锆合金α→β→α相变过程中的变体选择与织构控制研究

During thermomechanical fabrication, texture can be easily developed in Zr alloys and would significantly affect their ductility and in-reactor performance. The texture can be altered to a very limited extent by implementing plastic deformation and recrystallization annealing within the α phase domain. Phase transformation happened at high temperatures, on the other hand, is believed to be capable of producing a random texture if there is no phase variant selection. On the contrary, the occurrence of variant selection could make the original texture be perfectly inherited after phase transformation, i.e., the so called “texture memory” phenomenon. In this program, multiple modern techniques (such as EBSD and t-EBSD) of characterizing and analyzing materials will be employed to conduct a systematical study on the variant selection behavior in Zr alloys. Microstructure and orientation characteristics of all α- and β-variants will be investigated. Effects of heat-treatment parameters, cooling rates and grain/phase boundaries on the variant selection will be explored. In the end, the in-depth mechanism controlling the variant selection in Zr alloys will be clarified and a quantitative relationship between micro phase variant and macro texture is expected to be established. Work to be carried out in this program can not only contribute much to the fundamental theory of phase transformation and texture control, but also provide important suggestions for optimizing process parameters and enhancing in-reactor performance.

锆合金在生产加工过程中很容易形成稳定的织构，它们会显著影响其后续的塑性加工能力及在核反应堆内的最终服役表现。限定在α相区的塑性加工和再结晶退火对锆合金织构的改变非常有限；高温β相变可以使锆合金的织构极大弱化，但当存在变体选择时，相变前后的织构有可能完全相同。本项目拟采用包括EBSD和t-EBSD在内的多种材料测试分析手段，对锆合金在α→β→α相变过程中的变体选择行为进行系统深入地研究，明确所有相变变体的微观组织和晶体取向特征，探索热处理参数、冷却速率、晶界（相界）结构等对变体选择的影响，阐明变体选择行为产生的微观机理，并尝试建立微观相变变体与材料宏观织构间的定量关系等。该课题的顺利开展，不仅可以为锆合金的相变及织构控制理论提供重要的基础研究积累，还可以对优化其加工工艺和服役性能提供直接的理论指导。

锆合金在生产加工过程中很容易形成稳定的织构，它们会显著影响其后续的塑性加工能力及在核反应堆内的最终服役表现。限定在α相区的塑性加工和再结晶退火对锆合金织构的改变非常有限；高温β相变可以使锆合金的织构极大弱化，但当存在变体选择时，相变前后的织构有可能完全相同。本项目采用包括EBSD、t-EBSD、TEM、XRD等在内的多种材料测试分析手段，对两种典型锆合金在α→β→α相变过程中的变体选择行为进行了系统深入地研究，明确了相变变体的基本微观组织和晶体取向特征，探索了热处理参数（保温温度和时间）、冷却速率、晶界（相界）结构等对变体选择的影响，初步阐明了变体选择行为产生的微观机理，并尝试建立了微观相变变体与材料宏观织构间的定量关系等。本研究取得了较丰富的成果，它们不仅为锆合金的相变及织构控制理论提供了重要的基础研究积累，还为优化锆合金的加工工艺和服役性能提供了重要的理论指导。