Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Abstract

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy’s behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m 1/2 , which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

High Throughput Exsolution Design of CO2 Reduction Reaction Interface in a Copper/High-Entropy Oxide Tandem Electrode

“…High-entropy materials are attracting global attention as the entropy design paradigm holds promise for wide-ranging applications [1][2][3][4][5][6][7]. While most focus on entropy designed single-phase materials, we are exploring the potential of secondary phases in high-entropy and entropystabilized oxides (HEOs and ESOs) to introduce tunable and reversible composite properties [8][9][10][11].…”