Compositional engineering of CoCrCuFeNiAlx high entropy alloys to achieve superior yield strength-ductility synergy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2024-11, Vol.915, p.147235, Article 147235
• Main Authors: Mahato, Apurba, Chahar, Sonika, Singh, Ratnakar, Bajargan, Govind, Mula, Suhrit
• Format: Article
• Language: English
• Subjects: CoCrCuFeNiAlx high entropy alloys; Electron microscopy; Strain hardening; Tensile flow stress; Vacuum arc melting
• ISSN: 0921-5093
• DOI: 10.1016/j.msea.2024.147235

In this study, design strategy of high entropy alloys (HEAs) has been investigated to achieve a dual-phase structure with dominant FCC phase possessing a favorable balance of exceptional yield strength (YS) and ductility. CoCrCuFeNiAlx (x = 1, 0.8, 0.75, 0.7 and 0.6, henceforth denoted as Al1, Al0.8, Al0.75, Al0.7 and Al0.6) compositions were designed based on thermodynamic parameters and synthesized via vacuum arc melting, with composition accuracy validated through X-ray fluorescence (XRF) analysis. X-ray diffraction (XRD) phase analysis revealed favored BCC phase evolution with higher Al content, which gradually transformed into a predominant FCC phase with a gradual decrease in Al. Analysis through electron microscopy (SEM, EBSD and TEM) confirmed the homogeneity of the alloys, formation of precipitate phase(s) and their morphology (such as grain size and phase distribution). A decrease in Al content resulted in reduced yield strength (as well as hardness) with subsequent improvement in ductility, which correlates well with the observed phase evolution characteristic. Notably, alloys with FCC-dominant phases, such as Al0.7 and Al0.6, exhibited an impressive balance of YS (480–490 MPa) with a uniform elongation (32–34 %). The tensile deformation micro-mechanisms were analyzed using a slip activity-based strain hardening (SASH) model, which effectively tracked the flow stress and strain hardening behavior of the alloys. The model exhibited high KM (rate-defining parameter of orientation factor) values for high Al content alloys, indicating a rapid transition to multiple slip systems due to smaller inter-dendritic structures in these alloys. Fractography analysis of the tensile tested samples corroborated well with the tensile properties of the corresponding samples. •CoCrCuFeNiAlx (x = 0.6–1) alloys designed through thermo-physical parameters & produced by VAM.•XRD + EBSD studies confirmed a gradual transition from a single-phase fcc (Al0.6) to bcc dominated phase (Al1).•Al0.6 and Al0.7 exhibited superior YS (480–490 MPa) with uniform elongation of 32–33 %.•SASH model analyzes flow stress & SHR enlightening deformation micromechanisms efficiently.