报告人：普渡大学Janelle P. Wharry教授
时 间：2019年8月21日9：30-11：30
地 点：北二楼1402报告厅
邀请人：能动学院 卢晨阳教授
报告内容：
The objective of this talk is to understand how irradiation-induced defects control the deformation-induced martensitic phase transformation in austenitic stainless steels (SS). Austenitic SSs are amongst the most widely utilized structural alloys in nuclear energy systems, where SS components must bear mechanical load while also accumulating irradiation damage. Hence, understanding the role of irradiation on deformation mechanisms is critical to ensuring long-term safety and structural integrity of nuclear components. SSs typically deform through dislocation slip, although in the presence of irradiation, localized deformation mechanisms such as twinning and dislocation channeling can become active. Sometimes, a deformation-induced phase transformation can also occur, in which the 𝛾-fcc SS transforms into either 𝛼′-bcc or 𝜀-hcp martensite needles. This work will demonstrate how the presence of irradiation-induced cavities (e.g. voids and/or bubbles) can increase the tendency for the martensitic transformation to occur.
Work focuses on AISI 304L stainless steel specimens irradiated in EBR-II to damage doses of 320 displacements per atom (dpa) at 415°C, and containing ~0.1-3 atomic parts per million (appm) He. Portions of each specimen undergo post-irradiation annealing in order to alter the cavity microstructure. Micro-scale mechanical testing in situ within a scanning electron microscope (SEM) is carried out in both indentation and compression pillar geometries. Subsequently, site-specific transmission electron microscopy (TEM) enables us to precisely determine deformation mechanisms and their interaction with the microstructure. We find that a high number density of large cavities promotes the direct 𝛾→𝛼′ transformation. Post-irradiation annealing reduces the number density of cavities, causing the transformation pathway to change to 𝛾→𝜀→𝛼′. With an even further reduced cavity number density, twinning occurs instead of the phase transformation. These results are explained by the surface energy contribution from cavities. This work suggests that controlling the irradiated microstructure can enable localized tailoring of the deformation mechanism and phase transformation pathway.
报告人简介：
Janelle P. Wharry博士担任普渡大学核工程学院终身制助理教授，同时兼任材料工程学院教授。Wharry博士的研究方向为理解辐照材料的微观结构与性能之间的关系，尤其是纳米尺度/微观尺度下的变形机制和力学行为。 Wharry博士从事的科研项目涵盖核结构及包壳材料、先进制造及焊接的结构材料、金属和氧化物核燃料以及电陶瓷材料。Wharry博士已经发表超过55篇高水平学术文章。2012年，Janelle P. Wharry于密西根大学获得了核工程和放射科学博士学位。Wharry博士曾获得能源部（DOE）青年职业奖、国家科学基金会职业奖、橡树岭联合大学项目（ORAU）青年教师奖和TMS青年领袖专业发展奖。Wharry博士担任2019年MiNES会议的大会主席，ASTM国际辐射损伤模拟程序委员会主席，NEA-OECD辐照材料特性标准制定工作组受邀成员，美国核学会（ANS）材料科学技术部前主席。