Structural relaxation in a heavily cold-worked metallic glass

Influence of the shot-peening intensity on the structure and near-surface mechanical properties of Ti40Zr10Cu38Pd12 bulk metallic glass

“…This effect progressively decreases as the distance from the shot-peened surface is increased. This confirms earlier works 8,9 that SP induces an increase in V f . More V f is generated in the S2 sample, despite the greater heating presumably induced during the more intense SP.…”

“…5 SP also gives anisotropy in the surface layer and induces a less relaxed (damaged) glassy structure. [7][8][9] In a partially crystalline Zr 55 Cu 30 Al 10 Ni 5 BMG, SP can induce either amorphization (or full crystallization) at higher (or lower) temperature. 10 Crystallization was attributed to increased atomic mobility due to a large induced free volume V f rather than to temperature rise.…”

“…The large stored energy found in the S2 sample may be favored by the choice of steel shot instead of the glass beads used in previous works 8,9 on SP of BMGs. In addition, inducing more damage because they are heavier, the steel shot must be more effective in extracting from the sample the heat generated during successive impacts.…”

Stored energy in metallic glasses due to strains within the elastic limit

“…After heating above T g , the sample is cooled at the same rate as the initial heating, and a second heating run, now on the relaxed glass, again at the same rate, is used to obtain a baseline. The relaxation during the first heating run is then characterized as the difference between the first and second heating traces [28,31]. Alternatively, the first heating run can be taken to a temperature high enough to crystallize the glass; the crystalline state then sets the baseline in the second run [24,32].…”

“…As expected, ΔH rel is higher for glasses cooled at higher rate, and values as high as 5.5 kJ g-atom −1 have been reported for melt-spun ribbons that are only 20 μm thick [31]. More usual values are 1-1.5 kJ g-atom −1 (11-17% of ΔH m ) for melt-spun ribbons and ~300 J g-atom −1 (~3% of ΔH m ) for bulk metallic glasses (BMGs) [6,7,28], that are, of course, more slowly cooled. Figure 1 is schematic, but based closely on the BMG system Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 .…”