Heat treatment, microstructure, texture, and mechanical properties of electron beam melted Ti6Al4V

The findings from the microstructural and textural analysis of as-printed and heat-treated electron beam melted Ti-6Al-4V (EBM-Ti64) samples are discussed in this work. The initial microstructures of both samples were characterized precisely. The as-printed microstructure exhibits aligned grain boundaries parallel to the building direction, with the presence of alpha platelets. In contrast, the heat-treated microstructure reveals a lamellar alpha/beta structure with a considerably wide interlamellar spacing. This work addresses the transformations from beta ->alpha +alpha and alpha ->alpha +beta occurring when materials are heated up to below the beta-transus temperature. While the alpha ->(alpha) over dot+beta transformation is deemed unlikely to take place, the process can still occur through spinodal decomposition of beta, beta ->beta(V-poor) +beta(V-rich)->(alpha) over dot+beta(V-rich) where (alpha) over dot eventually transforms into alpha + beta. A thorough characterization of three primary morphologies of the alpha phase was revealed. Due to exposure to high temperatures, as experienced in the environment of a rocket engine fan, it was necessary to conduct isothermal hot compression experiments on the homogenized EBM-Ti64 alloy. These experiments aim to investigate the hot deformation behavior within the temperature range of 250-350 degrees C and a strain rate of 10 s- 1. The findings indicate that the modified JohnsonCook constitutive model and its corresponding numerical simulation, based on stress-strain and workhardening characteristics, effectively predict the flow behavior of this microstructurally complex alloy. Microstructure and mechanical properties of deformed as-printed and heat-treated samples at 250 degrees C, 300 degrees C, and 350 degrees C show that although dynamic recrystallization is not feasible under these conditions, we observe grain refinement and decreasing interlamellar spacing. These findings align with mechanical properties, where higher total strain and lower ultimate compression strength were noted as the testing temperature increased. Additionally, heat-treated materials exhibited inferior mechanical characteristics under each testing circumstance. Texture rotation (90 degrees) after deformation is evident in all pole figures. Considering the orientation distribution function maps, more intense <0001> fibre and {1010} <0001> textures were formed. Assessments of the slip systems revealed that the basal slip system has the lowest activity when considering texture orientations. Conversely, the most significant deformation contribution, particularly in the c-axis, comes from contraction twin and 1st order pyramidal.