WC-Co硬质合金晶粒生长抑制机理的球差校正电镜研究

WC-Co cemented carbide is the largest application area for tungsten. It is a hard material that is used extensively as cutting, machining, drilling, mining tools, as well as other industrial applications. Boosted by the rapid expansion of industry, China is the largest market for cemented carbides. However, the market share of deep-processing and high-end products is small. Understanding the role of additives played in grain growth inhibition is the key to high-end products. Two different grain growth inhibition mechanisms, namely, the decrease of W solubility in the binder and the interface poisoning on the WC/Co interface, have been the subject of debate for many years. There is also a long-standing dispute over the configuration of WC/Co phase boundaries with additives. Those debates cause confusion to the design of deep-processing products in industry. The current proposal aims to work close with the industry (Xiamen Tungsten Carbide (XTC) Cooperation) and focuses on the characterization of the microstructures of cemented carbides via advanced Cs-corrected scanning transmission electron microscopy (STEM). A comprehensive investigation on the WC/Co interface structures with different additives will be conducted, with a goal to setup a universal mechanism for additive segregation. Furthermore, quantitative studies will be conducted to clarify the role of ‘W solubility’ and ‘interface poisoning’during grain growth. Finally, the rules of grain growth inhibition will be applied to the design of high-end cemented carbides in industry.

硬质合金是金属钨的最大应用领域，作为“工业牙齿”被广泛用于国民经济重要领域。我国硬质合金行业呈现“大而不强”的特点，在高端产品上缺少话语权，无法充分发挥钨资源优势。调控硬质合金显微结构和性能的关键在于充分认识WC/Co相界面和晶粒生长抑制机理。然而，公开报道的相界构型不统一，晶粒生长机理也有“溶解度说”和“晶面吸附说”之争。本课题拟与国内硬质合金行业龙头企业-厦门钨业股份有限公司开展合作，通过系统的球差校正电镜表征，揭示添加剂在WC/Co相界偏聚的共性规律，建立添加剂界面偏聚的统一物理机制；定量考察“晶面吸附”和“溶解度”对晶粒生长的影响，解决学界争议；总结添加剂类别和浓度对晶粒生长的影响规律，指导行业高端研发。

WC-Co硬质合金被广泛应用于金属切削和岩石钻探等领域。WC-Co硬质合金主要由提供硬度的WC陶瓷相和提供韧性的Co相组成，该体系中存在大量界面，包括相界面和晶界；界面的结构和成分深刻影响了硬质合金的显微结构发育和力学性能。本项目借助于先进的球差校正电镜技术和自主开发的晶体学表征平台，在WC-Co硬质合金体系中，开展了不同掺杂剂的界面相稳定机制及晶粒生长抑制机理探究。本项目所取得的主要成果及科学意义为：1）揭示了V、Cr和Ti掺杂的WC-Co相界面通过各向异性的三层超结构实现界面电子结构过渡的普适规律，为硬质合金材料的界面调控奠定了坚实的理论基础；2）对比V、Cr掺杂的WC-Co界面微观结构，总结添加剂种类和掺杂浓度对WC晶粒生长抑制的影响，为“晶面吸附”机制在WC晶粒生长抑制中发挥的主导作用提供了直接的证据，指导工业界选择晶粒生长抑制剂种类和掺杂浓度，对调控硬质合金的机械性能具有重大指导意义；3）将自主开发的晶体学表征平台扩展到其他研究领域，指导了其他功能和结构材料的界面结构优化和性能调控。