Quantifying the origin of metallic glass formation

• Published in: Nature communications 2016-01, Vol.7 (1), p.10313-10313, Article 10313
• Main Authors: Johnson, W. L., Na, J. H., Demetriou, M. D.
• Format: Article
• Language: English
• Subjects: 639/301/923/218; 639/766/483/640; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms10313

The waiting time to form a crystal in a unit volume of homogeneous undercooled liquid exhibits a pronounced minimum τ X * at a ‘nose temperature’ T * located between the glass transition temperature T g , and the crystal melting temperature, T L . Turnbull argued that τ X * should increase rapidly with the dimensionless ratio t rg = T g / T L . Angell introduced a dimensionless ‘fragility parameter’, m , to characterize the fall of atomic mobility with temperature above T g . Both t rg and m are widely thought to play a significant role in determining τ X *. Here we survey and assess reported data for T L , T g , t rg , m and τ X * for a broad range of metallic glasses with widely varying τ X *. By analysing this database, we derive a simple empirical expression for τ X *( t rg , m) that depends exponentially on t rg and m , and two fitting parameters. A statistical analysis shows that knowledge of t rg and m alone is therefore sufficient to predict τ X * within estimated experimental errors. Surprisingly, the liquid/crystal interfacial free energy does not appear in this expression for τ X *. The crystal formation waiting time of a homogeneous supercooled liquid exhibits a pronounced minimum depending on temperature, and this minimum is a measure of glass forming ability. Here, the authors propose an expression for this minimum for all metallic glasses that depends only on two fitting parameters.