The Science & Technology
of Glass
Cambridge - Monday 4th to
Wednesday 6th September 2017

Abdelmalek Roula

article posted 17 Apr 2017

Abdelmalek Roula

I am metallurgist; I was passionate by the technical aspects of scientific research. Since I began teaching glass technology, my attention has shifted to the fundamental considerations related to thermodynamics of the firing/sintering/melting & cooling processes of molten inorganic materials. The glass forming ability of some oxide melts and some metallic alloys is an exciting subject. I am seduced by this particular behavior and doing my best to contribute with a new approach to quantifying this phenomenon.

A new theoretical approach to the never-ending quest
for assessing the Glass Forming Ability
of Bulk Metallic Glasses
Abdelmalek Roula

LIME-4, Fac. Sci. & Technol., MSB Jijel University, BP 98, Ouled Aissa, Jijel, 18000, Algeria

A brief but updated review of Glass Forming Ability (GFA) criteria for Bulk Metallic Glasses (BMGs) is given. This phenomenon is always and consensually discussed by the values of the Crystallisation Driving Force (CDF) and/or a lot of astute thermal criteria (the undercooled liquid range ΔTxg, the reduced glass transition temperature Trg, and the critical cooling rate Rc are the most used:

where Tx, Tg, Tl are, respectively the onset crystallisation temperature, the glass transition temperature, the liquidus temperature while tn is the time required for the crystallization of volume fraction 10-6 at the temperature Tn corresponding to the nose of the T-T-T diagram at the melting temperature Tm ). In this study, author is focussing on the common Crystallisation Driving Force:

where ΔG, T and R are Gibbs free energy change, temperature and the universal gas constant.

Author proposes an effective criterion for assessing GFA of BMGs while amending CDF:

Thus, the Crystallisation Driving Force CDF:

becomes the Relative Glass Forming Ability evaluated as:

The obtained criterion is also dimensionless and may be adopted as the real GFA (relatively quantifying the glass formation tendency of any melt). It seems to be more comprehensive because taking in account an indispensable thermodynamic characteristic that was omitted and replaced by constant. It shows also a physical sense while answering the question: why/how do some metallic alloys form glasses (considering that the lower the value of the crystallisation driving force, the higher is the vitrification driving one because being its inverse mathematical expression). Author presents the results of some calculations that verify the accurateness of this new approach.