Contrasting effect of compositional tuning and FCC-Al nanocrystals on stochastic shear-band behavior in Al-Ni-MM metallic glasses

Initiation and propagation of shear bands govern the deformation behavior of metallic glasses (MGs), yet how compositional variation and nanoscale heterogeneity tune stochastic yielding in MGs has not been systematically clarified. Here, we analyze pop-in statistics from a large number of nanoindentation tests on Al 100-x Ni 10 MM x MG ribbons (x = 2, 4, and 6; MM = Ce-rich misch metal) to investigate shear band behaviors. Despite pronounced composition-dependent changes in hardness and thermal properties, the stochastic signatures of shear bands remain largely insensitive in the fully amorphous Al 86 Ni 10 MM 4 and Al 84 Ni 10 MM 6 MGs. These alloys exhibit bimodal distributions of first pop-in loads with nearly invariant apparent Weibull moduli, together with similar pop-in size statistics. In contrast, as-spun and heated Al 88 Ni 10 MM 2 MGs, which contain FCC-Al nanocrystals, shows a trimodal distribution of the first pop-in loads, suggesting an additional shear band nucleation pathway associated with FCC-Al nanocrystals and a reduced nucleation barrier. Moreover, reduced interparticle spacing together with FCC-Al nanocrystal growth enhances nanoscale spatial heterogeneity and suppresses shear band propagation, shifting strain bursts toward smaller sizes and lowering their Weibull characteristic scale. Overall, compositional tuning in Al-based MGs primarily modifies macroscopic properties without substantially changing the stochastic characteristics of shear bands. In contrast, FCC-Al nanocrystals and reduced interparticle spacing govern the statistical behavior of shear band initiation and propagation. These changes are expected to promote enhanced plasticity in the MG composites.