Nimonic 90: Properties and Applications in High-Temperature Environments

# Nimonic 90: Properties and Applications in High-Temperature Environments

## Introduction to Nimonic 90

Nimonic 90 is a nickel-chromium-cobalt alloy that belongs to the family of superalloys. Developed in the mid-20th century, this material has become a cornerstone in high-temperature applications due to its exceptional mechanical properties and resistance to oxidation and corrosion.

## Chemical Composition

The unique properties of Nimonic 90 stem from its carefully balanced chemical composition:

– Nickel (Ni): 55-60%
– Chromium (Cr): 18-21%
– Cobalt (Co): 15-21%
– Titanium (Ti): 2.0-3.0%
– Aluminum (Al): 1.0-2.0%
– Iron (Fe): ≤2.0%
– Carbon (C): ≤0.13%
– Manganese (Mn): ≤1.0%
– Silicon (Si): ≤1.0%

## Mechanical Properties

Nimonic 90 exhibits outstanding mechanical characteristics that make it suitable for demanding applications:

– Tensile Strength: 900-1200 MPa at room temperature
– Yield Strength: 600-900 MPa
– Elongation: 20-30%
– Hardness: 250-350 HV
– Creep Resistance: Excellent performance at temperatures up to 815°C (1500°F)

## Thermal Properties

The alloy’s thermal properties contribute significantly to its high-temperature performance:

– Melting Range: 1320-1390°C (2410-2530°F)
– Thermal Conductivity: 11.2 W/m·K at 20°C
– Coefficient of Thermal Expansion: 13.5 μm/m·K (20-100°C)
– Maximum Service Temperature: Approximately 815°C (1500°F) in oxidizing environments

## Key Advantages

Nimonic 90 offers several distinct advantages over other high-temperature alloys:

– Excellent oxidation resistance up to 1000°C (1832°F)
– Good resistance to carburization and sulfidation
– High creep rupture strength
– Good fatigue resistance
– Maintains mechanical properties at elevated temperatures
– Good fabricability and weldability

## Heat Treatment

Proper heat treatment is crucial for optimizing the properties of Nimonic 90:

– Solution Treatment: Typically performed at 1080°C (1975°F) followed by rapid cooling
– Aging: Carried out at 700-800°C (1290-1470°F) for 16 hours to precipitate strengthening phases
– Stress Relief: Recommended after welding or forming operations

## Applications in High-Temperature Environments

Nimonic 90 finds extensive use in various industries where high-temperature performance is critical:

### Aerospace Industry

– Turbine blades and discs
– Combustion chamber components
– Afterburner parts
– Exhaust systems

### Power Generation

– Gas turbine components
– Steam turbine blades
– Heat exchangers
– Nuclear reactor components

### Industrial Applications

– Heat treatment furnace components
– Chemical processing equipment
– Glass manufacturing tools
– Fasteners for high-temperature service

## Fabrication and Machining

Working with Nimonic 90 requires special considerations:

– Machining: Requires rigid setups, sharp tools, and appropriate cutting speeds
– Forming: Can be cold worked but requires intermediate annealing
– Welding: Best performed using TIG or resistance welding methods
– Joining: Requires nickel-based filler metals

## Comparison with Other Superalloys

While similar to other nickel-based superalloys, Nimonic 90 offers specific advantages:

– Better creep resistance than Inconel 718 at intermediate temperatures
– Higher strength than Hastelloy X in the 600-800°C range
– More cost-effective than single crystal superalloys for certain applications
– Better fabricability than