Dissolution Kinetics of Inclusions in Titanium Alloys

钛合金在加拿大的许多重要行业中使用，包括航空航天，医疗，海洋，化学加工，石油和天然气，食品加工和汽车，通常用于关键应用。钛工业已经确定了各种类型的缺陷，因此，了解可以消除这些缺陷的机制对于降低加工成本和提高钛及其合金的性能至关重要。其中两种值得关注的缺陷是：1）I型，高间隙缺陷;和2）II型α稳定缺陷。两者都代表局部化学不均匀性，当存在时，其可导致合金的机械性能显著降低，特别是在涉及循环负载的应用中。商业上使用各种方法来避免它们的发生，包括原料控制和熔体精炼。在熔融固结过程中，它们的有效去除取决于在允许化学均匀化的温度下的足够时间。* I型Ti-N缺陷通常被认为是最麻烦的，因为在相对低浓度的氮下会显著提高熔化温度-例如，在溶液中只有5重量%的氮时，熔点从1670 oC提高到2250 oC以上。 因此，这种缺陷在用于初级钛加工的各种商业熔体固结技术中去除极具挑战性，包括电子束冷床重熔（EBH 40）和等离子弧重熔（PAM）。第二个缺陷与所谓的冷凝液落入事件有关，这可能在含Al钛合金的电子束加工过程中出现。冷凝物可以在Al基质中含有68至72%的化学计量的TiAl 3形式的Al。如果固体冷凝物进入模具或精炼炉（前者更成问题）并且没有完全熔化和均化，则结果可以是相对软的α稳定区域。* 迫切需要进行更多的基础性工作，以更好地了解液态钛中这些缺陷的溶解/熔化，从而设计下一代创新工艺。 为了解决我们的知识差距，拟议的研究计划涉及使用UBC的电子束纽扣炉（EBBF）对液体钛进行实验，其中相关成分的固体棒将在不同时间引入和移除，以量化溶解/熔化的程度。此外，将开发基于基本的数值模型来描述实验计划期间的热量，质量，动量和化学物质传输。这种结合的方法将产生关键信息的机制控制这些缺陷的均匀化，目前从文献中缺失。

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.