Grain coarsening inhibition in hard metals is regarded as controlled by formation of interface complexions. To date, however, direct experimental insights into the presence and evolution of interface complexions during sintering of hard metals have been lacking. We here present in-situ small-angle neutron scattering (SANS) experiments up to 1500 °C and provide first-hand evidence on the thickness and volume fraction evolution of (V,W)Cx interface complexions in V-doped hard metals at various sintering temperatures. The experimental data is complemented by simulations using a thermodynamic-based model to understand the mechanisms behind the nanostructure evolution. We show that there indeed exist (V,W)Cx interface complexions at liquid-phase sintering temperatures; and their thickness and volume fraction are strongly related to the presence of bulk (V,W)Cx precipitation, the V activity in the Co-rich binder phase, and the temperature. The thermodynamics-based model, including the geometry of the investigated material system, reveals that the formation of (V,W)Cx bulk precipitates is energetically favorable over the thickening of complexions in the stability range of bulk precipitation. This, explains the reduction in complexion volume fraction and thickness with increasing temperature up to the dissolution of bulk precipitates. Upon dissolution of bulk precipitates, enhanced interfacial layer formation occurs through the formation of new layers of lower thickness, leading to better coverage of WC grains. The provided understanding of the nanostructure evolution during sintering is expected to foster the further development of representative modelling tools.

中文翻译：

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通过原位小角中子散射和基于热力学的建模了解 V 掺杂硬质金属中竞争性纳米结构的演变


硬质金属中的晶粒粗化抑制被认为是通过界面络合的形成来控制的。然而，迄今为止，一直缺乏对硬质金属烧结过程中界面络合物的存在和演变的直接实验见解。我们在这里展示了高达 1500 °C 的原位小角中子散射 （SANS） 实验，并提供了各种烧结温度下 V 掺杂硬质金属中 （V，W）Cx 界面复合物的厚度和体积分数演变的第一手证据。实验数据由使用基于热力学的模型的模拟补充，以了解纳米结构演变背后的机制。我们表明，在液相烧结温度下确实存在 （V，W）Cx 界面络合物;它们的厚度和体积分数与大量 （V，W）Cx 沉淀的存在、富钴粘合剂相中的 V 活性和温度密切相关。基于热力学的模型，包括所研究的材料系统的几何形状，揭示了 （V，W）Cx 块沉淀物的形成在能量上优于本体沉淀稳定范围内的复合物增稠。这解释了随着温度的升高，肤色体积分数和厚度的减少，直到散装沉淀物溶解。在散装沉淀物溶解后，通过形成较低厚度的新层来增强界面层的形成，从而更好地覆盖 WC 颗粒。对烧结过程中纳米结构演变的理解有望促进代表性建模工具的进一步发展。