基于增材制造的高温钛合金单晶制备-结构制造一体化方法和机理研究

Single crystal is expected to greatly improve the service performance of high temperature titanium alloy, which has wide application prospects in the field of aeroengines and gas turbines. However, due to the high chemical activity of melted titanium alloys etc., it is difficult to use conventional single crystal preparation methods to fabricate single-crystal titanium alloy components. In this project, a new idea of fabricating single-crystal high temperature titanium alloy components is proposed base on additive manufacturing (AM). Single crystal preparation is realized by exploiting the unique “performance control” technical advantage induced by high temperature gradient generated during AM, while structural parts fabrication is realized by exploiting the unique “shape control” technical advantage of no mold and near net shape forming inherent to AM. Building on our prior work of preliminarily fabricating single crystal titanium alloy rod by arc AM, this project is aimed to further solve the key problems of tuning directional heat flow and internal stress during single crystal AM. Systematic experimental and numerical studies will be carried out to reveal the influence mechanisms of temperature gradient and growth rate at liquid-solid interface of micro-melting pool, disclose the evolution law of internal stress under the effect of high temperature gradient. These guide the development of key technologies, including controlling the single crystal growth heat flow of single melting pool, controlling the directional heat flow during layer depositing, removing residual stress through in-situ induction heating. Meanwhile, combined with the control of the crystal orientation and microstructure, high-performance high temperature titanium alloy blade can be obtained. This project has significant implications for developing new advanced method of fabricating single-crystal metals, which is of tremendous benefit to promote the development of additive manufacturing and high temperature structural alloys.

单晶有望大幅度提高高温钛合金的服役性能，在航空发动机与燃气轮机领域具有重要应用前景。然而，传统单晶制备方法，因钛合金的液态高化学活性等问题，难以实现钛合金单晶结构件的制造。本项目提出了钛合金单晶结构件增材制造的新思路，基于增材制造高温度梯度的“控性”能力实现单晶制备，基于增材制造无模具、近净成形的“控形”能力实现结构件制造。在前期已初步实现钛合金单晶棒材电弧增材制造的基础之上，进一步针对单晶增材制造面临的定向热流和内应力调控等难题，通过系统的实验和仿真模拟研究，揭示增材制造微熔池液固界面前沿温度梯度和生长速率影响机制，以及高温度梯度下内应力演化规律。继而，发展单熔池单晶生长热流调控、层内定向热流调控、感应加热原位去应力等关键技术，并通过晶体取向和显微组织调控，最终实现高性能高温钛合金单晶叶片的制造。本项目研究有望形成金属单晶制造新方法，对推动增材制造以及高温金属结构材料发展具有重要意义。

单晶有望大幅度提高高温钛合金的服役性能，在航空发动机与燃气轮机领域具有重要应用前景。本项目提出了钛合金单晶结构件增材制造的新思路，基于增材制造高温度梯度的“控性”能力实现单晶制备，基于增材制造无模具、近净成形的“控形”能力实现结构件制造。本项目揭示了增材制造微熔池液固界面前沿温度梯度和生长速率影响机制，发展了一种低成本的超低频脉冲单晶增材制造工艺。通过单熔池沉积可获得液固凸界面，进而通过电弧剪切应力和负马兰戈尼力引起的熔池向外表面流动促进了晶粒消除。同时，超低频脉冲电流保证熔池稳定，并确保了单晶的连续生长。本项目实现了米级单晶钛合金的制造，沉积态单晶表现出优异的高温蠕变性能。该方法可以扩展到复杂形状或难熔金属单晶的制造，为单晶制造技术开辟了新的途径。本项目支持下共发表24篇SCI，授权16项国家技术发明专利。