热力耦合作用下的动态相变对钛合金超塑性的作用机理研究

超塑成形技术在制备钛合金复杂形状结构件及精密零件方面可以显著提高成形效率和降低制造成本，是钛合金热加工领域的研究热点。热力耦合作用下的动态相变作为钛合金超塑变形过程中的一种重要的组织演变行为，有利于钛合金的超塑性，然而，其对钛合金超塑性的作用机理尚不清晰。本课题以Ti-6Al-4V合金为研究对象，采用高温拉伸原位和非原位观察技术，系统研究钛合金在超塑变形过程中的动态相变、界面滑动、扩散蠕变、位错运动和空洞演变过程。分析组织形貌特征、应变场、位错密度以及元素扩散和配分等规律。明确动态相变与界面滑动、扩散蠕变、位错运动和空洞演变的交互作用。阐明动态相变作用下的界面滑动机制、动态相变作用下的扩散蠕变和位错运动协调机制以及动态相变对空洞演变规律的作用机制，进而揭示动态相变对钛合金超塑性的作用机理。该研究可丰富和完善钛合金超塑性理论，可为钛合金超塑成形工业化生产和科学研究提供理论依据和技术参考。

Superplastic forming technology can significantly improve the efficiency and reduce the cost in manufacturing the complex-shaped and high-precision structured parts of titanium alloys, and thus, it has emerged as a focus of attention in the thermal processing field of titanium alloys. The dynamic phase transformation under the thermal and mechanical coupling, serving as an important role during the superplastic deformation of titanium alloys, which is conductive to the superplasticity. However, the effect of dynamic phase transformation on the influencing mechanism of superplasticity in titanium alloys is not clear. The Ti-6Al-4V alloy will be utilized in the present study. The dynamic phase transformation, boundary sliding, diffusion creep, dislocation motion and cavitation evolution during superplastic deformation will be observed by in-situ observation combined with non-in-situ observation techniques. Subsequently, the microstructural characteristics, strain field, dislocation density as well as the element diffusion and partition will be analyzed. And then the cross-coupling action between the dynamic phase transition and boundary slip, diffusion creep, dislocation movement and cavitation evolution will be confirmed. The boundary sliding mechanism as well as the diffusion creep and dislocation motion coordination mechanism under the dynamic phase transformation will be revealed. The effect of dynamic phase transformation on the cavitation evolution will be clarified. As a result, the dynamic phase transformation on the influencing mechanism of superplasticity in titanium alloys can be successfully revealed. The present research can enrich and perfect the superplastic theory of titanium alloys and provide theoretical basis and technical reference for scientific research and industrial production.