P/M 625M Corrosion Resistant Alloy, UNS N07626,E FORU

### **P/M Alloy 625M (UNS N07626) - Nickel-Chromium-Molybdenum-Niobium Superalloy** #### **Overview** **P/M Alloy 625M (UNS N07626)** is a modified, powder metallurgy (P/M) version of the classic Alloy 625 (UNS N06625). The "M" stands for "Modified," with key changes to the chemical composition specifically designed to enhance **long-term microstructural stability and strength at high temperatures** (typically above 650°C / 1200°F). While standard Alloy 625 derives its strength from solid solution hardening and the precipitation of the gamma double prime (γ'') phase (Ni₃Nb), it can be susceptible to the transformation of this metastable γ'' phase into a stable but brittle delta (δ) phase (Ni₃Nb) after prolonged exposure to high temperatures. This transformation leads to a loss of strength and ductility. Alloy 625M addresses this by reducing the niobium content and adding strengthening elements that form more stable phases, making it superior for high-temperature, high-stress applications where standard 625 would degrade over time. The P/M manufacturing route ensures a fine, homogeneous, and segregation-free microstructure, which is critical for achieving consistent mechanical properties and superior performance in complex components. --- #### **Chemical Composition (Weight % - Typical)** The chemical composition of 625M is carefully modified from the standard 625 composition. | Element | Content (%) - UNS N07626 (625M) | Content (%) - UNS N06625 (Standard 625) | Rationale for Modification | | :--- | :--- | :--- | :--- | | **Nickel (Ni)** | **Balance** | **Balance** | - | | **Chromium (Cr)** | **19.0 - 22.0** | **20.0 - 23.0** | Slightly adjusted for balance. | | **Molybdenum (Mo)** | **8.0 - 10.0** | **8.0 - 10.0** | Maintained for solid solution strength. | | **Niobium (Nb)** | **1.5 - 2.5** | **3.15 - 4.15** | **Reduced to inhibit δ-phase formation.** | | **Titanium (Ti)** | **0.5 - 1.2** | **≤ 0.40** | **Increased to form stable γ' (Ni₃Ti/Al).** | | **Aluminum (Al)** | **0.2 - 0.6** | **≤ 0.40** | **Increased to form stable γ' (Ni₃Ti/Al).** | | **Carbon (C)** | **≤ 0.03** | **≤ 0.10** | **Reduced to minimize carbide formation.** | | **Iron (Fe)** | **≤ 3.0** | **≤ 5.0** | Tighter control for purity. | | **Silicon (Si)** | **≤ 0.20** | **≤ 0.50** | **Reduced to improve stability.** | *Key Takeaway: The primary modifications are the **reduction of Niobium and Carbon**, and the **increase of Titanium and Aluminum**. This shifts the strengthening mechanism from a reliance on the metastable γ'' phase (Ni₃Nb) to a more stable and coarsening-resistant γ' phase (Ni₃(Ti,Al)).* --- #### **Physical & Mechanical Properties** The properties below are representative for P/M 625M in the HIPed and heat-treated condition. | Property | Value / Description (P/M 625M) | | :--- | :--- | | **Density** | ~8.4 g/cm³ | | **Melting Range** | ~1350 - 1400 °C (2460 - 2550 °F) | | **Thermal Conductivity** | ~12.0 W/m·K (at 100°C) | | **Mean Coefficient of Thermal Expansion** | ~13.0 μm/m·°C (20-1000°C) | | **Modulus of Elasticity** | ~210 GPa (30.5 x 10⁶ psi) | | **Tensile Strength (HIP + Aged, RT)** | ~1100 - 1300 MPa (160 - 190 ksi) | | **Yield Strength (0.2% Offset, HIP + Aged, RT)** | ~750 - 900 MPa (110 - 130 ksi) | | **Elongation (HIP + Aged, RT)** | ~20% | | **Creep Rupture Strength** | **Superior to standard 625.** Maintains high stress rupture strength after long-term aging at **650-750°C (1200-1380°F).** | --- #### **Key Characteristics & Applications** **Key Characteristics:** 1. **Enhanced Microstructural Stability:** The modified chemistry significantly delays the formation of brittle delta phase, maintaining ductility and toughness after long-term exposure to high temperatures. 2. **Superior High-Temperature Strength:** Offers higher strength and creep resistance than standard 625 at temperatures above 650°C (1200°F). 3. **Excellent Corrosion Resistance:** Retains the outstanding corrosion resistance of the 625 family, including resistance to pitting, crevice corrosion, and oxidation. 4. **Isotropic Properties:** The P/HIP (Powder/Hot Isostatic Pressing) process ensures uniform properties in all directions, free from the directionality of wrought products. 5. **Good Fabricability via P/M:** Ideal for manufacturing complex, near-net-shape components that would be difficult or expensive to machine from wrought bar. **Typical Applications:** P/M 625M is engineered for high-integrity applications in the aerospace and power generation industries where standard 625 would be inadequate. * **Aerospace Jet Engines:** * **Static structural components** in the high-pressure compressor and turbine sections. * **Casings, rings, and seals** that require long-term stability under stress at high temperatures. * **Engine mount components.** * **Power Generation:** * **Gas Turbine Disks** and hubs for land-based power turbines. * **Heat exchangers** and ducting in advanced ultra-supercritical power plants. * **High-Temperature Fasteners and Bolting.** --- #### **International Standards** As a more specialized, advanced alloy, P/M 625M is covered by specific aerospace standards. It is crucial to distinguish it from standard 625. | Product Form | Standard | Description | | :--- | :--- | :--- | | **Powder Preursor** | **AMS 7897** | This is the primary specification for "Alloy 625M (UNS N07626) Powder for Bearing Applications." It defines the strict chemical requirements for the powder. | | **HIPed Product** | **Specific OEM Specifications** | The final HIPed billets or components are typically governed by proprietary specifications from engine manufacturers (e.g., GE, Rolls-Royce, Pratt & Whitney) that detail HIP parameters, heat treatment, and final properties. | | **General Composition** | **UNS N07626** | The Unified Numbering System designation that uniquely identifies this modified composition. | **Important Note:** P/M 625M (UNS N07626) is **not** covered by the general ASTM standards for wrought Alloy 625 (e.g., B443, B444). It is a distinct material system controlled by more specialized specifications, primarily in the aerospace sector. --- #### **Summary** In summary, **P/M Alloy 625M (UNS N07626)** is a strategically upgraded version of the workhorse Alloy 625, specifically engineered for superior performance in high-temperature structural applications. By modifying the chemistry to promote a stable γ' strengthening phase and utilizing P/M processing for microstructural homogeneity, it overcomes the long-term stability limitations of standard 625. This makes it a critical material for the most demanding static components in modern jet engines and power generation turbines, where reliability and strength after thousands of hours of exposure to extreme conditions are non-negotiable.

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 3203 gallon liquid totes Special package is available on request.