# Alloy A286 (UNS S66286) High-Temperature Superalloy Overview

## Introduction to Alloy A286

Alloy A286, also known by its UNS designation S66286, is a high-performance iron-nickel-chromium superalloy renowned for its exceptional strength and corrosion resistance at elevated temperatures. This precipitation-hardening alloy finds extensive use in aerospace, gas turbine, and other high-stress applications where materials must withstand extreme conditions.

## Chemical Composition

The unique properties of Alloy A286 stem from its carefully balanced chemical composition:

– Iron (Fe): Balance
– Nickel (Ni): 24-27%
– Chromium (Cr): 13.5-16%
– Molybdenum (Mo): 1.0-1.5%
– Titanium (Ti): 1.9-2.35%
– Aluminum (Al): 0.35% max
– Manganese (Mn): 2.0% max
– Silicon (Si): 1.0% max
– Carbon (C): 0.08% max
– Boron (B): 0.003-0.010%
– Sulfur (S): 0.030% max
– Phosphorus (P): 0.025% max

## Key Properties and Characteristics

Alloy A286 offers an impressive combination of mechanical and physical properties:

### Mechanical Properties

– Tensile Strength: 140-160 ksi (965-1100 MPa) at room temperature
– Yield Strength: 85-110 ksi (585-760 MPa)
– Elongation: 10-25%
– Hardness: 30-40 HRC after heat treatment
– Excellent creep resistance at temperatures up to 1300°F (700°C)

### Physical Properties

– Density: 7.92 g/cm³ (0.286 lb/in³)
– Melting Range: 2500-2600°F (1370-1425°C)
– Electrical Resistivity: 78.0 μΩ·cm
– Thermal Conductivity: 11.2 W/m·K at 100°C
– Coefficient of Thermal Expansion: 14.2 μm/m·K (20-100°C)

## Heat Treatment

Alloy A286 achieves its optimal properties through a specific heat treatment process:

– Solution Annealing: 1800°F (980°C) followed by rapid cooling
– Aging: 1300-1400°F (705-760°C) for 16 hours, air cooling

This treatment sequence produces a precipitation-hardened microstructure with gamma prime (γ’) strengthening phases.

## Applications

The exceptional high-temperature performance of Alloy A286 makes it ideal for demanding applications:

– Aerospace components (turbine blades, engine mounts, fasteners)
– Gas turbine engine parts
– High-temperature bolts and fasteners
– Nuclear reactor components
– Industrial furnace parts
– High-performance automotive components
– Oil and gas equipment for sour service

## Fabrication and Machining

Alloy A286 can be fabricated using standard methods, though it requires special considerations:

### Forming

– Hot working should be performed between 1800-2200°F (980-1200°C)
– Cold working is possible but requires intermediate annealing

### Machining

– Use rigid setups and positive rake tools
– Maintain sharp cutting edges
– Employ slow speeds with moderate feed rates
– Use generous amounts of cutting fluid

### Welding

– Recommended methods: Gas tungsten arc welding (GTAW) and resistance welding
– Post-weld heat treatment is essential to restore properties
– Avoid oxyacetylene welding due to potential embrittlement

## Corrosion Resistance

Alloy A286 demonstrates excellent resistance to:

– Oxidation at high temperatures
– Sulfidation in sulfur-containing environments
– Stress corrosion