Development of Ti-based alloys and composite materials for additive manufacturing

Abstract

Additive manufacturing (AM) is a new emerging manufacturing process as a means of fabricating near net-shape fabrication of complex parts with little additional post-processing, which enables to utilize it in various fields such as aerospace, automobile, and medical industries. However, despite of the outstanding advantages of AM, there are still challenges impeding its widespread adoptability. The challenges are attributed to complex non-equilibrium physical and chemical metallurgical nature different from the parts fabricated by conventional processes, which is typically accompanied by the high cooling rate and steep temperature gradient (104 K/mm) originating from small melt pool. Ti-6Al-4V (Ti64) is one of the most widely studied alloys for AM because of its high strength to density ratio, good corrosion resistance, biocompatibility, and weldability. Ti64 samples fabricated via AM typically show columnar microstructures consisting of coarse prior β grains along the build direction. Columnar grains are usually unfavorable for AM builds, as an anisotropic microstructure causes anisotropic tensile mechanical properties. Therefore, we designed new Ti alloy and YSZ+Ti64 composite materials suited for AM process. In this dissertation, two strategies were considered: 1) the effect of CoCrMo (CCM) powder on the microstructure of as-deposited Ti64 and 2) the effect of yttria stabilized zirconia (YSZ) on the microstructure of as-deposited Ti64 were investigated. The findings from this research can be utilized in future research to develop commercially viable grain refiners for not only Ti, but other materials as well.