Microstructure of Fragile Metallic Glasses Inferred from Ultrasound-Accelerated Crystallization in Pd-Based Metallic Glasses

Abstract

By utilizing ultrasonic annealing at a temperature below (or near) the glass transition temperature Tg, we revealed a microstructural pattern of a partially crystallized Pd-based metallic glass with a high-resolution electron microscopy. On the basis of the observed microstructure, we inferred a plausible microstructural model of fragile metallic glasses composed of strongly bonded regions surrounded by weakly bonded regions (WBRs). The crystallization in WBRs at such a low temperature under the ultrasonic vibrations is caused by accumulation of atomic jumps associated with the beta relaxation being resonant with the ultrasonic strains. This microstructural model successfully illustrates a marked increase of elasticity after crystallization with a small density change and a correlation between the fragility of the liquid and the Poisson ratio of the solid.

Intrinsic correlation between fragility and bulk modulus in metallic glasses

“…42 Nevertheless, according to elastic models of glass forming, the barrier transition for a "flow event" ͑an atomic rearrangement͒ does take place on a very short time scale. 43 Furthermore, both Egami's atomistic theory 8 and the microstructural model of Ichitsubo et al 6 can perfectly explain the Novikov-Sokolov observations. Actually, in their models, the temperature-dependent modulus was neglected, which corresponds to b͑T ; m , G͒ϵ0 in our case.…”

“…5 Due to the technological and the scientific significance of this surprising finding, it has attracted a lot of discussions. [6][7][8][9][10] However, the question whether such a linear correlation universally exists still remains open up to now. As for metallic glasses, a number of important correlations among their properties have been revealed.…”

Kinetics of spontaneous change in the localized motions of D-sorbitol glass

“…Thus the interpretation of the NMR measurements 31,32 in terms of small-angle motions of all molecules would not be applicable to all types of glasses. Furthermore, a recent paper by Ichitsubo et al 59 has described a microstructural model for a glass consisting of a mixture of weakly regions ͑islands of mobility͒ and stronglybonded regions.…”

Chemical influence on β-relaxations and the formation of molecule-like metallic glasses

“…In addition to the primary (a-) relaxations that are responsible for the viscous flow, a kind of secondary relaxation, called Johari-Goldstein or b-relaxation [7][8][9] , often exists at high frequencies or low temperatures. Recent studies have demonstrated that b-relaxations are an intrinsic and universal feature of supercooled liquids and glasses 1,8,10 , and they are of significance to the understanding of many key issues in glassy physics and material sciences 1 , ranging from glass transition phenomenon [10][11][12][13] , diffusions [14][15][16][17] , physical aging 18,19 to mechanical properties 20,21 and mechanisms of plastic deformations [21][22][23] , as well as the stabilities and crystallization of glassy materials [24][25][26] .…”