Mapping the geometry of Ti-6Al-4V: From martensite decomposition to localized spheroidization during selective laser melting

The influence that complex component geometries can have on microstructure formation is investigated in a rocket engine impeller fabricated of a Ti-6Al-4V alloy by selective laser melting (SLM). The SLM melt pool monitoring, indicative of the component's thermal history during processing, is linked to the bulk mapping of martensite decomposition obtained by high energy synchrotron X-ray diffraction. In addition to the martensitic and lamellar microstructures typically obtained during SLM of Ti-6Al-4V, spheroidization is identified to take place in the component's down-skin regions. Grain boundary migration may contribute to the latter effect. Small recrystallized grains form along grain boundaries.