J.M. Pelletier

Amorphous physics and materials: Secondary relaxation and dynamic heterogeneity in metallic glasses: A brief review*

Understanding mechanical relaxation, such as primary (a) and secondary (s) relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, s relaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of s relaxation. In particular, we will discuss the correlation among s relaxation, structural heterogeneity, and mechanical properties of metallic glasses.

Insight on Viscoelasticiy of Ti16.7 Zr16.7 Hf16.7 Cu16.7 Ni16.7 Be16.7 High Entropy Bulk Metallic Glass

High entropy bulk metallic glasses show promising mechanical and physical properties. Dynamic mechanical properties of Ti16.7 Zr16.7 Hf16.7 Cu16.7Ni16.7 Be16.7 high entropy bulk metallic glass were investigated by mechanical spectroscopy (or called dynamic mechanical analysis). The main (a) relaxation was observed in the framework of the loss modulus G, which is related to the dynamic glass transition behaviour for the glassy materials. From physical model point of view, dynamic mechanical properties of the Ti16.7 Zr16.7 Hf16.7 Cu16.7.Ni16.7 Be16.7 high entropy bulk metallic glass show good agreement compared with the quasi-point defects theory.

Slow β relaxation in La-based metallic glasses based on mechanical spectroscopy measurements

Dynamic mechanical relaxations of La-based metallic glasses were investigated by mechanical spectroscopy. In the framework of the mixing enthalpy of constituent atoms, it was found that β relaxation was less evident by the addition of Cu to replace Ni in the LaCuNiAl glassy alloy. By introducing Cu into the LaNiAl metallic glass, the mixing enthalpy was less negative, which led to weaker β relaxation of the metallic glasses. The a relaxation of the La-based metallic glasses could be described by a Kohlrausch-Williams-Watts (KWW) function with a Kohlrausch exponent βKWW around 0.5. It should be noted that physical aging above the glass transition temperature Tg induced a decrease of β relaxation intensity in the La-based metallic glass.