Putting advanced metallic materials through their paces
In their solid state metals consist of a highly ordered crystalline atomic state. However, if metal alloys are cooled extremely quickly through the process of ‘quenching’, metallic glass is produced which has a disordered atomic structure. These materials can be specially moulded and efficiently cast, with less shrinkage for example, for customised applications. However, one limitation with metallic glass is that to avoid crystallisation, the quench speed needed limits the sample sizes achievable. The EU-funded VITRIMETTECH project trained a group of young European researchers in cutting edge methods for working with metallic glasses, especially in bulk, for functional, bio-mechanical, chemical and structural micro-part applications. The project succeeded in synthesising materials at the two quenching extremes: high pressure die casting for centimeter sized objects of complex shape made of a magnetic alloy, and thin films and glassy nano-grains joined by a glassy ‘glue’ a few hundred nanometers thick. Samples ranging from nanometers to centimeters Metallic glasses are used in applications according to their specific composition. For example, those which are iron and cobalt based are used in electromagnetic devices, while those titanium-based are suited as coatings for body implants. Metallic glasses are known to be inherently brittle which means that they can fracture due to intense stress and temperature, which cause so-called shear bands. VITRIMETTECH studied the origin and dynamics of these and found that their sliding velocity could be decreased and that the glass could be rejuvenated, by mechanical treatments affecting the glass microstructure such as high-pressure torsion or shot peening (shaping metal by bombarding it with metal shot). The principal aim of the project was to better understand the mechanical properties of metallic glass materials, to improve the availability of materials in fields where they are already on the production line (e. g. magnetic devices). It also set out to open up new fields in chemistry (e. g. in catalysis and spectroscopy) and electrical and electronic engineering (e. g. motor components). The project’s industrial partner – a manufacturer of die casting apparatuses – now has the capability to develop machines that can make magnetic metallic glasses in complex shapes. The researchers have also succeeded in producing a laminated transformer core for a patented induction motor. They have also improved the alloy formulation for amorphous and nanocrystalline soft magnets for electromagnetic machinery, which exhibit improved magnetic characteristics with respect to base materials. Metallic glasses have additionally been used to develop nanoporous gold and silver for use in methanol electro-oxidation and alkaline fuel cells, respectively. As project coordinator Prof. Livio Battezzati summarises, “We performed cutting-edge research on metallic glasses in all possible sizes from bulk to thin film, while training a group of young researchers to take our results to industrial companies and so expand their innovation potential.” Of increasing value to the European economy Research into advanced metallic materials will increase in strategic and technical value for the European manufacturing industry in the coming decades. Improvements might result in the use of less metals used in smarter ways, coupled with better recycling options. As Prof Battezzati says, “While metallic glasses will not change the life of millions of people directly, they will impact on the industrial applicability of materials to make improved products and new devices. Also, the project results will keep European research in this area at the forefront globally.” The research team is now working to build chemical sensors and electromagnetic devices, with the materials developed during the project. There are also a number of research offshoots which project partners are pursuing such as: further study into the ability of metallic glasses to withstand tensile stress (ductilisation), better understanding the dynamics of atoms in their glassy state and the mechanism of localised corrosion, while also making improvements to magnetic properties.
Keywords
VITRIMETTECH, metals, metallic glass, alloy, advanced materials, electromagnetic, shear bands, catalysis, spectroscopy, motors, corrosion
