If a metallic material is cooled through its melting temperature at an extremelyrapid rate, it will form a noncrystalline solid (i.e., a metallic glass)

Metallic Glasses: Metallic glasses are the newly developed engineering materials. Metallic glasses share the properties of both metals and alloys. Most metals and alloys are crystaline,i.e., their atoms arranged in some regular pattern that extends over a long distance. In contrast,glass is an amorphous,brittle and transparent solid. Thus,metallic glasses are metal alloys that are amorphous. 3.The major advantages of such glasses are that they are generally homogeneous in composition,and offer strong and superior corrosion resistance. To have this perculiar property,metallic glasses are to be made by cooling a molten metal rapidly at a rate . Thus,the liquid reaching the glass transition temperature Tg solidifies as metallic glass.Again, upon heating, metallic glasses show a reversible glass-liquid transition at Tg. that is, they do not have a long range atomic order. 4.Various rapid cooling techniques such as spraying,spinning and laser deposition are used for the production of metallic glasses. The melt spinning process technique involved in the preparation of metallic glass is illustrated in figure. In this technique,there is a spinning disc made of copper. In order to prepare a metallic glass of a particular type, a suitable combination of metal- metal or metal-metalloid alloy in bits stoichiometric ratio is taken in a refractory tube having a fine nozzle at its bottom.The nozzle side of the tube is placed just over the spinning disc. PREPARATION 5.An induction heater attached to the refractory tube melts the alloy. This melt is kept above its melting point till it gets transformed into a homogeneous mixture. An inert gas such as helium is made to flow through the tube containing the homogeneous mixture. As a result the melt gets ejected through the nozzle. The ejected melt is cooled at a faster rate with the help of the spinnig cooled copper disc. The ejection rate can be increased by increasing the pressure of the inert gas. Thus,a glassy alloy ribbon satrts getting formed over the spinning disc. The thickness of the glassy ribbon may be varied by increasing or decreasing thr speed of the spinnig disc. 6.1. The strength of metallic glasses is very high but they are lighter in weight. 2. They are ductile,malleable,brittle and opaque.The hardness is very high. 3. The toughness is very high,i.e.,the fracture resistant is very high. 4. They have high elasticity,i.e.,the yield strength is high. 5. They have high corrosion resistance. 6. They do not contain any crystalline defects like point defects,dislocation,stacking faults,etc. 7. They are soft magnetic materials.As a result,easy magnetisation and demagnetisation are possible. 8. They have high electrical resistivity which leads to a low eddy current loss. PROPERTIES OF METALLIC GLASSES:- 7.1. Metallic glasses are used as transformer core material in high- power transformers.Usage of metallic glasses in transformers is found to improve the efficiency of power distribution in transformers.These transformers are used to convert high-voltage current into low-voltage current to be used for domestic appliances(120 V and 240V). 2. Because of their high electrical resistivity and nearly zero temperature coefficient of resistance,these materials are used in making cryothermometers,magnetoresistance sensors and computer memories. 3. As the magnetic properties of the metallic glasses are not affected by irradiation they are used in making containers for nuclear waste disposal. 4. These materials are used in the preparation of magnates for fusion reactors and magnets for levitated trains,etc. APPLICATONS:- 8.1. Metallic glasses can also be used for making watch cases to replace Ni and other metals which can cause allergic reactions. 2. The excellent corrosion resistance property makes these materials ideal for cutting and in making surgical instruments. In addition,they can be used as a prosthetic material for implantation in the human body. 3. In future, the usage of metallic glasses in the electronic field can yield stronger,lighter and more easily moulded castings for personal electronic products. 4. Metallic glasses are used in tap reorders as heads,in the manufacture of sprongs and standard resistances

INTRODUCTION With the advent of material science and so many new engineering material are discovered having major application in industries. This are classified as metals and alloys,cermics,glasses,glass ceramics,composites and semiconductor. Our presentation is on one of such material which is METALLIC GLASS. 3.METALLIC GLASSES It shares the property of both metals and alloys. Metallic glasses are metal alloy that are amorphous.That is they dont have long range atomic order. The major advantages of such glasses are that they are generelly homogeneous in composition,offer strong and superior corrosion resistance. 4.TYPES OF METALLIC GLASSES Metallic glasses are of two types based on their base material used in preparation.1. Metal-Metal glasses. Eg. Ni-Nb,Mg-Zn and Cu-Zr.2. Metal-metalloid glasses:tra like Fe,Co,Ni and metalloids like B,Si,C and P are used 5.PREPARATION To have peculiar property, metallic glasses are to be made by cooling a molten metal rapidly at rate of 2*1060 Cs-1. During the proccess of solidification,atoms do not have enough time or enegy to rearrange for crystal nucleation.Thus,li reaching the glass tranition temperature Tg solidifies as metallic glass.Again,upon heating metallic glasses shows a reversible glass-liquid transition at Tg 6.TECNIQUES OF PREPARATION Various rapid cooling tecniques such as spraying,spinning and laser deposition are used for the production of metallic glasses. 7.Melt spining technique In this tecnique,there is a spinning disc made of copper . fig - 8.PROPERTIES High strenth but lighter in weight. They are ductile ,malleable,brittle and opaque.Hardness is very high. The toughness is very high i.e. the fracture resistance is very high. High elasticity. High Corrosion resistance. They are soft magnetic materials.As a result,easy to magnetisation and demagnetisation are possible. Narrow hytresis loop thus low hytresis energy losses. They have high electrical resistivity which leads to a low eddy current loss. 9.APPLICATION Metallic glasses are used as transformer core material in high powertransformers. Due to its high electrical resistivity and nearly zero temperature coeficient of resistance,these materils are uset in making cryothermometers,magnetoresistance sensor and computer memory. As the magnetic property of metalic glass are not affected by irradiation they are used in making container for nuclear waste disposal. These materials are used in preparation of magnets for fusion reactors and magnets for leviated trains etc. Metallic glasses can also be used for making watch cases to replace Ni and other metals which can cause allergic reactions. 10. Used in cutting and in surgical instrument. Infuture ,it will be used in electronic field can yield stronger,lighter,and more esaily moulded castings for personal electronics products. They are used in tap recoders as heads ,in the manufacture of springs and standard resistances.

Metallic glasses,or amorphous metals, are novel engineering alloys in which the structure is not crystalline (as it is in most metals), but rather is disordered, with the atoms occupying more-or-less random positions in the structure. In this sense metallic glasses are similar to the more familiar oxide glasses such as thesoda-lime glassesused for windows and bottles.From a practical point of view the amorphous structure of metallic glasses gives them two important properties. First, like other kinds of glasses they experience aglass transitioninto a supercooled liquid state upon heating. In this state the viscosity of the glass can be controlled over a wide range, creating the possibility for great flexibility in shaping the glass. For example, the company Liquidmetal Technologies produced the golfing putter shown here:

Second, the amorphous atomic structure means that metallic glasses do not have the crystalline defects called dislocations that govern many of the mechanical properties of more common alloys. The most obvious consequence of this is that metallic glasses can be much stronger (3-4 times or more) than their crystalline counterparts. Another is that metallic glasses are somewhat less stiff than crystalline alloys. The combination of high strength and low stiffness gives metallic glass very high resilience, which is the ability to store elastic strain energy and release it. This is dramatically illustrated in the following video.In the video, identical ball bearings are dropped onto a metallic glass (left) and a piece of stainless steel (right). The high strength and low stiffness of the glass allows the ball bearing to bounce for a long time, while in the stainless steel the low strength causes plastic deformation which quickly damps out the kinetic energy of the ball bearing.Another consequence of their amorphous structure is that metallic glasses, unlike most crystalline alloys, are weakened by deformation. This strain softening causes a concentration of deformation into very narrow shear bands like those shown here, from an earlier transmission electron microscopy study by our group:

From a scientific point of view, metallic glasses are fascinating because many of their important properties and behavior are only now beginning to be understood. Part of the challenge in understanding them comes about because it is much more difficult to characterize the structure (and, critically, the defects in the structure) of an amorphous material than it is of a crystalline material.Research in our group has covered a wide range of topics in metallic glasses, ranging from alloy design (including the development of novel metallic-glass-matrix composite materials) and studies of the atomic-scale structure to very practical studies of mechanical behavior, including both deformation and fracture. A list of a few papers from our group on these topics appears at the end of this article.In our most recent work, we are trying to understand the basic mechanisms by which metallic glasses fracture, which is of obvious importance for engineering applications. Metallic glasses are unlike crystalline alloys in that even though they have little or no ductility they can still be relatively tough (resistant to fracture).To explore this, we have recently conducted a series of experiments in which we perform fracture studies of metallic glass specimens at asynchrotron, which produces extremely intense beams of x-rays that we use to probe how the structure of the glass evolves as we increase the stress. The basic idea is shown here:

The metallic glass sample has a notch with a crack at its tip. Loading the sample at the three points shown causes bending which increases the stress at the crack tip. We using the x-ray beam to produce diffraction rings, from the shape of which we can deduce the strain (or stress) on the sample at any given point, and by moving the specimen we can map out these strains as a function of position around the crack tip. Analysis of these data suggests that at room temperature the glass can develop a substantial region of plastic deformation around the crack tip, but that this does not happen at cryogenic temperatures. The reason for the difference is under investigation.Another area of active investigation is the behavior and characteristics of the shear bands (regions of extensive plastic deformation) mentioned above. In collaboration with Wendy Wright (Bucknell University) and Karin Dahmen (University of Illinois) we are conductive detailed tests of the response of the material during shear banding events.This research is funded by the National Science Foundation (NSF). Earlier work on metallic glasses in our group was supported by the Department of Energy (DOE), the Army Research Office (ARO), and the Army Research Laboratory (ARL).