Study On Microstructure And Properties Of Large-size Bar Of TC4ELI

Titanium alloy materials are widely used in aviation industry because of their unique low density,high strength,high temperature resistance and other excellent comprehensive performance.With the continuous development of aviation industry,especially the introduction of "durability/damage tolerance" concept in aircraft design,the demand for damage tolerance alloys with high fracture toughness and low crack growth rate is increasing.TC4 ELI is a medium-strength damage tolerance titanium alloy with high fracture toughness and low crack growth rate,developed on the basis of TC4 titanium alloy by optimizing and adjusting its alloy element content,reducing impurities,strictly controlling "O" content,etc.The TC4 ELI alloy,with its simple composition,excellent forging and forming performance,is suitable for manufacturing important load-bearing structural parts of aircraft,such as large frame,beam and joint structure,so as to meet the design requirements of long life,safety and reliability.In this paper,according to the characteristics of TC4 ELI alloy,combined with the forging process of TC4 titanium alloy bar,the forging process of TC4 ELI large-size bar was studied,and the deformation amount,deformation temperature and deformation strain rate were determined.By comparing and analyzing the microstructure and properties of TC4 ELI large-size bar,the forging process of TC4 ELI large-size bar was determined: upsetting with multi-fire and large-deformation + reversing forging.By studying and analyzing the microstructure and mechanical properties of TC4 ELI large size bar under different heat treatment systems,it was determined that the heat treatment system was ordinary annealing.Meanwhile,the microstructure uniformity of TC4 ELI alloy rod was studied.The results show that the thermal deformation process of TC4 ELI alloy has a significant effect on the microstructure and comprehensive properties of the alloy.The microstructure of TC4 ELI titanium alloy bar was uniform fine equiaxial crystals,the content of primary alpha was up to 80%,and the microstructure uniformity of core,R/2 and side of the bar was good.The primary a-phase grain in the heart is slightly larger than the edge,and there is no big difference on content.Its mechanical properties are good at both room and high temperature,and the longitudinal properties are slightly better than that of transverse on the whole.The strength of the edge,R/2 and the heart are not different.TC4 ELI titanium alloy bar has high impact toughness and fracture toughness,and good uniformity in all directions.At the same time,testing level with a half sound process is a 2.00-9db grade for a 400 mm specification of TC4 ELI titanium alloy large specification bar and the testing level with a half sound process is a 3.2-6db grade for a 500 mm and 600 mm specification of TC4 ELI titanium alloy large specification bar.At the same time,the microstructure,mechanical properties and flaw detection level of foreign TIMET and VSMPO imported bars were compared with TC4 ELI titanium alloy of similar specifications developed in this project.It is proved that the properties of TC4 ELI bar developed in this project are equivalent to those of foreign bar,and its macroscopic structure and ultrasonic testing level are slightly better than those of foreign bar.