Text IV.

Ex. 20. Переведите на русский язык, пользуясь словарем, если это необходимо.

a) to reinforce - reinforcement - reinforcing filament - reinfor­ced metal - fiber reinforcement;

b) conventional alloys; metallurgical techniques; very fine particles; dispersion strengthening; normal alloys; inadequa­te strength; too high a weight; unlike dispersion hardened materials; lattice imperfection; minute quantities.

Ex. 21. Прочитайте и переведите.

a) etc., i.e.; e.g.; viz.; lb; ft; in.

b) 960°F; 180⁰C; 0.75%; 3,000 psi; 170.000 lb/in²; 16 ft; ,001"

THE DEVELOPMENT OP COMPOSITE MATERIALS

FOR SERVICE AT ELEVATED TEMPERATURES

Modern technology needs materials which can maintain their strength at higher and higher temperatures. Besides convention­al metallurgical techniques, other methods of developing high strength in materials are possible and, if successful, they will enable the engineer to use such materials at temperatures which conventional alloys cannot withstand. Thus, the addition of a stronger, basically¹ insoluble, second phase to convention­al metals or alloys has resulted in the development of the so-called "composite" materials, or composites.

The strengthening phase can he added in two possible forms: (1) as very fine particles, known as dispersion strengthening; (2) as fine filaments, known as fiber reinforcement.

Dispersion strengthening consists of very fine ceramic particles, usually oxides, distributed in a metallic matrix, the particles hardening, or strengthening, the matrix in the same way as in normal alloys. The greatest success in dispersion hard­ening; has been achieved with aluminum and nickel, where additions of fine particles of alumina (aluminum oxide, Al₂O₃,) and thoria (thorium oxide, ThO₂), respectively, have made these metals suitable for applications at temperatures approaching their mel­ting points.

Aluminum, dispersion hardened with alumina, was expected to further increase the strength level to that required, say, for compressor blades in gas turbines. But it turned out that strength obtained in the composites was inadequate under the conditions of high temperature and stress. Conventional alloys conserve safely at about 180⁰C, and above this temperature stainless steels and titanium alloys which are considerably stronger than aluminum alloys, can be used.

Unfortunately, stainless steels posses densities approxi­mately 2.7 times that of aluminum alleys used for compressor blade a end make them considerably heavier. The main problem with blades made from titanium alloys is associated with their extremely high cost of production, compared with similar blades made of aluminum alloys.

What alternative materials are there to steels² with their too high weight, titanium alloys with their high cost, or dis­persion strengthened aluminum with its inadequate strength? The answer may lie in the application of another type of com­posite materials already mentioned, i.e. fiber reinforced alloys.

Fiber reinforcement involves the addition of a strengthen­ing phase in the form of a filament to a softer matrix. Unlike conventional alloys or dispersion hardened materials, strengthening is not due to the locking of dislocations³. It is based upon the principle that a more ductile, matrix is capable of transferring an applied load from one high-strength reinforcing filament to the next and that these filaments carry most of the load. For example, short filaments of tungsten, 0.003-0.007 in diameter in a matrix of copper were found to increase the room temperature strength of the unreinforced metal from 50.000 lb/in² to as much as 170.000 lb/in. To produce the necessary strengthen­ing wires of tungsten were used as reinforcement.

The highest strengths obtainable in bulk materials⁴ are only a small part (1 per cent) of the strength theoretically expected from the cohesion of atoms in a metal. However, very fine fila­ments, the so-called "whiskers", possess exceptional strengths which in some cases approach the theoretical limit of atomic cohesion. The high strength of metallic whiskers is due to the absence of lattice imperfections such as dislocations and vacan­cies which are responsible for the relative weakness of built ma­terials. Unfortunately, whiskers with their very high strengths have, so far⁵, only been made in relatively minute quantities. Recently, methods have been developed for producing some whiskers in experimental quantities.

Research is still going on.

Notes to the Text:

1. basically- зд. в основном.

2. alternative materials ... to steels- другие материалы, кроме сталей

3. locing of dislocations - закрепление дислокаций

4. bulk materials -материалы, наиболее широко распространенные в промышленности

5. so far - до сих пор

Ex. 22. Найдите в тексте эквиваленты следующим словосочетаниям:

Позволить инженеру применять такие материалы; обычные сплавы; метода, принятые в металлургии; в основном нерастворимая вторая фаза; очень маленькие частицы; тонкая нить; дисперсионные уп­рочнение; армирование волокном;: таким же образом; оказалось; недостаточная прочность; к сожалению; нержавеющая сталь; в 2,7 раза больше; по сравнению с; слишком большой вес; в отличие от обычных сплавов; закрепление дислокаций; нести основную нагрузку; до 30.000 фунтов/дюйм²; межатомная связь; объяснить относительную непрочность; относительно ничтожное количество.

Ex. 23. Замените цепочку существительных с предлогом. Примеры:

water quenching - quenching in (by) water

stress distribution - distribution of stress

Fiber reinforcement; dispersion strengthening; strength level; compressor blades; titanium alloys; high-strength reinforcing-fibers; room temperature strength; lattice imperfection; stress relief; carburizing agents.

Ex. 24. Замените подчеркнутые словосочетания соответствующими сокращениями:

1. In composite materials the strengthening phase can be added in two possible forms, namely, as very fine particles and as fine filaments. 2. For some-parts operating under the conditions of high temperature and stress (for example, compressor blades in gas turbines) dispersion hardened aluminum cannot provide the adequate strength. 3. Very fine filaments, fibers, whiskers, and so on can be added to a softer matrix for reinforcement thereby increasing the strength of the resulting composite to about 6 times that of the unreinforced metal. 4. The high strength of metallic whiskers is due to the absence of lattice imperfections, that is the absence of dislocations and vacancies that are responsible for the relative weakness in conventional alloys. 5. To produce the necessary strengthening (up to 170.000 pounds per square inch), wires of tungsten have been added to the softer matrix as reinforcement.

Ex. 25. Вставьте слеза, соответствующие содержанию текста:

1. Composite materials have been developed for application under such conditions of temperature and stress where _ are inade­quate. 2. There are two main types of composite materials: _ and _. 3. A dispersion hardened material is composed of a matrix with a strengthening phase _ distributed in it. 4. Aluminum has been made suitable for applications at temperatures approaching its melting point due to addition of __ of alumina. 5. __, its strength has been found to be inadequate for compres­sor blades in gas turbines. 6. Fiber reinforcement is the pro­cess in which a strengthening phase in the form of a filament

???

a) hardness and strength

b) high electrical and thermal conductivity

c) deoxidizing action

2. Copper is __ hard and strong to be used for castings.

a) very b) not enough c) relatively

3. Deoxidizing elements combine with oxygen and form a slag on the surface which __ .

a) can be easily removed b) must remain there c) possesses a high thermal conductivity

4. As cold working of copper results in an increase in electri­cal resistance and decrease in conductivity, it is annealed after cold working __. ;

a) to improve its conductivity

b) to lower the amount of impurities

c) to make its electrical resistance higher

5. Using copper, one should know fiat after some time __ is formed on the surface of the metal.

a) a slag b) a protective film c) a deoxidizing element.

Ex. 29. Сделайте письменный перевод текста со словарем (время – 60 мин).