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.

中文翻译：

---

扭结带可提高 NbTaTiHf 难熔中熵合金的优异抗断裂性能

单相体心立方（bcc）难熔中熵或高熵合金可以在高温下保持抗压强度，但拉伸延展性和断裂韧性极低。我们检查了 bcc 耐火合金 NbTaTiHf（77 至 1473 开尔文）的强度和断裂韧性。该合金的行为与同类系统的不同之处在于其断裂韧性超过 253 MPa·m ^1/2，我们将其归因于螺旋位错和刃位错之间在控制裂纹尖端塑性方面的动态竞争。尽管螺旋位错和混合位错的滑移和交叉促进了控制均匀变形的应变硬化，但<111>刃位错与{110}和{112}滑移面的协调滑移通过形成扭结带延长了非均匀应变。这些带通过沿着更高分辨剪切应力的方向重新定向晶体的微尺度带来抑制应变硬化，并不断成核以适应局部应变并将损伤分散到远离裂纹尖端的位置。