超高强beta钛合金降序双级时效显微组织演变及作用机理研究

The application of ultra-high strength beta titanium alloy in aerospace and other fields subjected to limitations due to the lower matching degree of high strength and good plasticity and toughness. The extent of improving mechanical properties of ultra-high strength beta titanium alloy by traditional single stage aging process was limited. Although the advanced double stage aging in ascending order has improved the strength and hardness of the alloy, but the ductility decreased dramatically. Therefore, this application project adopts a double stage aging in descending method to use the thermodynamic instability of beta titanium alloy in aged state. The alloy was first aged at a higher temperature to make it as stable as possible at a higher plastic level, then the second aging process was conducted at a lower temperature to generate a micro transformation of microstructure. This method can continue to strengthen the alloy under the condition of small decrease of ductility, and then improved the matching of comprehensive mechanical properties of ultra-high strength beta titanium alloy. The previous study shows that the effect of double stage aging in descending order on the improvement of comprehensive mechanical properties matching of ultra-high strength beta titanium alloy was remarkable. However, the application of double stage aging in descending order method on ultra-high strength beta titanium alloy has hardly been reported. This application project mainly focuses on the scientific problems such as the influence law of mechanical properties, microstructure evolution and strengthening and toughening mechanism. The implementation of the project will provide theoretical and technical basis for the development and application of ultra-high strength beta titanium alloys.

由于超高强β钛合金的高强度与良好塑性、韧性的匹配未能得到很好改善，使其在航空航天等领域的应用存在一定的局限。传统的单级时效工艺对合金力学性能提高程度有限，继而提出的升序双级时效工艺对合金强度硬度等性能提高明显，但是塑性损失严重。因此，本申请项目采用降序双级时效手段，利用时效态β钛合金的热力学不稳定性，使其在较高温度下进行时效以尽量使合金稳定在较高塑性水平，之后再经较低温度的二级时效使合金发生显微组织结构的微转变，达到使合金在塑性损失很小的前提下继续强化合金的目的，进而提高力学性能匹配。前期研究表明，降序双级时效提高超高强β钛合金综合力学性能匹配的效果显著。目前关于降序双级时效方法在超高强β钛合金中的应用鲜有报道。本申请项目主要围绕由这一方法所产生的力学性能影响规律、显微组织演变及强韧化机理等科学问题展开深入研究，项目的实施将为推动超高强β钛合金的发展与应用提供理论与技术基础。

由于超高强钛合金的高强度与良好塑性、韧性的匹配未能得到很好改善，使其在航空航天等领域的应用存在一定的局限。传统的单级时效工艺对合金力学性能提高程度有限，而细化强化相α相的升序双级时效工艺对合金强度硬度等性能提高明显，但是塑性损失严重。因此，本项目采用降序双级时效手段，利用时效态钛合金的热力学不稳定性，使其在较高温度下进行时效以尽量使合金稳定在较高塑性水平，之后再经较低温度的二级时效使合金发生显微组织结构的微转变，从而获得多尺度微结构，达到使合金在塑性损失很小的前提下继续强化合金的目的，进而提高力学性能匹配。本项目研究了降序双级时效对超高强β钛合金力学性能影响规律、双级时效显微组织演变规律以及降序双级时效强韧化机理，结果表明降序双级时效提高超高强钛合金综合力学性能匹配的效果显著。