By sequential heat treatment of a Pd 40 Ni 40 P 20 metallic glass at temperatures and durations for which ␣-relaxation is not possible, dynamic, and quasistatic relaxation paths below the glass transition are identified via ex situ ultrasonic measurements following each heat treatment. The dynamic relaxation paths are associated with hopping between nonequilibrium potential energy states of the glass, while the quasistatic relaxation path is associated with reversible -relaxation events toward quasiequilibrium states. These quasiequilibrium states are identified with secondary potential energy minima that exist within the inherent energy minimum of the glass, thereby supporting the concept of the sub-basin/metabasin organization of the potential-energy landscape. © 2009 American Institute of Physics. ͓doi:10.1063/1.3266828͔In recent years, descriptions of the structural kinetic behavior of metallic liquids and glasses have been significantly revisited. 1 It became evident that various secondary structural relaxation modes instead of a single primary one are necessary to accurately describe the entire dynamic behavior of a metallic glass. 2 These secondary structural relaxation modes, termed Johari-Goldstein or slow -modes, and the primary structural relaxation termed ␣-mode merge at a temperature above the glass transition specific for each material. This merging temperature is very close to the critical temperature of mode-coupling theory. 3 At lower temperatures, the onset of the glass transition depends on the cooling rate 4 or the external frequency. 5 The viscosity of the material tends to follow a Vogel-Fulcher-Tammann ͑VFT͒ law upon cooling, 6 until the ␣-relaxation mode "freezes" at T g on experimental time scales of Ϸ100 s. The predicted divergence of the relaxation time at a finite VFT-temperature remains inconsequential, as has recently been demonstrated in a careful analysis of viscosity data. 7 In contrast, the slow -or Johari-Goldstein mode is believed to be responsible for lowtemperature diffusion, 8 which is found to operate at temperatures as low as 200°C below T g . 2 In the past, changes in Young's modulus, 9 decrease in free volume, 10 or irreversible effects in the diffusion mechanism in asquenched samples have been attributed to the -relaxation mode in these alloys, 3 suggesting that aging is a cooperative phenomenon as described in many earlier molecular dynamics simulations. 11 In a recent paper, 12 these secondary -relaxation events were identified with reversible anelastic excitations within the elastic matrix confinement, and an ␣-relaxation event was identified with the collapse of the matrix confinement and the breakdown of elasticity, a view consistent with Eshelby's concept of elastic confinement. 13 In a different approach Khonik et al. 14 showed very recently, that structural relaxation can change significantly the concentration of so called interstitiallylike defects leading also to a distinct change of the shear modulus depending on the quenched, annealed or initial condit...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.