激光熔覆再制造NiAl合金非平衡超常冶金熔池的碳迁移行为与阻隔机制研究

The project is aimed at some problems like chill tendency of the interface structure, the elimination of the pores and cracks which always appear during laser addictive remanufacturing of damaged cast iron, and the carbon migration behavior and its barrier mechanism at non-equilibrium metallurgical conditions will be studied. Specific studies are as follows: (1) Preparation of NiAl alloys with the barrier effect on carbon migration during laser forming of cast iron was designed. To realize the integrated design of NiAl alloy powder dedicated used for laser cladding cast iron and its preparation technology, the mapping relation model among effective laser heat input and chill structure zone width was built. (2) Carbon diffusion and its distribution in NiAl alloy layer on cast iron by laser cladding were elucidated, and existence forms of Ni, Al and C element at interface were characterized quantificationally, to reveal the non-equilibrium solidification and phase transition mechanism of partially melted zone of NiAl alloy layer. (3) The graphitizing nucleation, agglomeration and growth process of trace carbon element in molten pool were studied. The promoting graphitization effect, heterogeneous nucleation effect, carbon diffusion under the comprehensive function of material composition and convective motion of the melted pool were researched based on the low dilution rate character of molten pool of Ni-Cu metallurgical reaction. Blocking mechanism of carbon diffusion was illuminated under integrated effect. This project can solve key problems of profile remanufactured gray cast iron with laser addictive remanufacturing technology, and provide scientific basis for structural control, defects elimination and performance improvement of remanufactured coated layers.

针对损伤灰铸铁件激光熔覆再制造难以控制的结合界面组织白口化、气孔和裂纹等难题，研究非平衡超常冶金条件下熔池碳元素的迁移行为及其扩散阻隔机制。具体如下：（1）设计制备具有阻隔铸铁基体碳扩散效应的NiAl合金，获得激光有效热输入与界面白口区宽度之间映射关系，实现灰铸铁激光熔覆专用NiAl合金粉末/工艺一体化设计；（2）探明NiAl合金激光熔覆灰铸铁件过程中碳迁移形式及分布规律，定量表征界面熔合区Ni、Al、C元素存在形式，揭示熔池半熔化区非平衡凝固结晶与相变机制；（3）探明熔池中微量碳元素的石墨化形核、团聚、生长过程，揭示NiAl合金熔池冶金反应中的促石墨化效应、异质形核效应、碳原子上坡扩散效应以及熔体对流效应，阐明在这些效应交互作用下熔池阻隔碳扩散的机理。本项目研究成果可解决灰铸铁件激光熔覆再制造的关键理论与技术问题，为铸铁再制造专用材料设计、组织控制、缺陷消除和性能提升提供科学依据。

针对发生磨损、腐蚀、开裂等损伤铸铁零部件在再制造过程中难以控制的结合界面组织白口化、气孔和裂纹等难题，设计研制了镍基合金激光熔覆材料，研究了非平衡超常冶金条件下镍基合金熔池中碳元素的迁移行为及扩散阻隔机制。提出了激光熔覆再制造铸铁件时控制白口组织的粉末设计原则，并采用机械团聚法设计制备了NiAl合金粉末，达到了通过Ni、Al元素减小熔覆层结合界面白口组织宽度和断续状分布的目的。设计了NiCu合金打底与NiAl合金堆积熔覆的配合使用方法，通过Ni、Cu、Al元素在液态熔池中的促石墨化作用，控制了界面组织白口化倾向。探明了激光熔覆温度场的改变对熔覆层残余应力大小和分布规律，有效抑制了熔覆层开裂。.研究了非平衡超常冶金的NiAl合金激光熔覆层半熔化区碳迁移行为。获得了Ni、Al、C等元素在熔覆层底部界面两侧以及搭接熔覆层过渡边界两侧的元素分布规律，证明了熔池凝固时存在较大的内部对流。揭示了NiAl合金激光熔覆熔池凝固结晶与固态相变过程。在熔覆层内，碳元素以微小片状石墨形式分布于NiAl合金熔覆层底部，以C原子形式固溶于Ni基体内和以反应气体形式存在。揭示了半熔化区白口组织形成机制，发现C与Fe，Mn，Ni形成介稳定(Fe,Mn,Ni)3C合金渗碳体相，宽度小于80um。.探明了熔池中微晶石墨球的形核与生长过程，探明了NiAl合金熔池冶金反应中的促石墨化作用、形核长大、碳原子上坡扩散机制以及熔体对流运动行为，阐明了这些因素交互作用下熔池阻隔碳扩散的机理。.研究成果解决了灰铸铁件激光熔覆再制造的关键理论、技术与科学问题，为抑制铸铁再制造熔池碳扩散和避免组织脆硬化相变提供了科学依据，也为铸铁再制造专用材料设计、组织控制、缺陷消除和性能提升提供技术参考，研究成果已应用于损伤装备零件部的再制造，未来推广应用空间广阔。