"Microstructure and Mechanical Properties of (CuMgNiZnCo)O" 

Chang Liu, MSE PhD Candidate 

Advisor: Professor Haiyan Wang 

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ABSTRACT

Highly entropic materials (HEMs) have garnered considerable interest owing to their distinct characteristics, especially by the mixing of multiple components in nearly equal proportions. High-entropy ceramics, a subset of HEMs, represent a fascinating class of materials with distinctive attributes. Over the past decade, research on high-entropy ceramics has surged, ranging from oxides to carbides and nitrides. This paper focuses on a thorough investigation of high-entropy oxides, particularly the (CuMgNiZnCo)O system. These materials display exceptional properties stemming from fundamental aspects of high entropy, encompassing the high entropy phenomenon, pronounced lattice distortion impact, sluggish diffusion tendencies, multifaceted performance-enhancing "cocktail" effect. This study delves into the structure and phase evolution of (CuMgNiZnCo)O, emphasizing the significance of configuration entropy in achieving a single-phase rock-salt structure. Phase transitions are detailed, revealing the emergence of Cu2O at elevated temperatures, potentially due to chemical reduction or phase separation. Microstructure analysis indicates the role of sintering temperature in grain growth, highlighting the challenges of achieving both high densification and fine grain sizes. High-entropy oxide materials' mechanical characteristics are investigated, revealing a balance between achieving densification and controlling grain growth. High Vickers hardness values are achieved, rivaling traditional hard ceramic materials. Challenges in understanding the deformation mechanisms and fracture toughness remain, alongside the potential to optimize high-entropy ceramics for various engineering applications. Several knowledge gaps are identified, including the need for a comprehensive understanding of mechanical behavior, phase stability, and exploring new high-entropy systems with fewer components. Additionally, the study aims to investigate alternative sintering methods, such as flash sintering, to further enhance the properties of high-entropy ceramics. This work paves the way for a deeper understanding of high-entropy oxides and offers insights into their potential applications in various industries.