The Limits of Low Temperature Superplasticity in AA 5083 Produced By Accumulative Roll Bonding (ARB)
The Limits of Low Temperature Superplasticity in AA 5083 Produced By Accumulative Roll Bonding (ARB)
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DOI：
10.1007/s11661-022-06800-4
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发表时间：
2022-09
期刊：
影响因子：
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通讯作者：
B. McBride;A. Clarke;K. Clarke
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文献类型：
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作者：
B. McBride;A. Clarke;K. Clarke
累积叠轧焊（ARB）是一种用于产生有利于低温超塑性的显微组织的剧烈塑性变形技术。这种处理技术不仅产生亚微米晶粒，而且产生具有增加的晶界扩散率的非平衡晶界。低温超塑性（225 <T< 250 °C）以40和80 kJ/mol之间的活化能实现;显著低于通常报道的由晶界扩散限制的晶界滑动的活化能（84 kJ/mol）。这种活化能的降低是非平衡晶界发展的直接结果，其允许在显著较低的温度下增强的扩散速率。 在225 °C和250 °C之间热暴露15分钟后，活化能增加到100 kJ/mol以上，进一步证明低温超塑性在很大程度上依赖于ARB产生的亚稳晶界结构。在减薄率（to/tf）约为2.0（ε= 0.75，e = 1.12）时，最佳低温超塑性条件下的空穴空泡面积分数远低于1%，这远远上级应变到类似水平的常规加工材料（T= 500 °C）中达到的0.5%。本文不仅为亚微米晶材料超塑性的温度和应变速率极限提供了理论框架，而且还研究了与成形工业相关的关键参数，包括损伤累积、应变局部化和微观结构的热稳定性。
Accumulative roll bonding (ARB) is a severe plastic deformation technique used to produce microstructures conducive for low temperature superplasticity. This processing technique not only produces sub-micron grains but also non-equilibrium grain boundaries with increased grain boundary diffusivity. Low temperature superplasticity (225 <T< 250 °C) was achieved with activation energies between 40 and 80 kJ/mol; significantly lower than what is commonly reported for grain boundary sliding limited by grain boundary diffusion (84 kJ/mol). This reduction in activation energy is a direct result of non-equilibrium grain boundary development which allows for enhanced diffusion rates at substantially lower temperatures. Activation energies increased above 100 kJ/mol after 15 min of thermal exposure between 225 °C and 250 °C, providing further evidence that low temperature superplasticity relies heavily on the metastable grain boundary structure produced by ARB. The cavitation void area fraction for optimal low temperature superplastic conditions was well below 1 pct for thinning ratios (to/tf) around 2.0 (ε= 0.75,e= 1.12), which is far superior compared to the ≈ 5 pct achieved in conventionally processed material (T= 500 °C) strained to similar levels. This work not only provides a framework for the temperature and strain rate limits of superplasticity of submicron grained material, but also investigates critical parameters pertinent to the forming industry, including damage accumulation, strain localization and thermal stability of microstructure.