Temperature-dependent defect recombination mechanism in concentrated alloys from accelerated dynamics simulations

It is generally regarded that chemical disorder in concentrated solid solution alloys (CSAs) can significantly promote defect recombination, which is a primary contributor to the outstanding irradiation resistance observed in high-entropy alloys (HEAs). Nonetheless, the recent discovery of distinct temperature-dependent irradiation responses in NiFe and NiCoCr suggests that the role of chemical disorder is not consistent under different temperatures. In this work, we study the recombination of Frenkel pairs in CSAs at varying temperatures by means of accelerated dynamics simulation techniques, namely time-stamped force bias Monte Carlo (tfMC). The recombination radius R₀ is obtained and compared to that in pure Ni. Our results reveal that in Ni, R₀ continuously decreases with increasing temperature due to the weakened interactions between the Frenkel pair at elevated temperatures. However, in concentrated NiFe and NiCoCr alloys, the influence of alloy compositions on R₀ exhibits different trends at low and high temperatures. At low temperatures, chemical complexity fosters long-distance recombination by promoting the formation of 〈110〉 dumbbells. With elevated temperature, however, relatively stable 〈110〉 dumbbells in NiCoCr suppress recombination at long distances, leading to small R₀. In contrast, the increased ratio of energy-unfavorable Ni-Fe dumbbells in NiFe results in large R₀ at high temperatures. These distinct temperature-dependent recombination behaviors corroborate with experiment observations that NiCoCr no longer outperforms NiFe at high temperatures. Our study pinpoints two key factors influencing R₀: interstitial-vacancy interaction strengths and stability of dumbbells with different orientations and compositions, underscoring the intricate relationship between temperature and alloy composition in governing the Frenkel defect recombination mechanism in CSAs. © 2025 Acta Materialia Inc. Published by Elsevier Inc.