Fatigue behavior and fracture morphology of Zr 50Al 10Cu 40 and Zr 50Al 10Cu 30Ni 10 bulk-metallic glasses

Abstract

In the present work, 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 was used for the nondestructive evaluation of temperature evolutions during fatigue testing of the BMGs. A sparking phenomenon was observed at the final fracture moment of Zr 50Al 10Cu 30Ni 10 in air, while a bright notch section was observed near the final fracture moment of these two BMGs in vacuum. The effect of the 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) was somewhat greater than that of Zr 50Al 10Cu 40 (752 MPa) in air. The fatigue lives in vacuum and air were generally found to be comparable. The fatigue-fracture surface consisted of four main regions: the fatigue crack-initiation, crack-propagation, final-fast-fracture, and apparent-melting areas. Apparent fracture toughness was determined from the measurement of the crack-propagation region of the fatigue-fractured surface. The fracture-toughness values of Zr 50Al 10Cu 40 were greater than those of Zr 50Al 10Cu 30Ni 10. The vein pattern and droplets with a melted appearance were observed in the apparent melting region. There were 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.