Rotating-beam fatigue strength of Pd40Cu30Ni10P20 bulk amorphous alloy

By using a bulk amorphous Pd40Cu30Ni10P20 alloy rod with a diameter of 10 mm and a length of 80 mm, the rotating-beam fatigue strength was examined through the measurement of maximum applied stress versus number of cycles to failure (S-N) curve at room temperature. The bulk amorphous alloy rod has good 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 Charpy impact fracture energy of 70 kJ/m(2). Fatigue failure occurs at 900 MPa after 1.2 x 10(3) cycles and 600 MPa after 1.43 x 10(5) cycles, but an applied stress of 340 MPa does not cause fatigue failure even after 10(7) cycles. The fatigue limit defined by the ratio of the minimum fatigue stress without fracture after 107 cycles to the tensile fracture strength is measured to be 0.20. The fatigue limit is much higher than that (1/25) for a bulk amorphous Zr41Ti14Be22.5Ni10Cu12.5 alloy and nearly the same as the previous values (0.18 to 0.30) for a bulk amorphous Zr65Al10Ni10Cu15 alloy as well as melt-spun Pd80Si20, Ni75Si8B17 and Co75Si10B15 amorphous ribbons. On a macroscopic scale, the fatigue fracture lakes place along the plane perpendicular 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) cycles for the Pd-Cu-Ni-P bulk amorphous rod is encouraging for the future development of bulk amorphous alloys as engineering materials.