Rotating-beam fatigue strength of Pd40Cu30Ni10P20 bulk amorphous alloy

By using a bulk amorphous Pd40Cu30Ni10P20 alloy rod with a diameter of 10 m m and a length of 80 mm, the rotating-beam fatigue strength was examined th rough the measurement of maximum applied stress versus number of cycles to failure (S-N) curve at room temperature. The bulk amorphous alloy rod has g ood mechanical properties, i.e., high tensile fracture strength of 1700 MPa , Young's modulus of 80 GPa, high Vickers hardness of 510 and rather high C harpy impact fracture energy of 70 kJ/m(2). Fatigue failure occurs at 900 M Pa after 1.2 x 10(3) cycles and 600 MPa after 1.43 x 10(5) cycles, but an a pplied stress of 340 MPa does not cause fatigue failure even after 10(7) cy cles. The fatigue limit defined by the ratio of the minimum fatigue stress without fracture after 107 cycles to the tensile fracture strength is measu red to be 0.20. The fatigue limit is much higher than that (1/25) for a bul k amorphous Zr41Ti14Be22.5Ni10Cu12.5 alloy and nearly the same as the previ ous values (0.18 to 0.30) for a bulk amorphous Zr65Al10Ni10Cu15 alloy as we ll as melt-spun Pd80Si20, Ni75Si8B17 and Co75Si10B15 amorphous ribbons. On a macroscopic scale, the fatigue fracture lakes place along the plane perpe ndicular to the longitudinal direction of the testing specimen. Furthermore , the crack appears to initiate at the scratch site on the outer surface of the specimen. The high fatigue endurance limit of 340 MPa after 10(7) cycl es for the Pd-Cu-Ni-P bulk amorphous rod is encouraging for the future deve lopment of bulk amorphous alloys as engineering materials.