Relating fracture toughness to micro-pillar compression response for a laser powder bed additive manufactured bulk metallic glass

Abstract

A Zr-based bulk metallic glass produced using selective laser melting (SLM) was compared to the same alloy fabricated using traditional suction-casting. Analysis of the fracture toughness through single edge notched beam bending experiments showed a significantly reduced damage tolerance for the laser-processed material (KQ ~ 138.0 ± 13.1 → 28.7 ± 3.7 MPa √m), even though X-ray diffraction and microhardness responses were identical. Using uniaxial quasistatic micro-pillar compression, it was found that as-cast samples more readily underwent shear transformations (evidenced through discrete load drops) below the nominal 0.2% yield stress, which was connected to the higher macroscopic toughness. Differential scanning calorimetry demonstrated that the increased barrier to shear transformation for the SLM material could not be explained by the relative relaxation states. Rather, it was attributed to the greater dissolved oxygen concentration in the laser-processed material, which is postulated to decrease atomic mobility in the structure and thereby increase the activation energy required to initiate shear transformations.