Direct Observation of Vacancy‐Cluster‐Mediated Hydride Nucleation and the Anomalous Precipitation Memory Effect in Zirconium

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 19; no. 52; pp. e2300319 - n/a
• Main Authors: Liu, Si‐Mian, Zhang, Shi‐Hao, Ogata, Shigenobu, Yang, Hui‐Long, Kano, Sho, Abe, Hiroaki, Han, Wei‐Zhong
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.12.2023
• Subjects: Alloying elements; Clusters; dislocation; Dislocation loops; hydride; Hydrides; Hydrogen atoms; Lattice vacancies; Material properties; Nucleation; Phase transitions; Solid phases; vacancy; Zirconium; dislocation; nucleation; hydride; zirconium; vacancy
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202300319

Controlling the heterogeneous nucleation of new phases is of importance in tuning the microstructures and properties of materials. However, the role of vacancy—a popular defect in materials that is hard to be resolved under conventional electron microscopy—in the heterogeneous phase nucleation remains intriguing. Here, this work captures direct in situ experimental evidences that vacancy clusters promote the heterogeneous hydride nucleation and cause the anomalous precipitation memory effect in zirconium. Both interstitial and vacancy dislocation loops form after hydride dissolution. Interestingly, hydride reprecipitation only occurs on those vacancy loop decorated sites during cooling. Atomistic simulations reveal that hydrogen atoms are preferentially segregated at individual vacancy and vacancy clusters, which assist hydride nucleation, and stimulate the unusual memory effect during hydride reprecipitation. The finding breaks the traditional view on the sequence of heterogeneous nucleation sites and sheds light on the solid phase transformation related to vacancy‐sensitive alloying elements. Hydride reprecipitation occurs only on the vacancy loops rather than on the interstitial loops according to the dynamic defect characterizations. A new mechanism of hydride nucleation mediated by vacancy clusters is proposed, which explains the anomalous memory effect of hydrides precipitation and works for other materials containing alloying elements that have high binding energy with vacancies.