Nimonic 90 vs Nimonic 80A: Key Differences & Selection Guide

Nimonic 90 (UNS N07090 / W.Nr. 2.4632) and Nimonic 80A (UNS N07080 / W.Nr. 2.4631 / often just called Nimonic 80 or Nimonic 80A) are both γ′-precipitation hardened Ni–Cr–Co–Ti–Al superalloys​ originally developed by Henry Wiggin (UK) for 650–870°C creep-resistant turbine components. They share the same base strengthening mechanism — coherent γ′ [Ni₃(Al,Ti)] precipitation — but differ in cobalt content, titanium/aluminum ratio, allowable stress-rupture capability, and typical product form emphasis.

This article provides a rigorous side-by-side comparison to guide alloy selection between these two classic Nimonic grades.

1. Nominal Chemistry Comparison

Key takeaway:​ The presence of 15–18% Co in Nimonic 90​ is the principal metallurgical differentiator — it retards γ′ coarsening, elevates γ′ solvus, and improves creep-rupture strength particularly at 750–870°C. Nimonic 80A is essentially Co-free (< 2%).

2. Heat Treatment & Aging Practice

→ Both require solution quench + aging; Nimonic 90's higher solution and double-aging are tuned for max. stress-rupture. Nimonic 80A sometimes used with single-stage 700°C aging in less critical apps.

3. Typical Mechanical Properties (Aged Condition)

Room Temperature (Aged):

Elevated-Temperature Tensile (Aged — Typical):

4. Creep / Stress-Rupture Comparison (Typical Estimates)

→ Nimonic 90 shows clearly superior stress-rupture at 750–870°C​ due to Co-enhanced γ′ stability and slightly higher γ′ volume.

→ Nimonic 80A is acceptable for lower stressed / lower T (≤ 700–730°C design) turbine blades or fasteners​ where cost/spec legacy favors it.

5. Oxidation & Environmental Resistance

• Both form Cr₂O₃ scales (Cr ≈ 19.5%); Nimonic 90's minor Al (1.0–2.0%) can give a trace Al₂O₃ sub-layer → very slightlybetter scale adherence at > 950°C vs. 80A (Al 1.0–1.8% also present in 80A; difference minimal).

• Continuous oxidation limit for both ≈ 1040°C (1900°F) in static air.

• Sulfidation / hot corrosion: similar (Ni-base, Cr≈20%); Co-free in both → no Co-base sulfide advantage.

6. Weldability & SAC Susceptibility

→ Neither is a "weld-friendly sheet alloy"; — both are forged/machined part alloys​ (blades, vanes, springs). Differences in weldability are second-order vs. the creep/strength distinction.

7. Typical Applications by Grade

8. Selection Decision Guide

Is the design metal temperature > 730–750°C AND stress-rupture @ 750°C > 200 MPa required?
 ├─ YES → ✅ Specify Nimonic 90 (N07090)
 │          Reason: Co ~18% → γ′ solvus ↑ → superior 750–870°C creep/rupture
 └─ NO  → Is the drawing / legacy spec calling out Nimonic 80A (N07080)?
       ├─ YES & acceptable life at ≤ 700–730°C → ✅ Nimonic 80A (cost/avail legacy)
       ├─ YES but needs 750°C+ performance → Upgrade to Nimonic 90 (verify DWG allow)
       └─ NO  → Re-evaluate: maybe Nimonic 263 (welded sheet), Inconel 718 (disc/bolt ≤650°C),
                 Hastelloy X (low stress combustor), Haynes 188 (cyclic oxidation >950°C)

9. Summary Comparison Table

10. Conclusion

• Nimonic 90 (UNS N07090 / W.Nr. 2.4632)​ is the higher-performance evolution of Nimonic 80A, distinguished primarily by 15–18% Co​ which raises γ′ solvus and improves creep-rupture strength in the 750–870°C range. It is the preferred choice for modern turbine blades/NGVs and high-temp springs when design temperature exceeds ~730°C or stress-rupture requirements are demanding.

• Nimonic 80A (UNS N07080 / W.Nr. 2.4631)​ remains in use for legacy aero-engine MRO, lower-stressed blades/vaned < 730°C, and fasteners​ where original drawing specifies it and upgraded performance is not required.

• Neither alloy is intended for large welded thin-wall fabrications (that role belongs to Nimonic 263 or Hastelloy X in the Nimonic family context).