Microstructure and Mechanical Properties of Ti-6Al-4V Parts Fabricated by Electron Beam Melting under Dynamic Compression Tests

Abstract

In this research, the effect of strain rate on the microstructure evolution, mechanical properties, and deformation mechanisms of the horizontally printed Ti-6Al-4V cylindrical rods produced by electron beam melting (EBM) was investigated. The initial microstructure consists of α and β phases, and columnar prior β -grain boundaries oriented along the building direction. Dynamic compression tests at three different strain rates (690 s -1 , 1580 s -1 , and 2220 s -1 ) were performed using a Split-Hopkinson pressure bar (SHPB) apparatus. The variations in dynamic mechanical properties were correlated with the microstructural features such as α platelet width, interlamellar spacing, and fragmentation. Adiabatic shear bands (ASBs) formed in the thermally softened areas in the samples deformed at higher strain rates, which led to the fracture. The fracture of test specimen at high strain rates is attributed to the formation of voids and their subsequent growth and coalescence under thermal instability along the adiabatic shear bands during deformation. In the fractured samples, features of both ductile (presence of dimples) and brittle (smoother surfaces) were observed. With the increase in strain rate from 690 s -1 to 2220 s -1 , yield strength (YS), ultimate compressive strength (UCS), and strain-to-fracture increased by 48%, 28%, and 286%.