Alloy 80A (nimonic) is a nickel-chromium alloy with additions of titanium and aluminium, which enable it to be strengthened by precipitation hardening. This grade is supplied in the solution treated condition for ease of machinability, but an aging treatment will give the material very high mechanical properties, an outstanding resistance to creep at service temperatures up to 815ºC (1500ºF) and a high resistance to fatigue under very arduous conditions.
Alloy 80A offers excellent corrosion resistance in oxidising atmospheres including under cyclical conditions of heating and cooling. This corrosion resistance can be attributed to an adherent chromium oxide film (CrO3) that forms on the alloy surface, which protects it from progressive corrosion and also gives a high scaling resistance at elevated temperatures.
Alloy 80A offers a good machinability, is readily formable and weldable using common welding methods.
Chemical Composition
The chemical composition of nimonic 80A alloy is outlined in the following table.
|
Element |
Content (%) |
|
Chromium, Cr |
18-21 |
|
Iron, Fe |
3 |
|
Titanium, Ti |
1.8-2.7 |
|
Aluminum, Al |
1-1.8 |
|
Silicon, Si |
1 |
|
Manganese, Mn |
1 |
|
Copper, Cu |
0.2 |
|
Cobalt, Co |
0.2 |
|
Carbon, C |
0.1 |
|
Phosphorus, P |
0.045 |
|
Boron, B |
0.008 |
|
Nickel, Ni |
Balance |
Physical Properties
The following table shows the physical properties of nimonic 80A alloy.
|
Properties |
Metric |
Imperial |
|
Density |
8.19 g/cm3 |
0.296 lb/in3 |
|
Melting point |
1320-1365°C |
2410-2489°F |
Mechanical Properties
The mechanical properties of nimonic 80A alloy are displayed in the following table.
|
Properties |
Metric |
Imperial |
|
Tensile strength (Precipitation hardened) |
1250 MPa |
181000 psi |
|
Yield strength (Precipitation hardened) |
780 MPa |
113000 psi |
|
Elongation at break (Precipitation hardened) |
30% |
30% |
Thermal Properties
The thermal properties of nimonic 80A alloy are given in the following table.
|
Properties |
Metric |
Imperial |
|
Thermal expansion co-efficient (@20-100°C/68-212°F) |
12.7 µm/m°C |
7.06 µin/in°F |
|
Thermal conductivity |
11.2 W/mK |
77.7 BTU.in/hrft².°F |
Fabrication and Heat Treatment
Machinability
Nimonic 80A alloy can be machined using conventional machining techniques used for iron-based alloys.
Forming
The alloy has good ductility, and can be readily formed using all conventional methods.
Welding
Nimonic 80A alloy can be welded using conventional welding techniques such as gas-tungsten arc welding, shielded metal-arc welding and submerged-arc welding.
Heat Treatment
Nimonic 80A alloy can be heat treated at 1079°C (1975°F) for 8h and air cooled.
Forging
The alloy can be forged at temperatures ranging between 982 to 1177°C (1800 to 2150°F).
Cold Working
Cold working of this alloy can be done using standard tooling.
Annealing
The alloy can be annealed at 1079°C (1975°F) for 8 h and air cooled.
Hardening
The alloy can be hardened by cold working.
Other Designations
Other designations that are equivalent to nimonic 80A alloy include the following:
ASTM B637
DIN 2.4631
DIN 2.4952
Applications
The following are the list of applications of nimonic 80A alloy:
Gas turbine components (blades, rings and discs)
Bolts
Nuclear boiler tube supports
Die casting inserts and cores
Automobile exhaust valves.
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