| Electrochemical and mechanical experiments were conducted to analyze the environmentally influenced fatigue and fracture behavior of a bulk amorphous metal, Zr41.2Ti13.8Cu12.5Ni10Be 22.5 (at%), This study was motivated by a scientific interest in the mechanisms of fatigue crack propagation in an amorphous metal, and by a practical interest in the use of this amorphous metal in applications that take advantage of its unique properties, including high specific strength, large elastic strains and low damping. The objective of this work was to determine the rate and mechanism of fatigue-crack growth in this zirconium-based amorphous metal in an aggressive environment. To meet this objective, the synergism between mechanical loading and chemical environment was investigated experimentally. Specifically, fatigue crack propagation behavior was investigated at a range of stress intensities in representative service environments: ambient air, de-ionized water, and aerated aqueous sodium chloride solution. Based on these fatigue experiments, it was apparent that although water minimally increased growth rates compared to behavior in air, aerated 0.5 M sodium chloride solution dramatically increased growth rates by over two orders of magnitude near the fatigue threshold. In addition, values of crack velocity under sustained load (stress-corrosion) conditions in sodium chloride solution were comparable to crack-growth rates under cyclic loading in the same solution. Moreover, the effects of potential, concentration, stress intensity, anion type, and aeration on fatigue-crack growth, suggested that crack growth in sodium chloride solution was driven by a strain-assisted anodic reaction at the crack tip. Furthermore, the rate determining step appeared to differ near the fatigue threshold compared to that at higher stress intensities. |
