Abstract Scope |
Some refractory BCC high-entropy alloys (HEA) can show exceptional high temperature strengths but are very brittle at RT. To understand trends in ductility versus composition, we propose a criterion for RT ductility based on intrinsic ductility. We postulate that ductility is limited by fracture, and that fracture occurs when a sharp crack tip is unable to blunt by dislocation emission prior to Griffith cleavage. That is, the critical stress intensity KIe for emission is larger than that for cleavage KIc. Using fracture mechanics, first-principles theory, and experiments Nb, V, Ta, Mo, and W, we identify a critical ratio for KIe/KIc below which alloys are ductile. Applied to a range of HEAs using calibrated properties from interatomic potentials, our criterion is in broad agreement with experimental trends and enables the identification of ductile composition ranges. Coupled with recent theory for strength, strong and ductile compositions can be identified. |