First-principles modeling of complexions at the phase boundaries in Ti-doped WC-Co cemented carbides at finite temperatures,Physical Review Materials

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First-principles modeling of complexions at the phase boundaries in Ti-doped WC-Co cemented carbides at finite temperatures
Physical Review Materials ( IF 3.1 ) Pub Date : 2021-09-07 , DOI: 10.1103/physrevmaterials.5.093801
Erik Fransson ₁ , Martin Gren ₁ , Henrik Larsson ₂ , Göran Wahnström ₁

Affiliation

WC-Co cemented carbides have a unique combination of high hardness and good toughness, making them ideal as tool materials in applications such as metal machining or rock drilling. Dopants are commonly added to retard grain growth and thereby creating a harder material. Thin films with cubic structure have been observed experimentally at phase boundaries between hexagonal WC and fcc Co-rich binder when doping with, e.g., Ti, V, or Cr. These films are generally considered to play a crucial role in the grain growth inhibition effect. Therefore, the thermodynamics of these thin cubic films is important to understand. Here, we construct, using ab initio calculations and modeling, an interfacial phase diagram for thin cubic films in Ti-doped WC-Co. We consider

C \leftrightarrow vacancy

and

W \leftrightarrow Ti

substitutions by constructing alloy cluster expansions and use Monte Carlo simulations to calculate the configurational free energy. Furthermore, force-constant fitting is used to extract the harmonic free energy for the ground-state structures. Additionally, we use information from thermodynamic databases to couple our atomic-scale calculations to overall compositions of typical WC-Co materials. We predict that Ti segregates to WC/Co phase boundaries to form thin cubic films of two metallic layer thickness, both at solid-state and liquid-phase sintering temperatures. Furthermore, we predict that these films are stable also for low doping concentrations when no Ti-containing carbide phase precipitates in the material. We show that Ti essentially only segregates to the inner layer of the thin cubic film leaving an almost pure W layer towards Co, an ordering which has been observed in recent experimental high-resolution transmission electron microscopy studies.

中文翻译：

有限温度下 Ti 掺杂 WC-Co 硬质合金中相界络合的第一性原理建模

WC-Co 硬质合金具有高硬度和良好韧性的独特组合，使其成为金属加工或凿岩等应用中的理想工具材料。通常添加掺杂剂以阻止晶粒生长，从而产生更硬的材料。当掺杂有例如 Ti、V 或 Cr 时，已经在六方 WC 和 fcc 富钴粘合剂之间的相边界处通过实验观察到具有立方结构的薄膜。这些薄膜通常被认为在晶粒生长抑制作用中起关键作用。因此，了解这些薄立方薄膜的热力学很重要。在这里，我们使用ab initio计算和建模构建了 Ti 掺杂 WC-Co 中立方薄膜的界面相图。我们认为

C \leftrightarrow 空缺

和

宽 \leftrightarrow 钛

通过构建合金簇扩展并使用蒙特卡罗模拟来计算构型自由能。此外，力常数拟合用于提取基态结构的谐波自由能。此外，我们使用来自热力学数据库的信息将我们的原子尺度计算与典型 WC-Co 材料的整体成分相结合。我们预测，Ti 偏析到 WC/Co 相边界，在固态和液相烧结温度下形成两种金属层厚度的立方薄膜。此外，我们预测当材料中没有含钛碳化物相沉淀时，这些薄膜在低掺杂浓度下也是稳定的。我们表明 Ti 基本上只偏析到立方薄膜的内层，留下几乎纯 W 层朝向 Co，

更新日期：2021-09-08

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