Dissolution Kinetics of Inclusions in Titanium Alloys

钛合金被用于加拿大的许多重要行业，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。钛工业已经发现了各种类型的缺陷，因此了解消除这些缺陷的机制对于降低钛及其合金的加工成本和提高其性能至关重要。值得关注的两种缺陷是：1)i型，高间质缺陷；2) II型α稳定缺陷。两者都代表了局部的化学不均匀性，当这种不均匀性存在时，会导致合金的机械性能显著下降，特别是在涉及循环加载的应用中。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。在熔体固结过程中，它们的有效去除取决于在温度下足够的时间以允许化学均质化。*** i型（Ti-N）缺陷通常被认为是最麻烦的，因为在相对较低的氮浓度下，熔化温度会显著升高，例如，当溶液中氮含量仅为5wt %时，熔点从1670℃增加到2250℃以上。因此，在各种用于初级钛加工的商业熔固技术中，包括电子束冷炉重熔（EBCHR）和等离子体电弧重熔（PAM），该缺陷极具挑战性。第二个值得关注的缺陷与所谓的凝析液滴入事件有关，这可能在电子束加工含Al钛合金期间出现。在Al基体中，冷凝物以化学计量TiAl3的形式含有68 - 72%的Al。如果固体冷凝水进入模具或精炼炉（前者更有问题），并且没有完全熔化和均匀化，结果可能是相对软的α稳定区域。***迫切需要进行额外的基础性工作，以更好地了解这些缺陷在液体钛中的溶解/熔化，以便设计下一代创新工艺。为了解决我们知识上的空白，提出的研究计划包括在UBC使用电子束按钮炉（EBBF）对液体钛进行实验，在实验中，相关成分的固体棒将在不同时间被引入和移除，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过程中的热量、质量、动量和化学物质输运。这种结合的方法将产生关于控制这些缺陷均质化机制的关键信息，这些信息目前在文献中缺失。

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.