Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

Titanium alloys are employed in a number industries of importance to Canada including, aerospace, medical, marine, chemical processing, oil and gas, food processing and automotive, often in critical applications. Various types of defects have been identified by the titanium industry and understanding the mechanisms by which these defects can be eliminated is therefore critically important in reducing the processing cost and improving the performance of titanium and its alloys. Two of the defects of concern are: 1) the Type-I, high interstitial defect; and 2) the Type II alpha stabilized defect. Both represent localized chemical in-homogeneities that when present can lead to a significant degradation in the mechanical performance of the alloy, particularly in applications involving cyclic loading. Various approaches are used commercially to avoid their occurrence including feedstock control and melt refining. In the melt consolidation processes, their effective removal hinges on sufficient time at temperature to allow chemical homogenization.
The Type-I, Ti-N, defect is often referred to as the most troublesome, owing to the significant increase in melting temperature that arises at relatively low concentrations of nitrogen - e.g. the melting point increases from 1670 oC to over 2250 oC with as little as 5 wt% nitrogen in solution. As a consequence, this defect is extremely challenging to remove in the various commercial melt-consolidation technologies used in primary titanium processing, including Electron Beam Cold Hearth Remelting (EBCHR) and Plasma Arc Remelting (PAM). A second defect of concern is associated with the so-called condensate drop-in event, which can arise during the electron-beam processing of Al bearing Ti alloys. The condensate can contain 68 to 72% Al in the form of stoichiometric TiAl3 in an Al matrix. If the solid condensate enters the mould or refining hearth (the former being more problematic) and does not fully melt and homogenize, the result can be relative soft alpha-stabilized region.
There is a pressing need for additional work of a fundamental nature to better understand the dissolution/melting of these defects in liquid titanium in order to design the next generation of innovative processes. To address the gaps in our knowledge, the proposed program of research involves conducting experiments on liquid titanium using the Electron Beam Button Furnace (EBBF) at UBC in which solid rods of the relevant compositions will be introduced and removed at various times to quantify the extent of dissolution/melting. Additionally, fundamentally-based numerical models will be developed to describe heat, mass, momentum and chemical species transport during the experimental program. This combined approach will yield critical information on the mechanisms controlling homogenization of these defects that is currently missing from the literature.