高钛诱导平面滑移转变向超晶格外在堆垛fault和微孪晶在蠕变CoNi基超合金中
High-Ti induced planar-fault transformation toward superlattice extrinsic stacking faults and microtwins in crept CoNi-based superalloys
AI总结：
高钛含量促进CoNi基超合金中超晶格外在堆垛fault和微孪晶形成，通过改变平面滑移机制提升蠕变性能。
摘要：
控制平面滑移剪切机制是提高gamma prime强化高温超合金高温蠕变性能的关键。本研究探讨了在L12强化的CoNi基合金中，钛浓度如何影响蠕变期间平面滑移形成。在1223 K的空气中，以241 MPa的恒定负载应力进行了中断压缩蠕变试验。我们首次发现，高钛添加将主导的gamma prime剪切模式从无相界（APBs）在无钛和低钛合金中转移到超晶格外在堆垛fault（SESFs）。系统性的从头计算显示，在高钛合金中，升高的APB能量使APB剪切模式不利。然而，SESF能量相对于低钛组成减少，且复杂内在堆垛fault（CISF）与SESF能量比增加促进高能CISF向低能SESF转变。利用扫描透射电子显微镜结合能谱分析进一步发现，高钛合金中的SESF富含钛、钼和钨，但未观察到网格状排列。结合从头计算，高钛合金中的钼和钨添加可促进从L12结构到低能D024结构的转变，表明钼和钨沿SESF的偏析在能量上是有利的。此外，连续的SESF增厚在没有D024排列沿SESF的情况下促进微孪晶形成，作为额外的蠕变应变载体。这些新发现阐明了钛在控制平面滑移剪切机制中的作用，为优化下一代CoNi基超合金的蠕变性能提供了新的见解。
英文摘要：
Controlling planar fault shearing mechanisms is key for improving the high-temperature creep performance of gamma prime-strengthened high-temperature superalloys. This work examines how the Ti concentration in L12-strengthened CoNi-based alloys affects planar fault formation during creep. Interrupted compressive creep tests were conducted at 1223 K under air with a constant load stress of 241 MPa. We found, for the first time, that high Ti additions shift the dominant gamma prime shearing mode from antiphase boundaries (APBs) in Ti-free and low-Ti alloys to superlattice extrinsic stacking faults (SESFs). Systematic ab initio calculations show that in high-Ti alloys, the elevated APB energy renders APB-shearing mode unfavorable. Nevertheless, the SESF energy decreases relative to that in low-Ti compositions, and an increased ratio of complex intrinsic stacking fault (CISF) to SESF energy promote the transformation of high-energy CISFs into lower-energy SESFs. Chemical analysis using scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy further reveals that, SESFs in high-Ti alloys are enriched in Ti, Mo and W, yet no grid-like ordering is observed. Together with the ab initio calculations, Mo and W additions in high Ti alloys could facilitate the transformation from L12 structure to low-energy D024 structure, indicating Mo and W segregation along SESFs is energetically favourable. Furthermore, the successive SESF thickening facilitates microtwinning in the absence of D024 ordering along SESFs, as an additional big carrier for creep strain. These new findings clarify the role of Ti in controlling planar fault shearing mechanisms, providing new insights for optimizing the creep performance of next-generation CoNi-based superalloys.
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