Pengyuan Xiu

Profile Information
Mr. Pengyuan Xiu
University of Michigan
Graduate Student Research Assistant

Mr. Pengyuan Xiu is a 5th year Ph.D student in Department of Nuclear Engineering and Radiological Sciences (NERS) at University of Michigan (UM) working on ion radiation effects on Additive Manufactured HT9 alloy using combined techniques of scanning / transmission electron microscopy (S/TEM) and atom probe tomography (APT). He was previously working on radiation effects on FeCrAl and nickel-based concentrated solid solution alloys using scanning / transmission electron microscopy (S/TEM). His Ph.D advisers at UM-NERS are Prof. Kevin Field and Prof. Lumin Wang. Mr. Xiu will seek positions in academia / research after his Ph.D graduation.

APT, FeCrAl, Ion-Irradiation, Radiation Damage, Radiation Effects, STEM, TEM
"Dislocation loop evolution and radiation hardening in nickel-based concentrated solid solution alloys" Pengyuan Xiu, Journal of Nuclear Materials Vol. 538 2020 Link
Effects of chemical composition, ion irradiation dose and temperature on unfaulting of irradiation induced Frank dislocation loops to perfect loops in two nickel based single-phase solid solution alloys, Ni–20Fe and NiFe–20Cr, have been studied. The fraction of Frank loops decreases with irradiation dose from 7.2 to 38.4 dpa at 500, but with more Frank loops remaining in the ternary alloy. However, perfect loops and dislocation networks become the dominant features of defects at 580 in both alloys. The results indicate a thermally assisted loop unfaulting process that may be hindered by more sluggish defect motion in the alloy with more chemical components. Nano-indentation with both continuous stiffness method and single indentation method are used to measure radiation hardening. Loop unfaulting in both alloys irradiated at 580 reduced radiation hardening while significant hardening is observed after irradiation at 500. The quasi-static single indentation method exhibits lower hardness results compared to continuous stiffness method, because dislocations induced from the cyclic loading in the latter method get relaxed and stabilized, resulting in higher resistance to the indenter.
"Effect of dpa rate on the temperature regime of void swelling in ion-irradiated pure chromium" Adam Gabriel, Laura Hawkins, Aaron French, Yongchang Li, Zhihan Hu, Lingfeng He, Pengyuan Xiu, Michael Nastasi, Frank Garner, Lin Shao, JNM Vol. 561 2022 Link
"Microchemical evolution of irradiated additive-manufactured HT9" Pengyuan Xiu, Caleb Massey, T.M. Kelsey Green, Stephen Taller, dieter Isheim, Niyanth Sridharan, JNM Vol. 559 2022 Link
"STEM Characterization of Dislocation Loops in Irradiated FCC Alloys" Pengyuan Xiu, Journal of Nuclear Materials Vol. 544 2020 Link
In this study, we demonstrate the methodology systematically developed for dislocation loop (perfect and faulted loops) imaging and analysis in irradiated face-centered-cubic (FCC) alloys using scanning transmission electron microscopy (STEM). On-zone [001] STEM imaging was identified as the preferred choice for its accuracy and effectiveness based on the comparison with other dislocation loop imaging techniques including: (i) on-zone STEM imaging using other major low-index zone axes, (ii) kinematic two-beam conditions bright field imaging near the [001] zone axis in conventional TEM (CTEM) mode, and (iii) Rel-Rod CTEM dark-field (DF) imaging near the [011] zone axis. The effect of STEM collection angle on the contrast formation of dislocation loops was also investigated. The developed method was confirmed by imaging all populations of perfect and faulted loops of types a/2〈110〉{110} and a/3〈111〉{111} found in an ion irradiated Ni40Fe40Cr20 alloy. The proposed STEM-based technique can easily identify said loops with a size greater than 10 nm without any assumptions such as those commonly made using the conventional Rel-Rod CTEM-DF technique. The recommended methodology in this study is developed as a quick and convenient tool that can be generally applied to irradiated FCC-based materials due to their common crystallography.