Abstract The twinning behaviors and grain refinement mechanisms during friction stir processing (FSP) of Zircaloy-4 were studied. The main deformation mode changed due to temperature and strain gradient existed in different regions of FSP sample. The 10 1 ¯ 2 and 10 1 ¯ 1 twins were activated successively in thermo-mechanically affected zone (TMAZ) but reduced rapidly and replaced by dislocations slip in stir zone (SZ) because of the elevated temperature and decreased grain size. Accordingly, the grain refinement mechanisms also varied with the deformation modes. A new recrystallization mechanism, twinning induced dynamic recrystallization (TDRX) was proposed for the first time in FSPed Zr alloy, which resulted in grain refinement in TMAZ. The occurrence of TDRX included the formation of slipped 10 1 ¯ 2 twin boundaries and the transformation of 10 1 ¯ 1 twins into high angle grain boundaries (HAGBs); these were attributed to the interaction between twins and dislocations. In contrast, continuous dynamic recrystallization (CDRX) related to dislocations slip at higher temperatures dominated the process of grain refinement in SZ, and finally the ultrafine grains with average size of ~1 μm were obtained.

中文翻译：

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Zr合金搅拌摩擦加工过程中的孪晶行为及晶粒细化机制

摘要 研究了Zircaloy-4 搅拌摩擦加工(FSP) 过程中的孪晶行为和晶粒细化机制。由于FSP样品不同区域存在温度和应变梯度，主要变形模式发生了变化。10 1 ¯ 2 和10 1 ¯ 1 孪晶在热机械影响区（TMAZ）中相继被激活，但由于温度升高和晶粒尺寸减小，在搅拌区（SZ）中迅速减少并被位错滑移取代。因此，晶粒细化机制也随着变形模式而变化。首次在FSPed Zr合金中提出了一种新的再结晶机制，孪生诱导动态再结晶（TDRX），导致TMAZ晶粒细化。TDRX 的发生包括滑移的 10 1 ¯ 2 孪晶界的形成和 10 1 ¯ 1 孪晶向大角度晶界（HAGBs）的转变；这些归因于双胞胎和位错之间的相互作用。相比之下，在高温下与位错滑移相关的连续动态再结晶（CDRX）主导了 SZ 的晶粒细化过程，最终获得了平均尺寸约为 1 μm 的超细晶粒。