Fatigue behavior and fracture morphology of Zr_(50)Al_(10)Cu_(40) and Zr_(50)Al_(10)Cu_(30)Ni_(10) bulk-metallic glasses

摘要

In the present work, high-cycle fatigue (HCF) experiments were conducted on zirconium (Zr)-based bulk-metallic glasses (BMGs): Zr_(50)Al_(10)Cu_(40) and Zr_(50)Al_(10)Cu_(30)Ni_(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 = sigma_(min)/sigma_(max), where sigma_(min) and sigma_(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_(50)Al_(10)Cu_(30)Ni_(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_(50)Al_(10)Cu_(30)Ni_(10) (865 MPa) was somewhat greater than that of Zr_(50)Al_(10)Cu_(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_(50)Al_(10)Cu_(40) were greater than those of Zr_(50)Al_(10)Cu_(30)Ni_(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.