Fatigue crack propagation in a nanocrystalline Zr-based bulk metallic glass

A nanocrystitlline (NC) bull; glass Zr55Al10Cu30Ni5 (at%) which contains nano-scale crystals embedded uniformly in a glassy matrix has both high tensile strength of 1.7 GPa and high ductility. It is therefore expected to find practical application in machines and structures. The fatigue crack propagation behavior of the NC bulk glass was examined. The threshold stress intensity factor range DeltaK(th) was about 0.9 MPa rootm and the fatigue fracture toughness K-fc was about 13 MPa rootm. Fatigue crack propagation rate da/dn was approximately proportional to DeltaK(2) No significant difference in da/dn between the NC glassy alloy and single phase amorphous alloys in literature was seen when they are compared on the basis of BK divided by Young's modulus E. The da/dn values were nearly the same as those for steels with the same tensile strength level. The da/dn values were larger than those for low strength steels, Al alloys and Ti alloys in the low da/dn range. When compared with the effective stress intensity factor range DeltaK(eff) divided by E, the da/dn values for crystalline alloys were almost coincident with those under different stress ratios for the NC glassy alloy. This indicates that the da/dn values for the NC glassy alloy can be estimated on the basis of the da/dn data for crystalline alloys.