Enhancing ductility in bulk metallic glasses by straining during cooling

Abstract

Most of the known bulk metallic glasses lack sufficient ductility or toughness when fabricated under conditions resulting in bulk glass formation. To address this major shortcoming, processing techniques to improve ductility that mechanically affect the glass have been developed, however it remains unclear for which metallic glass formers they work and by how much. Instead of manipulating the glass state, we show here that an applied strain rate can excite the liquid, and simultaneous cooling results in freezing of the excited liquid into a glass with a higher fictive temperature. Microscopically, straining causes the structure to dilate, hence “pulls” the structure energetically up the potential energy landscape. Upon further cooling, the resulting excited liquid freezes into an excited glass that exhibits enhanced ductility. We use Zr44Ti11Cu10Ni10Be25 as an example alloy to pull bulk metallic glasses through this excited liquid cooling method, which can lead to tripling of the bending ductility.

Yielding transition in stable glasses periodically deformed at finite temperature

“…Here, we highlight a recent discovery that thermal cycling between the room and cryogenic temperatures can lead to rejuvenation of metallic glasses due to heterogeneous thermal expansion [7][8][9][10][11][12][13][14][15][16][17][18]. Remarkably, it was also recently demonstrated experimentally and by means of atomistic simulations that cooling across the glass transition temperature under applied stress rejuvenates amorphous alloys and increases their ductility [19,20]. However, despite extensive efforts aimed at exploring the operational parameter space in order to extend the range of glassy state, the optimization of processing routes remains a difficult task.…”

Relaxation dynamics in amorphous alloys under asymmetric cyclic shear deformation

“…Moreover, the process of rejuvenation during elastostatic compression can be accelerated when stress is temporarily applied along alternating directions [22,23]. In addition, it was also recently demonstrated experimentally and by means of molecular dynamics (MD) simulations that higher energy states can be realized via rapid freezing of a glass former under applied stress [24,25]. However, in spite of the progress made, the design of novel strategies for thermomechanical processing of metallic glasses is required to access a broader range of energy states and improved mechanical properties.…”

Characterization of Plastic Deformation in CuZr Metallic Glasses Subjected to the Rolling Process

“…Metallic glasses (MGs) are in the category of amorphous materials that are known to exhibit superior mechanical properties and excellent functional behaviors [1][2][3][4]. However, the poor ductility at room temperature is one of their drawbacks for application in the engineering systems [5][6][7]. It is generally accepted that the plastic deformation of MGs is occurred in the narrow sheared regions, named as shear bands, which is resulted from the sliding of energetically favorable defects under an external force [8][9][10].…”