航空用钛合金齿轮高强韧渗氮层的结构控制与性能研究

Titanium alloys are one of the main structural materials in aircraft manufacturing. Titanium alloys are seldom used in the field of gear manufacturing due to their low wear resistance, high temperature required for surface nitriding and carburization (higher than 800℃, causing degradation of matrix properties ) and thin nitride layer, etc. Our previous research indicates that nitriding can be performed at low temperature (600℃) under high magnetic field when a gradient nanostructured layer is produced on titanium alloy gear. Based on this process deep nanostructured nitride layer with high hardness and wear resistance can be obtained, whereas the matrix properties do not degrade. This technique shows the prospect of manufacturing gear for aerospace industry using titanium alloys. The present study intends to investigate the effects of volume fraction of grain boundary in the gradient nanostructure on the formation of titanium nitride using XRD, SEM, TEM and high-resolution EBSD local orientation analysis. The mechanisms of grain boundary diffusion of N atom and nucleation of titanium nitride in the nanostructure will be demonstrated. Methods controlling nanostructured Ti2N、TiN and composite nitriding layer containing N will be obtained. Through comparison, the effect of volume fraction and distribution of the Ti2N and TiN in the nano-composite structure on toughness of the nitride layer, hardness and wear resistance will be clarified. This project would lay the foundation for the application of titanium alloy gear containing nitride layer with high strength and toughness in the field of aerospace industry.

钛合金是飞机制造的主要结构材料之一，但由于其耐磨性差，表面渗氮、渗碳温度高（高于800℃，造成基体性能下降）、渗层薄等原因，很少被用于齿轮制造。我们预研发现，在钛合金齿轮上加工出纳米梯度结构后，可以在强磁场中实现低温（600℃）渗氮，并可获得高韧性、高耐磨的深层纳米结构渗氮层，由于渗氮温度低，其基体性能下降不大。这一技术为钛合金用于航空齿轮制造提供了可能性。本申请拟在现有研究基础上，使用XRD、SEM、TEM、纳米压痕仪和高分辨EBSD微区取向分析等手段，深入研究纳米结构中晶界及其体积分数对氮化钛形成的影响，阐明纳米结构中氮原子晶界扩散和氮化钛沿晶界形核的机制；获得控制纳米Ti2N、TiN和Ti基体复合渗氮层结构的方法。通过对比，揭示纳米复合结构中Ti2N与TiN的体积分数和分布等对渗氮层韧性、硬度和耐磨性的影响规律，为高强韧渗氮层钛合金齿轮在航空领域中应用奠定基础。

我们选定某型号的齿轮作为研究对象，采用钛合金进行制造，展开实验工作。根据自然科学基金的特点和要求，项目主要对钛合金齿轮加工和服役过程中所涉及的基本科学问题和机理等展开研究。首先通过对Ti6Al4V合金齿轮表面纳米梯度结构层的制备、结构和性能等研究，确定了钛合金表面纳米化的最优工艺方法；在此基础上对Ti6Al4V合金纳米结构渗氮层的相组成控制、渗氮反应扩散和性能等进行了研究。通过表面纳米化低温渗氮技术在样品表层制备混合结构氮化钛纳米合金化层，研究了其耐磨性和耐蚀性等。通过这些实验工作，项目的研究目标被顺利完成。在项目执行过中，参加国内会议 2 次，并做学术报告；发表论文10篇，其中 SCI 收录论文 10篇，EI 收录 10篇。申报相关发明专利3项。