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

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].…”

Toughness of Bulk Metallic Glasses

“…A characteristic of very brittle materials is a large difference in their tensile and compressive fracture strength, because any flaws in the material cause pre-mature fracture under tension. For BMGs, this can be seen in the work of Li et al [50] who studied the effect of annealing on tensile/compressive behavior of a Zr-based glass (Vit 105). The embrittled Vit 105 shows a tensile strength <600 MPa compared to compressive strength of 1660 MPa.…”

“…In this regard, tensile tests could be more reliable, particularly for probing brittleness, which should be evident in low fracture strength (hence area under the curve). A fine example can be found in the work of Li et al [50] on a Zr-based BMG. They conducted tensile and compressive tests on samples structurally relaxed by annealing below Tg for various times.…”

“…In crystalline materials, toughness is well known to depend upon the testing temperature and strain rate. Recent work has aimed to capture effects of such testing parameters on DBT in BMGs and correlating them with STZ size [50,90,91]. Li et al [50] related the DBT, caused by structural relaxation, in the Vit 105 BMG to the STZ size and it was demonstrated that STZ size depends on three factors: (i) test temperature; (ii) strain rate; and (iii) free volume fraction in the glass, through Equation (8).…”