Fatigue coaxing experiments on a Zr-based bulk-metallic glass

Understanding the Problem of Fatigue in Bulk Metallic Glasses

“…[16] Using a fatigue coaxing step test, where the mean stress was increased after each prescribed number of cycles, it was found that the mean stress at failure, which would normally be below 200 MPa, could be increased substantially up to 575 MPa (Figure 4). Thus, even below the fatigue limit, where one might guess little change is occurring in the glass, in fact, significant mechanical changes are induced in the BMG that affect the fatigue behavior.…”

“…Also, a different study on a Zr 41.8 Ti 12.9 Ni 9.5 Cu 12 Be 23.8 BMG suggests that the crack initiation process was not instantaneous for their material and may be affected by precycling below the fatigue limit, as discussed in Section II-B. [16] Such results suggest that instantaneous crack initiation is not an inherent trait of BMGs and may only occur in materials with a large defect population, unfavorable residual stresses, or unfavorable glass structure or chemistry.…”

“…[69] Further development of characterization techniques will certainly help in this area, especially when there is much still to be understood about the mechanisms of many observed thermomechanical phenomena affecting fatigue behavior. [6,[13][14][15][16][17][18] (3) Better control of defects. It has been well documented that fatigue cracks can initiate at defects in BMGs even after only a few fatigue cycles, [23][24][25] although not all studies have observed such rapid crack initiation.…”

“…It has been well documented that fatigue cracks can initiate at defects in BMGs even after only a few fatigue cycles, [23][24][25] although not all studies have observed such rapid crack initiation. [13,16] Several strategies might be employed to mitigate such effects. Eliminating defects is likely one effective strategy; for example, an arc furnace with tilt casting has been used to make crystalline inclusion-free BMGs for fatigue studies.…”

“…Such scatter suggests that some important variables affecting the fatigue behavior of BMGs are not adequately understood or controlled in the experiments. Studies over the last few years have suggested that factors such as the thermal history, [6,[13][14][15] mechanical history, [16][17][18] environment, [19][20][21][22] and defects [23][24][25] all may play a role in affecting the fatigue behavior of BMGs. However, most of those factors were rarely characterized, reported, or controlled in early fatigue studies on BMGs, which likely explains some of the reported scatter.…”