Jul 10 2013
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Fabrication
Machinability
Welding
Hot working
Forging
Cold working
Annealing
Applications
Introduction
NIMONIC alloys are composed of nickel and chromium, with the nickel content more than 50%. These alloys exhibit high-temperature low creep and are high performance alloys. Addition of metals like titanium, aluminium increases the strength of the alloy. The commercially available NIMONIC alloys are NIMONIC 75, NIMONIC 80A, 81, 86 and NIMONIC PE11 and 16.
NIMONIC alloy 81 is a precipitation hardenable nickel-chromium alloy with titanium and aluminium as additives for strengthening. This alloy exhibits excellent corrosion resistance at high temperatures. The chromium content of the alloy is higher than other NIMONIC alloys; hence the alloy is corrosion resistant at high temperatures. Apart from being corrosion resistant, the alloy also shows good creep resistance and tensile strength at elevated temperatures.
This datasheet will look into the chemical composition, properties and applications of NIMONIC alloy 81.
Chemical Composition
The chemical composition of NIMONIC alloy 81 is given in the following table.
|
Element |
Content (%) |
|
Nickel, Ni |
63 |
|
Chromium, Cr |
≤30 |
|
Cobalt, Co |
≤2 |
|
Titanium, Ti |
1.8 |
|
Iron, Fe |
≤1.0 |
|
Aluminum, Al |
0.9 |
|
Others |
Remainder |
Physical Properties
The following table discusses the physical properties of NIMONIC alloy 81.
|
Properties |
Metric |
Imperial |
|
Density |
8.06 gm/cm3 |
0.291 lb/in3 |
Mechanical Properties
The mechanical properties of NIMONIC alloy 81 are tabulated below.
|
Properties |
Metric |
Imperial |
|
Tensile strength(annealed) |
1050 MPa |
152 ksi |
|
Yield strength(annealed) |
600 MPa |
87 ksi |
|
Elongation at Break |
40% |
40% |
Fabrication
Machinability
The conventional machining methods used on iron alloys may be used for this alloy. This alloy work-hardens during machining and exhibits higher strength.
Welding
NIMONIC alloy 81 can be welded using common techniques, using a matching filler metal. A prerequisite for welding is that the metal should be solution treated. Fusion welding by tungsten inert gas welding is suitable for this alloy. Other techniques that may be used on the alloy include dip-transfer welding (in thicknesses up to 5 mm), resistance-spot, -stitch, and -seam welding and flash-butt welding.
Hot working
NIMONIC alloy 81 can be hot worked at temperature ranges of 950-1160°C (1742-2120°F).
Forging
NIMONIC alloy 81 can be hot forged at temperatures in the range of 1010-1176°C (1850-2150°F).
Cold working
Cold working may be done on the alloy for hardening.
Annealing
NIMONIC alloy 81 should be solution annealed at 1098°C (2010°F) for about 8 hours.
Applications
The NIMONIC alloy 81 is used in the following applications:
-
Gas turbine engineering
-
Piston engine exhaust valves
-
Heat exchange plant.