Investigating the effect of microstructure on the onset of ductile fracture of Ti-6Al-4V during isothermal forming

Ti-6Al-4V is one of the most common materials in the aerospace industry. For example, satellite fuel tanks are made of this alloy. Among manufacturing processes, forming processes is one of the most widely used areas in the manufacture of Ti-6Al-4V components. Due to the importance of determining the allowable deformation limit in the successful design of the Ti-6Al-4V forming process, in this paper, the amount of critical damage was studied. For this purpose, parts with double-cone geometry with grooves on the maximum diameter with two initial microstructure, lamellar and equiaxed, were fabricated and subjected to hot compression testing. The results showed that the initial equiaxed microstructure provides good accumulated damage tolerance. Up to 2.38, 2.67, and 5.89 accumulated damage values, according to Cockcroft-Latham, Brozo, and McClintock criteria, respectively, no crack was observed on the samples. However, with an initial lamellar microstructure, the damage tolerance was significantly reduced. The critical damage value based on Cockcroft-Latham, Brozzo and McClintock criteria was 1.05±0.02, 1.03±0.02, and 2.56±0.05, respectively.