Fracture morphology and quenched-in precipitates induced embrittlement in a Zr-base bulk glass

Abstract

The fracture morphology and quenched-in embrittlement in Zr52.5Ni14.6Al10Cu17.9 Ti5 bulk glass were investigated by tensile and compressive tests at room temperature at the same strain rates of 4 × 10-4 s-1 and scanning electron microscopy (SEM) observation. SEM analysis based on the deformation and fracture features indicates that the normal stress and shear stress on the fracture surface play a different role in the shearing-off of the specimens in tension and compression. The shear stress is the main controlling factor for the fracture in compression, and the fracture surface is along the maximum shear stress plane. In tension, however, both the shear and normal stresses govern the fracture process together, and the fracture surface is along the plane with an angle of 56 deg away from the axial direction. The fracture firstly starts from a random region on the surface where there is a stress concentration due to the voids or shear bands. The shearing-off leads to a dilatation and softening of the local glass. The softening then promotes the shearing-off and leads to final catastrophic fracture. The crystalline precipitates significantly influence the tensile and compressive properties. With increases in the volumetric fractions and the sizes of the precipitates, both the tensile and compressive strength and fracture strains decrease. The fracture mode changes from ductile to brittle. Vein patterns, shear-bands and local melting can still be observed when the volume fractions of quenched-in precipitates are less than 3 ∼ 5%. When the precipitates exceed 5% in volume fraction, fracture surface becomes rock strata-like feature, and samples lose almost their strength. The precipitates with larger sizes and no-spherical shapes play a role in rising stress concentration, resulting in decreasing the fracture strength.