Hangbo Alloy Group
Shanghai · Est. 2012
UNS N07220 — Chemical composition, mechanical properties, multi-step heat treatment, creep-rupture data, and applications in advanced gas turbine discs and high-temperature structural components.
Udimet 720 (UNS N07220) is a high-strength nickel-based precipitation-hardened superalloy developed by Special Metals Corporation (originally Uddeholm) as an evolution of the Udimet 700 and Udimet 710 alloy families. It represents one of the most advanced wrought disc alloys available, with a gamma prime (Ni3(Al,Ti)) volume fraction exceeding 40%, which provides exceptional tensile and creep-rupture strength at temperatures up to 870°C (1600°F).
The alloy was specifically designed for the most demanding gas turbine disc applications, where operating temperatures and stress levels exceed the capabilities of earlier-generation alloys like Waspaloy and Rene 41. The very high titanium content (4.5–5.0%) combined with substantial aluminum (2.0–2.5%) produces a dense network of fine gamma prime precipitates that resist coarsening at elevated temperatures, maintaining long-term creep resistance. Cobalt (14–16%) raises the gamma prime solvus temperature, extending the alloy's useful temperature range.
Udimet 720 is used primarily in advanced military and commercial gas turbine engines for high-pressure turbine discs, compressor discs, and shafts where burst margin and creep resistance are critical safety requirements. The alloy requires triple melting (VIM+ESR+VAR or VIM+VAR+VAR) to meet the stringent cleanliness specifications for rotating engine components. Its very high gamma prime fraction makes forming and welding extremely difficult, which limits its product forms primarily to forged components.
The chemical composition of Udimet 720 is designed to maximize the gamma prime volume fraction while maintaining sufficient solid-solution strengthening for elevated temperature service. The combined titanium + aluminum content of approximately 7% produces a gamma prime volume fraction exceeding 40%, which is among the highest achievable in wrought product forms. This high precipitate density provides the alloy's exceptional creep resistance but also limits formability and weldability.
| Element | Min % | Max % |
|---|---|---|
| Nickel (Ni) | Balance | Balance |
| Chromium (Cr) | 16.0 | 18.0 |
| Cobalt (Co) | 14.0 | 16.0 |
| Titanium (Ti) | 4.5 | 5.0 |
| Aluminum (Al) | 2.0 | 2.5 |
| Molybdenum (Mo) | 2.5 | 3.5 |
| Tungsten (W) | 1.0 | 1.5 |
| Iron (Fe) | — | 1.0 |
| Boron (B) | 0.01 | 0.03 |
| Zirconium (Zr) | — | 0.05 |
| Carbon (C) | — | 0.03 |
| Silicon (Si) | — | 0.20 |
| Manganese (Mn) | — | 0.20 |
| Sulfur (S) | — | 0.005 |
| Phosphorus (P) | — | 0.015 |
Udimet 720 exhibits physical properties characteristic of heavily alloyed nickel superalloys. The density is slightly lower than some earlier disc alloys due to the reduced molybdenum content and higher titanium/aluminum, which are lighter elements. The thermal conductivity is moderate and increases with temperature, while the electrical resistivity is high due to the substantial alloying element content.
| Property | Value | Unit |
|---|---|---|
| Density | 8.10 | g/cm³ |
| Melting Point (Range) | 1260–1330 | °C |
| Specific Heat (21°C) | 430 | J/kg·K |
| Thermal Conductivity (21°C) | 8.9 | W/m·K |
| Electrical Resistivity (21°C) | 1.40 | μΩ·m |
| Modulus of Elasticity (21°C) | 210 | GPa |
| Mean Coefficient of Thermal Expansion (21–93°C) | 12.8 | μm/m·°C |
| Mean Coefficient of Thermal Expansion (21–538°C) | 14.2 | μm/m·°C |
The mechanical properties of Udimet 720 are among the highest achievable in a wrought nickel superalloy. The very high gamma prime volume fraction (>40%) provides extraordinary yield and tensile strength in the fully heat-treated condition. In the solution-annealed condition, the alloy retains moderate ductility sufficient for limited forming operations, although its high alloy content makes extensive cold forming impractical.
| Property | Solution Annealed | Fully Heat Treated |
|---|---|---|
| Tensile Strength | 690 MPa (100 ksi) | 1380 MPa (200 ksi) |
| Yield Strength (0.2% offset) | 350 MPa (51 ksi) | 1140 MPa (165 ksi) |
| Elongation in 2 inches | 25–30% | 8–12% |
| Reduction of Area | 30–40% | 10–15% |
| Hardness (Rockwell C) | 15–20 HRC | 42–48 HRC |
| Impact Strength (Charpy V-notch) | 40 J | 15 J |
Udimet 720 requires a sophisticated four-step heat treatment sequence to achieve its intended mechanical properties. The multi-step aging process creates an optimized distribution of gamma prime precipitates in three distinct size ranges: coarse primary gamma prime (~0.5μm), intermediate secondary gamma prime (~0.2μm), and fine tertiary gamma prime (~0.05μm). This trimodal distribution provides the best combination of creep resistance, tensile strength, and ductility.
The complexity of this heat treatment reflects the alloy's advanced design philosophy. Each step serves a specific metallurgical purpose, and deviation from the prescribed sequence can result in suboptimal precipitate distributions with reduced creep or tensile properties. For turbine disc applications, heat treatment must be documented and traceable per aerospace quality system requirements.
Udimet 720 maintains exceptional strength at elevated temperatures, significantly exceeding the capabilities of Waspaloy, Rene 41, and Inconel 718 at temperatures above 650°C. The high gamma prime volume fraction provides a dense network of obstacles to dislocation motion that remains effective even at temperatures where earlier alloys have lost significant strength.
| Temperature (°C) | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) |
|---|---|---|---|
| 21 (Room) | 1380 | 1140 | 10 |
| 316 | 1250 | 1020 | 11 |
| 427 | 1200 | 980 | 12 |
| 538 | 1120 | 900 | 13 |
| 649 | 1000 | 800 | 14 |
| 760 | 830 | 660 | 16 |
| 816 | 650 | 510 | 18 |
| 871 | 420 | 340 | 22 |
| 982 | 200 | 150 | 35 |
Udimet 720 exhibits outstanding creep-rupture strength that significantly exceeds Waspaloy and Rene 41 at all temperatures in the 650–870°C range. The 100-hour rupture stress at 650°C is approximately 800 MPa, at 760°C approximately 420 MPa, and at 815°C approximately 290 MPa. These values are approximately 15–20% higher than Waspaloy and 25–30% higher than Rene 41 at the same temperatures. The exceptional creep resistance is directly attributable to the high gamma prime volume fraction, which provides a dense, stable network of obstacles to dislocation climb at elevated temperatures.
The creep-rupture properties of Udimet 720 are further enhanced by the boron addition (0.01–0.03%), which segregates to grain boundaries and prevents grain boundary sliding — a major creep mechanism at elevated temperatures. The zirconium addition similarly improves grain boundary strength and ductility, preventing premature intergranular fracture during long-term creep exposure.
Udimet 720 has moderate oxidation resistance typical of precipitation-hardened nickel superalloys designed primarily for structural strength. The 16–18% chromium content provides adequate oxidation protection for gas turbine service environments, but the alloy is not designed for chemical corrosion resistance applications.
Udimet 720 is used exclusively in high-performance gas turbine engine applications where its exceptional creep-rupture strength provides advantages over earlier-generation disc alloys. Its primary applications are rotating components in the hot section of military and commercial turbofan engines.
Hangbo Alloy Group supplies Udimet 720 primarily in forged product forms due to the alloy's limited cold formability. All material is produced via triple melting (VIM+ESR+VAR or VIM+VAR+VAR) to meet the stringent inclusion cleanliness requirements for rotating engine components per AMS 7179.
| Standard | Description |
|---|---|
| AMS 7179 | Bars, Forgings, and Rings |
| UNS N07220 | Unified Numbering System Designation |
| Special Metals U720™ | Proprietary Alloy Specification |
| AMS 2370/2375 | Ultrasonic Inspection of Bars and Forgings |
| AMS 2774 | Heat Treatment of Nickel Alloy Parts |
Udimet 720 has a density of 8.10 g/cm³ (0.293 lb/in³), which is relatively high for a nickel-based superalloy due to its substantial cobalt (14–16%) and molybdenum content combined with tungsten (1.0–1.5%).
Udimet 720 has a melting range of approximately 1260–1330°C (2300–2426°F). The solidus temperature is around 1260°C and the liquidus around 1330°C, typical for high-alloy nickel superalloys.
Udimet 720 is a nickel-cobalt-chromium-titanium-aluminum superalloy: Nickel balance (~46%), Chromium 16–18%, Cobalt 14–16%, Titanium 4.5–5.0%, Aluminum 2.0–2.5%, Molybdenum 2.5–3.5%, Tungsten 1.0–1.5%, Iron max 1%, with Boron (0.01–0.03%) and Zirconium. The very high Ti+Al content (~7%) produces over 40% gamma prime volume fraction.
Udimet 720 is covered by AMS 7179 (bars and forgings) and Special Metals proprietary specifications. It appears under UNS N07220. Due to its specialized nature, most procurement is governed by OEM-specific specifications.
Udimet 720 is designed for service temperatures up to approximately 870°C (1600°F) for short-term exposures and 760–870°C for long-term creep-rupture applications. Its high gamma prime fraction provides exceptional strength retention at intermediate temperatures.
Udimet 720 has significantly higher gamma prime volume fraction (~40% vs. ~25% in Waspaloy and ~20% in Rene 41), resulting in higher tensile and creep strength at temperatures up to 870°C. However, this also means greater susceptibility to strain-age cracking and more limited weldability. Udimet 720 represents a later-generation alloy optimized for the most demanding disc applications.
Udimet 720 has extremely limited weldability due to its very high gamma prime volume fraction. Fusion welding is generally not recommended. Electron beam welding can be used for specific joints. Post-weld heat treatment requires very rapid heating to avoid strain-age cracking. Brazing is the preferred joining method.
In the fully heat-treated condition, Udimet 720 exhibits tensile strength of 1380 MPa (200 ksi), yield strength of 1140 MPa (165 ksi), and elongation of 8–12%. These are among the highest room-temperature tensile properties achievable in a wrought nickel superalloy.
Hangbo Alloy Group supplies Udimet 720 primarily as round bars (12–300 mm diameter) and custom forgings (turbine discs, shafts, rings). Sheet and plate are available in limited sizes. All material is triple-melted (VIM+ESR+VAR) per aerospace cleanliness requirements.
Udimet 720 is primarily used in advanced aerospace and industrial gas turbine engines for high-pressure turbine discs, compressor discs, shafts, and seal rings. It is also used in high-temperature fasteners and springs requiring exceptional creep resistance at 650–870°C.
The standard heat treatment: Solution anneal at 1095–1135°C for 1–4 hours, oil quench; then four-step aging: 1065°C for 2 hours, air cool; 845°C for 4 hours, air cool; 760°C for 8 hours, air cool; 650°C for 16 hours, air cool. This multi-step process produces an optimized trimodal gamma prime distribution.
Udimet 720 is among the most expensive wrought nickel superalloys due to its high cobalt content, triple melting requirements, and limited production volume. Round bars typically range from $100–$200 per kg; forgings are $150–$300 per kg. Contact our sales team for current pricing and availability.
Hangbo Alloy Group supplies Udimet 720 round bars and custom forgings per AMS 7179 for advanced gas turbine disc applications. Our team can assist with triple-melting specification, multi-step heat treatment processing, ultrasonic inspection per AMS 2370, and complete OEM documentation packages. We support aerospace turbine manufacturers worldwide with reliable quality, competitive delivery, and full material traceability.
For quotations, material certifications, or technical consultation, contact our sales team or call +86-136-1165-6360. We typically respond within 10 minutes.
Request a quotation for Udimet 720 round bars or custom turbine disc forgings per AMS 7179. Triple-melted material with complete ultrasonic inspection and heat treatment certification available.