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

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 CrMn3 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 degrees C, the Cr/Mn-segregated regions gradually dissolved into the matrix and then disappeared, and from 900 degrees C to 1000 degrees C, they existed as CrMn3 precipitates. The crystallite size of the phase corresponding to CrMn3 precipitates was about 29.4 nm at 900 degrees C and 43.7 nm at 1000 degrees 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 CrMn3 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 CrMn3 precipitates.

Automated summary

In this study, the evolution of vacancy-like defects and the formation of brittle precipitates in a reduced-activation V-Cr-Mn medium-entropy alloy were investigated. Various characterization techniques were used to study the local electronic circumstances, vacancy defects, and CrMn3 precipitates. The results showed that the Mn and Cr enrichments dissolved into the matrix at high temperatures and formed as CrMn3 precipitates at elevated temperatures. The vacancy defects mediated the migration of Cr and Mn, leading to the formation of CrMn3 precipitates.