On the microstructural stability of TiAl/Ti3Al polysynthetically twinned crystals under creep conditions
On the microstructural stability of TiAl/Ti3Al polysynthetically twinned crystals under creep conditions
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DOI：
10.1080/01418610008216473
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发表时间：
2000-10
期刊：
影响因子：
--
通讯作者：
G. Wegmann;K. Maruyama
中科院分区：
文献类型：
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作者：
G. Wegmann;K. Maruyama
摘要通过定量描述微观结构变量（片层间距、α2间距和α2体积分数）来表征蠕变试验前后多合成孪生（PST）试样的片层结构。在1150 K保温时，不仅蠕变变形试样发生明显的α2 → γ相变，而且简单热处理试样也发生明显的α2 → γ相变。α2相向γ相的转变是通过α2相的部分溶解进行的。导致α2层间距的显著增加。α2分解的驱动力被确定为完成生长态PST晶体中未达到的热力学平衡的化学力。在蠕变变形过程中，片层细化有两个过程，即平行于片层界面的机械孪晶和α2片层中γ相的二次析出。平行于层状界面的机械孪晶在软取向PST试样中比在硬取向PST试样中明显得多。这两种细化过程导致界面总数的增加，即使一些α2-γ界面由于α2溶解而消失。这两种细化工艺都有助于层状α2 + γ合金在蠕变过程中的自强化，从而使层状组织具有上级抗蠕变性。
Abstract The lamellar structure of polysynthetically twinned (PST) specimens has been characterized before and after creep testing in terms of a quantitative description of the microstructural variables: lamellar spacing, α2 spacing and α2 volume fraction. An apparent α2 → γ phase transformation taking place when the samples were held at 1150k was encountered not only in creep-deformed specimens but also in a simply heat-treated specimen. The transformation of the α2 phase into the γ phase took place by partial dissolution of α2 lamellae. resulting in a substantial increase in the spacing of the α2 lamellae. The driving force for the α2 decomposition was identified as the chemical force to complete the thermodynamic equilibrium that was not reached in the as-grown PST crystals. Two processes of lamellar refinement during creep deformation were identified, namely mechanical twinning parallel to the lamellar interfaces and secondary precipitation of γ phase in α2 lamellae. Mechanical twinning parallel to the lamellar interfaces was much more pronounced in soft-oriented PST specimens than in hard-oriented PST specimens. Both refinement processes led to an increase in the total number of interfaces even though some α2–γ interfaces disappeared as a consequence of α2 dissolution. Both refinement processes may contribute to the self-strengthening of lamellar α2 + γ alloys in the course of creep and hence the superior creep resistance of the lamellar microstructure.