Thermographic Microstructure Monitoring in Electron Beam Additive Manufacturing

Abstract

To reduce the uncertainty of build performance in metal additive manufacturing, robust process monitoring systems that can detect imperfections and improve repeatability are desired. One of the most promising methods for in situ monitoring is thermographic imaging. However, there is a challenge in using this technology due to the difference in surface emittance between the metal powder and solidified part being observed that affects the accuracy of the temperature data collected. The purpose of the present study was to develop a method for properly calibrating temperature profiles from thermographic data to account for this emittance change and to determine important characteristics of the build through additional processing. The thermographic data was analyzed to identify the transition of material from metal powder to a solid as-printed part. A corrected temperature profile was then assembled for each point using calibrations for these surface conditions. Using this data, the thermal gradient and solid-liquid interface velocity were approximated and correlated to experimentally observed microstructural variation within the part. This work shows that by using a method of process monitoring, repeatability of a build could be monitored specifically in relation to microstructure control.

Invited review article: Metal-additive manufacturing—Modeling strategies for application-optimized designs

“…While the investigations shown in Figure 9 show techniques for DED, the same techniques have been applied to PBF techniques [89]. Other temperature measurement techniques for both investigating the thermal phenomena and verifying/validating thermal models have been investigated such as infrared thermography and pyrometry [90–93], which have equally shown strong agreement between experiment and modeling.…”

Micro-Macro Relationship between Microstructure, Porosity, Mechanical Properties, and Build Mode Parameters of a Selective-Electron-Beam-Melted Ti-6Al-4V Alloy

“…As the build grows along the z-direction, the measured temperature becomes less and less representative of the actual energy injected by the beam into the layer. Moreover, this poor temperature control of the process is responsible for weak correlation between the SEBM parameters and the microstructural and mechanical properties of any alloy but of the Ti-6Al-4V alloy in particular [29,30].According to current investigations, the tensile properties of an SEBM product provide a rough indication of the mechanical response of their build-scale microstructure, which may include phase gradients of different composition, distribution, and resolution, etc. As a result, the reported relationships between the microstructure and the tensile properties cannot be considered univocal.…”

“…As the build grows along the z-direction, the measured temperature becomes less and less representative of the actual energy injected by the beam into the layer. Moreover, this poor temperature control of the process is responsible for weak correlation between the SEBM parameters and the microstructural and mechanical properties of any alloy but of the Ti-6Al-4V alloy in particular [29,30].…”

Smart E-Beam for Defect Identification & Analysis in the Nanoscale Technology Nodes: Technical Perspectives

“…For example, Childres et al [1] used e-beam to study the effect of radiation damage on graphene for the development of radiation-hard graphene electronics. Raplee et al [2] presented robust process systems that can detect imperfections and improve desirable repeatability using in situ monitoring, such as thermographic imaging.…”