Dynamic compressive response of electron beam melted Ti–6Al–4V under elevated strain rates: Microstructure and constitutive models

Abstract

Cylindrical rods of Ti–6Al–4V (Ti64) alloy were additively produced using the electron beam melting (EBM) process in the horizontal and vertical directions. Optical microscopy, electron microscopy (scanning and transmission), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) techniques were employed to characterize the microstructure and phases of the EBM–Ti64 alloy. The microstructure consists of α and β phases, where in the vertical sample, the average α-width decreased, and the finer microstructure was formed. Both horizontal and vertical samples were subjected to several dynamic compression tests at various strain rates between 150 s−1 and 1100 s−1 using a Split-Hopkinson pressure bar apparatus to characterize the effect of the build direction. Peak stress increased with the increase in strain rate for both orientations. The dynamic compressive strength of the alloy in both directions was strain-rate dependent, where the maximum of 1880 MPa and 2000 MPa was attained for horizontal and vertical samples, respectively. Under similar loading conditions, the strength of the vertical specimens was consistently higher than that of the horizontal ones. This was attributed to the finer microstructure and near-parallel orientation of prior β-boundaries to the impact loading axis in the vertical samples. Furthermore, a constitutive mathematical model was developed to encompass the results of dynamic flow curves for both directions to interpret the elevated strain rate behavior of EBM–Ti64. Model predictions were in good agreement with the experimental data.

Publication Title

Additive Manufacturing

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