# Alloy 718 (UNS N07718) Properties and Applications

Introduction to Alloy 718

Alloy 718, also known as UNS N07718, is a nickel-chromium-based superalloy renowned for its exceptional strength and corrosion resistance. This precipitation-hardenable material maintains its mechanical properties at elevated temperatures, making it a preferred choice for demanding applications in aerospace, oil and gas, and other high-performance industries.

Chemical Composition

The chemical composition of Alloy 718 contributes significantly to its outstanding properties:

• Nickel (Ni): 50-55%
• Chromium (Cr): 17-21%
• Iron (Fe): Balance
• Niobium (Nb): 4.75-5.5%
• Molybdenum (Mo): 2.8-3.3%
• Titanium (Ti): 0.65-1.15%
• Aluminum (Al): 0.2-0.8%
• Carbon (C): ≤0.08%

Mechanical Properties

Alloy 718 exhibits remarkable mechanical properties across a wide temperature range:

Property	Value
Tensile Strength	1,240 MPa (180 ksi)
Yield Strength	1,030 MPa (150 ksi)
Elongation	12-20%
Hardness	35-45 HRC
Maximum Service Temperature	700°C (1,300°F)

Key Characteristics

Alloy 718 possesses several distinctive characteristics that make it valuable for critical applications:

• Excellent resistance to oxidation and corrosion
• High strength retention at elevated temperatures
• Good weldability compared to other superalloys
• Resistance to stress-corrosion cracking
• Outstanding fatigue resistance
• Stable microstructure in long-term service

Heat Treatment

The properties of Alloy 718 can be optimized through specific heat treatment processes:

1. Solution Annealing: Typically performed at 955-1010°C (1750-1850°F) followed by rapid cooling
2. Aging Treatment: Double aging at 720°C (1325°F) for 8 hours, furnace cool to 620°C (1150°F), hold for 8 hours, then air cool
3. Stress Relieving: Performed at 650-760°C (1200-1400°F) for components with residual stresses

Applications of Alloy 718

The unique combination of properties makes Alloy 718 suitable for numerous demanding