REVIEW ARTICLE: Glassy metals

The minimum solute concentration in a binary alloy system necessary to obtain a stable amorphous phase by rapid quenching, C B min , collected from the published reports on glass formation of 66 systems, was found to be inversely correlated with the atomic volume mismatch, | (v b −v A v A | , where v A is the atomic volume of the matrix and v B is the atomic volume of the solute. The atomic scale elasticity theory was developed to calculate the atomic level stresses in solid solution, which led to the stress criteria for the topological instability of solid solution. It was found that C B min is closely correlated with the critical solute concentration for the topological instability of solid solution. This result indicates that the atomic size ratio between the constituent elements is the most important factor in the determination of value of C B min , and the amorphous alloys are stabilized partly because the solid solutions of the corresponding compositions are topologically unstable.

Atomic size effect on the formability of metallic glasses

The Al-Si (Aluminum-Silicon) system

Nucleation in solids: The induction and steady state effects

A theory is developed which allows one to discuss the stability of multiply-twinned particles and to calculate critical sizes for stable and quasi-stable states. An icosahedral particle is essentially stable for r ≦ r i w * , quasi-stable for r i w * r i t 0 where r is an edge length of the particle, while a decahedral particle is not essentially stable but quasi-stable for r ≦ r d t 0 and unstable for r > r d t 0 . The critical sizes r i w * , r i t 0 and r d t 0 are formulated as functions of the specific surface energy γ h k l , the twin boundary energy γ t , the elastic strain energy W and the adhesive energy γ a to the substrate. Calculated critical diameters 2 r i w * ,2 r i t 0 and 2 r d t 0 for the particles grown in free space for several elements range between 15.5A and 106.8A, between 109.8A and 486.1A and between 725A and 3961A, respectively. These values are in good agreement with experimental results.

Stability of Multiply-Twinned Particles

The ability of rapid conduction cooling to produce new non-equilibrium phases is examined with particular attention on solidification rate. By matching the rate of solidification calculated numerically from the heat flow balance with the crystal growth rate calculated by a kinetic equation, the kinetic undercooling for a given experimental condition is estimated. A limiting condition of cooling is presented in which the cooling rate is so large that the crystal growth cannot cover the whole sample body before it is cooled down to a low temperature where the growth rate of the crystal is negligibly small.

Solidification rate in rapid conduction cooling

An amorphous phase in a splat-cooled Fe-3.8 wt%C alloy

Studies on the crystallographic growth habit of primary silicon crystals in an Al-16 wt% Si alloy were carried out by X-ray micro focus Laue analysis and ECP (electron channelling pattern) analysis.

Ryohei Ozaki

Papers

Solidification rate in rapid conduction cooling

An amorphous phase in a splat-cooled Fe-3.8 wt%C alloy

Crystal growth of the primary silicon in an Al-16 wt % Si alloy

On the Solidification Process of Nodular Cast Iron

Splat Cooling of Aluminum-Silicon Alloys