https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

Bulk metallic glass (BMG) formers are multicomponent alloys that vitrify with remarkable ease during solidification. Technological interest in these materials has been generated by their unique properties, which often surpass those of conventional structural materials. The metastable nature of BMGs, however, has imposed a barrier to broad commercial adoption, particularly where the processing requirements of these alloys conflict with conventional metal processing methods. Research on the crystallization of BMG formers has uncovered novel thermoplastic forming (TPF)-based processing opportunities. Unique among metal processing methods, TPF utilizes the dramatic softening exhibited by a BMG as it approaches its glass-transition temperature and decouples the rapid cooling required to form a glass from the forming step. This article reviews crystallization processes in BMG former and summarizes and compares TPF-based processing methods. Finally, an assessment of scientific and technological advancements required for broader commercial utilization of BMGs will be made.

Processing of Bulk Metallic Glass

Deformation behavior of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass over a wide range of strain-rates and temperatures

A nanoindentation study of serrated flow in bulk metallic glasses

Correlation between enthalpy change and free volume reduction during structural relaxation of Zr55Cu30Al10Ni5 metallic glass

The viscosity and flow stress of a bulk Pd40Ni10Cu30P20 alloy glass near the glass transition were measured as a function of temperature and strain rate under compression The steady-state viscosity of the glass for a given temperature remains constant at low strain rate, then decreases by many orders of magnitude above a critical strain rate A master curve in term of the viscosity ratio η/ηN and the product ηNe has been constructed, where η and ηN are, respectively, the steady-state viscosity and Newtonian viscosity, and e is the strain rate The flow stress also can be represented in terms of the product ηNe The master curves are fitted with a simple stress relaxation of the form 1−exp[−t/λ] with t=e−1

Newtonian to non-Newtonian master flow curves of a bulk glass alloy Pd40Ni10Cu30P20

http://saiya.msre.kumamoto-u.ac.jp/~chino/publication/pdfs/Scr.Mater.43.pdf

High strength and good ductility of Zr55Al10Ni5Cu30 bulk glass containing ZRC particles

We have investigated the viscosity of the supercooled liquids over a wide range of strain rate by constant-strain-rate tensile tests for La 55 Al 25 Ni 20 , Zr 65 Al 10 Ni 10 Cu 15 and Pd 40 Cu 40 P 20 (at.%) metallic glasses. The supercooled liquids exhibited Newtonian viscosity (equilibrium state) that transferred to a non-Newtonian viscosity (non-equilibrium state) with increasing temperature. The critical strain rate of the Newtonian viscosity increased with increasing temperature in accordance with the Arrhenius relation. The strain rate dependence of viscosity was described well with a master curve expressed by a stretched exponential function η/η 0 =1− exp (C/ e β ) . The Newtonian viscosity was successfully described with the free-volume model of Cohen and Grest. The fragility of the Newtonian viscosity revealed that the supercooled liquids of the metallic glasses were classified into the relatively strong liquids such as Ge 10 As 10 Se 80 , B 2 O 3 and Na 2 O–2SiO 2 glass formers.

Newtonian and non-Newtonian viscosity of supercooled liquid in metallic glasses

The evolution of specific heat near the glass transition temperature, Tg, of a Zr55Al10Ni5Cu30 glassy alloy subjected to different degrees of non-Newtonian flow conditions was investigated. At conditions in which non-Newtonian flow begins, a gradual exothermic relaxation near Tg was observed. This is attributed to the change in configuration of the long-range liquid structure of the alloy. At conditions in which a high degree of non-Newtonian flow is favored, the alloy exhibits both high-temperature and low-temperature relaxation due to a change in local short-range order. The enthalpy of relaxation is found to scale as the logarithm of the normalized viscosity and is interpreted in terms of the free volume model of viscous flow. The decrease in viscosity in the non-Newtonian flow region is associated with a highly disordered structure and induced free volume.

Thermal evidence of stress-induced structural disorder of a Zr55Al10Ni5Cu30 glassy alloy in the non-Newtonian region

A model, based on the hypothesis of stress-induced structural relaxation and a concept of fictive stress, is proposed for nonlinear viscoelastic behavior in glassy materials. A model calculation has been carried out on the stress-overshoot phenomenon observed in metallic glasses. The model calculation reproduces the experimental results of a Pd40Ni10Cu30P20 glass fairly well, in particular, the development of stress-overshoot behavior with increasing strain rate and lowered temperature. In addition, the model reveals a stress-overshoot and -undershoot oscillatory behavior which has not been reported previously in metallic glasses, but has been observed in many polymer solutions.

https://iopscience.iop.org/article/10.1143/JJAP.39.1808/pdf

Hidemi Kato

Papers

Newtonian to non-Newtonian master flow curves of a bulk glass alloy Pd40Ni10Cu30P20

High strength and good ductility of Zr55Al10Ni5Cu30 bulk glass containing ZRC particles

Newtonian and non-Newtonian viscosity of supercooled liquid in metallic glasses

Thermal evidence of stress-induced structural disorder of a Zr55Al10Ni5Cu30 glassy alloy in the non-Newtonian region

A Fictive Stress Model Calculation of Stress-Overshoot: A Nonlinear Viscoelastic Behavior in Metallic Glass