Dissolution Kinetics of Inclusions in Titanium Alloys

钛合金中夹杂物的溶解动力学

• 批准号: RGPIN-2017-03785
• 负责人: Cockcroft, Steven
• 金额: $ 1.75万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=679663
• 关键词: Dissolution; Kinetics; Inclusions; Titanium; Alloys

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.

钛合金应用于许多对加拿大重要的行业，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加工成本和提高钛及其合金的性能至关重要。值得关注的两个缺陷是：1）I 型，高间隙缺陷； 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，会导致合金机械性能显着下降，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实现化学均质化。 ***I 型 Ti-N 缺陷通常被认为是最麻烦的，因为在相对较低浓度的氮（例如，氮气浓度）下会出现熔化温度显着升高。当溶液中的氮含量低至 5 wt% 时，熔点就会从 1670 oC 升至 2250 oC 以上。 因此，在初级钛加工中使用的各种商业熔体固结技术（包括电子束冷床重熔（EBCHR）和等离子弧重熔（PAM））中，消除这种缺陷极具挑战性。第二个值得关注的缺陷与所谓的冷凝物滴入事件有关，这种现象可能在含铝钛合金的电子束加工过程中出现。冷凝物可以在Al基体中含有化学计量TiAl 3 形式的68％至72％的Al。如果固体冷凝物进入模具或精炼炉床（前者问题较多）并且没有完全熔化和均质化，则结果可能是相对较软的α稳定区域。 ***迫切需要进行额外的基础性工作，以更好地了解液态钛中这些缺陷的溶解/熔化，以便设计下一代创新工艺。 为了弥补我们的知识差距，拟议的研究计划包括使用 UBC 的电子束纽扣炉 (EBBF) 进行液态钛实验，其中将在不同时间引入和移除相关成分的固体棒，以量化程度溶解/熔化。此外，还将开发基于基础的数值模型来描述实验过程中的热量、质量、动量和化学物质的传递。这种组合方法将产生有关控制这些缺陷均质化机制的关键信息，而这些信息目前在文献中是缺失的。