Microstructure and Texture Evolution of TA19 Alloy Bar during Forging AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY24010029

Chinese Library Classification Number:TK91

Citation Information:

Titanium alloy offers high specific strength，fatigue resistance，and corrosion resistance，making it widely applicable in aviation，aerospace，weaponry，petroleum，and the chemical industry. TA19 titanium alloy，also known as Ti-6242S，features medium strength，good thermal stability，and creep resistance，is widely used in advanced engines and aircraft. As we all know，titanium alloy forgings mainly adjust the proportion and size of α phase and β phase through hot deformation and heat treatment to meet application needs. Currently，the relationship between the heat treatment process，structure，and properties of TA19 titanium alloy is relatively well understood. It is generally believed that as the solid solution temperature increases，the content of the primary α phase decreases，while the strength and high-temperature creep properties increase. For the thermal deformation process of TA19 titanium alloy，the influence of individual deformation process parameters such as deformation temperature and strain rate on the evolution of structure and orientation is primarily studied through thermal simulation experiments. Therefore，there is a lack of intuitive observation and analytical research on the structure and texture during multi-fire forging. This article used a TA19 titanium alloy ingot with a diameter of 600 mm and a weight of 3 ton on a 20 MN fast forging machine to prepare a finished bar with a diameter of 260 mm through a total of 16 forging passes，with an up setting amount of 45% for each pass. Among them，in the 1st to 3rd passes，the bar blank was upset and stretched at 1150，1100，and 1050 ℃，respectively，and was air cooled after forging；in the 4th and 5th passes，it was upset and stretched at T_β-35~40 ℃ （T_β is transformation temperature of β→α），while the T_β is 1004 ℃，and was air cooled after forging；in the 6th pass，it was upset and stretched at T_β+50 ℃，and water cooled after forging；In the 7th to 15th passes，it was upset and stretched at T_β-35 ℃，and air cooled after forging；in the 16th pass，it was upset and rounded at T_β-40 ℃，and air cooled after forging. Samples were taken from the center，mid-radius，and surface positions on the cross section of the bar blank after the 5th，6th，9th，12th，and 15th pass forging. Scanning electron microscopy （SEM） and electron backscattered diffraction （EBSD） techniques were used to systematically analyze the microstructure and orientation characteristics of the α phase and β phase. The texture and orientation characterization were performed using an Ultra 55 field emission scanning electron microscope （FE-SEM） equipped with an EBSD probe. The texture analysis was conducted using Channel 5 orientation analysis software. The research results showed that although varying degrees of variant selection occurred after the β→α transformation，resulting in transformation textures，the repeated upsetting and stretching during the forging of TA19 titanium alloy bar prevented the formation of strong α phase transformation and deformation textures. After forging in β region，multiple clusters of α phase clusters were formed within the original β phase，with the orientation of α phase clusters predominantly in the <0001> direction，perpendicular to the length of the bar blank. When the actual temperature at the end of forging was higher than T_β，the lamellar α phases in the cluster did not participates in deformation. When the actual temperature at the end of forging was lower than the T_β，lamellar α phases would undergo a certain degree of fragmentation and deviate from the original orientation of the cluster，causing <0001> texture to weaken. When forging in the α+β region，both the α phases and residual β phases participated in deformation. As the number of forging passed in the α+βregion increases，lamellar α phases continued to become equiaxed，and the number of new equiaxed α phases transformed from the deformed residual β phases increases. The <0001> texture gradually weakened and shifted to <10$\overline{1}$0> and < 11$\overline{2}$0> texture. The weakening of the macrotexture of α phases mainly relied on the increase in newly formed equiaxed α phases. This was because the orientation shift of lamellar α phases caused by deformation was limited，while the orientations of equiaxed α phases formed by the transformation of deformed residual β phases were more varied. In addition，during the entire forging process，the equiaxation of lamellar α phases on the surface of the bar blank occurred more quickly，followed by the mid-radius position，and was the slowest in the center. This showed that the lower forging temperature and the more complex the stress state were more beneficial to the equiaxation of α phases. The purpose of this article was to systematically and in-depth analyze the structure and texture evolution rules of the α phase and β phase during the forging process of TA19 titanium alloy，and to provide theoretical support for the optimization of bar preparation process.