钛合金中富Nd第二相纳米颗粒的调控及其置氢疲劳性能研究

The frequent occurrence of fatigue fracture stem from hydrogen embrittlement of titanium alloy seriously affects the safe operation of aerospace, nuclear power, military and other important fields. Hydrogen embrittlement is mainly derives from diffusible hydrogen in metals. Therefore, the key to solving the problem of hydrogen embrittlement and improving the hydrogenated fatigue property is to prepare a large number of irreversible hydrogen traps which can trap the diffusible hydrogen in the titanium alloy. In the early stage, the applicant have prepared a large number of dispersed second phase nanoparticles in the steel. The diffusible hydrogen has been successfully enriched around the irreversible hydrogen traps formed by these second phase nanoparticles. Around the key scientific problem on how to effectively increase the irreversible hydrogen traps in titanium alloy, this project will get a large number of dispersed neodymium (Nd) rich second phase nanoparticles in titanium alloy containing rare earth element neodymium (Nd) firstly. Then, the regulation mechanism of the size, shape, quantity, distribution and boundary structure of the Nd rich second phase nanoparticles will be explored. Next, hydrogenated fatigue properties of titanium alloys containing different Nd rich second phase nanoparticles also would be studied. Finally, the interaction mechanism between the Nd rich second phase nanoparticle and its hydrogenated fatigue property would be clarified. The results will contribute to optimizing the microstructure design of titanium alloys and improve the hydrogenated fatigue property of titanium alloys, thus providing a new method and theoretic proof for the research and development of anti-hydrogen embrittlement alloy materials.

钛合金氢脆引起的疲劳断裂事故频发严重影响了航空航天、核电军工等重要领域的安全运行。氢脆主要由金属中扩散氢所致，因此解决氢脆问题并提高置氢疲劳性能的关键是在钛合金中制备出大量不可逆氢陷阱以固定住扩散氢。前期，申请者在钢中制备出大量弥散分布的第二相纳米颗粒，这些颗粒形成了不可逆氢陷阱并成功富集了扩散氢。围绕如何有效增加钛合金中不可逆氢陷阱这一关键科学问题，本项目将首先在含稀土元素钕（Nd）的钛合金中调控出大量弥散分布的富Nd第二相纳米颗粒，其次探索富Nd第二相纳米颗粒尺寸、形状、数量、分布及界面结构的调控机制，然后研究含不同富Nd第二相纳米颗粒钛合金的置氢疲劳性能，最后阐明富Nd第二相纳米颗粒与其置氢疲劳性能之间的作用机理。本研究成果将有助于优化钛合金微观组织结构设计，提高钛合金置氢疲劳性能，从而为抗氢脆合金材料的研究与开发提供新的思路和理论依据。

钛合金氢脆引起的疲劳断裂事故频发严重影响了航空航天、核电军工等重要领域的安全运行。氢脆主要由金属中扩散氢所致，因此解决氢脆问题并提高置氢疲劳性能的关键是在钛合金中制备出大量不可逆氢陷阱以固定住扩散氢。在钢中制备出大量弥散分布的第二相纳米颗粒，这些颗粒形成了不可逆氢陷阱并成功富集了扩散氢。围绕如何有效增加钛合金中不可逆氢陷阱这一关键科学问题，本项目将首先在含稀土元素钕（Nd）的钛合金中调控出大量弥散分布的富Nd第二相纳米颗粒，通过对含Nd钛合金沉淀动力学PTT曲线的测定，探明了钛合金中富Nd第二相纳米颗粒析出量-时间-温度三者之间所构成的沉淀动力学机制。其次对富Nd第二相纳米颗粒萃取复型制样及其表征，并对调控工艺与富Nd第二相纳米颗粒之间影响规律的统计分析后，探索出富Nd第二相纳米颗粒尺寸、形状、数量、分布及界面结构的调控机制。然后对钛合金试样置氢处理后，完成置氢钛合金试样疲劳寿命试验。最后阐明富Nd第二相纳米颗粒形貌特征与其置氢疲劳性能之间的作用机理如下：1）充氢含量低于0.105%，氢以固溶形态存在于钛合金基体中，氢的加入引起β相晶格畸变；其疲劳寿命随平均氢含量增加剧烈下降。2）富Nd第二相纳米颗粒钛合金生成马氏体α΄相，马氏体片束取向分布导致扩展后期形成团簇结构。3）随氢浓度增加，晶格畸变加剧，氢加速疲劳裂纹扩展，钛合金合金韧性下降，脆性增加。4）富Nd第二相纳米颗粒在疲劳中以团为单位统一承受变形，氢对马氏体团的尺寸较敏感，氢浓度越大，裂纹扩展相对容易，造成断口团簇尺寸较大。并最终制定出控轧温度750℃，控冷速度20℃/s，热处理时间200min，温度900℃及冷却方式为水淬的最优调控工艺。本研究成果将有助于优化钛合金微观组织结构设计，提高钛合金置氢疲劳性能，从而为抗氢脆合金材料的研究与开发提供新的思路和理论依据。