Nimonic 75
Introduction to Nimonic 75
Nimonic 75 is a nickel-chromium-based superalloy known for its excellent oxidation resistance, moderate strength, and outstanding thermal stability at temperatures up to 1000°C. Originally developed for gas turbine components, it has since been widely adopted in aerospace, heat treatment, and nuclear industries, where reliable mechanical performance in high-temperature and oxidizing environments is essential.
Due to its balanced composition and relatively low strengthening additions compared to other Nimonic grades, Nimonic 75 is easier to fabricate and machine. It is often formed, welded, and precision-finished via CNC machining to produce tight-tolerance components such as brackets, exhaust structures, furnace parts, and control hardware.
Chemical, Physical, and Mechanical Properties of Nimonic 75
Nimonic 75 (UNS N06075 / W.Nr. 2.4951 / ASTM B409, B462) is a solid-solution strengthened alloy with a simple Ni-Cr matrix designed for oxidation resistance and dimensional stability in thermal cycling environments.
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Nickel (Ni) | Balance (≥76.0) | Base element for corrosion resistance and thermal stability |
Chromium (Cr) | 18.0–21.0 | Provides oxidation resistance through Cr₂O₃ scale formation |
Iron (Fe) | ≤5.0 | Residual element; enhances strength and cost-efficiency |
Titanium (Ti) | 0.2–0.6 | Enhances creep and rupture strength at high temperature |
Manganese (Mn) | ≤1.0 | Improves hot workability |
Silicon (Si) | ≤1.0 | Assists in oxidation resistance |
Carbon (C) | ≤0.08 | Controls carbide precipitation and creep properties |
Copper (Cu) | ≤0.5 | Limited to prevent hot shortness |
Sulfur (S) | ≤0.015 | Minimizes hot cracking during welding |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 8.37 g/cm³ | ASTM B311 |
Melting Range | 1345–1380°C | ASTM E1268 |
Thermal Conductivity | 11.0 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.02 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 | 205 GPa at 20°C | ASTM E111 |
Mechanical Properties (Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 760–880 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 300–370 MPa | ASTM E8/E8M |
Elongation | ≥35% | ASTM E8/E8M |
Hardness | 150–190 HB | ASTM E10 |
Creep Rupture Strength | 140 MPa at 800°C (1000h) | ASTM E139 |
Oxidation Resistance | Excellent up to 1000°C | ASTM G111 |
Key Characteristics of Nimonic 75
Superior Oxidation Resistance: Withstands prolonged exposure to oxidizing atmospheres and thermal cycling up to 1000°C.
Good Formability and Weldability: Easier to process than precipitation-hardened superalloys; suitable for welding and CNC machining in complex forms.
Stable Mechanical Properties at High Temperatures: Maintains dimensional stability and low creep rates in components exposed to heat for extended periods.
Corrosion Resistance in Mild Chemical Environments: Offers resistance to diluted acids, salt spray, and atmospheric corrosion.
CNC Machining Challenges and Solutions for Nimonic 75
Machining Challenges
Work Hardening
The alloy’s tendency to harden rapidly during cutting can increase tool wear and dimensional inaccuracies.
Built-up Edge (BUE)
Adhesion of workpiece material to the cutting tool under high-friction conditions affects surface quality and tool life.
Moderate Thermal Conductivity
This leads to heat concentration at the tool-work interface, increasing the risk of microchipping and surface damage.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Fine-grain carbide (K20–K30) or coated HSS tools | Maintains edge stability under heat |
Coating | AlTiN or TiAlCrN (3–5 µm PVD) | Enhances heat resistance and reduces BUE |
Geometry | Positive rake, 0.03–0.05 mm edge hone | Reduces cutting forces and improves surface finish |
Cutting Parameters (ISO 3685 Compliant)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 20–30 | 0.20–0.25 | 1.5–2.5 | 70–100 |
Finishing | 40–55 | 0.05–0.10 | 0.5–1.0 | 100–150 |
Surface Treatment for Machined Nimonic 75 Parts
Hot Isostatic Pressing (HIP)
HIP removes internal porosity and improves fatigue and creep life in cast or AM parts.
Heat Treatment
Heat Treatment enhances grain uniformity and mechanical stability at service temperatures above 800°C.
Superalloy Welding
Superalloy Welding enables robust joints using matching Nimonic filler rods for pressure- and heat-resistant assemblies.
Thermal Barrier Coating (TBC)
TBC Coating provides protection against high-velocity gas or radiant heat environments in aerospace applications.
Electrical Discharge Machining (EDM)
EDM enables high-precision features in hardened or hard-to-reach sections without thermal distortion.
Deep Hole Drilling
Deep Hole Drilling ensures concentricity and smooth finishes in cooling or fluid passages with L/D ratios above 15:1.
Material Testing and Analysis
Material Testing includes tensile, creep, fatigue, chemical analysis, microstructure evaluation, and NDT.
Industry Applications of Nimonic 75 Components
Aerospace and Gas Turbine Components
Combustion chambers, brackets, seals, and afterburner assemblies operating under sustained heat and oxidizing gases.
Industrial Heat Treatment
Fixtures, trays, and supports in high-temperature furnaces exposed to cycling and scale formation.
Power Generation and Nuclear Systems
Thermal stability and creep resistance are critical to bolting, springs, and shielding components.
Automotive and Engine Systems
Exhaust components, turbocharger support brackets, and manifold structures.
FAQs
What tool materials and coatings are optimal for CNC machining Nimonic 75 components?
How does Nimonic 75 compare to Nimonic 80A in terms of strength and machinability?
Can EDM be used for tight-tolerance features in Nimonic 75 parts?
What surface treatments are recommended for Nimonic 75 parts in furnace or turbine environments?
What industries most commonly use CNC-machined Nimonic 75 components?
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