Atomic scale redistribution of carbon during the transformation from austenite to martensite in steels

钢中从奥氏体到马氏体转变过程中碳的原子尺度重新分布

• 批准号: 406912286
• 负责人: Dr. Tilmann Hickel
• 金额: --
• 依托单位: Groupe de Physique des Matériaux (GPM) (UMR 6634)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/406912286?language=en
• 关键词: Atomic; scale; redistribution; carbon; during

Martensitic steels are of high applicational relevance due to their extraordinary strength and the adjustability of their strength, toughness and formability over a wide range by simple technological treatments. The bulk properties of martensitic steels are sensitively depending on the volume fraction, morphology, composition and intrinsic properties of the martensitic phase. These are determined by the local structural processes during the austenite-to-martensite transformation as well as the post-processing of the martensite. In this context, the non-equilibrium distribution of C atoms in the martensitic phase of steels plays a critical role. C atoms are super-saturated in freshly formed martensite and their concentration and distribution is decisive for the strength and toughness of the martensite. The distribution (and potential ordering) of carbon atoms happens at the transformation front, the austenite-martensite interface. These processes, and in particular the underlying kinetics of the C diffusion and the interface mobility are not yet understood in detail down to the atomic scale, although of high relevance for the design of martensitic steels with tailored mechanical properties. Both, theoretical and experimental investigations are so far restricted to either idealized material systems or limited resolution of joint structural and chemical data. Within the proposed project we aim to unravel these open questions by combining high resolution theoretical and experimental investigations in a complementary approach for Fe-TM-C steels. One major focus is on the role of the martensite-austenite interface on the C distribution and redistribution during the martensitic transformation. This includes the consideration and analysis of not only the local atomic interface structures, but also possibly formed interfacial states, medium range structural modulations and the tetragonal deformation of the martensite (Zener ordering). As competing mechanisms to the interface-dominated structural and chemical distribution of C in the martensite, the order-disorder transition of C atoms, the formation of carbides or other highly ordered C arrangements at the interface or in the bulk, and the formation of reverted austenite will be considered. To this end we will apply ab initio thermodynamics and kinetics based on density functional theory (DFT) including all finite temperature contributions, atomic density field (ADF) theory and the quasiparticle approach (QA) accomplished by mean-field approaches on the theoretical side. On the experimental side, atom probe tomography (APT) and (high resolution) transmission electron microscopy (TEM) will be used to combine structural and chemical data. Eventually, correlative TEM-APT analyses to achieve fully correlative data on the local structure and chemistry will be applied for selected key samples.

马氏体钢由于其非凡的强度以及通过简单的工艺处理在宽范围内可调节其强度、韧性和可成形性而具有高度的应用相关性。马氏体钢的整体性能敏感地取决于马氏体相的体积分数、形态、组成和本征性质。这些都是由当地的结构过程中的贝氏体到马氏体的转变，以及后处理的马氏体。在这种情况下，钢的马氏体相中C原子的非平衡分布起着关键作用。C原子在新形成的马氏体中是过饱和的，并且它们的浓度和分布对马氏体的强度和韧性是决定性的。碳原子的分布（和潜在的有序化）发生在转变前沿，马氏体-马氏体界面。这些过程，特别是潜在的动力学的C扩散和界面的流动性还没有详细了解到原子尺度，虽然与定制的机械性能的马氏体钢的设计高度相关。迄今为止，理论和实验研究都局限于理想化的材料系统或有限的联合结构和化学数据的分辨率。在拟议的项目中，我们的目标是通过结合高分辨率的理论和实验研究，在Fe-TM-C钢的互补方法来解开这些悬而未决的问题。一个主要的焦点是在马氏体相变过程中的C分布和再分布的马氏体-奥氏体界面的作用。这不仅包括考虑和分析局部原子界面结构，还包括可能形成的界面态、中程结构调制和马氏体的四方形变（齐纳有序）。作为竞争机制的界面占主导地位的结构和化学分布的C在马氏体中，C原子的有序-无序转变，碳化物或其他高度有序的C安排在界面处或在散装的形成，和形成的逆转奥氏体将被考虑。为此，我们将应用从头算热力学和动力学的基础上密度泛函理论（DFT），包括所有有限温度的贡献，原子密度场（ADF）理论和准粒子方法（QA）完成的平均场方法在理论方面。在实验方面，将使用原子探针层析成像（APT）和（高分辨率）透射电子显微镜（TEM）来联合收割机结合结构和化学数据。最后，相关的TEM-APT分析，以实现充分相关的数据，当地的结构和化学将适用于选定的关键样品。