Transient thermal effects on the performance of additively manufactured Ti-based alloys

Abstract

The design and performance of next-generation structurally critical components hinges on the ability to engineer metal alloys for specific applications. Ti-alloys are popular within the aerospace sector, with Ti-6Al-4V taking a majority stake within the Ti-alloy market due to its excellent strength-to-weight ratio. Decades of research into manufacturing this alloy via conventional techniques have garnered trust in well-understood processes that result in a reliable set of material properties. The design specifications of next-generation aerospace components brings forth the need for complete freedom-in-design and industrial scale bespoke component manufacturing - a set of criteria that traditional manufacturing methodologies simply cannot meet. Additive manufacturing (AM) is a disruptive technology that seeks to meet the demands of modern- and future-industry. The fabrication of complex components, a significant reduction in the buy-to-fly ratio and bespoke engineering are but a few highlights driving the demand for the wide-spread adoption of this technology to industry. However, relatively nascent technologies like electron beam powder bed fusion (E-PBF) induce an extreme thermo-mechanical environment during printing which includes complex thermal cycles that introduce unexplored metallurgical phenomena. Unusual phase transformation pathways, significant property variations within and between builds, complex grain boundary micro- and nano-structures, and microstructural heterogeneity that spans the milli- to nano- length scales are all as-yet unexplored. The goal of this thesis is to elucidate each of these factors, amongst others, in an effort to bring AM technology to the forefront of applications within industry. In doing so, this thesis offers 3 novel contributions to Ti-6Al-4V AM materials characterisation, and 2 novel methodological advancements.