Temperature-induced ductile-to-brittle transition of bulk metallic glasses

Abstract

Uniaxial tensile and uniaxial compressive tests for Zr-based bulk metallic glasses (BMGs) were conducted at room and cryogenic temperatures, respectively. It was observed that both the change of macroscopic fracture mode from ductile shear fracture to brittle normal tensile fracture and microscopic fracture feature from micron-scaled vein patterns to nano-scaled dimples with decreasing test temperatures were identified, indicating a significant ductile-to-brittle transition (DBT) behavior. The mechanism of DBT behavior was revealed by the competition between the intrinsic critical shear strength τ0 and critical tensile strength σ0 at different temperatures.

Effect of strain rate on yielding strength of a Zr-based bulk metallic glass

“…2. (2) and (3), we can see that the deformation of Vit 105 under dynamic cases is still governed by STZs [3,44,49]. In other words, there is still a free volume softening.…”

Ductile to brittle transition of fracture of a Zr-based bulk metallic glass: Strain rate effect

“…The free volume effect on the DBT behavior of metallic glasses was investigated previously [18,19,21]. Here, a careful analysis will be made only on the effect of applied strain rate.…”

“…This may due in large part to: (i) the DBT behavior is hard to occur under uniaxial compression as the tensile stress will gradually increase from zero, deriving from the shear induced dilatation during compressive loading. As a consequence, the samples should first shear, and then continue to fail in shear fracture mode or tensile fracture mode [19,21]. (ii) the reported enhanced compressive plasticity under cryogenic temperature might originate from the single shear band sliding along the principle shear plane as the velocity of shear-banding equals to that applied on the test machine cross-head [28,29], in addition, the geometrical constraints will also play an important role on the enhancement of the compressive plasticity [30].…”

The ductile to brittle transition behavior in a Zr-based bulk metallic glass

“…For example, the impact toughness of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 (Vit1) has been found to be closely related to the test temperature and dramatically decreased below a critical temperature, indicating a clear DBT behavior [25]. Our recent results have also shown that the DBT could be achieved in a Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 (Vit105) BMG under three-point bending and uniaxial tension through decreasing test temperatures, accompanied by the transition of both microscopic fracture feature and macroscopic fracture mode [26,27]. Additionally, these tough BMGs could be embrittled and suffered a DBT due to the reduction of free volume concentration by annealing at temperatures below the glass transition temperature T g [28,29], or decreasing cooling rates during casting [30].…”

“…Therefore, although monolithic BMGs usually show almost zero ductility in tension and limited malleability in compression, their advantage of high strength and good fracture toughness still entails their potential applications in space exploration, liquefied gas storage and cooling pipe of experimental thermonuclear reactor at cryogenic temperatures [11,14]. However, ductile to brittle transition (DBT) could occur in metallic glasses from ribbon (mainly Fe-based) [20][21][22][23] to BMGs [24][25][26][27] as temperature decreasing according to previous researches. For example, the impact toughness of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 (Vit1) has been found to be closely related to the test temperature and dramatically decreased below a critical temperature, indicating a clear DBT behavior [25].…”