基于固溶元素作用的激光3D打印专用单晶高温合金成分设计

Laser 3D printing is a prospective technology that can be used to prepare single crystal superalloy turbine blades with complex inner cooling structure. However, liquation cracking always happens to the nowaday single crystal superalloys during laser 3D printing process, which seriously limits the application of 3D printing technology to the preparation of turbine blades. So it is necessary to develop new single crystal superalloys according to the solidification characterization of 3D printing process. In this study, the influences of solid solution elements on the microstructure, crack susceptibility, lattice stress, solidification shrinkage, thermal physical properties, and residual stress of a Ni-6Al-2Ti ternary model single crystal alloy will be focused. The relationship between the composition and the microstructure including the solidification defects will be investigated systematically. And the evolution process and forming mechanism of the microstructure and cracks during the non-equilibrium fast solidification process will also be discussed. According to these results, the crack control strategy of the single crystal alloy during laser 3D process will be suggested from the view point of materials. In addition, mechanical behavior of the laser 3D manufactured single crystal superalloy will be characterized, and its failure mechanisms will also be discussed. Based on these above results, the relationship among compositions, microstructure/defects and properties will be found, and the microstructure control strategy of the single crystal superalloy during 3D printing process will be suggested. The results obtained in the present study are expected to enrich the basic knowledge and theory on single crystal superalloys prepared by 3D printing technology, and to instruct the development of the nickel-base superalloys prepared by laser 3D printing process.

激光3D打印技术已成为复杂型腔单晶高温合金涡轮叶片最具潜力的制备技术。但是，现有单晶高温合金在激光制备过程中极易出现裂纹等凝固缺陷。这种裂纹仅通过工艺优化无法消除，还与合金自身成分组织密切相关，已成为制约该技术向高温合金领域推广应用的瓶颈。本项目拟在已有研究工作的基础上，以Ni-6Al-2Ti三元模型单晶合金为研究对象，通过试验分析和理论计算，阐明固溶元素对合金组织结构、本征强度、热物性和残余应力等的影响规律，揭示固溶元素对合金3D打印裂纹敏感性的作用机制，从材料角度提出裂纹敏感性控制策略，构建单晶高温合金中固溶元素含量与合金裂纹敏感性关系图谱。在此基础上，分析单晶合金的力学行为和损伤失效过程，阐明3D打印单晶高温合金中固溶元素的作用及强韧化机制，为推动我国3D打印单晶涡轮叶片材料及制备技术的进步提供理论指导和技术支撑。

发展复杂型腔单晶高温合金叶片已经成为提升航空发动机和燃气轮机整体性能的关键手段。随着涡轮叶片型腔结构的精细化和复杂化，沿用传统熔模精密铸造技术面临极大挑战。激光3D打印的出现为这种叶片的制备提供了一种新途径。但现有单晶合金在3D打印过程中易出裂纹。这种裂纹与合金自身成分密切相关。已有研究表明，在保证单晶高温合金高温强度，即保证合金中强化相含量的基础上，有必要针对 3D 打印的工艺特点，从其他合金元素成分优化出发，研发适合3D 打印的专用镍基单晶高温合金材料。固溶元素是单晶合金中另一种主要合金元素，其在合金中含量总和一般超过20 wt.%。鉴于此，本项目以Ni-6Al-2Ti三元模型单晶高温合金为研究对象，分析了Co、Re、W、Mo、Cr几种固溶元素对沉积态组织中柱/枝晶生长规律的影响；同时也分析了固溶元素对裂纹、内应力的影响规律，发现随着W、Re的含量升高，合金的抗拉强度升高或基本不变，但是它们使得熔覆时的热应力增大，并且热应力的增大大于合金的抗拉强度升高量，所以造成了裂纹敏感性升高，而Co的添加增大了合金强度的同时减小了热应力，大大的减少了裂纹敏感性。而Cr与Mo试验结果没有符合预期的设想，出现了反常，综合分析后认为可能是此两种固溶元素主要在于形成了TCP相而产生了裂纹。在上述研究基础上，初步建立了固溶元素含量、内应力与裂纹敏感性之间的关系图谱。基于获得的实验结果，结合高温合金成分设计理论，选择出了一种合金进行微观组织和力学性能分析，分析了合金的增材制造的成形性及外加载荷作用下的拉伸和持久性能。研究结果对推动我国先进单晶高温合金涡轮叶片制备技术的进步具有重要的科学意义。