Revealing Cracking Behavior of Phase and Grain Boundaries in Dual-Phase High-Entropy Alloy at Elevated Temperatures

Abstract

Phase and grain boundaries are effective for strengthening dual-phase high-entropy alloys (HEAs), but they could also become a source of weakness and damage as service temperature increases. In this work, microstructures with different phase and grain boundary densities were designed for a hypoeutectic HEA to reveal their effects on cracking behavior at elevated temperatures. The results revealed that the phase boundary cracked preferentially but was highly resistant to crack propagation by its serrated morphology and defects emission at the crack tip. As grain-boundary density increased, the grain boundary was prone to crack at the triple junctions and served as the crack propagation path, leading to the intergranular fracture. The directional solidification was further adopted to reduce the intergranular cracking, achieving a higher yield strength of ~701 MPa and considerable tensile ductility of ~31.5% at 800 °C. These findings create a microstructural optimization pathway based on the cracking mechanisms, aiming to produce high-performance dual-phase HEA for application in a wide temperature range.

Keywords: High entropy alloys, High-temperature mechanical property, Phase boundary, Crack mechanism, Directional solidification