Effect of microstructure and crystallographic texture on high-temperature dynamic deformation behaviour of Ti-6Al-4 V alloy: a post-test analysis on texture evolution and deformation mechanism

To identify the optimum microstructure for aerospace industries, the dynamic flow properties of the Ti-64 alloy with equiaxed, bimodal, and lamellar microstructures have been comprehensively studied at three temperatures (RT, 300, and 450 degrees C) and strain rates (10-3, 1, and 102 s-1). The heat-treated Ti-64 alloy was subjected to uniaxial dynamic compression test and the tested specimens were characterised using SEM, TEM, and XRD-based bulk texture to determine the deformation mechanism. The results reveal that in the equiaxed microstructures, the interconnected alpha P (primary alpha) grains promote excellent deformation compatibility but the absence of alpha T (transformed alpha) limits its strength at high temperatures. Whereas, in the bimodal microstructure, the abundant presence of alpha P-alpha T/beta and alpha T-beta boundaries promote superior flow properties at high temperatures and high strain rates. However, in the lamellar microstructure, the absence of alpha P restricts strain accommodation. The severity of shear localisation is higher in specimens tested at 300 degrees C than those tested at 450 degrees C due to higher thermal softening in the latter. A higher volume fraction of alpha T promotes prism <c+a> slip, whereas a higher fraction of alpha P promotes prism <a> slip. Additionally, $\lcub {10\bar{1}0} \rcub${101<overline>0} slip is preferred over $\lcub {11\bar{2}0} \rcub${112<overline>0} slip at higher temperatures and higher strain rates. Factors such as restricted grain rotation in alpha T-beta colonies, severely kinked lamellae, and increased dislocation density promote pyramidal slip. Large strain accumulation inside the ASB leads to the formation of severely kinked lamellae containing dislocation walls, heavily deformed nano subgrains, dislocation networks, and elongated alpha P grains with dislocation substructures.