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Abstract: The purpose of this study was to make a direct comparison between four-point-bending and uniaxial fatigue tests with the Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 (at.%) BMG alloy (Vitreloy 105). The fatigue lifetimes in four-point bending were found to be greater than those reported in uniaxial testing. However, the fatigue-endurance limit found in four-point bending was slightly less than that reported for uniaxial fatigue. Thus, the significant differences between fatigue studies in the literature are not likely due to this difference in testing geometry. On the contrary, the fatigue lifetimes were found to be highly dependent upon surface defects and material quality. The four-point-bending-fatigue performance of the Vit 105 alloy was found to be greater than most BMGs and similar to the 300M high-strength steel and other crystalline alloys in spite of not being ‘perfectly amorphous.’ Due to the detrimental effects of these inhomogeneities and wear at the supporting pins, this fatigue behavior can be assumed to be a conservative estimate of the potential fatigue performance of a perfectly amorphous and homogeneous BMG. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to characterize the stress-life behavior of the Vitreloy 105 BMG alloy in the four-point bending configuration in a 0.6M NaCl electrolyte. At high stress amplitudes, the corrosion–fatigue life was similar to the fatigue lives observed in air. The environment became increasingly detrimental with decreases in stress, and the corrosion–fatigue endurance limit decreased to about 50MPa, an 88% decrease relative to testing in air. Similar to the tests conducted in air, oxide particles were found on the fracture surfaces but did not appear to significantly affect the corrosion–fatigue lives. However, wear and the resultant corrosion at the outer loading pins resulted in crack initiation in most of the samples. Thus, these results are considered conservative estimates of the corrosion–fatigue behavior of this BMG alloy. Monitoring of the samples and the open-circuit potentials revealed that the onset of significant crack growth occurred at an average of 92% of the total fatigue life. The mechanism of corrosion–fatigue degradation was found to be anodic dissolution. [Copyright &y& Elsevier]

Abstract: In this study, potentiodynamic experiments were conducted with a Ti-based BMG alloy with a nominal composition of Ti43.3Zr21.7Ni7.5Be27.5 [atomic percent (at.%)], commonly known as LM-010. Electrochemical characterization was performed in a phosphate-buffered saline (PBS) electrolyte at 37°C with a physiologically relevant dissolved oxygen content. This BMG exhibited passive behavior at the open-circuit potential with a low mean corrosion-penetration rate. A susceptibility to localized corrosion was observed but is not a concern at the open-circuit potentials. The resistance of the LM-010 alloy to localized corrosion was statistically equivalent to, or better than, all of the BMG materials and the 316L stainless steel for which direct statistical comparisons were possible. Microscopic examination revealed that the samples predominantly exhibited many scattered, small pits (diameter ⩽100μm) in addition to several larger pits. Based upon the pit morphology and comparisons with the literature, it appears that localized corrosion initiated at clusters of inhomogeneities within the amorphous matrix. [Copyright &y& Elsevier]

Cyclic-anodic-polarization tests were conducted on a Zr-based bulk metallic glass (BMG) with a chemical composition of Zr41.2Ti13.8Ni10Cu12.5Be22.5 [Liquidmetal-001, LM-001 (at.%)]. Samples were compared in two different electrolytes at two different temperatures. Tests were conducted at 22 and 37 °C in both, an aerated 0.6 M NaCl electrolyte and a phosphate-buffered saline (PBS) electrolyte with a physiologically relevant dissolved oxygen content. For all tested conditions, the alloy demonstrated passive behavior at the open-circuit potential with low corrosion rates. However, a susceptibility to localized pitting corrosion was observed in all of the tested conditions. At both temperatures, statistical analyses revealed that the LM-001 BMG exhibited comparable or improved values for every corrosion parameter in the PBS electrolyte, as compared to the NaCl electrolyte. The mean differences between the protection potentials and the open-circuit corrosion potentials were determined to be positive values with greater magnitudes for the PBS electrolyte. Thus, the material may undergo pitting corrosion at surface flaws or after incubation-time periods, depending on the local and bulk environments, with lower probabilities for the PBS electrolyte. [Copyright &y& Elsevier]

To date, few detailed corrosion studies of the new bulk metallic glasses (BMGs) have been presented. In the present work, the aqueous electrochemical corrosion properties of BMG-11, 52.5Zr–17.9Cu–14.6Ni–5.0Ti–10.0Al (atomic percent), were investigated. Cyclic-anodic-polarization tests were conducted on amorphous and crystalline specimens in a 0.6 M NaCl solution (simulated seawater) and on amorphous specimens in a 0.05 M Na2SO4 solution (simulated moisture condensation, as related to ongoing fatigue experiments in humid air), all at room temperature. In the NaCl solution, both amorphous and crystalline materials were found to exhibit passive behavior with low corrosion rates (15 μm/year or less). However, susceptibilities to pitting corrosion were observed. The amorphous material was found to be more resistant to the onset of pitting corrosion under natural corrosion conditions. In the 0.05 M Na2SO4 solution, the amorphous BMG-11 was found to exhibit passive behavior with a very low corrosion rate (0.4 μm/year), and to be immune to pitting corrosion. Furthermore, when the protective passive film was removed by scratching with a diamond stylus, it was found to quickly reform. This result suggested that a corrosion influence on the fatigue properties of BMG-11 in humid air would be minimal. [Copyright &y& Elsevier]