Overview

Nimonic 81 is a nickel-chromium austenitic superalloy that is hardened primarily by the controlled addition of titanium and aluminum. This alloy is designed to provide enhanced high temperature corrosion resistance and good high temperature strength.

Nimonic 81 shows good application value in high temperature environments, such as gas turbines, piston engine exhaust valves and furnace equipment, it is resistant to sediment corrosion caused by the combustion of impounded fuels, especially alkali metal sulfates and chlorides.

Its characteristics include excellent resistance to chloride pitting and crevice corrosion cracking, resistance to chloride ion stress corrosion, and high strength at high temperatures. The alloy resists seawater corrosion in both flowing and stationary conditions.

The Nimonic 81's operating practices are similar to those of the Nimonic 80A when it comes to melting, hot working, cold working and machining. In practice, the processing temperature of this alloy is roughly between 950-1160°C.

Limiting Chemical Composition, %

Nickel........................................................................................................................................................................................Balance.

Carbon .................................................................................................................................................................................. 0.05 max.

Silicon.....................................................................................................................................................................................0.50 max.

Copper....................................................................................................................................................................................0.20 max.

Iron..........................................................................................................................................................................................1.00 max.

Manganese.............................................................................................................................................................................0.50 max.

Chromium..............................................................................................................................................................................30.00max.

Titanium..................................................................................................................................................................................1.80 max.

Aluminum................................................................................................................................................................................0.90 max.

Cobalt......................................................................................................................................................................................2.00 max.

Molybdenum...........................................................................................................................................................................0.30 max.

Boron.....................................................................................................................................................................................0.003 max.

Ziconlum.................................................................................................................................................................................0.06 max.

Sulfur.....................................................................................................................................................................................0.015 max.

Physical Constants

Below are some physical constants and thermal properties of

Mechanical properties

Corrosion Resistance

Nimonic 81 is a nickel-chromium austenitic superalloy with corrosion resistance mainly due to its high chromium content. This alloy has excellent thermal corrosion resistance, especially in corrosive media such as alkali metal sulfate and chloride.

The high temperature strength characteristics of the Nimonic 81 are similar to those of the Nimonic 80A and are suitable for aerospace, gas turbines, piston engine exhaust valves and furnace equipment. In these applications, Nimonic 81 is resistant to the corrosion of sediments produced by the combustion of impurious fuels, especially corrosive media such as alkali metal sulfates and chlorides.

In addition to corrosion resistance, Nimonic 81 has good creep resistance and tensile strength at high temperatures. It can keep its strength and plasticity unchanged at high temperatures, and is widely used in aviation, aerospace engines and nuclear industry.

Heat Treatment

The heat treatment of NIMONIC Alloy 81 consists of two main processes: solid solution treatment and precipitation hardening.

Solution treatment is to heat the alloy to high temperature so that the alloying elements are fully dissolved in the matrix to form a uniform solid solution. This process is usually carried out at 1098°C(2010°F) and needs to be held for about eight hours before being air-cooled. This step helps to eliminate segregation and inhomogeneity inside the alloy, improving the plasticity and toughness of the alloy.

Precipitation hardening is an important link in the heat treatment process, through a long-term aging treatment at a certain temperature, the solute atoms are gradually precipitated from the matrix, and then the hardness and strength of the alloy are improved. This process takes place at 704°C(1300°F) and needs to be repeated for about 16 hours, followed by air cooling.

Through the above heat treatment steps, the mechanical properties and corrosion resistance of NIMONIC Alloy 81 can be significantly improved. It should be noted that the specific heat treatment parameters (such as heating temperature, holding time and cooling rate) need to be determined according to factors such as the composition, shape and size of the alloy. In actual operation, the heat treatment parameters should be strictly controlled to ensure the best comprehensive properties of the alloy.

Forms



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