Effect of defects on the phase transition of Al0.1CoCrFeNi high-entropy alloy under high pressure

Abstract

Knowledge pressure-driven phase transition in condensed physics requires an understanding of how phase-transition-pressure in a substance is affected by defect concentration and type. The effect of defects on phase transition was investigated in this paper by comparing structure evolutions in Al0.1CoCrFeNi high-entropy alloy (HEA) prepared by mechanical alloying with as-cast one using in situ synchrotron radiation X-ray diffraction technique and high-resolution transmission electron microscope (HRTEM), as well as the calculated dislocation density. Pressure-induced partial irreversible phase transitions from face-centered cubic (fcc) to hexagonal close-packed (hcp) phase has been observed in both ball-milled and as-cast Al0.1CoCrFeNi HEAs. In comparison to the as-cast Al0.1CoCrFeNi HEA, the ball-milled HEA has a large number of defects, especially higher density dislocations, and a low nucleation energy barrier, resulting in a lower phase-transition-pressure of 7.0 GPa and a higher fraction of hcp phase of 32.12% at pressure ∼30 GPa. The HRTEM result confirms that hcp and fcc phases coexist after pressure releasing. The investigation of the link between defects and phase transition process might lead to a potential approach for customizing the percentage of fcc and hcp phases in HEAs, allowing them to improve their structure and characteristics as a novel engineering material.