Effect of Zr composition and heat-treatment on fracture toughness in Zr-Cu-Al bulk metallic glass

Fracture toughness tests were carried out using different Zr composition in Zr-Cu-Al based bulk metallic glasses (BMGs) and heat-treated those just under the glass transition temperature (T _g) in order to examine the effects of Zr composition and heat-treatment on the fracture toughness (K _Q; fracture toughness including the values under unsatisfying the plane strain condition). Zr ₅₀Cu ₄₀Al ₁₀, Zr ₅₅Cu ₃₅Al ₁₀ and Zr ₆₀Cu ₃₀Al ₁₀ BMGs fabricated by a tilt ark casting method were used. Heat-treatments were done for 90 minutes just under the T _gs of each BMG. Tests were conducted based on ASTM E399. Compact type specimen was used (thickness = 2.3, 2.0 mm, thickness : width =1:4). Fatigue pre-crack was induced under ΔK less than 6 MPa ̇ m ^1/2 by a servohydraulic fatigue machine and the fracture toughness test was done by using the same machine. The K _Q dominantly increased with increasing the Zr composition. The K _Q in heat-treated BMGs decreased in comparison with that in unheat-treated BMGs in all Zr composition. In the BMG of the high Zr composition, however, the decrease was small after heat-treatment, and the K _Q showed enough high values. In heat-treated BMGs, the dispersion of K _QS did not become small, but fatigue pre-cracks were induced more vertical against the loading axis and less bifurcation than those in unheat-treated BMGs.