Refractory metals as it sounds the very definition of these alloys are very difficult to melt. Metals that are difficult to resplace are called refractory. The classification of these metals rather peculiar: some producers will be classified as alloys with a melting point of 1650° C and above, others with temperature more than 2000°C.
The classical refractory metal is 5 basic elements of the periodic system:
In addition to the categories include refractory metals, the melting temperature ranging from 1650 to 1800 degrees Celsius. This group includes the alloys based on titanium, chromium, zirconium, rhodium, hafnium, iridium, vanadium and some other elements.
Refractory alloys are sufficiently resistant to melting, because of their atomic structure. In the atoms there are electrons s and d-types. It d-electrons provide the strength of inter-atomic bonding, therefore, to break this "link" the required extremely high temperature.
The use of such materials as refractory metals and alloys, is quite extensive. Metal, made of refractory alloys that are in demand in many sectors of the economy. The application is not necessarily associated with high temperatures.
· machine tools;
· aerospace engineering;
· the nuclear industry;
· for energy and nuclear industry;
· iron and steel industry.
On a variety of refractory alloys, the price can vary greatly depending on the part of the alloying elements, which provide the unique properties of a material.
The refractory material is tungsten, which in its pure form is almost never used. In the tungsten alloy is added as the alloying elements Nickel, iron and copper Supplement, as well as rhenium or thorium.
Rhenium improves the corrosion resistance, the thorium makes the material more reliable and durable, Nickel ensures a high density. In the tungsten alloy main component is not more than 75-80%, the rest additives.
Properties of tungsten are quite unique, because this metal is solid and resistant to melting. That is why the alloys are also called "military": they are used for the production of missiles, shells, bullets, a variety of weapons equipment.
Molybdenum alloys can be subjected to alloying at a much smaller "doses" is only about a few percent. However, the ultimate properties of the alloy thus did not "suffer". The main alloying elements of molybdenum – titanium, zirconium and tungsten.
In the latter case, the alloy obtained is sufficiently inert with considerable resistance. Steel based on molybdenum are used in molds for casting items made of zinc, in the manufacture of tubular steel products in the automotive industry.
Alloys based on niobium and tantalum in electrical engineering are in demand for the production of capacitors. Aerospace, shipbuilding, nuclear power, high-precision electronics, medical industry – all these industries to a greater or lesser extent using niobium and tantalum refractory alloys.
The most rare of refractory metals and very expensive variety is rhenium. Production it time-consuming and very challenging technologically. In the earth's crust and not much of it, so always appears rhenium as an alloying element.
Often it is added to alloys of copper and platinum-rhenium improves the strength of soft metals and can be used in the processing of forging. The main field of use is related to nuclear energy, chemical and electronic industries.