Metal alloys are liquid and solid systems. They are formed by the fusion of two elements or more. Various metals are also combined. Initially, this concept applied only to materials with metallic properties. However, in connection with the intensive development of technology and physics, the definition has expanded significantly and spread.
Metals and metal alloys are used everywhere in the manufacture of structures for equipment, machinery, tools and other things. Despite the rather high prevalence of artificially created products, products from the above materials often form the basis of the design and, according to experts, will retain their positions in the foreseeable future.
Alkaline earth and alkali metals (K, Na, Ca, Li) in the free state are used in atomic reactors in the form of liquid metal coolants. Sodium is used as a catalyst in the manufacture of rubber, lithium - in the alloying of strong and light aluminum compounds. They are used in aircraft construction.
Metals (the main components of alloys) are found in nature in salts, oxides and ores. As a rule, in a pure form in nature are elements chemically stable (Au, Pt, Cu, Ag). Among the open elements in the periodic table, seventy-six belong to metals, Si, Se, Ge, Te, As - to intermediate elements between non-metals and metals, they are sometimes called semimetals.
Metallic materials are classified into two large groups. The first includes iron and its alloys (cast iron, steel), the second - non-ferrous metals and non - ferrous alloys. The latter, in turn, are divided into:
- light (with a density of up to 5 grams / cm3);
- heavy (density more than 10 grams / cm3);
- fusible (with a melting point from 232 to 410 degrees);
- refractory (with a melting point greater than that of iron);
- noble (possessing high anticorrosion resistance).
Metals have a variety of properties. So, for example, mercury freezes under the influence of temperature minus 38.8 degrees, tungsten is able to withstand operating temperatures up to 2000 degrees, sodium, lithium, potassium are lighter than water, and osmium and iridium are forty-two times heavier than lithium. Almost all metal alloys have characteristics that are determined by both the structure and composition of the compound, depending on the conditions of cooling and crystallization, mechanical and thermal processing. Cooling or heating will alter the structure of metallic compounds. This, in turn, affects the physical, mechanical and chemical properties, the behavior of the material during processing and operation.
Specialists distinguish the following general properties of metals and alloys:
- High thermal conductivity.
- Increased ductility.
- High conductivity.
- Positive temperature indicator of electrical resistance. This coefficient denotes an increase in resistance with increasing temperature, and at temperatures close to absolute zero - superconductivity of many metallic materials.
- High reflectivity. Metallic materials are not transparent and have a characteristic metallic luster.
- Thermoelectronic emission - the ability to emit electrons when heated.
- In the solid state, the crystalline structure.
To determine and verify the properties that metal alloys possess, specialists use various control methods, including destructive ones. Thus, metallic materials are tested for ductility, strength, heat resistance, as well as resistance to corrosion. Along with this, non-destructive control methods are also used. These include measurements of magnetic, optical, electrical properties, determination of the hardness index.