Fatigue behavior of bulk-metallic glasses

High-cycle fatigue (HCF) experiments were conducted on zirconium (Zr)-based bulk-metallic glasses (BMGs): Zr50Al10Cu40 and Zr50Al10Cu30Ni10, 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=σmin/σmax., where σmin and σmax 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 Zr50Al10Cu30Ni10. The effect of chemical composition on the fatigue behavior of the Zr-based BMGs was studied. The fatigue-endurance limit of Zr50Al10Cu30Ni10 (865 MPa) is somewhat greater than that of Zr50Al10Cu40 (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.