Activated slip and twin systems in electron beam melted Ti-6Al-4V subjected to elevated and high strain rate dynamic deformations

Abstract

This study presents an investigation on the effect of elevated (700 s−1) and high strain rate (2100 s−1) on the dynamic mechanical properties and deformation mechanisms of electron beam melted (EBM) Ti-6Al-4V cylindrical rod printed in the horizontal orientation. Optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques were utilized to characterize the microstructural and texture evolution. The typical microstructure consists of transformed α+β phase, grain boundary-α (αGB) along prior β-grain boundaries that are near-parallel to the build direction. Dynamic impact tests were conducted at room temperature using a Split-Hopkinson pressure bar (SHPB) apparatus, where the build direction is perpendicular to the impact loading. The dynamic mechanical properties of the sample deformed at the strain rate of 2100 s−1 exhibited higher compressive strength (~250 MPa) and total strain (~13%) that of the sample deformed at the strain rate of 700 s−1. Compared to the as-built sample, deformed samples exhibited finer microstructure, lesser α-interlamellar spacing, and higher α-lamella's fragmentation with the increase in the strain rate. EBSD Schmid factor distribution maps were used to discuss the effect of the initial texture and the strain rate on the deformation mechanisms' possible changes.