Developing Capabilities to Predict Fatigue and Fracture Behavior of Additively Manufactured Parts Containing a Range of Pore and Grain Structures

Materials of known, repeatable properties that are resistant to fracture are of prime importance for structural applications, but additively manufactured (AM) parts often contain internal voids and heterogeneities at the microstructural level which reduces strength and repeatability. In this work, Ti-6Al-4V parts were manufactured with different scan lengths (20 mm to 90 mm) during electron beam melting powder bed fusion method, which produced crystallographic textures that do not match the texture assumed for most Ti-6Al-4V AM parts (<001>_β-fiber in the build direction). The parts were also subjected to three different hot isostatic pressing (HIP) treatments, which are all effective in sealing internal porosity and manipulating texture and grain morphology. Validation of predicted mechanical behavior from a crystal plasticity model incorporates electron backscatter diffraction and X-ray computed tomography measurements conducted during and after tensile tests to failure. The high-cycle fatigue life and fracture toughness of specimens are predicted, based on observed changes in microstructures and defects. Our work shows potential for enabling rapid part design and qualification, beyond the Ti alloy system, by using microstructure-based predictive modeling to help identify and mitigate possible risk factors before conducting a physical build of an expensive aerospace or biomedical device component.