高能束熔覆再制造定向凝固镍基高温合金结构缺陷的跨尺度表征与热处理调控

It is of great scientific and application significance to develop the high-energy beam cladding technique to repair and/or remanufacturing the Ni-based superalloys to regain the shape, microstructure, and high-temperature mechanical properties to elongate the lifetime of the damaged turbo blades. In this project, it is proposed to prepare the directionally solidified DZ125L superalloy using both laser and electron beam as the heat resources under various power, scanning speed, and specimen temperature, and heat treat the remanufactured specimens under different solution temperature and aging time. The microstructure and mechanical properties of the remanufactured specimens will be studied before and after the heat treatment. Taking advantages of its sub-micron spatial resolution and large area scanning capability, synchrotron radiation based X-ray microdiffraction will be employed to not only map the crystal orientation, but also study the spatial distribution of dislocation types and densities from peak profile analysis of the Laue reflections. In order to realize the automatic analysis, computer programs will be developed. By using the combination of the Laue diffraction and energy scan, the distribution of the gamma/gamma prime lattice mismatch at various elevated temperatures will be studied using an in-situ heating and temperature control system. The morphology and size of the gamma prime precipitates and element distributions will be investigated using the advanced scanning electron microscope and electron probe micro-analyzer, respectively. The hardness and modulus distribution will be measured using the nano-hardness test equipped with a heating stage. Based on all these quantitative measurements, the relation among the processing parameters, microstructure, and mechanical properties will be established and the remanufacturing and heat treatment protocols will be optimized in order to advance the application of the high-energy cladding techniques in the repairing and remanufacturing of directionally solidified Ni-based superalloys.

对镍基高温合金叶片损伤部位进行修复再制造，恢复其形貌、组织与高温力学性能，具有重大战略意义。本项目分别利用激光、电子束熔覆再制造技术在定向凝固高温合金DZ125L上制备试样，采用不同的固溶温度和时效时间进行两步热处理，并对热处理试样的微观组织结构和力学性能进行定量研究。以同步辐射微衍射为主要研究手段，发挥其亚微米空间分辨和大面积扫描的能力，除晶体取向分布之外，通过发展海量衍射峰峰型分析的计算机算法，实现位错类型与密度空间分布的跨尺度表征；利用其优异的倒空间分辨率，原位加热条件下量化γ/γ’晶格错配度的空间分布；利用先进电子显微分析技术和高温纳米硬度仪对γ’析出相的尺寸/形貌、元素偏析、硬度、模量的空间分布进行表征。通过以上系统研究，优化熔覆再制造和热处理制度，建立“工艺-结构-性能”关系，实现对高温合金材料缺陷与力学性能的调控，从而为定向凝固涡轮叶片熔覆修复的成熟应用提供理论和实验依据。

作为先进航空发动机的核心材料，镍基高温合金在严苛的环境下服役，难以避免地产生开裂、磨损等损伤。因此，开发镍基高温合金单晶/定向晶的3D打印修复技术，恢复其形貌、组织与高温力学性能，具有重大战略意义。针对这一需求，本项目的研究内容主要包括三部分，即：高温合金的高能束增材制造及其微观结构的研究、针对增材制造高温合金的定制化热处理制度开发、以及跨尺度高通量同步辐射表征技术的开发： .根据研究计划，本项目研究了镍基高温合金单晶/定向晶的增材制造。以铸造镍基高温合金单晶/定向晶为基材，通过优化热源功率密度、扫描速率与路径、基材预热温度等重要功率参数，成功制备了无裂纹、晶体外延取向控制良好的镍基高温合金单晶/定向晶。利用电子显微镜、同步辐射等跨尺度先进材料表征手段定量研究了增材制造镍基高温合金单晶/定向晶的应力和微观组织结构。.为增材修复镍基高温合金单晶/定向晶定制化开发了热处理制度。创新发展了关于镍基高温合金塑性变形的回复理论，颠覆了镍基高温合金单晶几乎没有回复能力的传统观点，提出通过筏排化实现回复的新方法，为电子束、激光增材制造镍基高温合金单晶定制了回复-固溶-时效三步热处理制度，完全抑制再结晶，释放应力，位错密度降低一个数量级以上，实现了合金成分、析出相尺寸/形貌等微观组织结构和力学性能（硬度）的均匀化。.开发跨尺度高通量同步辐射表征方法与技术。在上海光源同步辐射装置测试线站BL09B上利用自主研制的聚焦镜系统获得了高通量、低发散角、微米尺寸的白光X射线，通过二维X射线探测器与高精度扫描样品台的协调控制，在我国大陆首次实现白光微束的实验，并对镍基高温合金GH3535铸态和焊接试样进行了研究，通过一次实验即获得晶体取向、晶格应变、显微缺陷等微观组织结构特征在试样中的空间分布，兼顾微米级空间分辨率和厘米级试样观测面积，达到了跨尺度、高通量的要求。.通过以上研究，优化了高能束增材再制造和热处理制度，建立“工艺-结构-性能”关系，实现对高温合金材料缺陷、微观组织结构与力学性能的调控，从而为定向凝固/单晶镍基高温合金涡轮叶片增材修复的成熟应用提供理论和实验依据。