Mechanical Behavior and Microstructure of Electron Beam Melted Ti-6Al-4V Using Digital Image Correlation

Abstract

The reputation of additive manufacturing technology has increased dramatically in recent years due to its freedom of design, customization, and waste minimization. The growing demand for complex profile components to achieve more economic and strength-to-weight efficient aero-engine components can be met by additive manufacturing technology. In this study, electron beam melting (EBM), a powder bed additive layer manufacturing process, is used to manufacture Ti-6Al-4V tensile specimens. The Ti-6AL-4V alloy has excellent corrosion and high temperature resistance with a high strength-to-weight ratio. It is widely used in the power generation, aerospace, and medical industries. An Arcam Ti-6Al-4V prealloyed powder with particle sizes ranging from 45μ–100μ is used in an Arcam A2 machine to manufacture three specimens at zero degree manufacturing orientation. The zero degree manufacturing orientation is expected to exhibit a higher strength over other orientations. The EBM manufacturing parameters were set at 15mA current and 4530 mm/sec beam speed. Tensile tests were performed at room temperature (25.5°C) under a strain rate of 0.003 mm/mm/min according to the ASTM E8 standard for strain-rate sensitive materials. Stress-strain curves are plotted and discussed. Tensile test results indicate a tensile strength of 1.2 GPa and an elongation of 8% approximately. Three Dimensional Digital Image Correlation (3D-DIC) is used to measure the full strain field and deformation evolution on the surface of the specimens. The 3D-DIC system compares digital photographs (taken at two different angles simultaneously) of the surface of a specimen and calculates the deformation and strain fields. Using the strain fields the mechanical properties are determined by the relationships in the strain tensor. The tensile test results show that for a zero degree manufacturing orientation, the yield strength (YS) and ultimate tensile strength (UTS) are higher than that typically reported for wrought products. Fractography using optical microscopy (OM) and Scanning Electron Microscopy (SEM) were conducted. Micrographs of transverse section of the specimen were obtained to identify and analyze the failure mechanism that took place during testing. The built direction, presence of voids, manufacturing defects, and unmelted particles are observed from the SEM views. Surface roughness and microstructure were observed in the OM. A comparison of the obtained results with the literature for additively manufactured Ti-6Al-4V and possible causes are discussed.