Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 76 Page 77 Page 78 Page 79 Page 80 Page 81 Page 82 Page 83 Page 84 Page 85 Page 86 Page 87 Page 88 Page 89 Page 90 Page 91 Page 92 Page 93 Page 94 Page 95 Page 96 Page 97 Page 98 Page 99 Page 100 Page 101 Page 102 Page 103 Page 104 Page 105 Page 106 Page 107 Page 108 Page 109 Page 110 Page 111 Page 112 Page 113 Page 114 Page 115 Page 116 Page 117 Page 118 Page 119 Page 120 Page 121 Page 122 Page 123 Page 124Nuclear Science User Facilities 106 were prepared at the ORNL LowActiva- tion Materials Development andAnalysis (LAMDA) facility using standard focused ion beam (FIB) lift‑out techniques. Atom probe data was collected using the CAMECA LEAP 4000X HR located at both the Center for Nanophase Materials Science (CNMS) at ORNL and the Microscopy and Characterization Suite (MaCS) at the Center forAdvanced Energy Studies (CAES).The samples were analyzed in laser mode at 50 K, with a pulse frequency of 200 kHz, laser pule energy of 50 pJ, and a detection rate of 0.005–0.02 atoms per pulse. Data was reconstructed and analyzed using CAMECA’s IntegratedVisualization and Analysis Software (IVAS)Version 3.6.8. Dependence of precipitation on Cr and Al content was determined by analyzing the 7-dpa condition of each model alloy composition. In addition, evolution of precipitate morphology with dose was investigated by analyzing specimens from the Fe‑18Cr‑2.9Al composition irradiated to 0.8, 1.8, and 7 dpa, in addition to the as-received state. Representative reconstructions of the specimens of different composi- tions irradiated to 7 dpa are found in Figure 1. Reconstructions of the Fe‑18Cr‑2.9Al specimens irradiated to different nominal damage doses are found in Figure 2. It was found that the volume fraction and Cr content of precipitates both increased with increasing Cr content and decreasingAl content. However, the Cr content of the α’ clusters in all FeCrAl alloys studied was consistently lower than the reported saturation composition of α’ clusters observed in the FeCr binary system. Furthermore, cluster number density trended upward with increasing bulk Cr content, but saw a decrease at the highest bulk Cr content coupled with an increase in average cluster size.With regards to dose dependence, a high number density of smaller precipitates is seen in the lower dose specimens with volume fraction and cluster Cr content increasing asymptotically with increasing neutron fluence.This indicates that these clusters are begin- ning to nucleate and grow after short irradiation times and proceed to coarsen as irradiation continues. Plots illustrating the composition and dose dependencies of observed cluster size and number density are shown in Figures 3 and 4. Figure 3. Trends in calculated cluster number density and average spherical equivalent cluster radius for α’ precipitates in 7 dpa Fe‑Cr‑Al for the four model alloy compositions. Atom probe tomography capabilities at the CAES facility has allowed for a detailed assessment of embrittlement mechanisms in candidate LWR accident- tolerant fuel cladding materials. — Samuel A.Briggs Ph.D.Candidate,Department of Engineering Physics,University of Wisconsin-Madison