Effect of Vacancy Behavior on Precipitate Formation in a Reduced-Activation V-Cr-Mn Medium-Entropy Alloy

• Published in: Materials Vol. 16; no. 1; p. 153
• Main Authors: Wang, Tianjiao, Zhu, Te, Wang, Dandan, Zhang, Peng, Song, Yamin, Ye, Fengjiao, Wang, Qianqian, Jin, Shuoxue, Yu, Runsheng, Liu, Fuyan, Kuang, Peng, Wang, Baoyi, Li, Liben, Cao, Xingzhong
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 23.12.2022; MDPI
• Subjects: Alloys; Annealing; Building materials; Chemical precipitation; coincidence Doppler broadening; Crystal defects; Crystallites; Ductility; Entropy; Evolution; Grain boundaries; Medium entropy alloys; Nuclear energy; Nuclear power plants; Nuclear reactors; Positron annihilation; positron annihilation lifetime; precipitate; Precipitates; Radiation; Radioactive wastes; Research methodology; Scanning electron microscopy; Spectrum analysis; vacancy; precipitate; positron annihilation lifetime; vacancy; coincidence Doppler broadening
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma16010153

In this work, we studied the evolution of vacancy-like defects and the formation of brittle precipitates in a reduced-activation V-Cr-Mn medium-entropy alloy. The evolution of local electronic circumstances around Cr and Mn enrichments, the vacancy defects, and the CrMn precipitates were characterized by using scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, and positron annihilation spectroscopy. The microstructure measurements showed that the Mn and Cr enrichments in the as-cast sample significantly evolved with temperature, i.e., from 400 °C, the Cr/Mn-segregated regions gradually dissolved into the matrix and then disappeared, and from 900 °C to 1000 °C, they existed as CrMn precipitates. The crystallite size of the phase corresponding to CrMn precipitates was about 29.4 nm at 900 °C and 43.7 nm at 1000 °C. The positron annihilation lifetime results demonstrated that the vacancies mediated the migration of Cr and Mn, and Cr and Mn segregation finally led to the formation of CrMn precipitates. The coincidence Doppler broadening results showed that the characteristic peak moved to the low-momentum direction, due to an increase in the size of the vacancy defects at the interface and the formation of CrMn precipitates.