β-γ型TiAl合金超塑变形过程中的相变行为研究

TiAl alloy is considered as top candidate metal for high-temperature structural use in new generation aerospace. However, the application of TiAl alloys is impeded by the intrinsic brittleness and deformation disability. Recently, the so called β-γ TiAl alloys have attracted intense attentions due to the outstanding processability and deformability at high temperature. The latest study found that β-γ TiAl alloys have lower superplastic temperature than other TiAl alloys. Besides, a β phase transformation was found during the superplastic deformation process due to the existence of metastable β phase in the initial microstructure. In this project, the phase field model coupling with metastable phase diagram calculation and crystal plasticity finite element theory is used to study the phase transformation behavior during the superplastic deformation process quantitatively. By using the model, the influence mechanism of deformation on phase transformation will be discussed. Combined with in situ superplastic tensile experiments, the interaction mechanism of phase transformation and deformation will be revealed. Besides, a crystal plasticity finite element model describing the superplastic deformation process of TiAl alloy with multi-grains and multi-phases. Based on the model, the influence of phase transformation on superplastic of β-γ TiAl alloys will be clarified. This project has significant potential to develop a novel infrastructure for new deformation technique of TiAl alloys, thus contributes to the application of TiAl alloys.

TiAl合金是一种新型高温金属结构材料，在新一代航空发动机上有着广泛的应用前景。然而，TiAl合金脆性极大且加工成形困难，严重阻碍了其工程应用。近年来，β-γ型TiAl合金因其具有优异的加工性能与热成形性能受到研究人员重视，最新研究发现β-γ型TiAl合金超塑性温度明显低于其他TiAl合金，且由于组织中存在大量亚稳β相，在超塑成形过程中伴随着β相变。本项目将亚稳相图计算、晶体塑性有限元计算与相场模型相耦合，定量研究超塑变形过程中的相变行为，探讨形变对相变的影响机制；结合原位分析实验，揭示形变与相变的交互作用机理；建立多晶多相TiAl合金超塑变形晶体塑性有限元模拟，并基于此阐明β相变对β-γ型TiAl合金超塑性的影响机理，为发展TiAl合金新型成形技术、推动工程化应用提供理论与技术支撑。

TiAl合金作为新型轻质耐高温结构材料，在航空发动机与高速航天飞行器上有着广泛的应用前景。针对TiAl合金脆性大且加工成形困难的问题，本项目通过阐明相变对β-γ型TiAl合金超塑性的影响机理，发展TiAl合金超塑成形技术，实现复杂结构件的成形。项目在Acta Mater、JMST等SCI期刊上发表学术论文17篇；申请发明专利6项，1项获得成果转化；登记软件著作权2项。首先，基于晶体塑性有限元理论，研究了β-γ型TiAl合金塑性与微塑性变形过程中的组织演变与相变行为；探讨了变形机制随变形参数、β/B2相含量变化的规律，获得了超塑变形对应的工艺区间；揭示了β-γ型TiAl合金超塑变形过程中的织构演化规律与相变行为，特别是β/B2相变行为，探讨了相变与形变的交互作用机理，为实现超塑变形过程中的组织控制奠定了基础。