Heat-resistant Alloys

Heat-resistant Alloys

 

alloys that have high creep resistance and strength at high temperatures. They are used as the construction material for parts of internal-combustion engines, steam and gas turbines, jet engines, and atomic-power installations. The great heat resistance of alloys is determined by two basic physical factors: the strength of interatomic bonds in the alloy and the alloy’s structure.

The structure necessary for high strength is usually produced by heat treatment that leads to heterogenization of the microstructure—most often precipitation hardening. In this case, the strengthening is caused mainly by the appearance within the alloy of evenly distributed very small particles of chemical compounds (intermetallides, carbides, and other compounds) and by the microscopic distortions of the crystal lattice of the alloy base generated by the presence of the particles. The corresponding structure of heat-resistant alloys retards the formation and movement of dislocations and also increases the number of bonds between atoms, which simultaneously participate in the resistance to deformation. On the other hand, a large number of interatomic bonds makes possible the retention of the required structure for long periods at high temperature.

According to the conditions of use, heat-resistant alloys may be divided into three groups: alloys subjected to significant but short-term mechanical stress (seconds or hours) at high temperatures, alloys subjected to loads at high temperatures for dozens and hundreds of hours, and alloys designed to perform under conditions of high loads and high temperatures for thousands of hours. The structural requirements for the alloys vary substantially in accordance with these requirements. For example, any factor causing instability of the alloy structure under operating conditions leads to acceleration of processes of buckling and failure. Therefore, alloys designed for prolonged service undergo stabilizing treatment, which renders them more resistant to prolonged action of loading, although it may lead to a certain decrease in resistance to short-term loads.

Heat-resistant alloys are classified according to their base, which may be nickel, iron, titanium, beryllium, and other metals. Classification according to the base gives a representation of the range of working temperatures, which is 0.4–0.8 of the melting point of the base, depending on the load applied and the duration of its application.

Composite materials (alloys strengthened by disperse particles of refractory oxides or by high-strength fibers) are a variety of heat-resistant alloys. Such materials are characterized by extremely high stability of their properties, which are not highly dependent on the residence time at high temperatures. Depending on their purpose, heat-resistant alloys are made with increased resistance to fatigue and erosion and low notch sensitivity, as well as with high thermal stability and short-term high-load resistance. For example, heat-resistant alloys for use in space technology must have low evaporability.

REFERENCES

Garofalo, F. Zakony polzuchesti i dliteVnoi prochnosti metallov i splavov. Moscow, 1968. (Translated from English.)
Kurdiumov, G. V. “Priroda uprochnennogo sostoianiia metallov.” Metallov’edenie i termicheskaia obrabotka metallov, 1960, no. 10.
Rozenberg, V. M. Polzuchest’ metallov. Moscow, 1967. Khimushin, F. F. Zharoprochnye stall i splavy, 2nd ed. Moscow, 1969.

V. M. ROZENBERG

References in periodicals archive ?
Heat-resistant alloys are used in environments subjected to oxidizing or corrosive atmospheres at temperatures above 650 [degrees]C.
It is suitable for machining materials up to a hardness of 54 HRC, including stainless steels, titanium and heat-resistant alloys based on nickel and chrome-cobalt.
Strong, heat-resistant alloys enable turbine engines to run cleanly and efficiently, explains Michael Mills, professor of materials science and engineering and leader of the project.
The Computationally Optimized Homogenization Heat Treatment Process is for alloys exposed to extreme environments, including heat-resistant alloys or those that require corrosion/oxidation resistance.
By manufacturing technology, titanium alloys are classified into deformable alloys, casting alloys, powder alloys; by physicochemical and mechanical properties--on high- and standard-hardness titanium alloys, high-ductile alloys, heat-resistant alloys, and corrosion resistant alloys.
The CA6535 insert is ideal for Ni-base heat-resistant alloys and 'martensitic' stainless steel.
Among specific topics are calculating the effective ground depth of cut by means of a grinding process model, comparing picosecond and femtosecond laser ablation for the surface engraving of metals and semiconductors, pulsed processes when cutting heat-resistant alloys, reactive atom plasma for the rapid figure correction of optical surfaces, and the thrust force of printed circuit board drilling.
Kubota Saudi Arabia Company will function to melt and cast heat-resistant alloys, crack pipelines, and steam in ethylene cracking units that are used in the petrochemical factories.
Recently, the repair brazing of nickel heat-resistant alloys (HRA) is used instead of the process of argon arc welding in restoration of components of a hot part of aircraft and industrial (power) gas-turbine plants.
Accelerated oxidation of heat-resistant alloys by molten salt is well known as the most dangerous damage, and often called as catastrophic oxidation.
For instance, while these strong and heat-resistant alloys can increase engine life, allowing smaller engines to do the work of larger ones, improving fuel efficiency, and decreasing operating costs, they also take their toll on cutting tools.