Microstructure and mechanical properties of additively manufactured Ti–6Al–4V alloy based on large area, high-resolution EBSD mapping

Abstract

The laser direct energy deposition (L-DED) is well-suited for metal manufacturing, offering advantages of excellent performance, high precision, intricate structures and material flexibility, etc. In this study, the microstructure and mechanical property of Ti–6Al–4V alloy were investigated using L-DED under various printing parameters. A large-area, high-resolution Electron Backscatter Diffraction (EBSD) mapping technique, enabling to characterize the coarse columnar β-grains with individual crystals up to a centimeter along the building direction, and the sub-grain acicular α′ phase down to 50 nm in the same image, was utilized to analyze the crystalline phases and their lattice orientations in additively manufactured Ti–6Al–4V parts. The microstructure evolution, involving the high temperature β grain structures, β+α phase transformation, as well as acicular α′ martensitic phases, were studied during the periodically attenuated thermal cycles of L-DED. The formation of the “fish-scale” morphology results primarily from the radically different α phase in size between the interior and edges of the “fish-scale” morphology. Additionally, the effect of processing parameters, i.e., scanning speed and laser power, on microstructures and mechanical properties is discussed in detail.

Keywords

• Phase transformation
• Acicular α′ martensitic phases
• Laser direct energy deposition
• Microstructure
• Mechanical property