Metallic glasses, or amorphous alloys, are obtained by cooling the melt at a rate exceeding the rate of crystallization. In this case, the nucleation and growth of the crystalline phase becomes impossible and the metal has an amorphous structure after solidification. High speeds cooling can be achieved various methods, however, melt quenching on the surface of a rapidly rotating disk is most often used (Fig. 177). This method allows you to obtain tape, wire, granules, and powders.

Obtaining an amorphous structure is in principle possible for all metals. The amorphous state is most easily achieved in the alloys Al, Pb, Sn, Cu, etc. To obtain metallic glasses based on Ni, Co, Fe, Mn, Cr, non-metals or semi-metallic elements C, P, Si, B, As, S are added to them and others (amorphous elements). Amorphous alloys most often correspond to the formula M 80 X 20, where M is one or more transition elements, and X is one or more non-metals or other amorphous elements (Fe 80 P 13 C, Ni 82 P 18, Ni 80 S 20).

Rice. 177. Scheme for producing amorphous alloys using rapid cooling from a melt: a - casting onto a disk; b - casting between two disks; 1 - inductor; 2 - melt; 3 - crucible; 4 - disk; 5 - ribbon of amorphous material

The amorphous state of metals is metastable. When heated, when the mobility of atoms increases, a crystallization process occurs, which gradually brings the metal (alloy) through a series of metastable ones to a stable crystalline state. The mechanical, magnetic, electrical and other structure-sensitive properties of amorphous alloys differ significantly from the properties of crystalline alloys. Characteristic feature amorphous alloys have a high elastic limit and yield strength with an almost complete absence of strain hardening.

High mechanical properties

Amorphous alloys based on cobalt have high mechanical properties.

Amorphous alloys are often brittle under tension, but relatively ductile under bending and compression. Can be cold rolled. 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 explained, on the one hand, by 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. Amorphous nickel-based alloys also have good corrosion resistance. Amorphous alloys of Fe, Co, Ni with additions of 15-25% amorphous elements B, C, Si, P are used as soft magnetic materials.

Amorphous alloy groups

Soft magnetic amorphous alloys are divided into three main groups:

1. amorphous iron-based alloys with high magnetic induction values ​​and low coercive force (32-35 mA/cm);
2. iron-nickel alloys with average values ​​of magnetic induction (0.75-0.8 T) and a lower coercivity value than that of iron alloys (6-7 mA/cm);
3. amorphous cobalt-based alloys with 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 electronics industries (magnetic cores of transformers, cores, amplifiers, choke filters, etc.). Alloys with a high cobalt content are used for the manufacture of magnetic screens and magnetic heads, where it is important to have a material with high wear resistance.

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

aluminum-steel wire (KAS-1A), nickel-tungsten wire (VKN-1).

Composite materials with a non-metallic matrix. German

thallic matrix is ​​polymer, carbon and ceramic materials. Epoxy, phenol-formaldehyde and polyamide matrices are used as polymers. Reinforcers are glass, carbon, boron, organic, inorganic (filamentary crystals of oxides, borides, carbides, nitrides) fibers; metal wires; dispersed particles. Based on the type of reinforcement, polymer composites are divided into glass, carbon, boron and organofiber.

IN layered materials (see rice. 8.3, c) fibers and threads, after impregnation with a binder, are laid in planes, which are collected into plates. By changing the method of laying fibers, isotropic or anisotropic CM is obtained.

Fiberglass is a composite of synthetic resin and fiberglass (reinforcing component). Non-oriented glass fibers have short fibers, and oriented fibers have long fibers. This gives fiberglass high strength.

Carbon fibers (carbon plastics) consist of a matrix - a polymer binder and a strengthener - carbon fiber(carbon fiber). The binder is a synthetic polymer (polymer carbon fiber) or carbon fiber with a carbon matrix - pyrolytic carbon (coke).

Boron fibers consist of a polymer binder and strengthener – boron fibers.

They have high strength (higher than carbon fiber) and hardness, thermal and electrical conductivity, high chemical resistance and fatigue resistance. They are superior to metal in vibration resistance.

Organofibers consist of a polymer binder and reinforcers - synthetic fibers. They have high specific strength and rigidity, are resistant to aggressive environments, and are insensitive to damage.

IN In mining engineering, composite materials are used for the manufacture of friction and anti-friction parts, drilling tools (bits), parts for conveyors, combines, electrodes, and electrical contacts.

8.4. Metal glass

Metal glasses(amorphous alloys, glassy metals, metglasses) are metal alloys in a glassy state, obtained after cooling melts at high speeds (< 106 К/с). Металлические стекла – это «замороженные» расплавы, т.е. метастабильные системы и поэтому они кристаллизуются при нагревании до температуры около 0,5 Tпл . Образуют металлические стекла переходные металлы (Fe, Mn, Cr, Co, Ni), благородные и поливалентные неметаллы (C, B, N, Si, P, Ge), которые являются стеклообразующими.

Metal glasses are single-phase and do not have structural defects (vacancies, dislocations). They have high strength, great ductility,

SECTION III. MATERIALS SCIENCE OF NON-FERROUS METALS AND ALLOYS

Chapter 8. Antifriction, powder and composite alloys

high corrosion resistance. Some of them are ferromagnetic or they weakly absorb sound.

Magnetic soft metal glasses are produced on the basis of Fe, Co, Ni with the addition of 15–20% amorphous elements - B, C, Si, P (for example, Fe81 Si3 5B13 C2 with a high value of magnetic induction). The amorphous alloy Co66 Fe4 (Mo, Si, B)30 has high mechanical properties.

Stable amorphous alloys have high corrosion resistance. For example, metal glasses based on Fe and Ni with 3–5% Cr.

The use of metal glasses is determined by their magnetic and corrosion properties.

Test questions and assignments

1. Give examples of brands of antifriction alloys.

2. Give examples of brands of lead and tin babbits.

3. What structure determines the antifriction properties of babbitts?

4. What is the purpose of babbitt alloying with copper?

5. Give examples of grades of zinc-based alloys.

6. What materials are called metal ceramics?

7. Describe porous metal ceramics and their properties.

8. Name the advantages and disadvantages of metal ceramics.

9. What process is called sintering?

10. Name the types of structural metal ceramics, their properties, and purpose.

11. Give characteristics of instrumental metal ceramics. What is its purpose?

12. What types of special-purpose metal ceramics with special properties exist and how are they obtained?

13. What materials are called composite?

14. What components are composite materials made of?

15. By what criteria are composite materials classified?

16. Describe metal composites with a metal matrix, dispersed ion-strengthened and with fiber reinforcement.

17. Characterize composite materials with a non-metallic matrix.

18. What materials are called metallic glasses? Describe their properties and types.

19. Name the types of protection of metals from corrosion and describe them.

SECTION IV. MATERIALS SCIENCE OF NON-METALLIC

MATERIALS

Chapter 9. Mineral loosened, dispersed stone materials

9.1. Natural stone materials

Inorganic minerals are chemical elements and compounds (oxides, oxygen-free compounds of elements) that do not have metallic properties. These materials have chemical resistance, non-flammability, hardness, resistance to heat, and stable properties. Their disadvantages are high fragility, low resistance to temperature changes, stretching and bending.

Natural stone materials (PCM) – Construction Materials,

obtained from rocks mechanical processing (crushing, melting, splitting, etc.), after which the structure and properties of the rock are almost completely preserved (Table 9.1).

Based on the nature of surface treatment, PCMs are divided into the following types:

natural building stones (stone products) – sawn wall materials and facing stones,architectural and constructionproducts (steps, window sills), road materials (paving stones, side stones), products for hydraulic structures, cladding of bridge supports, technical products (marble boards, calibration slabs, granite shafts for paper-making equipment),decorative and artistic products;

rough stone materials– rubble and boulder stones, crushed stone, gravel, sand.

The reasons for the destruction of PCM are the freezing of water in pores and cracks; frequent changes in temperature and humidity; chemical corrosion under the influence of gases (oxygen, hydrogen, etc.) and substances dissolved in ground and sea water.

Table 9.1

Classification of PCM according to manufacturing method

* Process of shaping natural stone the desired shape and exterior finishing.

To protect stone materials from destruction, the following methods are used:

constructive protection is giving the products a shape that facilitates water drainage and a smooth polished surface to the cladding;

physico-chemical protection is the impregnation of the surface layer with sealing compounds, the application of hydrophobic (water-repellent) compounds and film-forming polymer materials (transparent and colored) to the front surface.

Natural building stones (NSS) . This construction material from rocks after sawing them, preserving the structure and properties. Based on density they are divided into lungs (density less than 1,800 kg/m³) and heavy.

Strength is a consumer property of PSK. Its meaning is used

is indicated in the marking and is assessed by the compressive strength σcom, MPa, of samples in an air-dry state.

Consumer properties also include abrasion and wear. For road surfaces and floors, hard fine- and medium-grained rocks are used.

The water resistance of PSK is assessed by the softening coefficient Krm (for hydraulic structures, Krm is at least 0.8; for external walls - at least 0.6).

Frost resistance is assessed by the number of cycles of alternating freezing and thawing: F10, F15, ..., F500. It depends on the composition, structure and

SECTION IV. MATERIALS SCIENCE OF NON-METALLIC MATERIALS

Chapter 9. Mineral loosened, dispersed and stone materials

humidity PSK. High frost resistance is for dense stones with a uniform-grained structure and low for layered structures.

Fire resistance depends on the composition and structure of the stone. At elevated temperatures, some rocks (gypsum, limestone) can decompose, while others (granite) can crack.

According to their purpose, PSCs are divided into: wall, cladding, profiled, and road.

To impart texture to the surface, the following types of PSC processing are used: impact, abrasive, thermal.

Wall stones are obtained from dense, porous tuffs and limestones. General requirements for wall stones: solidity; density from 900 to 2,200 kg/m3; σco = 5–15 MPa for dense limestones and σco = 5–40 MPa for tuffs; Krm = 0.6–0.7; frost resistance – not lower than F15; decorative appearance. Finely porous natural stones are not covered. Wall stones for masonry walls (type I) and partitions (type II) are produced in grades 4, 7, 10, 15, 20, 25, 35, 50, 75, 100, 125, 150, 200, 300 and 400 (grade numbers correspond to

value σco).

Wall blocks have standardized linear dimensions with permissible deviations< 10 мм. Каждый камень заменяет в кладке от 8 до 12 кирпичей, а их масса – не выше 40 кг. Один из possible options the dimensions of wall stones are 390×190×188, and large wall blocks for mechanized

new installation – 300×800×900.

Sawn and crushed piece stones from limestone, dolomite, and tuff are used for laying bridge abutments and strengthening slopes.

Facing stones– these are rocks with beautiful colors and patterns (decorative) with the necessary frost resistance (at least F15), strength (σcompress at least 5 MPa), and solidity. Large blocks are obtained from blocks of natural stone after sawing and subsequent mechanical processing.

Facing stones can be from igneous, sedimentary and metamorphic rocks. The strength classification is as follows: strong (σcom > 80 MPa); medium strength (σcom = 40–80 MPa); low strength

(σcom< 40 МПа).

In terms of durability, there are 4 classes: very durable (beginning of destruction after 650 years); durable (200–250 years); relatively durable (75–120 years); short-lived (20–75 years). According to their decorative properties, they distinguish between highly decorative, decorative, low-decorative and non-decorative stones.

According to their purpose, facing stones are divided into:

for facing hydraulic structures (granite, igneous rocks with high strength and hardness);

slabs for external cladding of buildings (limestone, dolomites, sandstones, tuffs); The cladding of subway walls is most often made of marble;

base slabs (made of resistant rocks).

SECTION IV. MATERIALS SCIENCE OF NON-METALLIC MATERIALS

Chapter 9. Mineral loosened, dispersed and stone materials

The texture of the front surface of facing slabs can be mirrored (polished), polished (powder polished), ground with an abrasive tool, or sawn.

Road stone materials obtained from igneous and sedimentary rocks that do not weather.

Road stone materials are divided into the following types:

side stones in the form of timber length 70–200 cm of durable igneous rocks (diabase, basalt, granite); they are made straight and curved, high (up to 40 cm) and low (up to 30 cm);

paving stones in the form of bars for paving roads from fine and medium grain

low-lying, strong (σcompressor not lower than 100 MPa) igneous rocks (basalt, granite, diabase, etc.); paving stones can be high BN (height up to 160 mm), medium BN (130 mm), low BN (100 mm);

crushed and cobblestones shaped like a multifaceted prism (chipped) or oval (cobblestone) from diabase, basalt, granite;

paving slabs in the form of rectangular slabs from layered rocks

Rough stone materials . This group includes

rock and boulder stones, crushed stone, gravel and sand.

Rubble stone is large fragments of rocks that are obtained by blasting limestone, dolomite, and sandstone. Its types according to shape: torn, bedded, flakied (width is three or more times greater than thickness). Rubble is used to build hydraulic structures, lay foundations, and produce crushed stone.

Gravel is a loose material in the form of rounded grains 1–10 mm in size, which is obtained through the natural destruction (weathering) of sedimentary rocks. Impurities in gravel are dust, clay, if sand is present (25–40%), then the material is called a sand-gravel mixture. The properties of gravel depend on the rock and are regulated technical requirements standards.

The strength of the gravel grains should ensure that the concrete strength is 20–50% higher than the specified one. According to the degree of frost resistance, gravel is distinguished F15, F25, F50, F100, F150, F200, F300. This characteristic is important if gravel is used to make concrete structures for harsh climatic conditions. Natural gravel is also used to prepare reinforced and unreinforced concrete as coarse aggregate. Gravel is used for concrete grades up to 300; the requirements for it are given in GOST 8268-82.

Crushed natural stone obtained by crushing stones into pieces

5–70 mm in size from frost-resistant rocks with σcom = 120–200 MPa. Crushed stone is obtained from granite, diabase, igneous rocks, and sedimentary rocks (limestone, dolomite). Natural crushed stone is called grus. Crushed stone often has an acute-angled shape, and the best shape is a cube or tetrahedron. Crushed stone is cleaner than gravel.

Formation and propagation of shear bands on the surface of a metallic glass sample (Pd79Ag3.5P6Si9.5Ge2)

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

Similar shear bands form along the edges of 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 as flexible as polymer materials, they are capable of conducting electricity 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 tend to be brittle and have uneven resistance to fatigue, making their reliability questionable. The use of multicomponent amorphous metals (composites) solves this problem, but for monolithic metal glasses it is still relevant.

A new study conducted jointly by scientists from Berkeley Lab and the California Institute of Technology has found a way to improve the fatigue strength of bulk metal glasses. Palladium-based bulk metal glass, when subjected to fatigue loads, performed 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 metal glass—a local area of ​​significant deformation that 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 tips of the cracks and prevents their further propagation.

Palladium is characterized by a high ratio of bulk and shear moduli, which disguises the inherent fragility of glassy materials, since the formation of “multi-level” shear bands that prevent further crack growth turns out to be energetically more favorable than the formation of large cracks leading to rapid destruction of the sample. Together with high

Transmission electron microscope image different levels crystallization of amorphous metal

Engineers from the University of Southern California have developed a new type of metallic glass characterized by increased elasticity. The material combines seemingly incompatible properties - hardness, strength and elasticity. The material, technologically named SAM2X5-630, has the highest impact strength of all known metallic glasses.

Metallic glasses, or amorphous metals, are a class of metallic solids with an amorphous structure. Unlike metals with their crystalline structure, that of amorphous metals is similar to the atomic structure of supercooled melts.


On the left is a ball made of new metal glass, on the right – from ordinary steel.

The material is able to withstand strong impacts, while it does not crumble or break, but returns to its original shape. The potential for its applications is almost limitless - from drills and body armor to implants for strengthening bones and protecting space satellites.

Typically, amorphous metals are produced by heating to 630 °C and then very quickly (on the order of a degree per second) cooling. The material SAM2X5-630 was obtained by heating powder composition iron-based (Fe 49.7 Cr 17.7 Mn 1.9 Mo 7.4 W 1.6 B 15.2 C 3.8 Si 2.4).

The unique properties of the metal come from a successful combination of heating temperature and cooling rate - it is precisely these conditions that the resulting composition experienced that lead to the formation of local foci of a weakly defined crystalline structure. Other heating or cooling conditions result in completely amorphous metals with a random arrangement of atoms.

“It has almost no internal structure, and in this way it is similar to glass, but there are regions of crystallization,” says Veronica Elyason, an assistant professor at the university's Viterbi School of Engineering and lead author of the paper. “We have no idea yet why small amounts of crystallized sites in metallic glasses lead to such large differences in response to impact.”

The dynamic Hugoniot elastic limit (the maximum force that a material can withstand without permanent deformation) was determined for SAM2X5-630 to be around 12 GPa. For stainless steel this figure is 0.2 GPa, for tungsten carbide (used to create hard tools and armor-piercing bullet cores) - 4.5 GPa, for diamonds - up to 60 GPa.

The study of amorphous metals began in 1960 at the California Institute of Technology - a group of scientists obtained the first metallic glass Au 75 Si 25. Since then, many similar materials with interesting properties have been obtained, but so far their area practical application cannot be called widespread due to their high cost.

For example, Ti 40 Cu 36 Pd 14 Zr 10, recently obtained in Japan, is non-carcinogenic, three times stronger than titanium, wears out little, does not form powder during friction, and in terms of its longitudinal elasticity modulus practically coincides with human bones - potentially it can be used as excellent artificial joint replacement.

It is precisely this kind of 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. By adding 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 five elements, we ensure that the material, when cooled, “does not know” which crystal structure to adopt, and chooses an amorphous one,” explains one of the study participants, Robert Ritchie. Experiments have shown that such metallic glass actually combines the inherent hardness of glass with the resistance to crack development characteristic of metals.

It is not difficult to predict that in practice new material, containing extremely expensive palladium, will be used rarely - 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 Marios Demetriou, another participant in the work. “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, the atoms in which occupy 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 flow of glass can be adjusted in many ways, thereby creating a large number possible forms, attached to glass. For example, Liquidmetal Technologies made a short golf club.

Secondly, 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 that metallic glasses are harder 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 elastic deformation energy and release it.

Another consequence of the amorphous structure is that, unlike crystalline alloys, metallic glasses are weakened due to deformation. “Strain decompaction” causes strain to concentrate 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 metal 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 occurs when melts are cooled very quickly, due to which they simply do not have time to crystallize and retain an amorphous structure. First, in this way they learned to produce thin strips of metallic glass, which are easier to make quickly lose temperature. Volumetric metal glasses are much more difficult to produce.

Metal glasses have many advantages. The crystal lattices of ordinary metals and alloys always contain certain structural defects that reduce their mechanical qualities. Metal glasses do not and cannot have such defects, which is why they are particularly hard. Some metal glasses also resist corrosion even better than stainless steel. Therefore, experts believe that these materials have a bright future.

Until now, bulk metal glasses 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 bulk metal 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 they will first find application in the aerospace industry, and then, when their cost can be reduced, in other industries.

Metal glass: how to overcome fragility

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

Similar shear bands form along the edges of 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 plastic as polymer materials; they are capable of conducting 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 tend to be brittle and have uneven resistance to fatigue, making their reliability questionable. The use of multicomponent amorphous metals solves this problem, but for monolithic metal glasses it is still relevant.

As part of a new study. conducted jointly by scientists from Berkeley Lab and the California Institute of Technology, a way has been found to increase the fatigue strength of bulk metal glasses. Palladium-based bulk metal glass, when subjected to fatigue loads, performed 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 forms on the surface of palladium metal glass; a local area of ​​significant deformation 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 tips of the cracks and prevents their further propagation.

Palladium is characterized by a high ratio of bulk and shear moduli. which conceals the inherent fragility of glassy materials, since the formation of multi-level shear bands that prevent further crack growth turns out to be energetically more favorable than the formation of large cracks leading to rapid destruction of the sample. Together with the high endurance limit of the material, these mechanisms significantly increase the fatigue strength of palladium-based bulk metal glass.

A non-crystalline metal or alloy, usually produced by supercooling a molten alloy by vapor or liquid deposition or by external methods.

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

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