Microstructure of commercial sheet out of Ti-6Al-4V alloy after superplastic forming at 700°C

M.R. Shagiev, M.A. Murzinova show affiliations and emails
Received 07 December 2021; Accepted 07 December 2021;
Citation: M.R. Shagiev, M.A. Murzinova. Microstructure of commercial sheet out of Ti-6Al-4V alloy after superplastic forming at 700°C. Lett. Mater., 2021, 11(4s) 553-556
BibTex   https://doi.org/10.22226/2410-3535-2021-4-553-556

Abstract

Superplastic forming of Ti-6Al-4V commercial sheet with non-homogeneous initial microstructure (d=0.3-25 micrometers) at rather low temperature of 700C with a constant argon gas pressure of 2.5 MPa was performed for the first time. Superplastic forming of Ti-6Al-4V sheet at 700C led to an improvement of microstructure homogeneity and randomization of the rolling texture.The possibility of superplastic forming of commercial sheet out of Ti-6Al-4V alloy at rather low temperature T = 700°C was shown for the first time in the present study. Experimental hemisphere with a radius of 35 mm was successfully formed at 700°C with a constant argon gas pressure p = 2.5 MPa in 4352 seconds. Unlike to previous studies, preheating of the preform, superplastic forming process and subsequent cooling were carried out not in air but in vacuum, in order to avoid the formation of the surface oxide layer that limits the ductility resource of the material. Initial microstructure of Ti-6Al-4V alloy commercial sheet was found to be very non-homogeneous: along with ultrafine grains of α and β phases, the coarse elongated α grains with developed substructure were observed. After superplastic forming at 700°C a substantial improvement of microstructure homogeneity of the commercial sheet took place. Microstructure of the cross-section of the hemisphere did not contain coarse elongated grains. Although the average grain size remained almost unchanged (d =1.4 –1.5 μm), the coefficient of variation decreased significantly, from 1.3 to 0.6. Microtexture analysis revealed randomization of the rolling texture in Ti-6Al-4V commercial sheet and decrease in the texture maximums after superplastic forming at 700°C.

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