@article{selim_liedke_ayyappan_chung_butterling_agarwal_beausoleil_hattar_wagner_kaoumi_2025, title={Defect interactions with the microstructure in multi-principal element alloys and the role of phase separation and precipitation}, DOI={10.1038/s41529-025-00723-2}, abstractNote={Defects in materials form, interact, and evolve at the atomic level. The measurements and analysis of their atomic level generation and evolution can reveal the mechanisms of defect interactions which dictate the macroscopic material properties and strength. Here we investigate atomic scale defects in multi-principal element alloys (MPEAs) of four and five elements. We combine positron annihilation spectroscopy (PAS) with a rigorous analysis of the phases, microstructures, and chemical compositions by x-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX). PAS reveals an interesting phenomenon in which ion irradiation induced defects substantially reduce the size of the original vacancy clusters in alloys of specific chemical compositions. The study shows the strong impact of the nature of chemical disorder on atomic scale defect interactions and evolution during growth and irradiation. Replacing one element or changing its percentage modifies the phase and segregation and strongly impact defect formation. Depletion of Ni from the matrix enhances defect formation and clustering and hinders the alloy radiation tolerance while the formation of dendric structure reduces point defect formation and improves radiation resistance. This study manifests the complexity of the interaction between the chemical arrangement of atoms and defect migration and evolution in MPEAs and demonstrates that defect interactions are driven by phase nature, phase separation and segregation of elements.}, journal={npj Materials Degradation}, author={Selim, F. A. and Liedke, M. O. and Ayyappan, S. and Chung, T. and Butterling, M. and Agarwal, S. and Beausoleil, G. and Hattar, K. and Wagner, A. and Kaoumi, D.}, year={2025}, month={Dec} }
 @article{ayyappan_forrester_selim_beausoleil_kaoumi_2025, title={Effect of Al addition to the multi-principal elemental AlxCrFeNiCu alloy system in terms of the resulting microstructure and ion irradiation response}, volume={1031}, url={https://doi.org/10.1016/j.jallcom.2025.180882}, DOI={10.1016/j.jallcom.2025.180882}, journal={Journal of Alloys and Compounds}, author={Ayyappan, Saikumaran and Forrester, Jennifer S. and Selim, Farida and Beausoleil, Geoffrey and Kaoumi, Djamel}, year={2025}, month={May} }
 @article{ayyappan_kaoumi_2025, title={Irradiation induced martensitic transformation and ordering in AlxFeCrNiMn multi-principal elemental alloys}, volume={225}, DOI={10.1016/j.matchar.2025.115115}, journal={Materials Characterization}, author={Ayyappan, Saikumaran and Kaoumi, Djamel}, year={2025}, month={May} }
 @article{chung_liedke_ayyappan_butterling_ferguson_jones_wagner_hattar_kaoumi_selim_2025, title={Point Defects in MoNbTi-Based Refractory Multi-Principal-Element Alloys}, volume={15}, DOI={10.3390/met15090989}, abstractNote={As emergent material candidates for extreme environments, refractory high-entropy alloys (HEAs) or refractory multi-principal-element alloys (RMPEAs) comprising refractory metals feature qualities such as high radiation tolerance, corrosion resistance, and mechanical strength. A set of MoNbTi-based RMPEA samples with Al, Cr, V, and Zr additions are prepared by spark plasma sintering and investigated for their response to irradiation using 10 MeV Si+ ions with a dose of 1.43×1015 ions/cm2. Positron annihilation spectroscopy and transmission electron microscopy are employed as atomic- and meso- scale techniques to reveal how chemical complexity, nanotwinning, and phase fractions play an important role in radiation-induced defect accumulation and damage tolerance. The study provides experimental evidence of nanotwinning acting as an effective sink for radiation-induced point defects.}, number={9}, journal={Metals}, author={Chung, Thai and Liedke, Maciej Oskar and Ayyappan, Saikumaran and Butterling, Maik and Ferguson, Riley Craig and Jones, Adric C. L. and Wagner, Andreas and Hattar, Khalid and Kaoumi, Djamel and Selim, Farida A.}, year={2025}, month={Sep} }