Comparison of fatigue behavior of a bulk metallic glass and its composite

The X-ray diffraction results show that LM001 (Zr41.2Ti13.8Cu12.5Ni10Be22.5) is a monolithic bulk-metallic glass (BMG) and LM002 (Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5) is a BMG containing crystalline phases. High-cycle-fatigue (HCF) studies were performed on these zirconium (Zr)-based BMGs. The HCF experiments were conducted, using an electrohydraulic machine at a frequency of 10 Hz with an R ratio of 0.1 and under tension-tension loading, where R=σmin/σmax, where σmin and σmax are the applied minimum and maximum stresses, respectively. The test environment was air at room temperature. The vein pattern and droplets with a melted appearance were observed in the apparent melting region. The fatigue-endurance limit (239 MPa) of LM002 was found to be significantly shorter than that (567 MPa) of LM001, which indicates that the presence of crystalline phase could reduce the resistances to fatigue. The tension-tension fatigue S (applied stress)-N (lifetime) curve of the present composite was found to be comparable with the four-point-bend result of the composite in the literature. However, the tension-tension fatigue lifetime of the present monolithic BMG was much greater than that of the four-point-bend fatigue of the monolithic BMG in the literature. The fracture morphology indicates that fatigue cracks initiate from porosities or inclusions. The whole fracture surface of LM001 is perpendicular to the loading direction. However, a part of the fracture surface of LM002 is not perpendicular to the loading direction. It demonstrates a ductile facture feature. A mechanistic understanding of the fatigue behavior of the Zr-based BMGs is suggested.