The evolution of dual-phase core–shell structure and mechanical properties induced by Co addition in as-cast high-entropy intermetallic

• Published in: Materials & design 2023-08, Vol.232, p.112120, Article 112120
• Main Authors: Liu, Junqi, Wang, Xiaopeng, Zong, Xiao, Ding, Xianfei, Xu, Hui, Yang, Fei, Kong, Fantao
• Format: Article
• Language: English
• Subjects: Anomalous yield effect; Dual-phase core–shell structure; High-entropy intermetallic; High-temperature mechanical properties
• ISSN: 0264-1275
• DOI: 10.1016/j.matdes.2023.112120

[Display omitted] •Co element motivates dual-phase core–shell structure in our work, breaking out that only B element can promote similar structure in other works.•The dual-phase core–shell structure leads to a better combination of strength and plasticity at room temperature and the strengthening mechanism and plasticizing mechanism dominated by dual-phase core–shell structure at room temperature are obtained.•Anomalous yield effect is discovered in the alloy with dual-phase core–shell structure, which has never been found in high-entropy alloys.•The high-temperature yield strength is higher than room-temperature yield strength in the alloy with dual-phase core–shell structure until 950 ℃.•The yield strength of the alloy with dual-phase core–shell structure is higher than other high-entropy alloys above 400 ℃. In this work, three as-cast L12-type HEIs with different content of Co element were carefully examined combined with TEM, SEM and XRD technologies. The main matrix of three alloys was L12 ordered phase, and Si,Ti-rich grain-boundary precipitate phase generated with the addition of Co. In Co1 alloy, distinct dual-phase core–shell structure was found within grain due to the precipitation of extra FCC disordered secondary phase, which leads to a better strength-plasticity combination (compressive strength of 3441 ± 50 MPa, and fracture strain of 46.0 ± 1.5%) than Co0 and Co0.5 alloy at room temperature. With the increase of temperature, particular anomalous yield effect was discovered in Co1 alloy. It is clear that SFs became main deformation substructure in Co1 alloy at elevated temperature, and the interaction between non-coplanar SFs motivated the generation of L-C Locks, which assists the K-W Locks to pin dislocations movement and enhance the yield strength from room temperature to about 650 ℃. In addition, the interaction between SFs resulted in the formation of nano-spaced SF network, which contributes to the dynamic Hall-Petch effect. Finally, excellent high-temperature yield strength was achieved in as-cast Co1 alloy, which is higher than room-temperature yield strength until 950 ℃.