What AMS 5940 Covers: Scope and Definition
AMS 5940 is an SAE International Aerospace Material Specification (AMS) that governs a cobalt-nickel-iron (Co-Ni-Fe) precipitation-hardenable alloy — commercially designated Alloy 783 — in the product forms of bars, forgings, flash-welded rings, and stock for forging or heading. The current revision, AMS5940E (2024), specifies mandatory multiple melt practice, composition limits, heat treatment requirements, and minimum room-temperature mechanical property values for this alloy system.
AMS 5940 was first issued in September 1996 and has been revised five times. The alloy was originally developed by Carpenter Technology Corporation (Carpenter Technology®) and belongs to a small, specialized class of engineering alloys not designed for maximum temperature capability — where nickel superalloys such as UNS N07718 alloy (AMS 5663) or other high-temperature nickel alloys dominate — but for a precisely engineered combination of controlled low CTE, high tensile and fatigue strength, and oxidation resistance to 1,300°F (704°C).
The critical design driver for this alloy is dimensional stability in mixed-material assemblies containing titanium. In gas turbine compressor sections, outer casings are typically titanium alloy (Ti-6Al-4V). Structural forged components inside the casing must expand at the same rate as the titanium across wide thermal cycles. AMS 5940's CTE is engineered to match titanium's expansion behavior, eliminating blade-tip clearance variability without coatings or active clearance control systems.
AMS 5940 Specification Revision History
AMS5940 — Original Issue
Established the Co-Ni-Fe alloy composition limits, mandatory VIM+VAR melt practice, solution heat treatment windows, double-aging cycle requirements, and baseline room-temperature mechanical property minimums.
AMS5940A — First Revision
Refined solution heat treatment temperature tolerances. Added hold time calculation requirements for sections above 50 mm effective thickness.
AMS5940B — Second Revision
Updated tensile property minimums for bar vs. forging product forms. Enhanced traceability requirements for heat lot documentation.
AMS5940C — Third Revision
Aligned pyrometry requirements with AMS 2750. Clarified mechanical test frequency per heat lot delivered to a single purchaser order.
AMS5940D — Fourth Revision (Five-Year Review)
Updated niobium designation from "Cb" to "Nb(Cb)" to align with current IUPAC nomenclature. Refined purchaser notification clauses for deviations.
AMS5940E — Current Active Revision ✓ Active
Most recent issue. Prohibits all unauthorized exceptions to specification requirements. Strengthens purchaser notification requirements and updates format per current SAE AMS editorial standards. All purchase orders and MTCs must reference AMS5940E.
AMS 5940 (Alloy 783) Chemical Composition: Element-by-Element Analysis
Every alloying element in AMS 5940 serves multiple simultaneous metallurgical objectives. Unlike most high-temperature alloys where composition optimizes a single property, Alloy 783 must simultaneously achieve controlled CTE, precipitation hardenability, and oxidation resistance — a combination that tightly constrains the permissible composition space.
| Element | Nominal % | Primary Metallurgical Role | Quantity Rationale |
|---|---|---|---|
| Cobalt (Co) | ~34% | Matrix phase; dominant CTE controller; FCC structure stabilizer | Co content is the primary driver of low CTE via the magnetovolume effect in the Co-Ni-Fe ternary system. The 34% level places the alloy at the composition point yielding minimum CTE while maintaining adequate strength and processability. |
| Nickel (Ni) | ~28% | Austenite matrix stabilizer; enables γ' and γ'' precipitation hardening | 28% Ni enables formation of Ni₃Al (γ') and Ni₃Nb (γ'') precipitates. Below ~25% Ni, precipitation hardening response is insufficient. Above ~32%, CTE begins to rise outside the titanium-match window. |
| Iron (Fe) | ~25.5% | Matrix balance element; tunes CTE alongside Co and Ni | Fe is selected to reach the CTE minimum in the Co-Ni-Fe ternary at minimum alloy cost. Substituting Fe with more Co or Ni raises material cost without CTE benefit. |
| Aluminum (Al) | 5.5% | γ' (Ni₃Al) precipitate former; protective Al₂O₃ oxidation scale | 5.5% Al generates a volume fraction of γ' sufficient for meaningful strength improvement. Simultaneously forms protective alumina scale that compensates for the intentionally low Cr content at service temperature. |
| Niobium (Nb) | 3.0% | γ'' (Ni₃Nb) precipitate former; grain boundary pinning via carbides/nitrides | Nb's γ'' precipitates coarsen more slowly than γ' at high temperature, improving creep resistance. Nb also forms NbC and Nb(C,N) particles that pin grain boundaries during hot forging, preventing abnormal grain growth. |
| Chromium (Cr) | 3.0% | Supplementary oxidation resistance; minor solid-solution hardening | Only 3% Cr is used — far below the 12–18% in most superalloys. Higher Cr disrupts the CTE minimum in the Co-Ni-Fe system. Al₂O₃ formation from the 5.5% Al compensates for the reduced Cr₂O₃ protection. |
| Boron (B) | 0.008% | Grain boundary cohesion; hot ductility enhancement | Trace B segregates preferentially to grain boundaries, strengthening cohesion and reducing hot-cracking susceptibility during forging. The 0.008% level is tightly controlled — excess B above ~0.015% triggers hot tearing; deficiency leaves boundaries vulnerable to fatigue initiation. |
The Co-Ni-Fe Low-Expansion Mechanism Explained
AMS 5940's low CTE derives from a principle related to the Invar effect, first discovered in 1896 by Charles Édouard Guillaume in iron-nickel alloys near the 36% Ni composition. In Invar-type alloys, the spontaneous volume magnetostriction of the ferromagnetic state opposes normal lattice thermal expansion — the two effects cancel partially, producing an anomalously low or near-zero net CTE.
In the Co-Ni-Fe ternary system used in Alloy 783, a similar but distinct magnetovolume compensation occurs at the 34Co-28Ni-25.5Fe composition, producing a mean CTE of 13.9–16.4 × 10⁻⁶/°C across the RT–700°C range. This closely tracks the CTE of Ti-6Al-4V (approximately 8.6–9.7 × 10⁻⁶/°C) — the gap is small enough that differential thermal expansion between AMS 5940 structural components and titanium casings remains within tight engineering tolerances across full thermal cycles.
Fe-36Ni low-expansion alloy (commercially known as Invar® 36, a registered trademark of ArcelorMittal; 64% Fe, 36% Ni) achieves even lower CTE (~1.0–1.5 × 10⁻⁶/°C at room temperature) but fails in structural aerospace use because: (1) it cannot be precipitation-hardened to useful strength levels; (2) it oxidizes rapidly above 300°C; (3) it completely loses its low-expansion behavior above its Curie temperature (~260°C). AMS 5940 accepts a modestly higher CTE in exchange for 4× the tensile strength and 440°C more usable temperature range — the correct trade for all load-bearing aerospace applications above 260°C.
AMS 5940 Mechanical Properties and CTE Data
All AMS 5940 property values below apply to the solution heat treated + double aged condition per AMS5940E. Properties are for forging product form; verify exact minimums in the current specification table for your product form (bar, ring, or forging stock).
Coefficient of Thermal Expansion (CTE) vs. Temperature
| Temperature Range | Mean CTE (×10⁻⁶/°C) | Mean CTE (×10⁻⁶/°F) | Engineering Significance |
|---|---|---|---|
| RT to 100°C (212°F) | 13.9 | 7.7 | Close match to Ti-6Al-4V (~8.6 × 10⁻⁶/°C); compressor section operating range |
| RT to 200°C (392°F) | 14.4 | 8.0 | Better CTE match to Ti than UNS N07718 alloy (AMS 5663) at this range |
| RT to 400°C (752°F) | 14.8 | 8.2 | Intermediate compressor temperature range |
| RT to 600°C (1,112°F) | 15.3 | 8.5 | High-temperature compressor / steam turbine range |
| RT to 700°C (1,292°F) | 16.4 | 9.1 | Upper structural service limit per AMS5940E |
Ti-6Al-4V mean CTE from RT to 300°C: approximately 8.6 × 10⁻⁶/°C (4.8 × 10⁻⁶/°F). AMS 5940 at the same range: approximately 14.4 × 10⁻⁶/°C (8.0 × 10⁻⁶/°F). For comparison, UNS N07718 alloy (AMS 5663) at the same range: approximately 13.0 × 10⁻⁶/°C (7.2 × 10⁻⁶/°F). While none of these match titanium precisely, AMS 5940 tracks the titanium CTE curve more closely than any alternative precipitation-hardenable superalloy across the full operational temperature range of 0–700°C — making it the only engineered solution for tight-tolerance Ti-cased compressor seal ring applications.
Engineers specifying AMS 5940 for a new program can request material data sheets and production capability details for custom AMS 5940 forgings to specification, including minimum order quantities and lead times for bars, rings, and open die shapes.
AMS 5940 Heat Treatment: Solution Annealing and Double Aging
AMS 5940 is a precipitation-hardenable alloy. Its final mechanical properties are entirely determined by correct execution of the two-stage heat treatment specified in AMS5940E Section 3.5. Incorrect heat treatment — including incorrect temperatures, hold times, quench rates, or aging temperatures — is the primary root cause of mechanical property shortfalls in AMS 5940 forgings at incoming inspection.
Solution Heat Treatment — Dissolve All Precipitate Phases
Heat to 1,010–1,038°C (1,850–1,900°F) in an inert atmosphere or vacuum furnace. Hold for 1 hour per 25 mm (1 inch) of maximum effective section thickness, minimum 1 hour total hold. This fully dissolves all γ' (Ni₃Al) and γ'' (Ni₃Nb) precipitates into the FCC austenite matrix, resetting the microstructure. Inert atmosphere or vacuum prevents aluminum depletion at the surface (Al oxidizes readily at 1,010°C). Furnace must be qualified per AMS 2750 Class 2 (±8°C uniformity).
Rapid Quench to Room Temperature
After the solution hold, cool rapidly to room temperature using oil quench or forced air, depending on section thickness and allowable distortion. Cooling must be fast enough to suppress re-precipitation during the cool — typically faster than 8°C/min through the γ'' nose temperature range (~800–850°C). Slow cooling or air cooling from solution temperature without subsequent aging will yield partially re-precipitated, inhomogeneous microstructure with below-minimum properties.
Primary Aging — High-Density Precipitate Nucleation
Age at 718°C ± 8°C (1,325°F ± 15°F) for 8 hours. This temperature is above the γ'' coarsening onset but below the γ'' dissolution temperature, producing nucleation of fine γ' and γ'' precipitates at maximum number density. The precipitate size at this stage is typically 10–30 nm — the optimum range for dislocation cutting resistance (peak tensile strength) and fatigue crack initiation resistance.
Controlled Cool to Secondary Aging Temperature
Cool at a controlled rate of 55°C/hr ± 5°C/hr (100°F/hr ± 10°F/hr) from 718°C to 621°C (1,150°F). This controlled cool is critical — rapid quench from primary aging temperature produces a unimodal fine precipitate distribution that lacks creep resistance; controlled cool produces a bimodal distribution with both fine precipitates (tensile strength) and coarser precipitates (creep strength). Rate control is also necessary to prevent thermal gradient stresses in forgings above 150 mm section thickness.
Secondary Aging — Bimodal Precipitate Optimization
Hold at 621°C (1,150°F) for 8 hours, then air cool to room temperature. Secondary aging at the lower temperature grows the larger γ' particles seeded during the controlled cool, while maintaining the fine γ'' population from primary aging. The resulting bimodal precipitate distribution — documented to yield the optimum strength/creep/ductility balance for AMS 5940 — is not achievable with a single-temperature aging cycle.
Post-Aging Inspection and Certification
After the complete cycle, all AMS 5940 forgings at Jiangsu Liangyi undergo: hardness verification (38–44 HRC per heat lot); tensile coupon testing per AMS5940E Section 4.5 (one coupon per heat per product form); and ultrasonic inspection per purchaser-specified acceptance criteria (ASTM A 388 or equivalent). Full heat treatment records — cycle chart, furnace calibration certificate, load configuration — are archived and referenced on the EN 10204 3.1 MTC.
AMS 5940 aging is sensitive to temperature uniformity. Furnace qualification per AMS 2750 Class 2 (±8°C throughout the qualified working zone) is required. Thermocouples must be calibrated with current calibration certificates. Batch loads must be calculated to maintain uniform temperature across all charge positions before programming the cycle. Overshooting 718°C primary aging by more than 8°C risks dissolving γ'' back into solution; undershooting delays nucleation and produces below-minimum tensile strength.
Why AMS 5940 Mandates VIM+VAR Multiple Melting
Per AMS5940E Section 3.1: "Material shall be multiple melted. If consumable electrode remelting is not performed in vacuum, electrodes which have been produced by vacuum induction melting (VIM) shall be used for remelting." Compliant melt routes: VIM+VAR (Vacuum Induction Melting + Vacuum Arc Remelting) or VIM+ESR (VIM + Electroslag Remelting). Single-melt practice by EAF, AOD, or any non-vacuum process is a specification non-conformance.
Metallurgical Reasons for the Mandatory Dual-Melt Requirement
AMS 5940's 5.5% aluminum content creates processing challenges impossible to resolve with single-melt practice:
- Aluminum oxide and nitride inclusions: In conventional EAF or AOD melting, Al reacts aggressively with atmospheric O₂ and N₂ to form Al₂O₃ and AlN inclusions. These inclusions, if present in forgings, act as fatigue crack initiation sites — catastrophic in gas turbine applications. VIM melting in high vacuum (<0.01 Pa) prevents these reactions entirely.
- Cobalt and niobium macro-segregation: Large ingots (>300 mm diameter) solidified conventionally develop centerline concentration gradients of Co, Nb, and Al due to dendritic solidification and selective solute partitioning. These gradients create local zones with excess γ'' precipitation (brittle) or deficient precipitation (soft) that heat treatment cannot homogenize. VAR remelting refines the solidification structure and reduces segregation ratios by 3–5× compared to air-melt ingots.
- Dissolved gas content: High hydrogen content (>2 ppm) in nickel alloys causes hydrogen-assisted cracking under stress. VIM degassing routinely achieves <0.5 ppm H in the final electrode; single-melt EAF cannot achieve this without separate vacuum degassing equipment.
- Sulfide inclusion morphology: ESR practice, when selected over VAR, provides flux-based slag refining that modifies MnS and other sulfide inclusions from elongated stringer morphology (notch effect, reduced ductility) to globular form — improving transverse ductility and fatigue life in forgings loaded perpendicular to the forging direction.
Require the melt route explicitly on every purchase order and verify it on the MTC: look for furnace charge records showing VIM heat number and VAR/ESR remelt records with electrode weight and remelting parameters. Accept: VIM+VAR or VIM+ESR. Reject: EAF only, AOD only, EAF+VD without VAR/ESR remelting. Per AMS5940E, the melt practice is not subject to deviation without written purchaser authorization — do not accept verbal assurances.
AMS 5940 vs. UNS N07718 (AMS 5663) vs. Fe-36Ni Low-Expansion Alloy: Selection Guide
These three alloy types appear together in aerospace material selection decisions for components requiring elevated-temperature performance, dimensional stability, or both. They solve fundamentally different engineering problems, and selecting the wrong one has significant consequences for blade clearance, fatigue life, or structural integrity.
| Property | AMS 5940 — Alloy 783 | UNS N07718 (AMS 5663) commonly known as Inconel® 718 |
Fe-36Ni Alloy (ASTM F1684) commonly known as Invar® 36 |
|---|---|---|---|
| Alloy System | Co-Ni-Fe (ternary) | Ni-Fe-Cr-Nb | Fe-Ni (binary, 64/36) |
| UTS min (ksi / MPa) | 195 / 1,344 Highest | 185 / 1,276 | 75–90 / 517–621 (not hardenable) |
| 0.2% YS min (ksi) | 165 / 1,138 | 150 / 1,034 | 30–45 (soft annealed) |
| Mean CTE RT→300°C (×10⁻⁶/°C) | ~14.4 Best Ti-match | ~13.0 | ~1.5 (RT only; loses at 260°C) |
| CTE match to Ti-6Al-4V? | Yes — closest available ✓ | Marginal | No — CTE too low at ambient; none above 260°C |
| Max structural service temp | 704°C (1,300°F) Highest | ~650°C (1,200°F) | ~260°C (500°F) — Curie limit |
| Oxidation resistance | Good — Al₂O₃ scale to 704°C | Excellent — Cr₂O₃ scale | Poor above 300°C |
| Precipitation hardenable | Yes — dual γ' + γ'' | Yes — primary γ'' (Ni₃Nb) | No |
| Weldability | Limited (5.5% Al → HAZ cracking risk) | Good with pre/post-heat | Good |
| Melt practice requirement | VIM+VAR or VIM+ESR (mandatory) | VIM+VAR or VIM+ESR (standard) | EAF+AOD (standard) |
| Density (g/cm³) | 8.07 | 8.19 | 8.05 |
| Relative material cost | High (Co price-sensitive) | Moderate | Low–Moderate |
Application-Based Decision Guide
- Choose AMS 5940 (Alloy 783) when the component must maintain dimensional compatibility with a titanium casing or structure AND carry significant structural load at temperatures between ambient and 704°C. Gas turbine compressor seal rings are the prototypical application.
- Choose UNS N07718 alloy (AMS 5663) when maximum temperature capability above 650–700°C, weldability for repair operations, or lower material cost are the driving requirements and some CTE mismatch with titanium is acceptable (with coatings or clearance compensation).
- Choose Fe-36Ni low-expansion alloy only when the application is below 260°C, absolute minimum CTE is the sole requirement, and the part carries no significant structural load. Optical metering rods and reference length standards are typical uses.
AMS 5940 Forging Applications: Where Alloy 783 Is Used
AMS 5940 (Alloy 783) appears in components where the simultaneous requirements of CTE control and elevated-temperature structural performance cannot be separated. The applications below have documented field performance history with this alloy.
Gas Turbine Compressor Seal Rings
Primary application. Outer seal rings in high-pressure compressor sections must CTE-match titanium blisks and OGVs across thermal cycles from ground-cold (−40°C) to flight-hot (+550°C). AMS 5940 eliminates tip clearance variability that causes either aerodynamic efficiency loss or destructive blade-tip rub.
Steam Turbine Components
Valve stems, control rings, and shroud segments in medium-temperature steam turbines up to ~650°C. Higher strength and oxidation resistance than Type 422 stainless steel (AMS 5655) at comparable temperature ranges, extending maintenance intervals in power generation plants.
Precision Aerospace Structural Frames
Metering structures, mirror mounts, and sensor payload frames in aerospace equipment where dimensional stability across ground-to-orbit or day-night thermal cycles (>200°C Δt) is critical for measurement accuracy or antenna pointing precision.
Flight Control Actuator Housings
Actuator housings and guide rods installed near aircraft engines where thermal cycling from cold ground conditions to flight-hot must not introduce positional errors in primary flight control surfaces. CTE-matched housing prevents differential expansion between actuator shaft and housing bore.
Industrial Gas Compressor Rings
High-performance compressor seal rings in gas processing, petrochemical, and LNG plants, particularly in mixed-material assemblies where differential CTE between ring and casing materials at steady-state operating temperature creates fretting fatigue failure under load cycling.
High-Temperature Energy Systems
Emerging application in solid-oxide fuel cell (SOFC) structural components and advanced power generation systems where repeated thermal cycling between ambient and 700°C operating temperatures over a 25–30 year service life demands CTE-controlled materials to prevent interfacial delamination and seal failure.
Need AMS 5940 (Alloy 783) Forgings?
ISO 9001:2015 certified manufacturer. Open die forgings & seamless rolled rings, 30 kg – 30,000 kg. Factory-direct quote within 24 hours.
Get a Free Quote →How to Source AMS 5940 Forgings: What to Look for in a Manufacturer
When sourcing AMS 5940 components, verify that the supplier controls the full production chain in-house: VIM+VAR billet sourcing, hot die forging and ring rolling, AMS 2750-compliant heat treatment furnaces, in-house chemical analysis per ASTM E 354, and ultrasonic inspection before shipment. Batch sizes should range from small prototype quantities to large structural rings (18 tonnes+), and the supplier should provide EN 10204 3.1 Material Test Certificates traceable to the VIM+VAR heat number.
Jiangsu Liangyi Co., Limited is an ISO 9001:2015 certified open die forging manufacturer in Jiangyin, China, with 28+ years of experience producing AMS 5940 components for customers in 50+ countries. For product forms, size ranges, and pricing, see the AMS 5940 forged rings and bars from a certified manufacturer.
| Product Form | Available Size Range | Typical End Applications |
|---|---|---|
| Round Bars and Billets | Ø50 mm – Ø2,000 mm diameter | Valve stems, actuator shafts, further machining stock |
| Seamless Rolled Rings | OD up to Ø6,000 mm; wall from 30 mm | Compressor seal rings, containment rings, flanged housings |
| Forged Discs and Plates | Thickness 50–800 mm | Turbine discs, structural flanges, mounting plates |
| Open Die Forged Blocks | Up to 30,000 kg per piece | Large structural frames, custom pressure vessel bodies |
| Hollow Forgings / Shells | Wall thickness from 50 mm minimum | Pressure housings, cylinders, casing bodies |
| Near-Net-Shape Custom | Per customer engineering drawing | Complex shapes; typically reduces machining time by 30–50% |
All shipments include EN 10204 3.1 Material Test Certificates covering: chemical composition analysis; room-temperature tensile properties per heat lot; hardness verification; complete heat treatment cycle records including furnace calibration reference numbers; and ultrasonic inspection results and acceptance statement. Third-party inspection by SGS, Bureau Veritas, Intertek, or any other customer-nominated independent inspection body can be arranged at our Jiangyin facility prior to shipment.
How to Write an AMS 5940 Purchase Order: Mandatory Line Items
Incomplete or incorrect purchase orders are the leading cause of AMS 5940 supply chain disputes and incoming inspection failures. The table below lists every mandatory purchase order element, with the specification basis for each requirement.
| PO Field | Required Entry | Specification Basis | Consequence of Omission |
|---|---|---|---|
| Specification + Revision | AMS5940E | Always cite current revision (E, 2024) | Supplier may ship to earlier revision with lower property minimums |
| Melt Practice | VIM+VAR or VIM+ESR only | AMS5940E Sec. 3.1 | Risk of receiving single-melt material with inclusions and segregation |
| Heat Treatment Condition | Solution HT + Double Age per AMS5940E §3.5 | AMS5940E Sec. 3.5 | May receive annealed (soft) stock not meeting tensile minimums |
| Product Form | Bar / Forging / Seamless Ring (state explicitly) | AMS5940E Table 1 | Different product forms have different min property values |
| Check Analysis | AMS 2269 check analysis required on finished product | AMS 2269 / AMS5940E Sec. 4.3 | Composition verified only on ingot, not on product you receive |
| MTC Type | EN 10204 3.1 minimum; 3.2 if third-party required | Purchaser requirement | Type 2.2 certificate is not manufacturer-certified — insufficient for aerospace |
| UT Acceptance Class | State explicitly (e.g., ASTM A 388, per drawing) | AMS5940E does not specify UT class | Supplier applies no UT or uses their own lower standard |
| Country of Melt & Mill | State country and mill name if required by your quality plan | Customer / regulatory requirement | Supply chain traceability gap; required by some defense and nuclear procurement standards |
AMS 5940 (Alloy 783) — Frequently Asked Questions
What is AMS 5940 and what does the specification cover?
AMS 5940 is an SAE International Aerospace Material Specification (current revision: AMS5940E, 2024) that covers a cobalt-nickel-iron precipitation-hardenable alloy — commercially known as Alloy 783 — in the product forms of bars, forgings, flash-welded rings, and stock for forging or heading. The specification mandates multiple melt practice (VIM+VAR or VIM+ESR), defines composition limits, specifies the solution heat treatment and double aging cycle, and sets minimum room-temperature tensile property requirements.
What are the minimum mechanical properties of AMS 5940?
Per AMS5940E for forgings in the solution heat treated and double aged condition: Ultimate Tensile Strength (UTS) ≥195 ksi (1,344 MPa); 0.2% Yield Strength ≥165 ksi (1,138 MPa); Elongation ≥8% in 4D gauge length; Reduction of Area ≥15%. Density is 8.07 g/cm³ (0.292 lb/in³). Maximum structural service temperature is approximately 704°C (1,300°F).
What heat treatment is required for AMS 5940 (Alloy 783)?
AMS5940E requires a two-stage heat treatment: (1) Solution anneal at 1,010–1,038°C (1,850–1,900°F) for 1 hour per 25 mm section, with rapid quench to room temperature. (2) Double aging: primary age at 718°C ±8°C for 8 hours, then controlled cool at 55°C/hr to 621°C (1,150°F), hold 8 hours, then air cool. Total aging cycle: approximately 16–18 hours. Furnace must comply with AMS 2750 Class 2 (±8°C).
What is the CTE of AMS 5940 and how does it compare to titanium?
AMS 5940 (Alloy 783) mean CTE: 13.9 × 10⁻⁶/°C at RT–100°C; 14.4 × 10⁻⁶/°C at RT–200°C; 16.4 × 10⁻⁶/°C at RT–700°C. Ti-6Al-4V mean CTE: approximately 8.6 × 10⁻⁶/°C at RT–300°C. AMS 5940 tracks titanium's CTE curve more closely than UNS N07718 alloy (~13.0 × 10⁻⁶/°C), 17-4 PH (~10.8 × 10⁻⁶/°C), or any other precipitation-hardenable superalloy across the full 0–700°C range, making it the engineering-preferred material for Ti-cased gas turbine compressor seal ring applications.
Why must AMS 5940 be multiple melted (VIM+VAR)?
AMS5940E Section 3.1 mandates multiple melt practice because the alloy's 5.5% aluminum content causes severe oxide and nitride inclusion formation under conventional air-melt conditions (EAF or AOD). Additionally, cobalt, niobium, and aluminum segregation during large-ingot solidification creates chemical heterogeneity that cannot be corrected by heat treatment. VIM eliminates dissolved gases (O₂, N₂, H₂) and prevents Al oxidation; VAR or ESR refines the solidification structure to within acceptable macro-segregation limits.
What is the current revision of AMS 5940?
The current active revision is AMS5940E, issued by SAE International in 2024. AMS5940E prohibits unauthorized exceptions and strengthens purchaser notification requirements. All purchase orders, material test certificates, and quality plans for new procurement should reference AMS5940E. Previous revisions (AMS5940A through AMS5940D) are historical and should not be cited on new procurements.
AMS 5940 vs. UNS N07718 alloy (AMS 5663): which should I choose?
Choose AMS 5940 (Alloy 783) when: (1) the component must maintain dimensional compatibility with titanium hardware across thermal cycles; (2) service temperature is up to 704°C; (3) weldability is not required. Choose UNS N07718 alloy (AMS 5663) when: (1) CTE matching to titanium is not the critical design driver; (2) weldability for field repairs is needed; (3) material cost is a constraint. AMS 5940 offers higher UTS (195 ksi vs. 185 ksi), higher max service temperature (704°C vs. ~650°C), and better titanium CTE matching — but at higher material cost and with weldability limitations due to the 5.5% Al content. Note: Inconel® is a registered trademark of Special Metals Corporation.
Key Takeaways: AMS 5940 (Alloy 783)
- AMS 5940 (Alloy 783) is a Co-Ni-Fe precipitation-hardenable alloy governed by SAE AMS5940E (current revision 2024) for bars, forgings, and rings. Nominal composition: ~34% Co, ~28% Ni, ~25.5% Fe, 5.5% Al, 3.0% Nb, 3.0% Cr, 0.008% B.
- Minimum mechanical properties (forgings, aged condition): UTS ≥195 ksi (1,344 MPa), 0.2% YS ≥165 ksi (1,138 MPa), elongation ≥8%, RA ≥15%. Max service temperature: 704°C (1,300°F).
- CTE closely matches Ti-6Al-4V across 0–700°C — making AMS 5940 the only engineering-grade precipitation-hardenable alloy suitable for structural components in titanium-cased assemblies where differential thermal expansion would otherwise cause blade-tip clearance problems or fretting fatigue.
- Heat treatment is mandatory and two-stage: solution anneal at 1,010–1,038°C + double aging (718°C / 8 hr → controlled cool 55°C/hr → 621°C / 8 hr). Furnace must comply with AMS 2750 Class 2.
- VIM+VAR or VIM+ESR multiple melting is non-negotiable per AMS5940E Section 3.1. Single-melt material must be rejected. Require the melt route on the MTC.
- Always specify AMS5940E (the 2024 current revision) on purchase orders and verify on MTCs. Specify melt practice, heat treatment condition, product form, AMS 2269 check analysis, EN 10204 3.1 MTC, and UT acceptance criteria explicitly.
- Jiangsu Liangyi manufactures AMS 5940 open die forgings and seamless rolled rings from 30 kg to 30,000 kg per piece, ISO 9001:2015 certified, with full in-house heat treatment, ASTM E 354 chemical analysis, AMS 2750-compliant calibrated furnaces, and EN 10204 3.1 MTC documentation.