Time-resolved characterization of novel alloys for additive manufacturing

Abstract

Many manufacturing processes have alloys particularly developed for them: brittle alloys not presenting appreciable deformation during forming are ordinarily cast, while alloys amenable to mechanical deformation can be wrought processed. Thought metal-based additive layer manufacturing (ALM) is resulting in a paradigm change that could revolutionize manufacturing across multiple industries such as the aerospace, biomedical and automotive sectors, limited alloys are compatible with ALM. Nowadays, most of the alloys being used in ALM are mostly based on compositions inherited from conventional manufacturing such as casting and forging where microstructure engineering involves thermo-mechanical processing (TMP). In TMP, breaking up of anisotropy, control of grain size, recrystallization and texture, occurs during sequences of forming steps that give the final shape of components. Differently, the metallurgical conditions of ALM do not consider forming owing to the attractiveness of near net-shape fabrication, and present a more complex thermal history of rapid solidification where the alloys undergo sharp cycles of steep heating (~106-107 °C/s) and cooling (~ 103-108 °C/s) rates. Thus, in ALM, the activation of alternative phase transformations plays a key role in order to obtain microstructures with direct properties in the as-built state. Our contribution will present advances in time-resolved characterization providing insights in the influence of phase transformations on microstructure formation and in the deformation mechanisms of Ti-alloys particularly developed for ALM. The strategies taken for these alloys include tackling anisotropy by exploring alternative transformation paths of alpha-phase formation altering the regular Burgers-related beta-to-alpha transformation, as well as exploitation of the grain size-refinement provided by fast solidification for the fabrication of high strength components. On the other hand, phase evolution of alloys fabricated via selective laser melting is provided by in situ synchrotron tomography and in situ high energy synchrotron X-ray diffraction.