Ti2AlNb基合金激光焊接晶界析出相微合金化调控及高温脆性抑制机理

There has been a constant and urgent demand from the aviation and aerospace industry for the light and high-temperature resistant Ti2AlNb-based alloys. Laser welding is deemed as an ideal welding technology for joining Ti2AlNb-based alloys in order for their engineering applications. However, the high-temperature embrittlement of the laser welded Ti2AlNb-based alloys is found at service temperature. To solve the high-temperature embrittlement caused by the grain-boundary precipitate phase, a regulation method for the precipitate phase is proposed based on microalloying. The project will start with physical experiments to screen the elements and establish the screening standards, laying the foundation for the following microalloying process of fusion zone. Laser-additive welding process with the addition of filler powder is adopted to realize the microalloying process. The high-quality microalloyed joints will be obtained by investigating the welding stability and homogeneousness of the fusion zone. Under this basis, the regulation pathways of element type and addition amount on the state parameters of the grain-boundary precipitate phase will be systematically investigated and analyzed. The regulation mechanism of microalloying elements on the precipitate phase will be elaborated using phase transformation kinetics. The high-temperature properties and fracture mechanism before and after the regulation will be tested and analyzed to demonstrate the effects of the regulation on the precipitate phase. The relationship among the microalloying elements, the state of the precipitate phase, and the high-temperature fracture mechanism will also be established to reveal the inhibition mechanism of the high-temperature embrittlement. The results of this project will not only benefit the promotion of Ti2AlNb-based alloys in aviation and aerospace industry, but also will provide a new solution to solve the welding embrittlement of other intermetallics.

轻质耐高温的Ti2AlNb基金属间化合物受到航空航天领域的青睐，激光焊接是其工程应用的理想焊接方法，但在服役温度区间存在高温脆性。针对由焊缝晶界析出相导致的高温脆性问题，提出基于微合金化的晶界析出相调控方法以改善焊缝高温性能。本项目拟首先通过物理实验方法筛选合金元素，确立合金元素选择标准，为后续实现焊缝微合金化奠定基础；采用激光填粉焊接方法实现焊缝微合金化，通过对焊接过程稳定性、焊缝均匀性的研究获得高质量的微合金化焊缝；在此基础上分析合金元素类型、添加量对晶界析出相状态参数的调控规律，并从动力学角度阐明合金元素对析出相的调控机理；对比分析调控前后焊缝高温力学性能及高温断裂机制，建立合金元素-析出相-高温断裂机制关系，揭示晶界析出相调控对高温脆性的抑制机理。项目研究成果可以为Ti2AlNb基合金在航空航天领域的推广应用提供理论支撑，并为解决其他金属间化合物的焊接脆性问题提供新思路。

为解决Ti2AlNb基合金激光焊接焊缝的高温脆性问题，本项目提出基于微合金化的晶界析出相调控方法来抑制焊缝高温脆性。核心思想是通过激光填粉焊接工艺实现焊缝微合金化，利用合金元素对β/B2→O相变的抑制作用来调控析出相，改变裂纹的形核及扩展方式，改善焊缝高温性能，抑制高温脆性。通过物理实验方法验证β相稳定元素Mo、Si、W对β/B2→O高温转变的抑制效果，并结合焊缝成型质量最终确定Mo元素更加适合激光填粉焊接工艺。采用热分析动力学方法，揭示了合金元素加入后对晶界析出相的抑制机理。在此基础上优化激光填粉焊接工艺，在保证焊缝成型质量的基础上实现焊缝微合金化。650°C高温原位拉伸实验结果显示，微合金化后焊缝的断裂方式由沿晶断裂开始向穿晶断裂转变。在项目的支持下，进一步开展了焊缝实现B元素微合金化后对焊缝组织及性能的影响。结果表明，微合金化的焊缝B2相晶界处有TiB相生成，可以有效避免高温时晶界处的β/B2→O转变，与此同时焊缝晶粒得到细化，其形态由柱状晶转变为等轴晶。添加B元素实现微合金化后焊缝延伸率显著提高。以上结果表明，通过微合金化的方法有效改善了Ti2AlNb基合金激光焊接焊缝的高温脆性问题。