Fatigue behavior of bulk-metallic glasses

High-cycle fatigue (HCF) experiments were conducted on zirconium (Zr)-based bulk-metallic glasses (BMGs): Zr 50Al 10Cu 40 and Zr 50Al 10Cu 30Ni 10, in atomic percent. The HCF tests were performed using an electrohydraulic machine at a frequency of 10 Hz, with a R ratio of 0.1, and under tension–tension loading. Note that R= σ min/ σ max., where σ min and σ max are the applied minimum and maximum stresses, respectively. The test environments were air and vacuum. A high-speed and high-sensitivity thermographic infrared (IR) imaging system has been used for nondestructive evaluation of temperature evolution during fatigue testing of BMGs. Limited temperature evolution was observed during fatigue. However, a sparking phenomenon was observed at the final fracture moment of Zr 50Al 10Cu 30Ni 10. The effect of chemical composition on the fatigue behavior of the Zr-based BMGs was studied. The fatigue-endurance limit of Zr 50Al 10Cu 30Ni 10 (865 MPa) is somewhat greater than that of Zr 50Al 10Cu 40 (752 MPa) in air. The fatigue-endurance limits of these two BMGs were comparable to those of ductile crystalline alloys. The fatigue lives in vacuum and air were generally found to be comparable. The vein pattern and droplets with a melted appearance were observed in the apparent melting region. There are microcracks on the outer surface of the specimen, which could be associated with multiple fatigue crack-initiation sites. These microcracks might result from shear bands and shear-off steps.