激光熔覆Al2O3-C纳米管增强镍基高温合金组织调控与强韧机理

To overcome the hot cracking and low mechanical strength of the laser additive manufactured nickel-based superalloy. In the present project, carbon nanotubes (CNTs) is proposed to be incorporated into the additive alloy to increase the hot cracking resistance and mechanical properties of the alloy. To increase the structural integrity of CNTs during laser additive manufacturing, nano Al2O3 layer and electroless plated Ni layer are proposed to be deposited on the surface of CNTs and uses the coaxial powder feeding laser cladding technology, Al2O3-CNTs composite reinforced nickel-based IN718 superalloy is fabricated. It is proposed to control the microstructure and mechanical properties of the alloy through the control of the morphology, thickness and homogeneous of the deposited Al2O3 layer and electroless plated Ni layer, and also through the optimization of the laser cladding processing and parameters. It is proposed to elucidate the structural evolution of CNTs and Al2O3 under the laser irradiation and molten pool heat effect, discover the influence of the Al2O3 coating on the high temperature structural stability of CNTs, and also reveal the effect of Al2O3-CNTs addition on the element segregation and crystal growth behavior of IN718 alloy. It is also proposed to reveal the strengthening and toughening mechanism of Al2O3-CNTs through the hot cracking investigation, mechanical properties test and fractural microstructure analysis.

针对激光增材制造镍基高温合金易热致开裂且合金力学性能弱的问题，本项目拟通过碳纳米管（CNTs）的添加以抑制合金热裂纹并提高合金的综合力学性能。为提高激光增材制造过程中CNTs的结构完整性，本项目拟在CNTs表面包覆纳米Al2O3层和化学镀Ni层，并采用同轴送粉激光熔覆技术，制备Al2O3-CNTs复合增强镍基IN718高温合金。拟通过Al2O3层及化学镀Ni层形貌、厚度及包覆均匀性的控制以及激光熔覆工艺和参数的优化实现合金组织与力学性能的调控。拟通过Al2O3-CNTs及IN718合金微观组织结构的表征，全面掌握激光及熔池热致作用下Al2O3-CNTs的结构演变规律，阐明Al2O3包覆层对CNTs高温结构完整性的影响机制，揭示Al2O3-CNTs对IN718合金元素偏析及晶体生长行为的作用机理。拟通过合金热裂纹的表征、力学性能的测试及断裂组织的分析，揭示Al2O3-CNTs的复合强韧机理。

针对激光增材制造镍基高温合金强度偏弱，无法在高端热端部件中应用的行业难题，本项目通过添加碳纳米管（CNTs）以提高增材制造合金的综合力学性能。项目通过在CNTs表面包覆Al2O3、再化学镀铜镀镍处理，获得多层包覆的CNTs增强体，以提高CNTs在激光增材制造过程中的结构稳定性。但研究中发现，大部分CNTs仍无法保留其完整的管状结构。通过微观组织表征及熔池快速熔凝行为的有限元模拟，揭示了CNTs在激光增材制造过程中的结构转化机制：在高能激光及熔池高温的作用下，CNTs的管壁先从缺陷位置开始被“撕开”，形成石墨烯纳米片层（GNSs）；大部分GNSs被进一步“撕碎”成细小的GNSs碎片，在冷却过程中相邻的GNSs碎片间实现部分连接，形成大面积膜状的碳纳米带（CNRs）结构。CNTs及其结构转化产物的引入，有效地抑制了熔池合金的元素偏析，提高了合金的力学强度、摩擦磨损性能及耐腐蚀性能。但是，由于脱水处理过程中Al2O3-CNTs的团聚导致其在最终熔覆层中得不到均匀的分散，加之在激光增材制造过程中大部分CNTs被转化成碳-碳键连接不充分的CNRs结构，导致Al2O3-CNTs的复合强韧化效果有限，有待进一步提高完善。