钽对激光熔覆镍基涂层高温耐磨性的影响机理及其凝固行为

Due to the limits of high temperature performance of matrix, reinforcement and matrix/reinforcement interface, high temperature wear resistance (above 700℃) of laser clad Ni-based coating is not ideal. The applicant use tantalum (Ta) to solid solution strengthen Ni matrix, improve thermal stability of carbide, and reinforce the coating with TaC particle which is produced through reaction of with C element and has good wettability on Ni, in order to increase high temperature wear resistance (700℃-900℃) of Ni-based coating. Based on non-equilibrium solidification condition, this project will study Ta solute distribution, the coating’s solidification, precipitation, and phase transition process, Ni matrix and TaC’s evolutions in high temperature environment, TaC/Ni interface’s mechanical properties and reaction mechanism, and the coating’s oxidation mechanism and high temperature wear behavior in order to reveal effects of Ta on microstructure, mechanical properties, and thermal stability of Ni_based coating. Further, Ta’s behavior on Ni_based coating can be understood, and mechanism of Ta improving high temperature wear resistance of Ni based coating can be revealed.The way to improve the thermal stability of carbides (such as TaC) and matrix can be found. Our research will provide theoretical foundation and technical reference for designing coating composition, evaluating coating’s performance, optimizing clad process, promoting Ta’s application in field of high temperature coating (700℃-900℃).

受基体相、增强相以及两者之间界面高温性能的限制，激光熔覆镍基涂层在700℃以上的耐磨性并不理想。申请人利用钽（Ta）元素固溶强化镍基相，提高碳化物的热稳定性，生成高热硬性、与镍（Ni）润湿性良好的TaC颗粒强化涂层，以提高镍基涂层700℃～900℃的高温耐磨性。通过研究激光非平衡凝固条件下Ta增强镍基涂层的钽溶质分配行为，涂层材料凝固析出相变规律，Ni基相和TaC的高温演化规律，TaC/Ni界面力学性能和反应机制，涂层高温氧化磨损机理，以及涂层的高温摩擦磨损行为来揭示Ta对镍基涂层的组织、力学性能和高温稳定性的影响，进而全面认识Ta在激光熔覆镍基涂层中的特性，揭示Ta对镍基涂层高温耐磨性的强化机理,获得进一步提高TaC等碳化物和基体相高温稳定性的方法。本项目将为设计涂层成分、评价涂层高温摩擦磨损性能、优化熔覆工艺、促进Ta在700℃～900℃高温耐磨涂层中的应用提供技术借鉴和理论依据

本项目以高碳NiCrBSi合金为主要基材，研究Ta对激光熔覆镍基涂层高温耐磨性的影响机制。首先通过相图计算分析了Ta强化复合涂层在平衡和非平衡条件下的凝固行为，揭示了物相的析出规律，分析了Ta所起作用。然后优化合金成分，制备涂层，分析了物相组成，主要物相以及TaC/Ni界面的高温演变规律。随后研究了复合涂层高温摩擦磨损和氧化机理。结果显示复合涂层在较低的温度下耐磨性和未改性涂层相当。600℃以上耐磨性优于未改性涂层，700℃时耐磨性提升1倍以上。物相的凝固顺序为TaC、M3B2、M7C3、γ、γ’、M23C6，随着Ta含量的增加，TaC含量增加，M7C3和M23C6含量降低。实验中，当Ta含量为10wt.%时，涂层的物相以Ni固溶体、TaC、Ni3Fe、CrB、M23C6为主，没有发现有γ’。基体的强化机制仍然以Cr、Fe和Ta的固溶强化为主，这限制了复合涂层在700℃以上的耐磨性。Ta通过抑制固溶强化元素的扩散提高基体的高温稳定性。700℃时，Ni基和Ni3Fe保持稳定，但M23C6不稳定；有棒状M7C3在基体边缘二次析出；TaC/Ni界面干净，没有界面反应物生成。TaC在900℃时仍能保持稳定。700℃摩擦时，TaC与Ni基结合良好，TaC能够抵抗磨粒的切削，阻止裂纹扩展并能承受接触载荷。未改性涂层在常温到700℃范围内都未形成氧化层，这对涂层的高温耐磨性不利。而Ta能够促进氧化层的形成。600℃时，磨损表面开始形成氧化层，700℃能形成大面积的致密氧化层，其主要由Cr2O3，Fe2O3, Fe3O4，NiO，Ni2O3和Ta2O5构成。总之，Ta能够固溶强化Ni基，生成硬质TaC，降低亚稳相M7C3的含量，促进致密氧化层的形成，并具有良好的工艺性，可用于提高传统NiCrBSi的高温耐磨性。