镍基高温合金电磁辅助激光立体成形组织性能调控机理研究

The fatigue property of the laser solid forming GH4169 superalloy samples is too low to satisfy the actual using in aeronautics and astronautics industries for there large columnar grain structure and there uneven distribution, even there tensile property is good. And for this reason, the application of laser solid forming technique in manufacturing of superalloy parts is restricted in recent years. Electromagnetic stirring has been successfully used in the welding process for the changing of solidification behavior of liquid metls in the melting pool and the reduction of metallurgical defects. The solidification behavior of liquid metls in melting pool has the same characteristics compared with that of the welding process, so the combination of electromagnetic stirring and laser solid forming can give a new solution to improve the microstructure and mechanical property of laser solid forming samples. In this program, electromagnetic stirring is introduced to laser solid forming, and some basic questions are investigated experimentally. The crystallization of the menting pool will be analyzed, as well as the primary crystal phase and the solid-liquid interface, in order to assure the influence of electromagnetic stirring on the solidification behavior of the melting pool. Through the analysis of grain structure and residual stress distribution, the information of the crack of dendrites, the precipitation of secondary phase and the changing of interface will be gathered. The regulatory of the microstructure and mechanical property will be achieved by the study of tensile and fatigue properties combined with structure transforming analysis. The more broadly using of laser solid forming in aeronautics and astronautics industries and national defence industries and the enrich and consummate the theoretical system will be supported by this program.

激光立体成形GH4169合金具有晶粒粗大且分布不均匀及孪晶界面体积分数大的特点，虽然合金拉伸性能可达到锻件标准，但其疲劳性能仍不能满足使用要求，限制了该方法在航空发动机制造中的应用。电磁搅拌被证明可以改善焊缝晶粒尺寸和减少冶金缺陷，可实现焊缝组织和性能的调控。激光立体成形熔池金属的凝固与焊缝金属凝固特点类似，电磁搅拌技术与激光立体成形技术的结合有望为改善激光成形合金组织和性能开辟一条新的途径。通过对电磁搅拌熔池的结晶过程、一次结晶组织和界面结构特征分析，把握电磁场对熔池金属凝固行为的影响；通过沉积态和热处理态组织中的晶粒形貌以及应力分布分析，获得合金中枝晶破碎、二次相析出和界面转变规律；通过拉伸和疲劳性能分析，结合组织转变规律，获得合金强化机理，实现合金组织和性能的调控。项目的实施可为激光立体成形技术在航空航天和国防军工等领域的更广泛应用和该技术理论体系的丰富和完善提供依据。

激光立体成形GH4169合金具有晶粒粗大且分布不均匀及孪晶界面体积分数大的特点，虽然合金拉伸性能可达到锻件标准，但其疲劳性能仍不能满足使用要求，限制了该方法在航空发动机制造中的应用。电磁搅拌被证明可以改善焊缝晶粒尺寸和减少冶金缺陷，可实现焊缝组织和性能的调控。激光立体成形熔池金属的凝固与焊缝金属凝固特点类似，电磁搅拌技术与激光立体成形技术的结合有望为改善激光成形合金组织和性能开辟一条新的途径。项目主要得到了以下结论：（1）电磁搅拌可以加速熔池液态金属的对流，进而影响熔池的温度场和溶质场，对合金的结晶过程、一次结晶组织和界面结构特征等造成影响。（2）电磁场作用对晶粒结构影响不大，合金仍为柱状晶组织，但是对枝晶、合金元素分布和脆性Laves相形貌等影响较大；在电磁场作用下Laves相有长条状变为颗粒状，且数量减少，枝晶干处Nb元素含量大幅提高。（3）后续热处理过程中由于Laves相尺寸减少，更容易固溶消除，且后续直接热处理过程中γ"相析出更均匀，体积分数增加；随磁场电流增大，残余应力分布更均匀，再结晶后等轴晶组织更均匀。（4）电磁搅拌辅助激光立体成形GH4169合金静载拉伸强度和塑性均有较大提高，其中塑性指标提高较多，这得益于更均匀的显微组织和Laves相的减少，同时发现，电磁搅拌的优势在经过高温固溶处理后消失，这说明此方法更适合于对合金直接时效的场合，例如激光修复。疲劳性能测试显示由于显微组织更加均匀，各试样疲劳性能有2-3倍的提高。(5)项目共发表学术论文17篇，其中SCI收录9篇，EI收录3篇，中文核心5篇；申请专利4项，授权2项；培养硕士研究生5人；参加各类学术会议9次。项目的实施得到了预期的研究成果，可为激光立体成形技术在航空航天和国防军工等领域的更广泛应用和该技术理论体系的丰富和完善提供依据。