Metallic glasses from "alchemy" to pure science. Present and future of design, processing and applications of glassy metals.

Available in sizes up to several centimeters, with many novel, applicable properties, metallic glasses have also been the focus of research advancing the understanding of liquids and of glasses in general.



Metallic Glasses (MGs) , called also bulk metallic glasses (BMGs) ( or glassy metals , amorphous metals , liquid metals) are considered to be the materials of the future. Due to their high strength, metallic glasses have a number of interesting applications, for example as coatings. Metallic glasses can also be corrosion resistant. Metallic glasses, and the crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Combined with their strength – and now, toughness – this makes them ideal candidates for bio-implants or military applications. Prestigious Journals such as “Nature Materials”, “Nature” frequently publish new findings on these unusual glass materials.   Moreover Chinese and Asian  scientists have also been showing an interest in the study of metallic glasses.



This review paper is far from exhaustive , but tries to cover the areas of interest as it follows : a short history , the local structure of BMGs and the glass forming ability ( GFA) , BMGs’ properties , the manufacturing and some applications of BMGs and finally , about the future of BMGs as valuable materials.



In 1960 ,in the modern sanctuary of science from California ( California Institute of Technology)   , an act of inversed “alchemy”   was produced : a metal , a gold based alloy was transformed in a glass (…a metallic glass)  . And the philosopher's stone was the extremely  rapid cooling  of melted alloy ( cca. 106 kelvin per second).



Short history of BMGs

The first reported metallic glass , scientific obtained, was the alloyMetallic glasses-historical background , Duwez describes the first experiment , based on  “ the  gun technique”  as “ a success combined with  a failure “. The success was given by sufficient metallic glass obtained to make The  Debye- Scherrer patterns .  The failure  was the  destruction of experimental apparatus. Duwez says : “ the shock pressure was too high and about half of apparatus disintegrated, sending hot broken pieces into the laboratory”   Au75Si25 produced at Caltech by  Klement ,  Willens & Duwez in 1959.[ 2 ] In a book chapter, entitled Fabrication and processing techniques of BMGs, the most recent method to obtain a metallic glass that is ordered at a large scale was reported in a study conducted by Geophysical Laboratory at the Carnegie Institution for Science Zhejiang University from China, Stanford University and SLAC. Ho-Kwang Mao from Carnegie and other scientists are conducting research on metallic glass produced from aluminum and cerium. The team , created a single crystal by applying 25 GPa of pressure (equivalent of 1800 tons per square inch !)  to the cerium-aluminum glass and the new order formed is preserved even when the glass is restored to ambient pressure.



Schroers and colleagues developed Pt57.5Cu14.7Ni5.3P22.5 bulk metallic glass (Pt-BMG) nanowires. The Pt-BMG nanowires have high surface areas, thereby exposing more of the catalyst, and also maintain their activity longer than traditional fuel cell catalyst systems. After 1,000 cycles, these nanowires maintained 96% of their performance—2.4 times as much as conventional Pt/C catalysts



NASA and a team composed by William Johnson, Chris Veazey, Marios Demetriou ( Caltech)  and William Kaukler ( University of Alabama) investigate the fabrication of BMGs foam in space conditions . Investigations tests and produces hardened foam from bulk metallic glass. The absence of gravity facilitates the creation of a more uniform metallic glass foam, a material with an extremely high strength to weight ratio. Developing lighter and stronger materials can lead to a more durable spacecraft that will require less propellant to travel long distances. Three planned runs for the Foam experiment were successfully completed on station during Expedition 9. Samples, were returned to Earth in August 2005, have been analyzed and reported. The experiment was designed to test the hypothesis that amorphous metals exhibit foam-making qualities on the ground that mimic metallic foam textures made in microgravity conditions

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In Rare earth based bulk metallic glasses, Journal of Non-Crystalline Solids 355 (2009) 759–775, Luo & Wang revealed the excellent thermoplastic behavior of rare earth based BMGs at room temperature. This make from these materials environmentally friendly because the small energy consumption for machining and forming.



About the future of metallic glasses

Dr. Physicist Joerg Heber,Senior Editor at Nature Materials and science writer, comment for readers of Materials & Design and of this review paper  : “ Metallic glasses have come a long way since their discovery 50 years ago. It is now possible to fabricate a large variety of compounds in bulk quantities. What's more, the properties of metallic glasses have been enhanced considerably. We will see more of this in future. New alloys designed with certain properties in mind. Whether as structural materials, or for novel applications. For centuries researchers have exploited the properties of crystals, because their properties seemed easier to control. But this doesn't necessarily hold true. In future, we will see much more emphasis on amorphous materials.”



Professor Marios Demetriou from Caltech declare for this review paper : "Owing to their attractive mechanical properties and unique processing capabilities, metallic glasses have the potential to dominate metal-hardware engineering in the 21st century."



Professor Jan Schroers from Schroerslab –Yale University declare for this review paper : “In my opinion the future of metallic glasses stem from the fact that when thermoplastic formed they combine previously mutually exclusive attributes, the properties of a very high strength metals and the processibility of plastics.  The materials science community must develop processing strategies based on thermoplastic forming, processing protocols, and equipment. In terms of material, up to date there are only a few BMG compositions that can widely used for TPF. These are either based on precious metals or on alloys that contain beryllium. A non-toxic and inexpensive BMG forming alloy with high TPF processibility, would certainly have tremendous ramifications for the wide spread commercial use of BMGs.”