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They are metal and glass. Metallic glass and method for producing metallic glass

metal glass(amorphous alloys, vitreous metals, metglasses)- metal alloys in a glassy state, formed at super rapid cooling metal melt when crystallization is prevented by rapid cooling (cooling rate< 10 6 К/с).

Metallic glasses are metastable systems that crystallize when heated to a temperature of ~ 1/2 t sq. Heating, when the mobility of atoms increases, gradually brings the amorphous alloy through a series of metastable states into a stable crystalline state. Many metallic glasses experience structural relaxation already at a temperature just above room temperature. The imposition of a deforming stress enhances the diffusion mobility and the related structural rearrangement of the alloys.

The composition of metallic glasses is most often expressed by the formula M 80 X 20, where M are transitional (Cr, Mn, Fe, Co, Ni, etc.) or noble metals, and X are polyvalent non-metals (B, C, N, Si, P, Ge, etc.), which are glass-forming elements.

Metallic glasses differ from crystalline alloys by the absence of such structural defects as vacancies, dislocations, grain boundaries, and by unique chemical homogeneity: there is no segregation, the entire alloy is single-phase.

The structural features of metallic glasses determine the absence of the anisotropy of properties characteristic of crystals, high strength, corrosion resistance and magnetic permeability, and low magnetization reversal losses.

The physicochemical properties of metallic glasses differ significantly from those of cast alloys. Characteristic features consumer properties metallic glasses are high strength combined with great ductility and high corrosion resistance. Some metallic glasses are ferromagnets with very low coercivity and high magnetic permeability (eg Fe 80 B 20), while others are characterized by very low sound absorption (rare earth alloys with transition metals). Metallic glasses are widely used due to their magnetic and corrosive properties.

Magnetically soft metallic glasses are made on the basis of Fe, Co, Ni with additions of 15 ... 20% of amorphous elements B, C, Si, P. .6 T) and low coercive force (32...35 mA/cm). Amorphous alloy Co 66 Fe 4 (Mo, Si, B) 30 has a relatively low value of magnetic induction (0.55 T), but high mechanical properties (900 ... 1000 HV).

Only stable amorphous alloys have high corrosion resistance. So, for the manufacture of corrosion-resistant parts, metal glasses based on iron and nickel are used, containing at least 3 ... 5% chromium and some other elements. The critical concentration of chromium, which ensures the stability of an amorphous alloy, is determined by the ratio between the alloying elements of the alloy and the activity of the corrosive environment. The resistance of metal glasses to corrosion is reduced by processes that enhance chemical heterogeneity, namely:

the appearance of fluctuations in the chemical composition; separation of the original amorphous phase into two other amorphous phases or phases with another chemical composition;

· transition of an amorphous phase into a two- or multi-phase mixture of crystals of different chemical composition;

· formation of a crystalline phase of the same chemical composition as the surrounding matrix.

Cooling? 106 K / s). Rapid heat dissipation is achieved if at least one of the dimensions of the sample to be produced is sufficiently small (foil, tape, wire). By flattening a drop of melt between cooled anvils, a foil 15–25 mm wide and 40–70 µm thick is obtained, and by cooling on a rotating drum (disk) or by rolling a jet between two rolls, a tape 3–6 mm wide and 40–100 µm thick is obtained. By squeezing the melt into a cooled one, M. s can be made. in the form of a wire.

Composition MS: = 80% transitional (Cr, Mn, Fe, Co, Ni, Zr, Pr, etc.) or noble metals and approx. 20% polyvalent non-metals (B, C, N, Si, P, Ge, etc.), which play the role of glass-forming elements. Examples are binary alloys (Au81Si19, Pd81Si19 and Fe80B20) and pseudobinary alloys consisting of 3-5 or more components. MS - metastable systems, to-rye crystallize when heated to a temperature equal to approx. 1/2 melting temperature.

M.'s studying with. allows you to explore the nature of metallic., Magnet. and other St. TV. tel. High (approaching the theoretical limit for crystals) in combination with high ductility and high corrosion resistance makes M. s. promising strengthening elements for materials and products. Some M. s. (eg, Fe80B20) - ferromagnets with a very low coercive force and high magnetic permeability, which determines their use as soft magnetic materials. Another important class of amorphous magn. materials - alloys of rare earths with transition metals. The use of electric power is promising. and acoustic sv-in M. s. (high and weakly temperature-dependent electrical resistance, weak sound).

Physical Encyclopedic Dictionary. - M.: Soviet Encyclopedia. . 1983 .

METAL GLASS

(metglasses) - variety amorphous metals, amorphous alloys with metal. type of conductivity, to-rye have no long-range order in space, the arrangement of atoms and are characterized by macroscopic. coefficient shear viscosity Pa. They are made in the form of films, tapes and wires with the help of special. tech. methods (quenching from the melt at typical cooling rates of ~10 V K/s, thermal spraying or in vacuum on a cooled substrate, etc.), which lead to rapid solidification of the alloyed components in a relatively narrow temperature range of about t. . glass transition temperature T g .

M. s. have a unique combination of high mech., magn., electric. and corrosion properties.

M. s. exceptionally hard and have high strength on; e.g. s at for M. s. Fe 80 B 20 reaches 3.6-10 ° N / m 2 (370 kgf / mm 2), which far exceeds the value of s at best steels; for this reason, M. s. used for reinforcement in composites. materials (composites).

By magn. properties of M. with. are divided into two technologically important classes. M. s. class "ferromagnetic transition metal (Fe, Co, Ni, in the amount of 75-85%) - non-metal (B, C, Si, P - 15-25%)" are soft magnetic materials with little coercive force N with due to the absence of magn.-crystal. anisotropy (macroscopic magnetic anisotropy due to non-zero magnetostriction ext. or ext. stresses, which can be reduced during annealing, as well as induced anisotropy in the arrangement of neighboring atoms). magnetic atomic structure main such systems can be represented as a set of parallel oriented localized magnets. moments in the absence of broadcasts. periodicity in their spaces, placement, and thanks to the effects of the local environment of the magnetic. ions can fluctuate in size (see amorphous magnets). M. s. of this class have an almost rectangular loop hysteresis magnetic with a high value of saturation induction B s , which in combination with high beats. electric resistance r and, consequently, low losses at makes M. s. compared to electrical engineering. steels more preferred when used, for example, in transformers.

Comparative characteristics some crystalline. and foreign amorphous magnetically soft alloys (as well as one of the homelands. M. p. 94 ZhSR - A based on iron) are shown in the table.

M. s. class "rare earth element - transitional d- metal", usually prepared in the form of films using cathode sputtering, in some cases (Gd - Co, Gd - Fe) reveal a collinear ferromagnetic structure with properties that are promising for creating devices with memory on cylindrical magnetic domains(CMD), e.g. low saturation magnetization M s and high anisotropy perpendicular to the film plane . In most other cases, a strong local single-ion with a random distribution of easy magnetization axes, which is inherent in rare-earth ions with a nonzero orbital angular momentum, usually leads to M. s. this class to chao-tich. non-collinear type structure spin glass.

Comparative characteristics of some magnetically soft crystalline and amorphous alloys (at 300 K).

* T c is the transition temperature to the paramagnetic state ( Curie point).

** Metglass - registered trademark Allied Chemical Corporation.

From electric properties of M. with. naib, a significant amount of residual electric. resistance (usually 2-4 times greater than that of crystalline analogues) and a low value of the temperature coefficient. resistance (outside the temperature range of the processes of structural relaxation and crystallization).

Row M. s. class "transition metal - non-metal" with the addition of Cr and P reveals exclusion, corrosion resistance in aggressive environments, exceeding several. orders of magnitude resistance of stainless steels. The disorder of the atomic structure of M. s. is also the reason for the high resistance of their properties to radiation.

The amorphous structure of MS, being metastable, has a very long lifetime. For example, estimates of the time interval of operation, determined by the beginning of the crystallization process, give one of the least stable M. s.oc. 550 years at 175 0 C and 25 years at 200 0 C.

The peculiarity of physical properties of M. with. is a consequence of the amorphous nature of their structure (its chemical homogeneity, the absence of grain boundaries and linear defects of the type dislocations). On x-ray, electron and neutron grammes of M. s. there are several diffuse halos, which are described using the function of the radial distribution of atoms (FRRA), where p (r) is the average atomic at a distance G from a random atom chosen as the origin (Fig.). FRRA does not provide complete information about the arrangement of atoms in three-dimensional space, however, in combination with other methods (study of the fine structure of X-ray absorption spectra, positron annihilation, etc.), it makes it possible to select those structural models of M. s.,

The normalized function of the radial distribution of atoms is the average atomic density of a substance) for amorphous iron.

which best fit the experiments. data. The similarity of FRRA for amorphous and liquid states, especially at large and cf. distances, allowed at first to use for monatomic M. s. model of random close packing of hard spheres, in its proposed by J. D. Bernal (J. D. Bernal) for monatomic liquids, and for M. s. type "metal - non-metal" - a modification of this model, according to which small non-metal atoms fill large voids ("holes" of Bernal) in a random dense packing of metal atoms and do not coexist with each other. However, the diffraction data experiments (eg, the splitting of the second FRRA peak, which is absent in liquid metals) speaks of the existence in M. of page. short-range atomic order. thermodynamic calculations. the stability of atomic microclusters and the structural factor for M. s. indicate the preference for them of the short-range order model, in which the main. the element of the structure is an icosahedron - a regular twenty-hedron, obtained by packing 12 slightly distorted tetrahedra and having 12 vertices with 5 converging edges, through which 6 fifth-order symmetry axes can be drawn.

Although the icosahedral cannot be an element of building a crystal, since it is impossible to densely fill the three-dimensional by periodic. translations of the icosahedron without the appearance of inconsistency in the structure, a strong argument in favor of the icosahedron. short-range order in M. s. is also the recent discovery in the Al 86 MnI 4 alloy of a fundamentally new type of atomic structure of solids - quasi-crystalline. structures with icosahedral long range (see Quasicrystal). Like M. s., quasicrystals are obtained by rapid quenching from the melt / yatt. a look of ash-covered compositions in systems

Xf_Fe), but, unlike M. s., they give coherent Bragg reflections on X-ray patterns corresponding to fifth or even tenth order symmetry. Some-ryeM. from. (eg, Pd 60 U 20 Si 20 ) after annealing go into quasi-crystalline. state, un-ruzhiva thereby close genetic. connection of the structural state of M. with. and quasicrystalline. states.

Lit-1) Petrovsky G. A., Amorphous magnets, "UFN", "1981, v. 134, p. 305; 2) Lyuborsky F. V., Prospects for the use of amorphous alloys in magnetic devices, in the book Magnetism of amorphous systems , translated from English, M., II)Sl; 3) Handrich K., Kobe S., Amorphous ferro- and ferrimagnets, translated from German, M., 1982; 4) Kraposhin V. S., Linetsky Ya. L., Physical properties metals and alloys in the amorphous state, in: Itogi Nauki i Tekhniki. Metal science · heat treatment, v. 16, M., 1982; 5) Metal glasses, lane. from English, M., 1984; 6) Amorphous metallic alloys ed by F. Luborsky, L.-, 1983; 7) Amorphous alloys, M., 1984; 8) Preobrazhensky A. A., Bishard E. G., Magnetic Materials i, 3rd ed., M 1986; 9) Ichikawa, T., Electron diffraction study of the local atomic arrangement in amorphous iron and nickel films, "Phys. Stat. Sol. (a)", 1973, v. 19, N, 2, p. 707; 10) Polk D. E The structure of glassy metallic alloys, "Acta Metall.", 1972, v. M, No. 4-485; 11) Sachdev S., Nelson D. R., Order m metallic glasses and icosahedral crystals, "Phys. Rev. B", 1985, v. 32, no. 7-4592" 12) Shechtman D. et al., Metallic phase with long-range orientational order and no translational symmetry, "Phys. Rev. Lett.", 1984, v. 53, M 20, p. 1951; 13) Levine D., Steinhardt P. J., Quasicrystals. 1-2, "Phys. Rev. B", 1986 v. 34, MJ 2, p. 596; 14) Nelson D. R., Quasicrystals translated from English, "In the world of science", 1986, No. 10, p. 19; 15) Po-o h S J., Drehman AJ, Lawless KR, Glassy to icosahedral phase transformation in Pd - U - Si alloys, "Phys. Rev Lett", 1985, v. 55, Mi 21, p. 2324. M. V. Medvedev.

Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Chief Editor A. M. Prokhorov. 1988 .

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metal alloy glass

Introduction

1. Metal glasses

2. Composition, structure, properties

3. Mechanical properties of metallic glasses

4. Scope

Conclusion

Bibliography

Introduction

Strength and plasticity are topical areas of research in fracture mechanics. These areas of solid mechanics are intensively developing to a large extent due to the ever-increasing demands of industry, which is why the role of new materials and technologies is increasing every year. Their development, obtaining and studying properties is an objective necessity for the development of human society.

The discovery of the electroplastic effect on metals led to a deeper understanding of the mechanism of plastic deformation. It became possible to control the mechanical properties of metallic materials.

In experiments with pulsed current, an increase in plasticity and a decrease in the brittleness of the metal were found. Electric current also causes an increase in the rate of stress relaxation in the metal and turns out to be a convenient technological factor for relieving internal stresses. The electroplastic effect linearly depends on the current density, it is most pronounced with a pulsed current, and is absent with an alternating current.

The expediency of expanding the use of the electroplastic effect has become obvious, since its use reduces energy costs, and hence economic ones. In particular, in industry, various materials are widely used in electric fields, as a result of which their mechanical characteristics change.

The physical properties of metallic glasses (high strength combined with plasticity, high hardness, corrosion resistance, abrasion resistance and electrical resistivity, etc.) are determined not only by the chemical composition, but also by the structural state of these materials.

The mass use of amorphous metal alloys operating in electric fields poses the problem of studying their mechanical properties under the action of a pulsed electric current.

1. Metal glasses

Vitreous metals, metglasses, metallics. Alloys in a glassy state formed during ultrafast cooling of a metal melt (cooling rate 106 K/s). Rapid heat dissipation is achieved if at least one of the dimensions of the sample to be produced is sufficiently small (foil, tape, wire). By flattening a drop of melt between cooled anvils, a foil with a width of 15–25 mm and a thickness of 40–70 microns is obtained, and by cooling on a rotating drum (disk) or by rolling a jet between two rolls, a tape 3–6 mm wide and 40–100 mm thick is obtained. µm. By extruding the melt into a cooled liquid, they can be made in the form of a wire.

The study of metallic glasses makes it possible to investigate the nature of metallic, magnetic, and other properties of solids.

High strength (approaching the theoretical limit for crystals) combined with high ductility and high corrosion resistance makes metallic glasses promising reinforcing elements for materials and products.

Some metallic glasses, such as Fe80B20, are ferromagnets with a very low coercive force and high magnetic permeability, which determines their use as soft magnetic materials. Another important class of amorphous magnetic materials is alloys of rare earths with transition metals. It is promising to use the electrical and acoustic properties of metallic glasses (high and weakly dependent on temperature, electricity, resistance, weak sound absorption).

In the 90s, bulk metallic glasses (OMGs) with a size of > 1 mm in each of the 3 spatial dimensions (Fig. 1) were obtained on the basis of widely used metals: magnesium, titanium, copper, iron, etc. in binary, ternary, quaternary and multicomponent alloys.

Rice. 1. Samples of castings of bulk metal glass (optical image)

Statistical analysis of the available information on OMS showed an increase in their glass-forming ability from binary to ternary and quaternary alloys.

2. Composition,structure, properties

The composition of metallic glasses is 80% transitional (Cr, Mn, Fe, Co, Ni, Zr, Pr, etc.) or noble metals and about 20% polyvalent non-metals (B, C, N, Si, P, Ge, etc.) , playing the role of glass-forming elements. Examples are binary alloys Au81Si19, Pd81Si19 and Fe80B20) and pseudobinary alloys consisting of 3-5 or more components. Metallic glasses are metastable systems that crystallize when heated to a temperature equal to ½ of the melting point.

The atomic structure of glasses, which demonstrates the absence of long-range order in the arrangement of atoms (Fig. 2), determines their properties, in particular, mechanical ones. In terms of strength and specific strength, they significantly exceed the corresponding crystalline alloys due to the impossibility of using the mechanisms of accommodative deformation of the dislocation or twin type. The conditional yield strength of bulk metallic glasses reaches ~2 GPa for bulk metallic glasses based on Cu, Ti, and Zr, ~3 GPa for Ni, ~4 GPa for Fe, ~5 GPa for Fe and Co, and 6 GPa for cobalt alloys. The structure of metallic glass also provides elastic deformation up to 2%, which, in combination with a high yield strength, leads to large values of the stored energy of elastic deformation (indicators yy2/E and yy2/cE, where yy, c and E are the yield strength, density and Young's modulus, respectively). It should be noted that recent studies indicate the presence of atomic clusters in bulk metallic glasses.

Rice. 2. Transmission electron microscopy image high resolution and diffraction patterns from a selected sub-microscopic (SAED) and nano-sized (NBD) region. The absence of long-range order in the arrangement of atoms is noticeable. The size of the scattering regions is shown by circles conventionally. (In Russia, the study of the structure is carried out, in particular, by A.S. Aronin and G.E. Abrosimova)

Volumetric metal glasses have not only high strength, hardness, wear resistance and large values elastic deformation before the onset of plastic deformation, but also high corrosion resistance, including spontaneous passivation in some solutions. High hardness, wear resistance, surface quality of bulk metallic glasses, as well as fluidity upon heating determine their use in micromachines as transmission mechanisms (gears), components of high-precision mechanical systems. Bulk metallic glasses based on iron and cobalt with a saturation magnetization of up to 1.5 T have record low values of the coercive force of less than 1 A/m and are actively used as soft magnetic materials. It should be noted that in Russia metal glasses based on iron and cobalt were studied by such scientists as A.M. Glezer, S.D. Kaloshkin and many others. The phenomenon of glass transition observed during the transition from liquid to glass and devitrification upon heating is one of the most important unsolved problems in solid state physics. Namely, are the amorphous and liquid phases the same phase, only observed at different temperatures, or is there a phase transition from the liquid to the amorphous state and vice versa, and if so, what kind of this phase transition? Some progress has been made using computer simulations, but it is not yet completely clear.

Plastic flow in metallic glasses occurs in the form of highly localized shear deformation bands. When the mechanical conditions are such that catastrophic instability of the process can be avoided, there are multiple shear bands during uniaxial compression, bending, rolling, and drawing, as well as during localized indentation.

The deformations in individual bands are exceptionally large. In the study of surface replicas from sharply bent Pd80Si20 tapes using transmission electron microscopy, Masumoto and Maddin observed shear bands ~200 Å wide. Using interference microscopy, steps associated with them up to 2000 λ high were detected on the surface, which indicates shear deformations in the band . Such bands appear long before fracture, therefore, the shear strain of fracture of the material exceeds 200 E. The ability to withstand large strains is associated with the absence of a rigid spatial orientation of the bonds of the structure or with the fact that the amorphous matrix is relatively free from such macroscopic defects as pores, oxide inclusions, individual crystals, etc. The first explains the plasticity of metallic glasses compared to other inorganic glasses such as silicon dioxide having covalent bonds; the second explains the presence of a more localized plasticity of metallic glasses in comparison with the bending plasticity of steel sheets.

Strong localized shear deformation in itself indicates the absence of strain hardening in metallic glasses. Further confirmation of this is provided by compression tests performed by Pampillo and Chen on the amorphous Pd77.5Cu6Si16.5 alloy. Glass of this composition is amorphized, which makes it possible to obtain rods of large diameter (~ 2 mm), which are convenient for compressive testing. The samples were subjected to compression until deformation bands appeared. After that, they were polished to remove the steps formed by the stripes on their surface and subsequently loaded again.

It turned out that the bands that appeared after the first loading reappeared, although there were no stress concentrators associated with slip steps on the surface. This would not have happened in the presence of strain hardening of the strips. The shape of the "stress - strain" curves indicates the absence of strain hardening: the stress required for plastic flow remains approximately constant.

3. Mechanical properties of metallic glasses

Due to the absence of strain hardening, the deformation of glasses in the mode of uniaxial tension is mechanically unstable, and plastic flow develops into fracture. For wires, tension creates catastrophic shear instability. In the case of tapes, in order to exclude tearing, the manifestation of such instability is preceded by the formation of a neck. In this case, the neck is difficult to detect, although the orientation of the shift clearly indicates its existence, and at more high temperatures a more developed neck is formed and is easily observed.

For strips of metallic glasses with a constant cross section in tension, failure by tear propagation is typical, which is characteristic of thin strips of high-strength materials. Destruction usually begins in the grips due to the stress concentrations existing there. The tear propagates similarly to a screw dislocation in a plane oriented at an angle of ~45° with respect to the tension axis and the normal to the ribbon surface. In the plastic zone adjacent to the crack, localized shear deformation occurs, and a shear rupture occurs along the deformed material.

In a radially symmetrical sample, the tearing tendency is eliminated, and failure occurs simultaneously with shear instability. Throughout cross section sample at an angle of 45° to the tension axis, an exceptionally strong shear band develops, along which a shear rupture occurs.

A small smooth region corresponding to the initial shear is usually observed on the fracture surface of glasses. The rest of the surface is marked by a "vein pattern" first observed and described by Leamy. Using stereo scanning electron microscopy, Leamy and co-workers determined that the veins were raised against a flat background. Disk-shaped shear cracks are generated in the material and propagate along the shear band. Where they meet, the material breaks down by forming internal necks, resulting in gently rounded "veins". The formation of disk-shaped shear cracks occurs with the participation of dilatation (expansion or compression) of the sample. This is confirmed by the fact that when an amorphous wire is stretched under conditions of superimposed hydrostatic pressure, a crack occurs preferentially at the outer periphery of the shear zone. In this case, the fracture surface is dominated by a family of closely spaced, approximately parallel veins oriented perpendicular to the shear direction. Short crack segments propagate as helical components of a dislocation loop, leaving behind veins that are analogous to edge dislocation dipoles.

The final destruction of the wire tested for fatigue always occurs simultaneously with the general flow over the remaining part of the section, through which the fatigue crack has not yet propagated. The destruction of the tape with the base occurs in the same way, if the applied tensile stress is approximately 99% of the flow stress. In the case of lower stress levels, failure occurs at an angle of 45°. In the latter case, a triaxial stress state takes place in the central part of the section immediately before the fatigue crack. The catastrophic fracture surface is oriented at an angle of 90° to the tension axis. Macroscopically, such fracture is brittle. In this case, the fatigue crack propagates from the place of its origin over the area, which is a semicircle. This is followed by rapid destruction. The fracture surface, oriented at an angle of 90° to the tension axis, is characterized by a classic V-shaped "chevron" pattern, the lines of which are oriented towards the place of crack formation. In a more detailed examination of the fracture surface, the chevrons have a sawtooth shape with surfaces located obliquely with respect to the tension axis. A detailed study of these surfaces showed that they are covered with a fine mesh of an equiaxed "vein-like" pattern. This indicates that even under macroscopic conditions of plane deformation, local fracture occurs by a shear path.

4. Scope

Interest in metallic glasses was initiated, first of all, by the possibilities of their application in technology, based on the unusual properties of these materials.

The mechanical properties of metallic glasses make it possible to use them as reinforcing threads in composite materials used in construction, aeronautics and sports, as well as for the reinforcement of concrete and similar materials. The strong tapes can be used as windings to reinforce pressure vessels or to build large flywheels used for energy storage. High hardness and lack of grain boundaries allow excellent cutting edges, in particular for razor blades. Some types of springs made of metallic glasses may find application.

The magnetic properties of metallic glasses open up the possibility of their use as materials for the cores of inductive components. electronic circuits, in power transformers, where they can replace conventional grain-oriented Fe-Si alloys, and in motors, as soft magnetic materials for magnetic shielding, as magnetic recording heads, sensors, mechanical filter exciters and delay lines.

Due to their electrical properties, metallic glasses can be used, for example, as resistance thermometers and heaters at low temperatures and precision resistors with zero temperature coefficient of resistance. Superconducting metallic glass ribbons are insensitive to radiation damage and therefore may be preferred for fusion applications.

Good corrosion resistance makes them very valuable for chemistry, surgery, biomedicine. However, for such applications, general case metal glasses should not have a ribbon-like shape, but some other shape.

Other applications of metallic glasses are also possible, for example as brazing foils, emission cathodes, fuses and hydrogen storage.

Conclusion

Initially, metallic glasses were the subject of only scientific interest, as a new, unusual state of a solid, but now they are intensively used in industry.

The appearance of metallic glasses (alloys with a low critical cooling rate, which makes it possible to obtain ingots weighing up to 1 kg or more in the amorphous state) created the prospect of their use as structural materials. Metal glasses also have disadvantages. They have a rather low ductility, and also lose strength with increasing load speed. However, amorphous alloys can still be considered plastic glasses: they can be punched and cut into strips in stamps, into wire, they can be woven and bent. They can be used to make woven meshes that will successfully replace reinforcement in reinforced concrete slabs, ropes, durable fiber composites and a variety of products, which will save a huge amount of metal.

Bibliography

1. Gilman D.D., Leimi H.D. Metal glasses. Moscow: Metallurgy. 1984. 264p.

2. Bobrov O.L., Laptev S.N. , Khonik V.A. Stress relaxation in bulk metallic glass Zr52.5Ti5CU17.9Ni14.6 AII0 // FTT. 2004. T. 46. Issue. 6. S. 457 - 460.

3. Kozhushka A.A., Sinani A.B. Loading rate and brittleness of solids. // FTT. 2005. T. 47. Issue. 5. S. 812 - 815.

4. Alshits V.I., Darinskaya E.V., Koldaeva M.V., Petrzhik E.A. Magnetoplastic effect: basic properties and physical mechanisms // Crystallography. 2003. T. 48. Issue. 2. S. 826-854.

5. Morgunov R.B., Baskakov A.A., Trofimov I.N., Yakunin D.V. The role of thermally activated processes in the formation of magnetically sensitive complexes of point defects in NaCl: Eu single crystals // FTT. 2003. T. 45. Issue. 2. S. 257-258.

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High mechanical properties

Amorphous alloys based on cobalt have high mechanical properties.

Amorphous alloys are often brittle in tension, but relatively ductile in bending and compression. May be subject to cold rolling. A linear relationship has been established between the yield strength and hardness for alloys based on iron and cobalt. The strength of amorphous alloys is close to theoretical. This is due, on the one hand, to the high
value of m, and on the other hand, lower values of the elastic modulus E (by 30-50%) compared to crystalline alloys.

Amorphous alloys based on iron and containing at least 3-5% Cr have high corrosion resistance. Nickel-based amorphous alloys also have good corrosion resistance. Amorphous alloys of Fe, Co, Ni with additions of 15-25% of amorphous elements B, C, Si, P are used as soft magnetic materials.

Groups of amorphous alloys

Soft magnetic amorphous alloys are divided into three main groups:

amorphous iron-based alloys with high values of magnetic induction and low coercive force (32-35 mA/cm);
iron-nickel alloys with average values of magnetic induction (0.75-0.8 T) and lower coercive force than iron alloys (6-7 mA/cm);
amorphous alloys based on cobalt, having a relatively low saturation induction (0.55 T), but high mechanical properties (900-1000 HV), low coercive force and high magnetic permeability. Due to the very high electrical resistivity, amorphous alloys are characterized by low eddy current losses - this is their main advantage.

Soft magnetic amorphous alloys are used in the electrical and electronic industries (magnetic cores of transformers, cores, amplifiers, choke filters, etc.). Alloys with a high cobalt content are used for the manufacture of magnetic shields and magnetic heads, where it is important to have a material with high wear resistance.

The scope of metallic glasses is still limited by the fact that they can be obtained by rapid cooling (quenching) from the liquid state only in the form of thin ribbons (up to 60 μm) up to 200 mm wide or more or wire with a diameter of 0.5–20 μm. However, there are broad prospects for the development of this group of materials.

It is this material, for which the energy of formation of shear bands will be much less than the energy required for their transformation into cracks, that the authors tried to create. After trying many options, they settled on an alloy of palladium, phosphorus, silicon and germanium, which made it possible to obtain glass rods with a diameter of about 1 mm. With the addition of silver, the diameter was increased to 6 mm; the size of the samples, we note, is limited by the fact that the initial melt requires very rapid cooling.

“By mixing the five elements, we ensure that the material, when cooled, “does not know which crystal structure to take, and chooses an amorphous one,” explains Robert Ritchie, one of the participants in the study. Experiments have shown that such metallic glass indeed combines the inherent hardness of glasses with the characteristic crack resistance of metals.

It is not difficult to predict that in practice the new material containing extremely expensive palladium will be rarely used - perhaps for the manufacture of dental or some other medical implants.

“Unfortunately, we have not yet determined why our alloy has such attractive characteristics,” says another participant in the work, Marios Demetriou. “If we succeed, we can try to create a cheaper version of glass based on copper, iron or aluminum.”

Metallic glasses, or amorphous metals, are new technological alloys whose structure is not crystalline, but rather unorganized, with atoms in a somewhat random arrangement. In this sense, metallic glasses are similar to oxide glasses such as soda-lime glasses used for windows and bottles.

From a certain point of view, the amorphous structure of metallic glasses determines two important properties. First, like other types of glass, they undergo a glass transition to a supercooled liquid state when heated. In this state, the flowability of the glass can be controlled in many ways, thereby creating a large number of possible shapes to be given to the glass. For example, Liquidmetal Technologies has made a golf club.

Second, the amorphous atomic structure means that metallic glass does not have crystal lattice defects, so-called dislocations, which affect many of the strength properties of most conventional alloys. The most obvious consequence of this is the greater hardness of metallic glasses than their crystalline counterparts. In addition, metallic glasses are less rigid than crystalline alloys. The combination of high hardness and low rigidity gives metallic glasses high elasticity - the ability to accumulate the energy of elastic deformation and release it.

Another consequence of the amorphous structure is that unlike crystalline alloys, metallic glasses are weakened due to deformation. "Deformation decompression" causes a concentration of deformation in very narrow slip bands, transmission electron microscopy.

Metallic glass or transparent metal?

developed at the California Institute of Technology new method production of extremely promising structural materials - volumetric metallic glasses. They are alloys of several metals that do not have a crystalline structure. In this they are similar to ordinary glass - hence the name. Metallic glass arises during very rapid cooling of melts, due to which they simply do not have time to crystallize and retain an amorphous structure. First, in this way, they learned how to obtain thin ribbons of metallic glasses, which are easier to make quickly lose temperature. Volumetric metal glasses are much more difficult to manufacture.

Metal glasses have many advantages. The crystal lattices of ordinary metals and alloys always contain certain structural defects that reduce their mechanical properties. In metallic glasses, there are no such defects and cannot be; therefore, they are distinguished by special hardness. Some metallic glasses also resist corrosion even better. of stainless steel. Therefore, experts believe that a bright future awaits these materials.

Until now, bulk metallic glasses have had one major drawback - low ductility. They withstand bending and compression well, but break when stretched. Now Douglas Hoffman and his colleagues have invented a technology for manufacturing volumetric metallic glasses based on alloys of titanium, zirconium, niobium, copper and beryllium, which leads to the birth of materials that are not inferior in strength to the best titanium and steel alloys.

The developers believe that at first they will find application in the aerospace industry, and then, when they manage to reduce their cost, in other industries.

Metal glass how to overcome fragility

Under a scanning electron microscope, the stepped structure of the shear band is clearly visible.

Similar shear bands are formed along the edges of the cracks, which leads to the destruction of the crack tip and prevents its further growth.

Due to their amorphous structure, metallic glasses can be as strong as steel and ductile as polymer materials, they are able to conduct electric current and have high corrosion resistance. Such materials could be widely used in the manufacture of medical implants and various electronic devices, if not for one unpleasant property: fragility. Metallic glasses are generally brittle and unevenly resist fatigue loads, which calls into question their reliability. The use of multicomponent amorphous metals solves this problem; however, it is still relevant for monolithic metallic glasses.

As part of a new study. conducted jointly by scientists from the Berkeley Laboratory and the California Institute of Technology, a way was found to increase the fatigue strength of bulk metallic glasses. Bulky palladium-based metal glass, subjected to fatigue loading, performed just as well as the best composite metal glasses. Its fatigue strength is comparable to that of commonly used polycrystalline structural metals and alloys such as steel, aluminum and titanium.

Under load, a shear band is formed on the surface of palladium metallic glass, a local area of significant deformation, which takes on a stepped shape. At the same time, the same shear bands appear along the edges of the cracks separating the steps, which blunts the crack tips and prevents their further propagation.

Palladium is characterized by a high ratio of bulk and shear moduli. which masks the brittleness inherent in glassy materials, since the formation of multilevel shear bands, which prevent further crack growth, is energetically more favorable than the formation of large cracks, which lead to rapid destruction of the sample. Together with the high fatigue strength of the material, these mechanisms significantly increase the fatigue strength of palladium-based bulk metallic glass.

A non-crystalline metal or alloy, usually obtained by supercooling a molten alloy through vapor or liquid phase deposition, or by external impact methods.

Sources: www.nanonewsnet.ru, tran.su, www.razgovorium.ru, www.popmech.ru, enc-dic.com

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