A comparison of different approaches to study the porosity and surface defects for Electron Beam Melting

The high power obtainable by the EBM and the pre-heating temperature (e.g., around 750 °C - 1100 °C) makes this process interesting for thermal crack susceptible materials such as γ-TiAl alloys and Ni-based superalloys with high contents of γ′. In this work, γ-TiAl (Ti-48Al-2Cr-2Nb) specimens were produced by EBM using different process parameters and characterized with different porosity analyses, to establish the reliability of the process as well as correlate the surface defects with the internal defects. The surface defects were characterized by stereomicroscope image analysis, while internal porosity was investigated by Archimedes density, optical microscope and X-ray computed tomography (µ-CT) analyses. All these methods were compared, and the top surface defects are correlated to the internal porosity, samples with low surface defects present a reduced internal porosity. Therefore, the top surface defects analysis can help to select in a fast and economic way, the most promising specimens, thus select the conditions that require a more in-depth and time-consuming investigation. This approach can be easily employed for faster optimization of process parameters for material development by EBM.