Overview
ЭИ698 (ХН77ТЮР-ВД) is the Russian equivalent of the world's most widely used superalloy — Inconel 718 (UNS N07718 / 2.4668). This precipitation-hardenable nickel-iron-chromium alloy is strengthened by both gamma prime (γ') and gamma double-prime (γ″) phases, with niobium as the key strengthening element. With outstanding strength and creep resistance to 650°C, it is the workhorse material for aerospace turbine discs, shafts, and high-temperature structural components.
Chemical Composition
| Element | ЭИ698 / Inconel 718 |
|---|---|
| Nickel (Ni) | 50–55% |
| Chromium (Cr) | 17–21% |
| Iron (Fe) | Balance |
| Niobium (Nb) | 4.75–5.5% |
| Molybdenum (Mo) | 2.8–3.3% |
| Titanium (Ti) | 0.65–1.15% |
| Aluminum (Al) | 0.2–0.8% |
| Cobalt (Co) | ≤ 1.0% |
| Carbon (C) | ≤ 0.08% |
| Density | 8.19 g/cm³ |
Mechanical Properties (AMS 5662)
| Property | Room Temperature | 650°C |
|---|---|---|
| Tensile Strength (Rm) | ≥ 1240 MPa | ≥ 1000 MPa |
| Yield Strength (Rp0.2) | ≥ 1034 MPa | ≥ 827 MPa |
| Elongation | ≥ 12% | ≥ 6% |
| 100-hr Creep Rupture (650°C) | ≥ 690 MPa | |
| Fatigue Strength 650°C (10⁷ cycles) | ~340 MPa | |
Heat Treatment — Double Aging
- Solution Annealing: 950–980°C, 1 hour, air cool
- First Aging: 710–730°C, 8 hours, furnace cool to 620°C at ≤ 50°C/hour
- Second Aging: 610–630°C, 8 hours, air cool
This two-stage aging precipitates both γ' Ni₃(Al,Ti) and γ″ Ni₃Nb, achieving the alloy's signature high strength.
International Equivalents
| Standard | Designation |
|---|---|
| GOST (Russia) | ЭИ698 / ХН77ТЮР-ВД |
| GB (China) | GH4169 |
| UNS (USA) | N07718 |
| EN/DIN | 2.4668 (NiCr19Fe19Nb5Mo3) |
| AMS | 5662, 5663, 5664 |
| ASTM | B637 (bar/forging) |
ЭИ698 vs ЭИ698-ВД — Triple Melt
For critical aerospace applications, ЭИ698-ВД (Vacuum Double Melt) is produced via VIM (Vacuum Induction Melting) followed by VAR (Vacuum Arc Remelting) or ESR (Electroslag Remelting). For the most demanding turbine disc applications, a triple melt process (VIM + ESR + VAR) is specified under AMS 5662/5663, ensuring:
- Ultra-low gas content (O, N, H)
- Superior micro-cleanliness (minimal non-metallic inclusions)
- Enhanced fatigue life
- Maximum property consistency
Aerospace Applications
- Turbine discs and compressor discs — to 650°C
- Turbine shafts
- High-temperature fasteners (bolts, studs)
- Nozzle guide vanes
- Gearbox housings
- Engines: GE CF6, Pratt & Whitney PW4000, SaM146, PS-90A (Russian)
Weldability
Inconel 718 has limited weldability — it is susceptible to HAZ cracking and strain-age cracking. Preferred methods include TIG (GTAW) with ERNiFeCr-2 filler, electron beam welding (EBW), and friction welding. Post-weld full double aging is mandatory. SMAW is not recommended for aerospace components.