A geometrically complex Ti6Al4V component was manufactured as a test object on an EOS M270 (titanium version). This sample is approximately 30 mm in diameter and 60 mm high, with the build direction in the long axis. During the DMLS process of manufacturing this component it was observed that support structures from neighboring parts came loose from the titanium substrate/base. These loose support structures made lines through the powder bed during the recoating phase. The build was interrupted on several layers but it was decided to continue with the process to see afterwards which defects can be detected by microCT.
This sample was subjected to X-ray micro computed tomography (microCT), before and after HIP treatment. The microCT scans were done at 48 μm resolution, such that the entire sample fits in a single scan volume. These “before” and “after” scans were scanned and processed under identical conditions to ensure direct comparison is possible. A higher resolution scan at 25 μm was done additionally after treatment, by scanning the object in 4 parts and stitching the volumes together automatically. MicroCT scans were done with a General Electric Phoenix V|Tome|X L240 system at 160 kV and 100 μA, 500 ms per image, with 2000 images in one full rotation. Reconstruction is done with system-supplied software including beam hardening correction. The “before” scan of this object was reported in a conference paper without detailed analysis [6]. Subsequent HIP treatment and scans of the “after” state where done approximately 1 year later. The scan settings were chosen identical to facilitate best comparison. Due to the potential for improved image contrast, an improved scan with better resolution was also done at 25 μm as mentioned above.
All analyses reported here were done with Volume Graphics VGStudioMax 2.2 including the defect analysis module. For direct comparison of two volume data sets, both were imported into the same project and alignment done manually by rotating and moving the one object relative to the other. This was done in a manual process to ensure best overlap of exterior and interior surfaces, followed by an offset in one axis to view them side by side. In this way an unchanged pore could be visualized in the before and after condition and other changes viewed directly.
HIP treatment was done at Bodycote in Belgium at a temperature and pressure of 920 °C +/− 10 °C and 1000 bar for a dwell time of 120 minutes under an Argon atmosphere.