A cracking oxygen story: A new view of stress corrosion cracking in titanium alloys
A cracking oxygen story: A new view of stress corrosion cracking in titanium alloys
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DOI：
10.1016/j.actamat.2022.117687
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发表时间：
2022-02-02
期刊：
影响因子：
9.4
通讯作者：
Dye, David
中科院分区：
文献类型：
--
作者：
Joseph, Sudha;Kontis, Paraskevas;Dye, David
钛合金在高温下会出现卤化物相关的应力腐蚀开裂，例如，在喷气发动机中，氯化物和ti -氧化物促进气流中的水蒸气开裂，在裂纹尖端沉积脆化物质。通过同位素标记实验，我们发现工业Ti-6Al-2Sn-4Zr-6Mo合金的裂纹尖端富集（bbb5 at）。从水蒸气中吸收的氧含量（%）远高于（0.25 %）。%)以使材料脆化。令人惊讶的是，尽管进行了仔细的准备和分析，但测量到的氢（氘）相对较少。因此，我们认为O和H的共同作用导致了裂纹，其中O起着至关重要的作用，因为众所周知它会导致合金的脆化。相反，在α + β Ti合金中，H可能由于其在β Ti中的高溶解度而流失到基体中，而不是保留在裂纹尖端的应力场中。因此，虽然氢化物可能在断口表面形成，但氢的进入可能不是下垫层基体脆化的唯一合理机制。这种可能性挑战了几十年来对应力腐蚀开裂的理解，因为它仅仅与氢增强的局部塑性（HELP）机制有关，这解释了为什么掺h的钛合金脆化。这将改变对应力腐蚀脆化的看法，不再仅仅关注氢，而是考虑来自水蒸气的O的进入，这对设计耐腐蚀材料至关重要。(c) 2022 materials Inc.Elsevier Ltd.出版。版权所有。
Titanium alloys can suffer from halide-associated stress corrosion cracking at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide promote the cracking of water vapour in the gas stream, depositing embrittling species at the crack tip. Here we report, using isotopically-labelled experiments, that crack tips in an industrial Ti-6Al-2Sn-4Zr-6Mo alloy are strongly enriched (> 5 at.%) in oxygen from the water vapour, far greater than the amounts (0.25 at.%) required to embrittle the material. Surprisingly, relatively little hydrogen (deuterium) is measured, despite careful preparation and analysis. Therefore, we suggest that a combined effect of O and H leads to cracking, with O playing a vital role, since it is well-known to cause embrittlement of the alloy. In contrast it appears that in alpha + beta Ti alloys, it may be that H may drain away into the bulk owing to its high solubility in beta-Ti, rather than being retained in the stress field of the crack tip. Therefore, whilst hydrides may form on the fracture surface, hydrogen ingress might not be the only plausible mechanism of embrittlement of the underlying matrix. This possibility challenges decades of understanding of stress-corrosion cracking as being related solely to the hydrogen enhanced localised plasticity (HELP) mechanism, which explains why H-doped Ti alloys are embrittled. This would change the perspective on stress corrosion embrittlement away from a focus purely on hydrogen to also consider the ingress of O originating from the water vapour, insights critical for designing corrosion resistant materials. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.