Revealing cracking behavior of phase and grain boundaries in dual-phase high-entropy alloy at elevated temperatures

Phase and grain boundaries can effectively strengthen dual-phase high-entropy alloys (HEAs), but as service temperature increases, they could also become sources of weakness and damage. In this work, microstructures with different phase and grain boundary densities were designed in a hypoeutectic HEA to compare their different effects on cracking behavior at elevated temperatures. The tensile ductility significantly increased by reducing the intergranular fracture with decreased grain boundary density. The analyses revealed that the grain boundary was prone to crack at the triple junctions and served as the crack propagation path. Differently, although the phase boundary also cracked preferentially, it was highly resistant to crack propagation by its serrated morphology and defects emission at the crack tip. The directionally solidified sample further proved the benefit by suppressing 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 HEAs for application in a wide temperature range.