Nimonic 86
Introduction to Nimonic 86
Nimonic 86 is a high-strength, nickel-chromium-cobalt superalloy engineered for outstanding mechanical stability, creep resistance, and oxidation protection in extreme high-temperature environments, with significant additions of molybdenum and aluminum, Nimonic 86 offers enhanced strengthening through both solid-solution and precipitation mechanisms. It is optimized for service temperatures up to 950°C, making it highly suitable for turbine blades, combustion chambers, and high-load bolting systems. Nimonic 86 is often processed through CNC machining services to meet the exacting demands of aerospace, power generation, and nuclear industries.
Known for its resistance to thermal fatigue and oxidation, Nimonic 86 is typically processed by forging and precision-finished through CNC machining to meet stringent dimensional tolerances required in aerospace, power generation, and nuclear sectors.
Chemical, Physical, and Mechanical Properties of Nimonic 86
Nimonic 86 (UNS N07086 / W.Nr. 2.4972 / AMS 5854) is a precipitation-strengthened alloy characterized by excellent high-temperature performance and thermal stability due to a combination of gamma prime (γ′) and molybdenum-rich phases.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Nickel (Ni) | Balance (≥55.0) | Provides thermal stability and base matrix strength |
Chromium (Cr) | 19.0–22.0 | Enhances oxidation and hot corrosion resistance |
Cobalt (Co) | 15.0–20.0 | Increases creep and fatigue resistance |
Molybdenum (Mo) | 4.0–6.0 | Solid solution strengthening and carbide formation |
Titanium (Ti) | 2.0–2.6 | Forms Ni₃Ti gamma-prime precipitates |
Aluminum (Al) | 1.0–1.5 | Enhances γ′ phase hardening for high-temperature strength |
Iron (Fe) | ≤2.0 | Residual element |
Carbon (C) | ≤0.10 | Improves creep strength via carbide precipitation |
Manganese (Mn) | ≤1.0 | Improves hot working characteristics |
Silicon (Si) | ≤1.0 | Aids in oxidation resistance |
Sulfur (S) | ≤0.015 | Controlled to avoid hot cracking during machining and welding |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.35 g/cm³ | ASTM B311 |
Melting Range | 1320–1380°C | ASTM E1268 |
Thermal Conductivity | 11.0 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.10 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 13.4 µm/m·°C (20–1000°C) | ASTM E228 |
Specific Heat Capacity | 430 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 200 GPa at 20°C | ASTM E111 |
Mechanical Properties (Solution Treated + Aged)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 1050–1180 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 730–800 MPa | ASTM E8/E8M |
Elongation | ≥18% | ASTM E8/E8M |
Hardness | 230–260 HB | ASTM E10 |
Creep Rupture Strength | 220 MPa at 850°C (1000h) | ASTM E139 |
Fatigue Resistance | Excellent | ASTM E466 |
Key Characteristics of Nimonic 86
High-Temperature Strength Retention Maintains tensile strength >1050 MPa and yield strength >730 MPa at 850°C, enabling prolonged operation in gas turbines and power plant components.
Long-Term Creep Resistance Exhibits creep rupture strength of 220 MPa at 850°C for 1000 hours, verified under ASTM E139, making it ideal for structural parts exposed to sustained load at high temperatures.
Oxidation Resistance up to 1000°C With 20% Cr and 15–20% Co, the alloy forms a stable and adherent Cr₂O₃ oxide layer, reducing mass loss to <0.3 mg/cm² in cyclic oxidation tests at 1000°C.
Thermal Fatigue Durability Low thermal expansion coefficient of 13.4 µm/m·°C reduces stress accumulation in components subjected to frequent heating and cooling cycles.
Enhanced Structural Stability Dual-phase strengthening from γ′ (Ni₃Al, Ni₃Ti) and Mo-rich carbides improves resistance to grain boundary sliding, critical for fatigue-exposed rotating parts and fasteners.
CNC Machining Challenges and Solutions for Nimonic 86
Machining Challenges
High Hardness and Abrasiveness
Gamma prime and molybdenum-rich phases accelerate flank wear and crater formation on uncoated carbide tools.
Poor Heat Dissipation
Low thermal conductivity causes cutting zone temperature buildup, leading to thermal expansion and dimensional drift.
Work Hardening
The alloy surface rapidly hardens during machining, requiring high rigidity and sharp tools to maintain tolerance.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Fine-grain carbide (K30), CBN inserts for finishing | High-temperature wear resistance |
Coating | AlTiN or TiSiN (3–5 µm PVD) | Protects against heat and galling |
Geometry | Positive rake, honed edge (~0.05 mm) | Lowers cutting force and vibration |
Cutting Parameters (ISO 3685 Compliant)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 10–16 | 0.20–0.30 | 1.5–2.5 | 100–120 |
Finishing | 25–40 | 0.05–0.10 | 0.3–1.0 | 120–150 |
Surface Treatment for Machined Nimonic 86 Parts
Hot Isostatic Pressing (HIP)
HIP improves fatigue strength by >20% and eliminates internal porosity. Typical processing conditions include 1100°C and 100–150 MPa for 2–4 hours, ensuring 100% densification for structural components.
Heat Treatment
Heat Treatment involves solution annealing at ~1120°C followed by aging at 850–870°C to maximize γ′ precipitation. This process improves creep resistance and dimensional stability in long-term service.
Superalloy Welding
Superalloy Welding using matching filler metal (e.g., ERNiCrCoMo-1) ensures weld strength >90% of base metal and minimal cracking in pressure-retaining joints.
Thermal Barrier Coating (TBC)
TBC Coating applies a 100–300 µm yttria-stabilized zirconia (YSZ) layer via APS or EB-PVD methods, reducing substrate temperatures by up to 200°C in turbine components.
Electrical Discharge Machining (EDM)
EDM enables feature tolerances of ±0.005 mm on hardened sections without inducing thermal stress, ideal for cooling holes and thin-walled structures.
Deep Hole Drilling
Deep Hole Drilling with L/D ratios >30:1 ensures straightness <0.3 mm/m and Ra <1.6 µm, suitable for cooling channels in high-temperature hardware.
Material Testing and Analysis
Material Testing includes creep rupture validation at 850°C/1000h, XRD phase analysis, SEM microstructure review, and ultrasonic flaw detection to ASME standards.
Industry Applications of Nimonic 86 Components
Aerospace Turbine Engines: Turbine blades, vanes, and disk components subjected to extreme thermal and mechanical stress.
Power Generation: Combustors, transition ducts, and structural bolting in gas turbines and high-efficiency heat recovery systems.
Nuclear Energy Systems: Springs, valve internals, and spacers used in high-radiation, high-pressure reactor environments.
Automotive Performance Systems: Exhaust brackets, turbo components, and thermal shields requiring oxidation and fatigue resistance.
Industrial Heating Equipment: Retorts, radiant tubes, and heat-treating fixtures exposed to temperatures up to 1000°C.
FAQs
What are the optimal CNC machining techniques to handle the hardness and abrasiveness of Nimonic 86 for high-precision parts?
How can tool wear be minimized when machining Nimonic 86 for turbine blades and other high-temperature components?
What specific heat treatment processes are recommended for Nimonic 86 to ensure maximum strength and stability at temperatures exceeding 850°C?
How does Nimonic 86 perform in CNC machining compared to other Nimonic alloys for applications like gas turbines and power plants?
What is the typical lead time for machining complex Nimonic 86 parts, such as turbine vanes or fasteners, with high tolerance requirements?
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