Plane-Strain Fracture Toughness in Cu-Zr-Ag-Al Bulk Metallic Glass

Fracture toughness of the Cu-Zr-Ti bulk metallic glass (Former Cu-Zr BMG) under plane-strain condition could not be evaluated because the BMG with a sufficient thickness for the plane strain condition had not been fabricated. However, as the fracture morphology was similar to that in the Zr-based BMGs having the large plane-strain fracture toughness (K-IC), e.g. about 50 MPa center dot m(1/2), it was presumed that the Former Cu-Zr BMG has a large K-IC. Recently, in Cu-Zr-Ag-Al BMG (New Cu-Zr BMG), a large sample of 25 mm in diameter became possible to be made. Therefore, in this study, K-IC of the New Cu-Zr BMG was investigated. The New Cu-Zr BMG plate sample of Cu36Zr48Ag8Al8 was made by a copper mold casting method. Tensile strength was 1850 MPa and Young's modulus was 115 GPa. Compact type specimen with 2.3 mm in thickness and 9.2 mm in width was used. Fatigue pre-crack was induced under stress intensity factor range (Delta K) less than 6 MPa center dot m(1/2), and the fracture toughness test was conducted at a loading rate of 1 MPa center dot m(1/2)center dot s(-1). The new Cu-Zr BMG exhibited a K-IC of 17 MPa center dot m(1/2). The former Cu-Zr BMG that could not satisfy the plane-strain condition exhibited a fracture toughness of 62 MPa. m(1/2). The stretched zone width along the inner fatigue crack front and vein pattern size on the unstable fracture surface in the new Cu-Zr BMG were smaller than those of the former Cu-Zr BMG. Therefore, it seems that the K-IC of the new Cu-Zr BMG is smaller than that of the former Cu-Zr BMG.