NIMONIC Alloy 81

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.

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