Fracture toughness of Zr₅₅Al₁₀Ni₅Cu ₃₀ bulk metallic glass by 3-point bend testing

In order to evaluate the fracture toughness of a Zr₅₅Al ₁₀Ni₅Cu₃₀ bulk metallic glass and to identify possible sources associated with data variability of Zr-based metallic glasses, three-point bending (3PB) precracked and notched specimens with thicknesses of 2.0 to 2.9 mm were prepared. Miniaturized 34 specimens were subjected to plane strain fracture toughness tests at room temperature. The measured fracture toughness values are in a range of 35.9-76.2 MPam^1/2 and 20 specimens satisfy the K_IC criterion, the K_IC being in a range of 35.9-50.3 MPam^1/2 with an average of 43.3 MPam^1/2. No appreciable difference in fracture toughness is observed between the precracked and notched specimens with root radii of 0.06 and 0.13 mm. Whereas the fracture toughness value varies significantly for each of the precracked and notched specimens. Fracture surfaces show not only a vein pattern typical of fully amorphous alloys but also a flower-like pattern which is less resistant to fracture. All specimens with the entire fracture surface of the vein pattern exhibit very high K_Q values of 70.0-76.2 MPam^1/2. The cause of large variability in the fracture toughness data including literature data is discussed.