Alloy 901 UNS N09901: Properties and Applications

# Alloy 901 UNS N09901: Properties and Applications

## Introduction to Alloy 901 UNS N09901

Alloy 901, also known as UNS N09901, is a precipitation-hardening nickel-iron-chromium superalloy. This material is renowned for its excellent combination of high strength, corrosion resistance, and thermal stability, making it suitable for demanding applications in various industries.

## Chemical Composition

The chemical composition of Alloy 901 plays a crucial role in its performance characteristics. The primary elements include:

– Nickel (Ni): 40-45%
– Iron (Fe): Balance
– Chromium (Cr): 11-14%
– Titanium (Ti): 2.8-3.1%
– Molybdenum (Mo): 5.0-6.5%
– Aluminum (Al): 0.1-0.3%
– Carbon (C): 0.03% max

## Mechanical Properties

Alloy 901 exhibits impressive mechanical properties, especially after heat treatment:

– Tensile Strength: 1200-1400 MPa
– Yield Strength: 800-1000 MPa
– Elongation: 10-15%
– Hardness: 35-40 HRC (after aging)
– Fatigue Strength: Excellent resistance to cyclic loading

## Physical Properties

The physical characteristics of UNS N09901 include:

– Density: 8.14 g/cm³
– Melting Point: 1320-1390°C (2410-2530°F)
– Thermal Expansion: 13.5 μm/m·°C (20-100°C)
– Thermal Conductivity: 11.4 W/m·K (at 100°C)
– Electrical Resistivity: 1.05 μΩ·m

## Heat Treatment

Alloy 901 achieves its optimal properties through specific heat treatment processes:

– Solution Annealing: 1095-1120°C (2000-2050°F) followed by rapid cooling
– Aging Treatment: 720-745°C (1325-1375°F) for 16 hours, air cool
– Stress Relieving: 650-675°C (1200-1250°F) for 4 hours

## Corrosion Resistance

UNS N09901 offers good resistance to various corrosive environments:

– Excellent resistance to oxidation up to 815°C (1500°F)
– Good resistance to sulfur-containing atmospheres
– Moderate resistance to chloride stress corrosion cracking
– Performs well in mildly reducing and oxidizing environments

## Applications of Alloy 901

Due to its unique combination of properties, Alloy 901 finds applications in several critical industries:

### Aerospace Industry

– Turbine engine components
– Afterburner parts
– High-temperature fasteners

### Power Generation

– Gas turbine components
– Steam turbine blades
– High-pressure turbine casings

### Oil and Gas

– Downhole tools
– Wellhead components
– Valve stems for sour service

### Industrial Applications

– High-temperature springs
– Fasteners for elevated temperature service
– Pressure vessels for chemical processing

## Fabrication and Machining

Working with Alloy 901 requires special considerations:

– Machining: Use rigid setups, positive rake tools, and adequate cooling
– Welding: Can be welded using TIG, MIG, and resistance welding methods
– Forming: Requires higher forces than carbon steels; hot forming recommended for complex shapes
– Heat Treatment: Must be performed after welding to restore properties

## Comparison with Similar Alloys

Alloy 901 offers distinct advantages compared to similar materials:

– Higher strength than Inconel 718 at elevated temperatures
– Better thermal stability than A-286
– More cost-effective than some nickel-based superalloys
– Superior creep resistance compared to many iron-nickel