多元无Co硬质合金的相图热力学及碳平衡控制研究

One trend for the R&D of hardmetals is to replace the toxic and scarce Co binder with the green and abundant (Fe,Ni) solid solution, and exert the effect of grain growth inhibitors such as Cr3C2 and VC. However, for WC-(Fe,Ni)-Cr3C2-VC hardmetals, the lack of phase diagram data and the instable magnetic saturation of binders, bring difficulties in composition design and carbon balance control, which makes the microstructure of hardmetals vulnerable to the unwanted phases of M6C, M7C3, graphite, etc. To solve this problem, this project intends to: 1) efficiently determine sub-ternary phase equilibrium data using diffusion multiples and key alloys, and develop a thermodynamic database for the C-Fe-Ni-W-Cr-V senary system by coupling first-principle calculations and the CALPHAD approach; 2) design model alloys which share the same activity of each component with commercial hardmetals to update the thermodynamic database; 3) optimize compositions of multi-component WC-(Fe,Ni)-Cr3C2-VC hardmetals using the updated database, and develop a generally applicable method of carbon balance control by combining phase transformation determination and thermodynamic calculation, to overcome the limitations of magnetic saturation measurement. The completion of this project is expected to lay an important theoretical basis for the microstructure control of multi-component Co-free hardmetals, and to provide a scientific guidance for the design of green and high-performance hardmetals in the future.

用环保且资源丰富的(Fe,Ni)固溶体替代具毒性且储量匮乏的粘结剂Co，并充分发挥Cr3C2及VC的晶粒生长抑制作用，是未来硬质合金研发的趋势。然而，多元WC-(Fe,Ni)-Cr3C2-VC硬质合金相图数据的缺乏及粘结剂磁饱和的不稳定，使其成分设计与碳平衡控制变得非常困难，导致合金微观结构中易出现M6C、M7C3、石墨等不利相。据此，本项目拟开展以下工作：1)利用多元扩散节与关键合金高效测定边际三元相图数据，并结合第一性原理计算及相图计算建立一套C-Fe-Ni-W-Cr-V六元系的热力学数据库；2)设计与工业硬质合金各组元活度相等的模型合金，实测关键多元相图数据以完善热力学数据库；3)利用数据库优化硬质合金成分，并摆脱磁饱和法的限制，结合相变测定及热力学计算发展一种普适的碳平衡控制方法。本项目的完成将为多元无Co硬质合金的微观结构控制奠定理论基础，并为未来高性能环保牌号设计提供科学指导。

用环保且资源丰富的(Fe,Ni)固溶体替代具毒性且储量匮乏的粘结剂Co，并充分发挥Cr3C2及VC的晶粒生长抑制作用，是未来硬质合金研发的趋势。掌握WC-(Fe,Ni)-Cr-V硬质合金的多元相图数据并精准控制其碳平衡是实现其工艺参数优化和结构-性能改善的关键。据此，本项目在资助期间开展了相关研究，并取得了如下成果：1) 耦合关键实验、第一性原理计算和相图计算方法建立一套C-Fe-Ni-W-Cr-V六元系的热力学数据库，并扩展加入了Mo、Ti、Zr等重要的添加元素；2)基于热力学计算设计了WC-(Fe,Ni)模型合金，利用EPMA及DSC测定了关键的多元相图数据，拓展了微观结构的表征方法；3)利用热力学计算设计关键合金，实现贫碳相η微观形貌的精准控制，并发展一种结合相变测定及热力学计算控制碳平衡的新方法。项目资助期间，在 CALPHAD、 Ceramics Internatinal、 J Phase Equilib Diff 等国内外知名学术期刊发表论文16篇，其中标注本项目资助号5篇。培养博士研究生1名、硕士研究生4名。