集成DOE的激光熔覆工艺及先进镍基高温合金熔覆质量控制机理研究

Laser deposition is an important additive manufacturing technology, and has great potentials in the repairing and near-net-shape manufacturing of nickel based superalloy components. Currently, in the laser deposition of advanced single crystal and directionally solidified superalloys, it is very difficult to prevent the formation of hot cracks and stray crystals, which makes the components not suitable for the service in high temperature environment. This project proposes to adjust the laser energy distributions using diffractive optical element (DOE), so as to optimize the thermal, mechanical and crystallization processes during laser deposition, avoid hot cracks and realize controlled growth of columnar crystals. Firstly, a novel laser deposition system will be developed which is capable of integrating DOE modules; tailored laser energy distributions can be realized by using DOE modules of different designs. Secondly, multi-physics numerical simulation models will be established to accurately predict the thermal, mechanical and solidification behaviors during laser deposition process. Thirdly, the influences and related mechanisms of process parameters on crystal morphologies and hot cracks will be experimentally and numerically studied for the laser deposition of typical single crystal and directionally solidified superalloys, based on which the distribution modes of laser energy and corresponding process parameter windows can be determined. Finally, specimens will be fabricated with novel deposition system with DOE modules under selected process parameters, of which the mechanical properties under high temperatures will be experimentally tested to study the effectiveness of the novel deposition process with integrated DOE in controlling the properties of deposits. For the first time, the project introduces the advanced DOE technology to laser deposition process, and the outcomes of the project can provide technical supports to the repair and direct fabrication of advanced superalloys components in aeroengines and gas turbines.

激光熔覆是一项重要的增材制造技术，在航空发动机和燃气轮机热端部件的修复及近净成形制造中得到了广泛重视。目前，在先进的单晶和定向凝固镍基高温合金的激光熔覆中，由于热裂纹、杂晶等缺陷很难消除，无法满足高温服役要求。本项目提出采用衍射光学单元（DOE）对激光能量分布进行调整，以优化热、力及结晶过程，防止热裂纹的形成，实现晶粒的可控生长。首先，开发可集成DOE的激光熔覆系统，通过不同设计的DOE模块，实现定制的激光能量分布；其次，建立熔覆过程多物理场数值仿真模型，实现对熔覆过程中的热、力及凝固行为的准确预测；第三，针对典型的单晶和定向凝固合金，研究揭示工艺参数对凝固组织形貌和热裂纹的影响规律和机理，确定激光能量分布模式及工艺参数窗口；最后，对激光熔覆件高温力学性能进行测试，研究DOE模块在性能调控中的有效性。项目首次将DOE用于激光熔覆，预期成果可为先进镍基合金部件的修复和直接制造提供技术支持。

激光熔覆是一项重要的增材制造技术，在航空发动机和燃气轮机热端部件的修复及近净成形制造中得到了广泛重视。目前，在先进的单晶和定向凝固镍基高温合金的激光熔覆中，由于热裂纹、杂晶等缺陷很难消除，无法满足高温服役要求。这已经成为制约先进镍基高温合金部件制造和维护的关键“卡脖子”问题之一。.本项目以激光熔覆中的热管理为核心，探索采用衍射光学单元（DOE）对激光能量分布进行调整，以优化热、力及结晶过程，防止热裂纹的形成，实现晶粒的可控生长。首先，基于现有激光加工系统，开发可集成DOE的激光熔覆系统，通过不同设计的DOE模块，实现定制的激光能量分布；其次，基于所开发的激光熔覆系统，通过系列工艺实验，获得了推荐工艺参数窗口；在此基础上，实验研究了激光能量分布及冷却条件对我国自主开发的IC10定向凝固镍基高温合金激光熔覆中柱状晶定向生长及热裂纹形成的影响规律，并通过建立熔覆过程多物理场数值仿真模型，数值分析揭示了柱状晶定向生长和热裂纹形成的机理，为熔覆层组织和缺陷控制提供了依据；第三，基于以上研究，提出了“激光重熔+激光熔覆”复合修复工艺，通过重熔处理对基体组织形态和成分分布进行优化，在此基体上进行熔覆，成功制备了无热裂纹且柱状晶组织连续定向生长的激光熔覆层，进而分析了熔覆试样不同区域组织和性能（纳米硬度、蠕变速率、抗磨损性能）之间的关系，为组织优化提供了依据；最后，为提高熔覆效率、减小对基体的热损伤，对新型光粉作用模式及相应的高速激光熔覆工艺进行了研究。对比研究了新工艺与常规工艺在显微组织及力学性能（强度、硬度、耐磨性、抗氧化性等）方面的不同。在以上几方面工作的基础上，揭示了镍基高温合金激光熔覆中“材料成分-工艺参数-微观组织-力学性能”之间的内在关联，为高性能激光熔覆组织的制备提供了依据。.本项目研究成果可为先进镍基合金部件的修复和直接制造提供技术支持，对解决我国航空发动机和燃气轮机“两机”研发中的相关“卡脖子”问题具有重要意义和参考价值。