目的 探讨纳米晶NiCrC涂层长时高温条件下的显微组织和硬度演变规律。方法 采用超音速火焰（HVAF）喷涂低温球磨纳米晶合金粉末（液氮介质）制备了纳米晶NiCrC涂层，在650 ℃空气环境中对涂层进行总时长200 h的等温热处理。采用扫描电子显微镜、X射线衍射仪、透射电子显微镜、维氏显微硬度计等方法，对涂层样品的显微组织、物相构成、晶粒尺寸和显微硬度进行了测试分析，同时对原料粉末也进行了相同条件下的对比分析。结果 NiCrC涂层显微组织的主要特征为：纳米晶金属相基体中弥散分布着细小的碳化物颗粒。在保温过程中，纳米晶涂层发生了再结晶和晶粒长大，并伴随有合金基体的脱溶及碳化物的析出、相变和后续生长等现象。该涂层显示出优良的高温热稳定性，在650 ℃保温50 h后，晶粒平均尺寸由初始态的41 nm增长至相对稳定值约100 nm。保温后涂层的硬度总体有所提升，由初始的697HV300（15 s）先升高至最大值801HV300（15 s），而后降至相对稳定值729HV300（15 s）左右。纳米晶粉末的组织和硬度变化特点与涂层相似。结论 在650 ℃保温过程中，纳米晶NiCrC涂层中的合金相脱溶和晶粒长大导致涂层金属相基体的软化，但细小碳化物颗粒的析出强化以及由相变（Cr7C3→Cr23C6）引起的体积分数增加，不但补偿了基体的软化，而且使涂层的整体硬度有所提高。

The work aims to discuss the variation of microstructure and hardness of nanocrystalline NiCrC coating after long-term heat treatment. The coating was prepared by high velocity air-fuel (HVAF) spraying with cryomilled nanocrystalline NiCrC powder as the feedstock and then heated at 650 ℃ for up to 200 h. The microstructure, phase constitution, grain size and hardness of coating were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis and a Vickers microhardness tester. In addition, the nanocrystalline NiCrC powder was also studied for comparison. The microstructure of coating was characterized by a nanocrystalline metallic matrix with dispersed small carbide particles. During long-term heat treatment, recrystallization and grain growth occurred in the coating material, together with exsolution of metal matrix and the precipitation, phase transformation and growth of the carbides. The NiCrC coating exhibited good thermal stability. The average grain size grew up to a relatively stable length of 100 nm from the original size of 41 nm after heat treatment for 50 h. The coating hardness increased to the maximum value of 801HV300 (15 s) from the original hardness of 697HV300(15 s) and then dropped to a relatively stable number of 729HV300(15 s) after heat treatment. The nanocrystalline NiCrC powder possessed the similar variation trend of microstructure and hardness with the coating. The exsolution and grain growth of metallic phase cause the softening of nanocrystalline NiCrC coating matrix during thermal exposure at 650 ℃. However, the precipitation of fine carbide particles and the carbide content increasing resulted from phase transformation (Cr7C3→Cr23C6) compensate the matrix hardness softening, and further lead to the increase in the overall coating hardness.