Fatigue behavior of an Fe₄₈Cr₁₅Mo₁₄Er₂C₁₅B₆ amorphous steel

Four-point-bend fatigue experiments were conducted on the Fe₄₈Cr₁₅Mo₁₄Er₂C₁₅B₆ bulk metallic glass (BMG), amorphous steel, under load control, employing an electrohydraulic machine, at a frequency of 10 Hz (using a sinusoidal waveform) with an R ratio of 0.1, where R = σ_min./σ_max. (σ_min. and σ_max. are the applied minimum and maximum stresses, respectively). The test environment was laboratory air. Fe₄₈Cr₁₅Mo₁₄Er₂C₁₅B₆ exhibited a high fatigue-endurance limit (682 MPa), which is found to be greater than those of the Zr-based BMG, Al-alloy, and high-nitrogen steel. However, the stress versus number of fatigue cycles curve of Fe₄₈Cr₁₅Mo₁₄Er₂C₁₅B₆ has a significantly brittle fracture mode. Some fatigue cracks initiated from the inclusions or porosities, and the fatigue-crack propagation region was large. However, other cracks initiated from the outer tensile surface of the specimen, and the fatigue-crack propagation region was very small. The mechanisms of fatigue-crack initiation are suggested.