The bcc-to-9R martensitic transformation of Cu precipitates and the relaxation process of elastic strains in an Fe-Cu alloy
The bcc-to-9R martensitic transformation of Cu precipitates and the relaxation process of elastic strains in an Fe-Cu alloy
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DOI：
10.1080/01418610008212077
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发表时间：
2000-03
期刊：
影响因子：
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通讯作者：
R. Monzen;M. Jenkins;Adrian P. Sutton
中科院分区：
文献类型：
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作者：
R. Monzen;M. Jenkins;Adrian P. Sutton
摘要利用高分辨电子显微镜研究了Fe-Cu合金在550°C时效过程中Cu析出相的bcc-9 R相变和随后的弹性弛豫。结果表明，电子辐照（在400 kV的电子能量）和热退火引起的（009）9 R平面在孪晶9 R Cu沉淀物中的紧密堆积的旋转。对于400 kV的电子辐照，这样的旋转观察到在直径小于约12 nm的沉淀。对于从550°C的时效温度冷却到-60 °C的给定温度，然后在400°C退火的样品，发现（009）9 R平面的旋转仅发生在尺寸取决于样品冷却温度的沉淀物中。这个临界尺寸范围从冷却到400°C的样品的约9 nm到冷却到−60°C的样品的4 nm。有人认为，这些临界尺寸是指示的尺寸在不同的温度下，一致的体心立方沉淀物转变马氏体。在550°C时效时，析出相尺寸约为12 nm，发生向9 R的转变。在转化的9 R沉淀物中的孪晶段的数量由转化决定，取决于沉淀物的尺寸。退火引起的平面旋转被证明是与弹性应变的扩散松弛，这是创建后的马氏体相变。从沉淀物的尺寸和退火时间的依赖性的旋转，它的结论是，通过原子扩散沿着Fe基体和Cu沉淀物之间的界面的弹性应变松弛。界面扩散的激活能为1.7eV。
Abstract High-resolution electron microscopy experiments have been performed to explore the bcc—9R transformation and the subsequent elastic relaxation of Cu precipitates in an Fe—Cu alloy aged at 550°C. It was found that both electron irradiation (at an electron energy of 400 kV) and thermal annealing caused rotation of the close-packed (009)9R planes in twinned 9R Cu precipitates. For 400 kV electron irradiation, such rotations were observed in precipitates smaller than about 12nm in diameter. For specimens cooled from the ageing temperature of 550°C to a given temperature up to −60°C, and then annealed at 400°C, the rotation of (009)9R planes was found to occur only in precipitates above a size which depended on the temperature to which the specimen had been cooled. This critical size ranged from about 9 nm for specimens cooled to 400°C, to 4 nm for specimens cooled to −60°C. It is argued that these critical sizes are indicative of the sizes at which coherent bcc precipitates transform martensitically at different temperatures. At the ageing temperature of 550°C, the transformation to 9R takes place when precipitates reach a size of about 12nm. The number of twin segments in the transformed 9R precipitates is determined by the transformation, depending on the precipitate size. The annealing-induced plane rotations are shown to be connected with the diffusional relaxation of elastic strains, which are created upon the martensitic transformation. From the precipitate size and annealing time dependence of the rotations, it is concluded that the elastic strains relax by atomic diffusion along the interfaces between the Fe matrix and Cu precipitates. The activation energy for the interfacial diffusion is evaluated to be 1.7eV.