Amorphous alloys, more commonly referred to as metallic glasses, represent a striking advance in inorganic materials technology of recent times. While the probable atomic arrangements in noncrystalline alloys have aroused scientific curiosity, their unusual mechanical strength, attractive magnetic properties and remarkable corrosion resistance have excited technological interest. This report describes the progress of research at Varanasi on the following aspects: adaptation, innovation and development of techniques for rapid solidification, study and refinement of structural models, calculation of thermodynamic quantities, evaluation of strength and corrosion resistance and studies of glass to crystal transition.

The investigation reported here was undertaken to study the beneficial influence of indium on the internal oxidation behaviour of silver-tin alloys in the context of electrical contact material development. Five compositions of varying indium content, namely Ag-6Sn-xIn (x = 2·0, 2·5, 3·0, 3·5, 4·0 wt%) were prepared and internally oxidized at different temperatures and oxygen pressure. The kinetics of internal oxidation was studied and an attempt made to correlate the same with microstructure.

The twentieth century has been an exciting and fruitful period for materials scientists involved in probing the structure of metals and alloys at different levels. The Science of Metallography dealing with the macrostructure, microstructure, submicrostructure and crystal structure of metallic materials has made impressive strides in many directions during this century, particularly during the last four decades coinciding with the author’s own research career. The steady advances in optical microscopy, the growing sophistication in electron microscopy and diffraction, the welcome advent of field ion microscopy, the increasing precision in X-ray diffractometry and the powerful back-up provided by Computer Science have all combined to open out many a new and bright vista in Structural Metallurgy in recent decades.

In this lecture some of the notable developments in the fascinating area of metallic structures are highlighted with special reference to the researches of the author, his students and coworkers in several Indian and overseas Laboratories, particularly Oxford (UK), Stuttgart (Germany), Pasadena (USA) and Bangalore, Varanasi and Patiala (all three in India).

Recent developments in the complex and controversial, but fertile and fascinating field of aluminium-transition metal alloys are reviewed with particular reference to the so-called quasicrystalline phases and their rational approximants. Pauling’s several approaches to icosahedral phases on the basis of twinning in cubic crystals with large unit cells are described and examined along with the difficulties in checking the structures proposed by him. A new unified crystallographic approach is presented by the author, starting with icosahedral atomic clusters in concerned alloy melts, and it is shown that this integral approach leads to a reasonably good understanding of the interrelationship between the numerous known solid phases in aluminium alloys, including icosahedral phases, decagonal phases and their rational approximants.

X-ray and electron diffraction data from the Al-Cu-Fe icosahedral phase are compared and analysed on the basis of the microcrystalline and multi-domain model developed by the author. It is shown that a crystallographic explanation is now possible for both the enigmatic five-fold symmetry and non-periodicity of reflections observed in electron diffraction patterns of icosahedral phases.

In recent decades some complex crystalline phases, as also many rational approximants to quasicrystalline phases with rather large unit cells, have been reported with orthorhombic symmetry in aluminium-transition metal (Al-TM) alloys. Furthermore, quite a few quasicrystalline phases, icosahedral as well as decagonal, forming in Al-TM alloys on normal or rapid solidification have been interpreted during the last decade as multiply-twinned orthorhombic crystals growing as superstructures of an orthorhombic cell that forms through welding in three perpendicular directions in the liquid state of 13-atom icosahedral clusters.

Following exemplification of this new approach to quasicrystals based on the analysis of the Debye-Scherrer diffraction data from the comparatively defect-free Al-Cu-Fe icosahedral phase, the three types of orthorhombic phases in aluminium-rich Al-TM alloys, numbering 36 in all, have been examined as icosahedral cluster compounds nucleating from icosahedral atomic clusters present in the molten alloys. A detailed analysis of their lattice parameters supports the postulate that all such phases can be viewed as complex and, occasionally, as very large superstructures of a small basic orthorhombic cell.