Study On Process-Microstructure And Microstructure-Properties Of Ti-22Al-25Nb Alloy Based On Model

High strength and toughness is the current development direction of Ti2AlNb-based alloys for aerospace applications,and the development of advanced Ti2AlNb-based alloys with high strength and high plasticity can effectively reduce energy consumption and improve safety performance.Therefore,it is crucial to carry out the optimization of Ti2AlNb-based alloy heat treatment process as well as the quantitative analysis of tissue evolution law and key mechanical properties by establishing process tissue model and tissue property model to achieve quantitative feedback.In this thesis,the phase transformation points of each phase zone were determined by DSC and metallographic methods,and the microstructure evolution of different heat treatment processes in the O+B2 phase zone andα2+O+B2 phase zone were investigated.The effects of multiple factors such as solid solution temperature,solid solution time,aging temperature and aging time on the organization were analyzed,and the relationship models of solid solution temperature and average thickness of primary lath O,solid solution temperature and B2 grain size quantitative relationship model,aging temperature and average thickness of secondary lath O quantitative relationship model were established,and the error analysis of the models was carried out,which is a strong guide for the process-temperature relationship study of Ti-22Al-25 Nb alloy.The model has a strong guiding significance for the study of the process-tissue relationship of Ti-22Al-25 Nb alloy.On this basis,several sets of high temperature(700℃)tensile experiments were conducted to further analyze the influence of microstructure on mechanical properties,and the quantitative relationship models between the average thickness of primary lath O and tensile strength and the average thickness of secondary lath O and elongation were established and the error analysis was carried out,which are of strong guidance for the study of the organization-property relationship of Ti-22Al-25 Nb alloy.The model has strong guiding significance for the study of the organization-property relationship of Ti-22Al-25 Nb alloy.The fracture mechanism of the O+B2 phase zone under pure solid solution treatment was determined to be quasi-dissociative fracture dominated by striated tough fracture;the fracture mechanism of the α2+O+B2 phase zone under pure solid solution treatment was quasi-dissociative fracture dominated by B2 grain dissociative fracture;the fracture mechanism of the α2+O+B2 phase zone under solid solution+O+B2 phase zone after aging treatment was quasi-dissociative fracture dominated by macro-dissociative fracture mixed with micro-dissociative fracture.The fracture mechanism in the α2+O+B2 phase zone after aging treatment is a mixture of macroscopic decoupling fracture and microscopic tough fracture.The effects of different tissue morphologies such as slats,bimorphs(single-size slats),bimorphs(two-size slats)and different tissue parameter variations(average thickness of slat O,B2 grain size,etc.)on the mechanical properties are then highlighted.Ultimately,in this paper,by modeling the quantitative relationship between solid solution aging treatment process,tissue and properties,a better heat treatment process regime is determined,and at the same time,the quantitative optimization of the tissue by process and the tissue enhancement of the properties are realized,and then the preparation of Ti2AlNb-based alloy with high strength and high plasticity is realized,which provides a new idea for the factoryization of Ti2AlNb-based alloy.