CALPHAD辅助设计粉末母合金法制备K418合金及其烧结机理研究

With the rapid development of automotive industry, the K418 superalloy prepared by powder metallurgy has received great attention recently. However, some problems have still existed in the K418 superalloy prepared by powder metallurgy, such as the high cost of pre-alloyed powders, the obvious sintering deformation and the low rate of finished products. Master alloy technique provides the possibility to solve these problems. However, the development of master alloy is quite slow due to the lack of direction of thermodynamics simulation. Meanwhile, the key problems, such as the phase equilibrium thermodynamics of the master alloy and the diffusion dynamics during sintering process, still remain to be solved. In this research, the master alloy technique will be used to prepare the K418 superalloy. The CALPHAD method will be used to design the composition of master alloy powders by Thermo-Calc software and the diffusion process between the master alloy powder and the base powder will be simulated by DICTRA software in order to reveal the interaction rule between the master alloy and base powder and the densification mechanism. Furthermore, this research will lay the theoretical and technical foundation for the establishment of master alloy technique for high-alloyed materials, and will expand the application of PM superalloys with high performance and the master alloy technique.

汽车工业的高速发展使粉末冶金法制备K418合金受到了极大的关注，然而粉末法制备K418合金得到广泛工业化应用必须解决预合金粉末原料价格昂贵、烧结变形较大、成品率低等关键问题。粉末母合金法在镍基高温合金中的应用为这些问题的解决提供了可能，但由于当前研究缺乏相关热力学、动力学计算指导，故研发效率较为低下，且母合金相平衡热力学和烧结扩散动力学等关键科学问题有待于深入研究。本项目拟使用CALPHAD方法，借助Thermo-Calc软件辅助设计母合金成分，使用DICTRA软件辅助研究母合金和基体粉末的合金元素扩散动力学，揭示烧结过程中母合金和基体粉末的相互作用规律和烧结致密化机理，进而为建立高合金化材料的母合金法技术奠定理论基础，扩大高性能粉末高温合金和母合金技术的应用。

本项目针对预粉末法制备K418合金成本高、烧结易变性、成品率低等关键问题，使用CALPHAD方法辅助设计母合金成分，并通过元素扩散动力学研究揭示烧结过程中母合金和基体粉末的相互作用规律和烧结致密化机理。研发优化了可以达到瞬时液相强化烧结目的MA1和MA2母合金。MA1母合金和纯镍的润湿性最好，在多孔镍中渗透的也最快。在MA1母合金添加多余的B元素既不利于初期瞬时液相的产生，也不利于后期固相扩散的均匀化。在MA1母合金添加多余的Zr元素有利于烧结过程中的扩散均匀化，但不利于K418合金中的组织稳定性。MA2母合金比MA1母合金含有更多的合金元素，在制备K418合金中需要的雾化粉更少，成本更低。但是过高的合金元素含量促使过多的NiAl相、σ相和少量的α-(Cr, Mo)相产生，容易形成σ相和NiAl相双阻挡层，不利于获得元素分布均匀、组织稳定性高的K418合金。使用MA1母合金粉末和羰基镍粉为原料制备的注射成形K418合金的抗拉强度、屈服强度为1047MPa、746MPa，相比铸造合金提高了66.5%、113.7%。使用MA1母合金粉末和羰基镍粉为原料制备的SPS烧结K418合金其抗拉强度、屈服强度、延伸率为1438MPa、986MPa、14%，相比铸造合金提高了128.6%、182.5%、75.0%。母合金法制备的K418合金组织稳定，在600-800℃区间热曝露后力学性能和微观组织变化不大。本研究成果为高性能材料的粉末母合金法制备提供了提供理论和技术借鉴。