Synthesis and mechanical properties of highly structure-controlled Zr-based metallic glasses by thermal rejuvenation technique.

A novel thermal rejuvenation treatment facility for Zr-based bulk metallic glass (BMG) was developed, consisting of a rapid heating and indirect liquid nitrogen quenching process. The re-introduction of free volume into thermally rejuvenated BMG results in more disordered state. The rejuvenation improves ductility, implying that the re-introduced free volume aids in the recovery of the shear transformation zone (STZ) site and volume.

Breakdown of One-to-One Correspondence in Energy and Volume in a High-Pressure Heat-Treated Zr-Based Metallic Glass During Annealing.

The glassy state of a high-pressure heat-treated ZrCuAl metallic glass was investigated from energetic and volumetric perspectives. The specific heat (C) data of initial heating and subsequent cooling from the supercooled liquid region indicates that the sample behaviour cannot be explained simply by the derivative of the well-known enthalpy (H)-temperature (T) curve. Unlike the C data, the thermal-expansion coefficient (α) value increased monotonically during the first heating step, which suggests the collapse of a one-to-one correspondence between the energy and volume during the process.

Heterogeneous structural changes correlated to local atomic order in thermal rejuvenation process of Cu-Zr metallic glass.

In this study, we investigated the atomistic mechanism of structural excitation in a thermal process (thermal rejuvenation) of metallic glass. In a molecular dynamics framework, Cu-Zr metallic glass was rejuvenated by a thermal process composed of an isothermal heat treatment at a temperature above the glass transition temperature , followed by fast cooling. Atomistic analyses of the local rearrangement, potential energy, and geometrical structure revealed structural changes correlating to the local atomic order in the rejuvenation process.

Various Rejuvenation Behaviors of Zr-Based Metallic Glass by Cryogenic Cycling Treatment with Different Casting Temperatures.

The rejuvenation behavior of an ZrCuAl (at.%) metallic glass upon cryogenic cycling treatment has been investigated. At a high casting temperature, the microstructure of the glass is quite homogenous and thus, internal stress cannot be generated during cycling.

Thermal rejuvenation in metallic glasses.

Structural rejuvenation in metallic glasses by a thermal process (i.e. through recovery annealing) was investigated experimentally and theoretically for various alloy compositions.

Controlled rejuvenation of amorphous metals with thermal processing.

Rejuvenation is the configurational excitation of amorphous materials and is one of the more promising approaches for improving the deformability of amorphous metals that usually exhibit macroscopic brittle fracture modes. Here, we propose a method to control the level of rejuvenation through systematic thermal processing and clarify the crucial feasibility conditions by means of molecular dynamics simulations of annealing and quenching. We also experimentally demonstrate rejuvenation level control in Zr(55)Al(10)Ni(5)Cu(30) bulk metallic glass.

Change in local environment upon quasicrystallization of Zr-Cu glassy alloys by addition of Pd and Pt.

The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structure in Zr(70)Cu(30) glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certain temperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization is accompanied by a significant change in the local environment around the Zr atoms and a slight change around the noble metal.

Evaluation of the local environment for nanoscale quasicrystal formation in Zr(80)Pt(20) glassy alloy using Voronoi analysis.

The local atomic structure of nano-quasicrystal-forming Zr(80)Pt(20) binary glassy alloy was investigated by reverse Monte Carlo modeling based on the results of x-ray diffraction. A prepeak at Q∼17 nm(-1) originating from the unique bonding between the Pt-Pt pair is observed in the structure factor. Voronoi analysis indicates that an icosahedral-like polyhedron is formed around Pt.