Rotating-Beam Fatigue Strength of Pd<SUB>40</SUB>Cu<SUB>30</SUB>Ni<SUB>10</SUB>P<SUB>20</SUB> Bulk Amorphous Alloy

Abstract

By using a bulk amorphous Pd 40 Cu 30 Ni 10 P 20 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 × 10 3 cycles and 600 MPa after 1.43 × 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 10' 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 Zr 41 Ti 14 Be 22.5 Ni 10 Cu 12.5 alloy and nearly the same as the previous values (0.18 to 0.30) for a bulk amorphous Zr 65 Al 10 Ni 10 Cu 15 alloy as well as melt-spun Pd 80 Si 20 , Ni 75 Si 8 B 17 and Co 75 Si 10 B 15 amorphous ribbons. On a macroscopic scale, the fatigue fracture takes 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.