, e.g., in terms of new kinetic scaling laws? What kind of kinetic rules does the initial growth of the solidifying microstructure follow? An overview of the most important results of that priority program has recently been presented in Ref. 5. In this section of JOM we go a step further and present some of the more applied recent results acquired in the priority program, which build the bridge from fundamental investigations in model systems toward industrially more relevant multicomponent and multiphase metallic systems. The more applied specific questions related to heterogeneous nucleation and initial microstructure formation in such systems addressed here range from the identification of the quantitative influence of inoculation process parameters on the amount of achievable grain refinement, over a comprehensive assessment of the kinetics in four-phase peritectic reactions, pointing out differences in different types of peritectica, to a quantitative assessment of nucleation energies in solid–solid systems based on newly established simulation methodologies. In toHeike Emmerich is the guest editor for the Phase Transformations Committee of the TMS Materials Processing & Manufacturing Division, and coordinator of the topic Heterogeneous Nucleation and Initial Microstructural Formation in this issue. JOM, Vol. 66, No. 8, 2014