# Alloy 718 (UNS N07718) Properties and Applications

## Introduction to Alloy 718

Alloy 718, also known as UNS N07718, is a nickel-chromium-based superalloy that offers exceptional strength and corrosion resistance at high temperatures. This material is widely used in demanding industries such as aerospace, oil and gas, and power generation due to its unique combination of properties.

## Key Properties of Alloy 718

### Mechanical Properties

Alloy 718 exhibits excellent mechanical properties across a wide temperature range:
– High tensile strength (up to 180 ksi at room temperature)
– Good fatigue resistance
– Excellent creep resistance at elevated temperatures
– Maintains strength up to 1300°F (704°C)

### Corrosion Resistance

The alloy demonstrates outstanding resistance to:
– Oxidation and scaling
– Pitting and crevice corrosion
– Stress corrosion cracking
– Corrosion in marine environments

### Physical Properties

Some notable physical characteristics include:
– Density: 8.19 g/cm³
– Melting range: 1260-1340°C (2300-2445°F)
– Thermal expansion coefficient: 13.0 μm/m·°C (20-100°C)
– Electrical resistivity: 1.25 μΩ·m

## Heat Treatment and Processing

Alloy 718 is typically solution treated and aged to achieve optimal properties:
1. Solution treatment at 1700-1850°F (927-1010°C)
2. Rapid cooling (air or water quench)
3. Aging at 1325°F (718°C) for 8 hours
4. Furnace cool to 1150°F (621°C)
5. Hold for 8 hours, then air cool

## Applications of Alloy 718

### Aerospace Industry

Alloy 718 is extensively used in aircraft and spacecraft components:
– Jet engine components (turbine blades, discs, casings)
– Rocket motor cases
– Fasteners and structural components

### Oil and Gas Sector

The material’s corrosion resistance makes it ideal for:
– Downhole tools
– Wellhead components
– Subsea equipment
– Valves and pumps

### Power Generation

Alloy 718 finds applications in:
– Gas turbine components
– Nuclear reactor parts
– Steam turbine blades
– Heat exchangers

## Advantages Over Other Superalloys

Alloy 718 offers several benefits compared to similar materials:
– Better weldability than many nickel-based superalloys
– Lower cost than cobalt-based alternatives
– Excellent fabricability (can be forged, rolled, and formed)
– Good balance of strength and corrosion resistance

## Conclusion

Alloy 718 (UNS N07718) remains one of the most versatile and widely used superalloys due to its exceptional combination of mechanical properties, corrosion resistance, and workability. Its applications continue to expand as industries demand materials that can perform under increasingly severe conditions.