Alloy X-750 (UNS N07750) Properties and Applications

July 12, 2025 / By

# Alloy X-750 (UNS N07750) Properties and Applications

## Introduction to Alloy X-750

Alloy X-750, also known by its UNS designation N07750, is a nickel-chromium superalloy that exhibits excellent mechanical properties and corrosion resistance at elevated temperatures. This alloy is precipitation-hardenable, making it suitable for applications requiring high strength and durability in extreme environments.

## Chemical Composition

The chemical composition of Alloy X-750 plays a crucial role in its performance characteristics:

– Nickel (Ni): 70% minimum
– Chromium (Cr): 14-17%
– Iron (Fe): 5-9%
– Titanium (Ti): 2.25-2.75%
– Aluminum (Al): 0.4-1.0%
– Niobium (Nb) + Tantalum (Ta): 0.7-1.2%
– Carbon (C): 0.08% maximum
– Manganese (Mn): 1.0% maximum
– Silicon (Si): 0.5% maximum
– Sulfur (S): 0.01% maximum
– Copper (Cu): 0.5% maximum

## Physical Properties

Alloy X-750 demonstrates remarkable physical properties that make it suitable for demanding applications:

– Density: 8.28 g/cm³ (0.299 lb/in³)
– Melting Range: 1393-1427°C (2540-2600°F)
– Electrical Resistivity: 1.22 μΩ·m
– Thermal Conductivity: 11.4 W/m·K (at 100°C)
– Coefficient of Thermal Expansion: 13.1 μm/m·K (20-100°C)

## Mechanical Properties

The mechanical properties of Alloy X-750 vary depending on heat treatment condition:

### Annealed Condition

– Tensile Strength: 827 MPa (120 ksi)
– Yield Strength: 345 MPa (50 ksi)
– Elongation: 30%

### Precipitation Hardened Condition

– Tensile Strength: 1241 MPa (180 ksi)
– Yield Strength: 827 MPa (120 ksi)
– Elongation: 20%

## Heat Treatment

Alloy X-750 achieves its optimal properties through specific heat treatment processes:

– Solution Annealing: 1150-1200°C (2100-2200°F) followed by rapid cooling
– Aging Treatment: Typically 705°C (1300°F) for 20 hours, air cooled
– Double Aging: Sometimes used for enhanced properties (705°C + 620°C)

## Corrosion Resistance

Alloy X-750 offers excellent corrosion resistance in various environments:

– Outstanding resistance to oxidation up to 870°C (1600°F)
– Good resistance to chloride-ion stress-corrosion cracking
– Performs well in high-temperature steam and combustion atmospheres
– Resistant to many organic and inorganic compounds

## Applications of Alloy X-750

Due to its exceptional properties, Alloy X-750 finds use in numerous demanding applications:

### Aerospace Industry

– Gas turbine engine components
– Rocket engine parts
– Aircraft structural components
– Fasteners and springs

### Power Generation

– Nuclear reactor components
– Steam turbine blades
– Combustion liners
– Heat exchanger tubing

### Industrial Applications

– High-temperature fasteners
– Forming tools and dies
– Pressure vessels
– Chemical processing equipment

## Fabrication and Machining

Alloy X-750 can be fabricated using standard techniques, though some considerations apply:

– Hot working should be performed between 925-1205°C (1700-2200°F)
– Cold working requires intermediate annealing
– Machining requires rigid setups and positive rake tools
– Welding can be performed using matching filler metal