The Anelastic Behaviors of Co–Fe–Ni–P Metallic Nano-glasses: Studies on the Viscous Glass–Glass Interfaces

Structural relaxations of grain boundary and glass–glass interfaces (GGIs) play an important role in the mechanical behaviors of polycrystalline metals and metallic nano-glasses (NGs), respectively. Although the former has been well investigated by anelastic or mechanical spectrum measurement, such meaningful technique has not been applied to characterize the structural relaxation of GGIs in NGs as far. In this work, the structural relaxations in Co–Fe–Ni–P NGs with various average sizes (D _avg) of glassy grains are investigated by anelastic measurements, which have been synthesized by a pulse electrodeposition method. The results provide direct evidences that a new glass phase could be formed at interfaces in NGs, as characterized by an activation energy (0.91 eV) for glass transition of GGIs much different than that (1.99 eV) in the interiors of glassy grains. From the analyses on dynamical scaling for mechanical losses (Q ⁻¹) in the glass and supercooled-liquid (SC-liquid) states, i.e., Q ^{- 1}∝ (ω) ^{- n}, where ω is the angular frequency, it is suggested that the atomic structures at GGIs in NGs with D _avg < 150 nm could be dominated by solid-like atomic clusters, whereas those in NGs with D _avg > 250 nm might be liquid-like. The size effects on the glass forming ability of NGs are also quantitatively measured by exponents of the dynamical scaling in the SC-liquid state, suggesting that NGs with D _avg < 40 nm could be good glass formers. The atomic structures at GGIs revealed in this work could facilitate the development of NGs with desirable mechanical properties through GGI engineering.