Glassy metals not only exhibit technologically interesting properties, e.g. high fracture strength, excellent soft magnetic behaviour and good corrosion resistance, they also constitute ideal materials for the studies of low-temperature transport, critical behaviour and electrical properties of disordered metals. Considerable efforts at understanding their structure, atomic and electronic transport properties and low-temperature behaviour have been made. The author describes the nature of the glassy state, various quenching techniques and glass-forming alloys, and discusses structural models, experimental structural data and atomic transport properties including diffusivities and kinetics of structural relaxation, magnetic aging and crystallisation. The mechanical properties and magnetic behaviour are summarised, with emphasis laid on the influence of modification of these properties due to changes in structural and chemical disorder and states of magnetisation. Finally the electrical transport properties, spin wave excitations and critical behaviour, thermal and acoustic behaviour at very low temperatures, and chemical properties are presented.

REVIEW ARTICLE: Glassy metals

New amorphous alloys exhibiting a wide supercooled liquid region before crystallization were found to form by melt spinning in wide composition ranges of LaAlM, MgYM and ZrAlM (M = Ni or Cu) systems consisting of the constituent elements with significantly different atomic sizes. The temperature span between glass transition temperature, Tg, and crystallization temperature, Tx, ΔTx ( = Tx − Tg) is > 50 K in the compositional ranges around La2AlM, Mg6Ln3M and Zr3AlM and the largest ΔTx reaches 126 K. The critical cooling rate for the glass formation, Rc, is as low as 87–115 K/s and Tg/Tm is > 0.6 in the composition range where ΔTx > 50 K. There is a clear tendency for Rc to decrease with an increase of ΔTx and Tg/Tm. The crystallization of the alloys with large ΔTx occurs through the simultaneous precipitation of several compounds. Based on these results, it is presumed that the large glass-forming ability for these alloys is due to a combined effect of the difficulty of long-range atomic redistribution required for the precipitation of the compounds, the rapid increase of viscosity with decreasing temperature and the large liquidus-solidus interfacial energy which originates from the optimally bonding and packing states resulting from large negative heat of mixing and large atomic size ratios.

Glass-forming ability of alloys

The critical need for high strength, high performance, and cost effective materials has resulted in the use of novel processing techniques for the development of new aluminium alloys for structural applications. The highly attractive combinations of microstructure and mechanical properties achievable through rapid solidification technology (RST) have prompted the study and application of rapid solidification as a means of improving the behaviour of existing alloy systems and also developing novel alloying compositions. The rapid extraction of thermal energy associated with RST permits large deviations from equilibrium, as evidenced by the extension in solid solubility limits, sharp reductions in grain size, and a reduction in the size and number of segregated phases with concomitant development of non-equilibrium phases. In the present paper, the fundamental scientific principles underlying RST are discussed and particular emphasis is given to published studies of composition-processing-microstruc...

Rapid solidification processing with specific application to aluminium alloys

Rapid solidification of Al-Cu eutectic alloy by laser remelting

The formation and stability of amorphous alloys are discussed in terms of the configurational entropy and in connection with the potential barrier, Δμ. The structure analysis of amorphous alloys using Bernal's dense random packing model (D.R.P.) shows quite good agreement with the actual observations. These results indicate that some degree of short range order (∼ 15 A) exists in amorphous metallic alloys, which is slightly different from the arrangement expected in a liquid. The model still shows a continuous structure without the formation of internal boundaries between ordered regions such as is characteristic of polycrystals. Although the D.R.P. does not completely reflect the structure of amorphous alloys, it is still an attractive model in understanding the amorphous state. These subjects are reviewed in this article.

Amorphous structures and their formation and stability

An apparatus for splat-quenching by the gun technique in a sealed, inert atmosphere is described. The importance of a low-oxygen quenching atmosphere in promoting efficient spreading of liquid particles and good thermal contact with the quenching surface is shown. A cooling rate of ∼1010 K sec−1 was estimated from the interlamellar spacing in a quenched Al-17.3 at. % Cu alloy. The process mechanisms of the gun technique are discussed with particular reference to the atomized droplet size and the effective specimen thickness for heat transfer.

Some aspects of splat-quenching in an inert atmosphere and of the formation of non-crystalline phases in Al-17.3 at. % Cu, germanium and tellurium

A non-crystalline phase has been formed in electron-transparent (0.1 to 0.5Μm thick) areas of splat-quenched foils of nickel. The positions in diffraction co-ordinates of the first two peaks and of a shoulder on the high-angle side of the second peak of the electron diffraction pattern agree closely with those for non-crystalline vapour-deposited Ni. The presence of the shoulder suggests that the structure is similar to that of dense random packed hard spheres, i.e. that it is amorphous rather than microcrystalline. The crystallization behaviour of the glassy phase studiedin situ in 1 MV electron microscope also supports this view. The crystallization temperature of about 150‡ C is unexpectedly high and suggests that stabilization by impurities (possibly up to 0.7 wt %) was occurring. The critical cooling rate for the formation of the glassy phase has been estimated from theories of homogeneous nucleation, crystal growth and transformation kinetics to be ∼1010 K sec−1 which is in satisfactory agreement with experimentally derived estimates of the maximum cooling rate in electron-transparent areas of foils.

The formation, structure and crystallization of non-crystalline nickel produced by splat-quenching

Comments on “On the presence of amorphous regions in splat-quenched Al-Cu alloys”

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Some aspects of splat-quenching in an inert atmosphere and of the formation of non-crystalline phases in Al-17.3 at. % Cu, germanium and tellurium

The formation, structure and crystallization of non-crystalline nickel produced by splat-quenching

Comments on “On the presence of amorphous regions in splat-quenched Al-Cu alloys”