WC-(Cr,Nb,Ti)(C,N)-Co梯度硬质合金烧结过程中微结构演变的定量描述

Due to the excellent mechanical properties, cemented carbides have been widely used in applications such as cutting, drilling and so on. Their manufacture processes involve complex thermodynamics and kinetics and are controlled by various technical parameters (sintering temperature, sintering time, partial pressure of N2 and so on). In order to develop high-performance cemented carbides, it is critical to understand the influence of alloy composition and process parameters on the gradient zone formation during sintering. Using the W-C-Co-Cr-Nb-Ti-N multicomponent system as a target system, this project is devoted to 1) develop the thermodynamic and diffusivity databases through a combination of CALPHAD approach, first-principles calculations and experiments, 2) design micro-structural experiments with the aid of CALPHAD-type simulation to study the formation mechanism of fcc cubic "core-rim" structure and the formation of gradient zone during sintering, and 3) simulate the microstructure evolution during sintering with the variation of alloy composition and process parameters, using phase field technique based on thermodymic,diffusivity databases and interfacial energy information. The simulation results will be compared with experiments. The completion of this project is expected to quantitatively describe the microstructure evolution during sintering for multicomponent cemented carbides for the first time, provide a scientific method for the microstructure simulation of other cemented carbides, and lay a basis of theoretical importance for the design of new type of cemented carbide with independent intellectual property rights.

硬质合金因其优良的力学性能广泛用作刀具、钻具等，其制备涉及复杂的热力学和动力学现象，并受众多工艺参数（烧结温度、时间及气氛等）的影响。掌握梯度硬质合金烧结过程中合金成分和工艺参数对梯度层微结构演变的影响是研发高性能硬质合金的关键。本项目拟以W-C-Co-Cr-Nb-Ti-N为研究对象，开展以下工作：1）综合实验、第一性原理和相图计算建立梯度硬质合金热力学和扩散动力学数据库；2）基于数据库模拟进行微结构表征实验，分析烧结过程中面心立方相"芯-壳"结构形成机理及梯度层微结构演变；3）集成热、动力学及界面能信息，用相场方法定量模拟合金成分和工艺参数变化下梯度硬质合金烧结过程中的微结构演变，并辅以实验来细化模拟结果。项目的完成将首次实现多元梯度硬质合金烧结过程中微结构演变的定量描述，为其它硬质合金微结构的模拟提供一种可借鉴的科学方法，并为设计具有自主知识产权的新型硬质合金奠定重要的的理论基础。

硬质合金因其优越的力学性能广泛用作刀具、钻具等，其制备涉及复杂的热力学和动力学现象，并受众多工艺参数的影响。掌握硬质合金烧结过程中合金成分和工艺参数对梯度层微结构演变的影响是研发高性能硬质合金的关键。项目以W-C-Co-Cr-Nb-Ti-N多组元硬质合金体系为研究对象，在资助期间取得了如下重要成果：（1）建立了迄今为止国际上最准确的多组元硬质合金体系的相图热力学和扩散动力学数据库；（2）通过相图计算、动力学模拟和关键实验的集成，建立了描述梯度硬质合金梯度层形成过程的方法；（3）实现了梯度硬质合金梯度层硬度分布的理论预测；（4）建立了用于描述固−液界面能的新型热力学模型；（5）结合第一性原理计算和关键实验的方法，获得了WC相、Co相及面心立方相之间的界面能；（6）解决了超细硬质合金中TaC分散不均的工业难题；（7）利用相场方法，实现了硬质合金液相烧结过程中液相迁移过程的定量模拟。在Scipta Mater.、Metall. Mater. Trans. A、J. Alloy Compd.等国际知名刊物发表论文44篇（其中，SCI收录论文44篇）。培养博士研究生5名，硕士研究生1名。