Size, grains, shiny, solidify, directions, nuclei, deposition, pattern, particles, homogeneous

1. Crystallization proceeds by … of solid particles of iron from the melt.

2. You can see crystalline … in a fractured surface of low carbon steel.

3. The term "fine grained" means that the … of crystals is rather small.

4. … are imperfect crystals formed in the process of the crystallization of iron.

5. Dull is the antonym of "…".

6. Atoms are grouped according to a definite geometrical ….

7. The melt is considered to be ….

8. The skeleton structure extends in three ….

9. The molten metal will … on cooling.

10. Certain positions in the melt where solidification begins are called the … of solidification.

1. Disagree with the following statements. Prove your reason. Use the expressions: On the contrary… It is clearly seen from the text …

1. Only iron crystallizes in solidifying.

2. The iron particles always form perfect cubes.

3. The process of crystallization starts at one centre.

4. The term "coarse- grained" means that crystals are very small.

5. At ordinary temperatures iron crystallizes as a face- centered cube.

6. The metal less rich in iron solidifies first.

7. There is only one pattern according to which atoms form the crystalline structure.

8. The process of crystallization does not depend on any change of temperature.

1. Translate the text in writing. Use a dictionary. Find answers to the questions:

1. What kind of metal structure testing is used when the structure is visible to the naked eye?

2. What can be investigated with the help of an electron microscope?

3. How deep can X-rays penetrate into steel?

4. Why is it possible to determine the chemical composition of alloys by means of the spectrum analysis?

5. What method of metal structure testing is used to detect the degree of wear of structural elements?

The methods of investigating metal structures determine the serviceability of metals and their alloys in various operating conditions. The basic methods include: macroscopic analysis, microanalysis, X-ray (diffraction) analysis, thermal analysis, and also such methods of flaw detection as magnetic-field testing, ultrasonic testing and radioactive testing.

Macroanalysis is the method of studying the structure which is visible to the naked eye or through a magnifying glass on a macrosection of the test piece ground on one side and etched with an acid. It can disclose cracks, gas pockets and the arrangement of grains in rolled products and forging.

Microanalysis reveals the structure on microsections through an electron microscope. It permits us to investigate most thoroughly the quality of metals and determine the structure components, the shape and size of grains, microflaws on the surface, nonmetallic inclusions and the quality of heat treatment.

X-ray analysis is used to investigate the structures of crystals and to detect flaws at a certain depth below the surface. It is possible to detect internal defects without destructing the metal. The depth of penetration of X-rays into steel is 100mm.

Spectral analysis is used to determine the chemical composition of metals and alloys from the emission spectrum produced by the metal in its hot-red state. Some metals yield the spectrum line of a yellow colour; others produce the line of green colour and so on, thereby indicating the presence of any metal.

Magnetic-field testing applies to ferromagnetic metals such as steel, cobalt, and nickel, for detecting cavities, cracks and nonmetallic inclusions at a depth of 2mm, for example, in welds.

Ultrasonic testing ensures an effective quality control of products of any metal to a large depth. It is used for the quality control of forgings, rolled stock, rails, turbine wheels and other products.

Radioactive tests using radioisotopes can detect the traces of slag in the metal, the degree of wear of structural elements, the rate of carbon diffusion in steel during carburizing, etc.

Unit 9

1. Memorize the following words and expressions:

young's modulus form enhance join measure possess manufacture instrument solution compound antimony fluidity fuse soldering forging rolling stamping shear strengh brittle composition range refractory

модуль упру гости образовывать усиливать соединять измерять обладать производить прибор раствор соединение сурьма текучесть плавкий предохранитель пайка ковка прокатка штамповка срезывающая сила хрупкий состав диапазон огнеупорный

модуль пружності утворювати посилювати поєднувати вимірювати володіти виробляти прилад розчин сполука, сполучення сурма текучість плавкий запобіжник паяння кування прокатка штампування сила що зрізує крихкий склад діапазон вогнетривкий

1. Practise the reading of the following words:

Require, crystalline, prehistoric, constituent, enhance, reactivity, Young's modulus, thermal, conductivity, tensile, shear, substantially, processes, structure, mixture, multiphase, chemical, compound, antimony, type, fluidity, bearing, possess, manufacture, measuring, forging, whereas, binary, ternary, quaternary.

1. Read and translate the text:

Alloys

Pure metals find relatively rare application in industry because they do not always have required properties. Unlike pure metals alloys can be made in any compositions so that they have almost any desired properties. Alloys are crystalline substances obtained by mixing metals with other metals and also metals with nonmetals. For example, carbon steel is an iron-carbon alloy, and brass is a copper-zinc alloy. Bronze, an alloy of copper and tin, was the first alloy discovered during the prehistoric period now known as the Bronze Age. Being harder than pure copper it was originally used to make tools and weapons, but later it was superseded by metals and alloys with better properties.

The metallic elements present in the base (parent) metal are known as alloying elements (alloying agents). All the constituent elements that form an alloy are the alloy components. Alloys may consist of two, three or four components, and are called binary, ternary and quaternary alloys, respectively.

Alloys usually have different properties from those of the component elements. Alloying one metal with other metal(s) or non-metal(s) often enhances its properties. For example, steel is stronger than iron, its primary element. The physical properties of an alloy, such as density, reactivity, Young's modulus and electrical and thermal conductivity, may not differ greatly from those of its elements, but engineering properties, such as tensile strength and shear strength, may be substantially different from those of the constituent materials.

The properties of alloys depend on the character of joining the atoms of alloying elements with the atoms of the base metal and the process of alloy formation. There are several types of alloys that differ in structure, composition and the way they are formed: mechanical mixtures (multiphase alloys); solid solutions (single-phase alloys); and chemical compounds. The differences in the properties of alloys which result from the differences in their structure, determine the specific application of alloys in industry.

A mechanical mixture forming an alloy contains crystals of all the constituents. This type of an alloy can contain alloying elements in any proportions. The examples of mechanical mixtures are lead-antimony, copper-nickel and aluminum-silicon alloys. The alloys in the form of mechanical mixtures have good casting properties, good fluidity and relatively low melting point. Such alloys find wide application in fuses of electrical networks and in soldering.

Solid solutions are widely used in industry. They are much harder and stronger than their constituents and, besides, possess high ductility which is often higher than that of alloying elements. These are copper-zinc alloys (brasses) and copper-nickel alloys. They are used for the manufacture of parts which must withstand impact loads and friction. Such alloys have a higher electrical resistance than pure metals, and this resistance changes very little with temperature. Nickel-chromium alloys also display these properties; therefore they are widely used to manufacture electrical measuring instruments. Due to their high ductility solid solutions work well under pressure, so they are suitable for forging, rolling and stamping.

As chemical compounds alloys are extremely hard, strong and electrically resistant materials. They are suitable for cutting tools, but are impracticable for plastic working as they are highly brittle. The hardness of these alloys is sometimes ten times as much as that of their pure components. For example, copper and tin are soft whereas their alloys have a very high strength. The same is true for iron and carbon which, when alloyed, form very strong materials. Thus, Cementite is a chemical compound of iron and carbon which is the hardest structure of steel. It is magnetic, strong, but very brittle.

At present over ten thousand different alloys find wide application in industry. Thermal and nuclear power stations use highly refractory alloys of enhanced strength. Electronic, semiconductor and laser technologies require alloys of the highest purity, up to 99.999% pure. Alloys showing a rare combination of physical and chemical properties are used in precision machine-building, automatics and in a number of other applications.

1. Find in the text English equivalents for the following words and word-combinations:

Первинний елемент, для виготовлення зброї, відповідно, міцність на розрив, особливе застосування, істотно, низька точка плавлення, пластичність, крім того, витримувати ударні навантаження, надзвичайно, хімічна активність, у той час як, основний метал (сплаву), чистота, підвищена міцність, точне машинобудування.

1. Answer the following questions:

1. What is an alloy?

2. How many components can alloys consist of?

3. What factors do properties of alloys depend on?

4. What types of alloys do you know?

5. What can you say about mechanical mixtures?

6. Where are mechanical mixtures used?

7. What useful properties of solid solutions do you know?

8. Where are solid solutions used?

9. What are the advantages and disadvantages of chemical compounds?