Using X-ray imaging and diffraction to assist the development of novel Ti alloys tailored for additive manufacturing

Kurzfassung

Eutectics alloys are a special class of multiphase materials that grow directly from the melt following a eutectic reaction. Often termed in situ composites because it is possible to control their dual phase microstructure through careful control of the solidification conditions to obtain remarkable periodic microstructures with unique mechanical and functional properties. Their properties depend on the eutectic spacing, which can be below 200 nm at high solidification rates. These size effects provide the ultrafine eutectics with improved plasticity when compared with coarse eutectics. Laser additive manufacturing (LAM) has the potential to produce ultrafine eutectics in bulk samples and components and to verify if a favorable trade-off between strength and ductility can be achieved. The development of metals tailored to the metallurgical conditions of laser-based additive manufacturing is crucial to advance the maturity of these materials for use in structural applications. Previous studies have shown that rapid solidification techniques can result in ultrafine microstructures with excellent mechanical performance, albeit for small sample sizes. In the present work, eutectic Ti-Fe-based alloys have been produced by laser powder bed fusion, with the aim of exploiting rapid solidification and the capability to produce bulk ultrafine microstructures provided by this processing technique. Here we will present the resulting microstructures and provide an overview of powder production, laser processing, and on the details of microstructure formation. The microstructure was studied three dimensionally using near-field synchrotron ptychographic X-ray computed tomography with an actual spatial resolution down to 39 nm to analyze the morphology of the eutectic and dendritic structures as well as to quantify their mass density, size, and distribution. Characterization is complemented by SEM, EBSD, and SXRD. Additionally, operando synchrotron radiography during laser processing was conducted to elucidate the melting and solidification mechanisms of these alloys.