UDIMET alloy D-979 Fe-Ni Alloy,UNS N09979; AMS 5746，1

### **Product Datasheet: UDIMET® Alloy D-979 (UNS N09979)** **A Precipitation-Hardenable Fe-Ni-Based Superalloy for High-Temperature Service** --- #### **1. Overview** UDIMET® Alloy D-979 is a high-strength, **iron-nickel-based superalloy** strengthened by precipitation hardening. It is engineered to offer an excellent combination of **high tensile and creep strength**, **outstanding oxidation resistance** up to 815°C (1500°F), and good stability for long-term service at elevated temperatures. A key characteristic of D-979 is its **lower coefficient of thermal expansion** compared to nickel-based superalloys, which can be a critical design advantage in applications involving thermal cycling. It is typically supplied in the solution-annealed condition for machinability and then hardened to high strength levels through a single aging treatment. This alloy is commonly used for components that require high strength and excellent resistance to oxidation in environments where thermal expansion mismatch must be minimized. #### **2. Chemical Composition (Typical Weight %)** The composition balances the Fe-Ni matrix with potent strengthening elements. | Element | Content (%) | Role in the Alloy | | :--- | :--- | :--- | | **Iron (Fe)** | Balance | Base element of the alloy matrix. | | **Nickel (Ni)** | ~38.0 | Stabilizes the austenitic matrix and provides base corrosion resistance. | | **Chromium (Cr)** | ~14.5 | Imparts exceptional resistance to oxidation and scaling. | | **Molybdenum (Mo)** | ~4.0 | Provides solid solution strengthening. | | **Titanium (Ti)** | ~2.0 | Primary strengthening element; forms the γ' (gamma prime) Ni₃Ti phase. | | **Aluminum (Al)** | ~1.4 | Contributes to γ' formation (Ni₃(Al,Ti)) for strengthening. | | **Niobium (Nb)** | ~1.0 | Contributes to strengthening via carbide and intermetallic formation. | | **Carbon (C)** | ~0.05 | Forms carbides for grain boundary control. | | **Boron (B)** | ~0.010 | Enhances creep strength and grain boundary cohesion. | | **Manganese (Mn)** | ≤ 0.50 | Residual element. | | **Silicon (Si)** | ≤ 0.50 | Residual element. | #### **3. Physical Properties (Typical)** | Property | Value / Condition | | :--- | :--- | | **Density** | 7.99 g/cm³ (0.289 lb/in³) | | **Melting Range** | ~1370 - 1425 °C (~2500 - 2600 °F) | | **Thermal Expansion Coefficient** | ~14.5 μm/m·°C (20 - 540°C)
*Note: Lower than typical nickel-base alloys.* | | **Thermal Conductivity** | ~17.5 W/m·K (at 100°C) | | **Modulus of Elasticity (Elastic)** | ~200 GPa (29 x 10⁶ psi) at 20°C | #### **4. Mechanical Properties** Properties are developed through a solution treatment and a single aging step. The following are typical for bar stock per AMS 5746. **After Solution Treatment (Annealed Condition):** * This condition is soft and optimized for machining and forming. * **Typical Hardness:** ≤ 321 HB **After Full Heat Treatment (Solution Treated & Aged):** * **Tensile Strength:** ≥ 1100 MPa (160 ksi) * **Yield Strength (0.2% Offset):** ≥ 760 MPa (110 ksi) * **Elongation:** ≥ 10% * **Reduction of Area:** ≥ 12% **At Elevated Temperature (e.g., 650°C / 1200°F):** * Retains a significant portion of its room-temperature strength and offers excellent creep resistance. #### **5. Heat Treatment** A standard heat treatment cycle for UDIMET D-979 is as follows: 1. **Solution Treatment:** Heat to 980°C (1800°F), hold for a sufficient time, then rapidly cool (water quench or fast air cool). This results in a soft, machinable condition. 2. **Aging / Precipitation Hardening:** Heat to 730°C (1350°F), hold for 8-16 hours, then air cool. This step precipitates the strengthening γ' phase throughout the matrix. #### **6. Product Applications** UDIMET D-979 is used in high-integrity components that operate under high stress and temperature, particularly in aerospace and power generation: * **Aerospace:** Gas turbine engine casings, compressor casings, turbine shrouds, afterburner components, and high-temperature fasteners. * **Power Generation:** Turbine blades, disks, and structural components in industrial gas turbines. * **General Engineering:** Components for high-temperature furnaces and fixtures. #### **7. International and Industry Standards** UDIMET D-979 is covered by several key aerospace and international specifications. * **AMS:** **AMS 5746** (Bars, forgings, and rings, 38Ni - 14.5Cr - 2.0Ti - 1.4Al, solution heat treated, precipitation hardenable) * **UNS:** **N09979** * **Common Forms:** Bar, wire, billet, ring, and forged shapes. --- **Disclaimer:** The information provided is typical and for reference purposes only. Mechanical properties are highly dependent on section size, heat treatment parameters, and manufacturing process. For design and procurement, the applicable material specification (e.g., AMS 5746) and the manufacturer's technical data must be consulted. UDIMET is a registered trademark of Special Metals Corporation (a PCC company).

Packing of Standard Packing: Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 3364 gallon liquid totes Special package is available on request.