Fatigue behavior and fracture morphology of Zr50Al10Cu40 and Zr50Al10Cu30Ni10 bulk-metallic glasses

In the present work, 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 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 Zr50Al10Cu30Ni10 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 Zr50Al10Cu30Ni10 (865 MPa) was somewhat greater than that of Zr50Al10Cu40 (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 Zr50Al10Cu40 were greater than those of Zr50Al10Cu30Ni10. 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.