Prof. Dr. Anthony D. Rollett, Additive Manufacturing Inspired Synchrotron Experiments and Computation: Diffraction and Dynamic X-ray Radiography
Dept. Materials Science & Engineering, Carnegie Mellon Univ., Pittsburgh PA, USA
Synchrotron-based 3D X-ray computed microtomography was performed at the Advanced Photon Source on additively manufactured samples of Ti-6Al-4V using both laser (SLM) and electron beam (EBM) powder bed; Al-10Si-1Mg form SLM was also characterized. Outside of incomplete melting and keyholing, porosity is inherited from pores or bubbles in the powder. This explanation is reinforced by evidence from dynamic x-ray radiography (DXR), also conducted at the APS. DXR has revealed entrapment of voids (from powder particles) in melt pools, keyholes (i.e., vapor holes) and hot cracking. Concurrent diffraction provides information on solidification and phase transformation in, e.g., Ti-6Al-4V. High Energy (x-ray) Diffraction Microscopy (HEDM) experiments are also described that provide data on 3D microstructure and local elastic strain in 3D printed materials, including Ti-6Al-4V and Ti-7Al. The reconstruction of 3D microstructure in Ti-6Al-4V is challenging because of the fine, two-phase lamellar microstructure and the residual stress in the as-built condition. Both the majority hexagonal phase and the minority bcc phase were reconstructed. Representative 3D synthetic microstructures were generated based on additively manufactured Ti-6Al-4V characteristics, and the input structures were modified for features of interest. The sensitivity to microstructure was quantified by performing full field simulations using a spectral elasto-viscoplastic code that uses parallelized fast Fourier Transforms (FFTs) and Hierarchical Data Format (HDF) for input/output.