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Haynes 188 (UNS R30188 / W.Nr. 2.4683 / GH5188) is a solid-solution strengthened cobalt-chromium-nickel-tungsten superalloy with 0.04–0.08 % lanthanum (La). It is engineered for continuous oxidation resistance to 1095°C (2000°F) and exceptional oxide-scale adherence under thermal cycling—its defining advantage over Haynes 25 (L-605). This article consolidates the quantitative high-temperature dataset: tensile properties, typical creep-rupture values, oxidation kinetics, and physical constants as a function of temperature, sourced from Haynes International technical bulletins, AMS 5608/5772 references, and ASM Handbook Volume 2 (Properties of Precious and Superalloys).
1. Physical Constants (Temperature Dependent)
|
Property |
20°C |
100°C |
300°C |
600°C |
800°C |
1000°C |
|---|---|---|---|---|---|---|
|
Density |
9.09 g/cm³ (const.) |
— |
— |
— |
— |
— |
|
Elastic Modulus E (GPa) |
214 |
210 |
200 |
178 |
165 |
155 |
|
Mean CTE α (20–T)×10⁻⁶/K |
— |
13.5 |
15.1 |
16.0 |
16.5 |
16.8 |
|
Thermal Conductivity λ (W/m·K) |
19 |
20 |
23 |
26 |
28 |
29 |
|
Specific Heat cp(J/kg·K) |
460 |
470 |
490 |
520 |
545 |
570 |
|
Electrical Resistivity (µΩ·m) |
1.27 |
1.32 |
1.42 |
1.58 |
1.68 |
1.76 |
|
Melting Range |
1300–1360°C (solidus ~1300°C) |
— |
— |
— |
— |
— |
|
Magnetic State |
Paramagnetic (FCC γ) all T |
— |
— |
— |
— |
— |
Note: CTE values are mean coefficients referenced to 20°C. Elastic modulus measured by sonic method (dynamic).
2. Tensile Properties vs. Temperature (Solution-Annealed Sheet/Plate, Typical)
Data below represent typical average values for 1.2–3.2 mm (0.05–0.125 in) sheet in the solution-annealed condition (1175–1230°C → water quench). Minimum values per AMS 5608: Rm ≥ 860 MPa, Rp0.2 ≥ 380 MPa, A ≥ 45 % (thin sheet).
|
Temp (°C) |
Rm (MPa) |
Rp0.2 (MPa) |
Elong. A50mm(%) |
Reduction of Area (%) |
|---|---|---|---|---|
|
20 (RT) |
930–1000 |
430–470 |
48–55 |
50–60 |
|
100 |
900–970 |
415–455 |
47–53 |
50–58 |
|
205 (400°F) |
860–925 |
395–435 |
46–52 |
48–56 |
|
315 (600°F) |
825–890 |
375–415 |
45–51 |
47–55 |
|
425 (800°F) |
785–850 |
355–395 |
44–50 |
46–54 |
|
540 (1000°F) |
720–790 |
310–360 |
40–48 |
44–52 |
|
650 (1200°F) |
625–685 |
270–320 |
38–45 |
42–50 |
|
760 (1400°F) |
525–580 |
230–275 |
35–42 |
40–48 |
|
870 (1600°F) |
380–430 |
175–210 |
30–38 |
38–45 |
|
980 (1800°F) |
260–300 |
130–160 |
28–35 |
35–42 |
|
1095 (2000°F) |
195–230 |
100–125 |
25–32 |
32–40 |
Key observations:
No ductile-to-brittle transition — elongation remains > 25 % even at –196°C (test data: ~50 % RA, 40 % A at LN₂ temp).
Strength retention to 870°C is moderate — suitable for lightly loaded hot-section sheet metal; not a disc or high-stress rotor alloy.
3. Creep-Rupture / Stress-Rupture Typical Values (Reference Only)
Haynes 188 is a solid-solution alloy; creep strength is derived from W and C solutes plus minor M23C6/ M6C at grain boundaries after exposure. Values below are typical Larson-Miller / isothermal rupture data trends — not design allowables per ASME Section II-D (which does not list cobalt alloys in most editions).
|
Test Temp (°C) |
Stress (MPa) |
Rupture Life (approx.) |
Note |
|---|---|---|---|
|
650 |
415 (60 ksi) |
~ 100 h |
— |
|
760 (1400°F) |
275 (40 ksi) |
~ 100 h |
— |
|
815 (1500°F) |
170 (25 ksi) |
~ 100–200 h |
— |
|
870 (1600°F) |
105–110 (15–16 ksi) |
~ 100 h |
Common design check point |
|
870 |
70 (10 ksi) |
~ 1000 h |
Usable life bracket |
|
980 (1800°F) |
34–41 (5–6 ksi) |
~ 100 h |
— |
→ For primary load-bearing > 815°C long-term, consider Inconel 617 or precipitation-hardened Ni-base alloys. Haynes 188 is optimized for self-supported or lightly stressed hot-section sheet (liners, shrouds, nozzles) where oxidation resistance and formability dominate.
4. Oxidation / Corrosion Rate Data (Air / Flue Gas)
4.1 Static Air Oxidation (Continuous Exposure)
|
Temp (°C) |
Time |
Mass Gain (mg/cm²) |
Scale Character |
Service Assessment |
|---|---|---|---|---|
|
870 |
1000 h |
0.15–0.35 |
Adherent Cr₂O₃ (+ trace spinel) |
Excellent |
|
980 |
1000 h |
0.30–0.60 |
Intact, slight darkening |
Good |
|
1095 (2000°F) |
100 h |
0.6–1.2 |
Protective but Cr₂O₃ volatilization begins |
Max. continuous rec.; La retards breakaway |
|
1095 |
500 h |
1.5–2.5 |
Edge micro-spall possible if cyclic |
Short-term / transient OK |
4.2 Cyclic Oxidation (Heat ↔ Cool)
Test: 980°C × 1 h hold ↔ air cool to RT × 15 min cycles.
|
Alloy |
Cycles to Detectable Spallation / Excess Wt Loss |
Note |
|---|---|---|
|
Haynes 188 (La-doped) |
Typically > 500–1000 cycles before minor edge spall |
La pins oxide/metal interface |
|
Haynes 25 / L-605 (no RE) |
Often 50–150 cycles visible spall |
No rare earth benefit |
4.3 Sulfidizing / Mixed Combustion Gas (Fuel-rich, low O₂ + S-species)
Generally superior to Ni-base (Inconel 617/625) due to absence of low-melting Ni–S eutectic (mp ~ 625°C).
No quantitative "rate" published as it is highly dependent on pS₂/pO₂ ratio — qualitative ranking: Good (better than Ni-base) in fuel-rich partially oxidized combusted gases.
4.4 Other Media
Dilute HCl / SO₂ (≤ 5 %, ≤ 400°C): fair
Seawater / Cl⁻: not recommended (PREN ≈ 22–25,靠Cr only — 316L/625 cheaper for ambient seawater)
Strong oxidizing acids (HNO₃, hot conc. H₂SO₄ + oxidant): poor → not a corrosion alloy per se
5. Thermal Expansion & Stress Calculations (Worked Example)
Thermal strain for a free unconstrained bar from 20°C → T:
εth(T) ≈ αmean(20–T)× (T – 20)
Example: 20 → 800°C, α ≈ 16.5×10⁻⁶/K
εth= 16.5×10⁻⁶ × 780 ≈ 0.01287 ≈ 1.29 % linear expansion
Thermal stress if constrained: σ = E(T) × εth. At 800°C, E ≈ 165 GPa → σ ≈ 212 MPa (indicative; actual relaxed by creep in service).
6. Recommended Design Temperature Limits
|
Criterion |
Recommended Limit |
Rationale |
|---|---|---|
|
Continuous Oxidizing Air |
≤ 1095°C (2000°F) |
Cr₂O₃ scale stable; La extends life via adherence |
|
Cyclic Oxidizing Air |
≤ 980°C (1800°F) preferred |
Below Cr₂O₃ rapid volatilization threshold |
|
Primary Load-Bearing (Creep Controlled) |
≤ 760–815°C (short) / ≤ 650°C (long-term design) |
Solid-solution strength |
|
Cryogenic / Subzero |
To –196°C |
No DBTT — used in high-temp bellows seeing cryo purges |
|
Sulfidizing Combustion Gas |
≤ 980°C (depending on S-partial pressure) |
Co-base superior to Ni-base |
7. Summary Data Takeaways
Tensile: Rm 930–1000 MPa @ RT → 260–300 MPa @ 980°C; Rp0.2 430–470 → 130–160 MPa over same range; A > 45 % @ RT, > 28 % @ 980°C.
Creep: Usable ~870°C / 70 MPa for ~1000 h class; not a high-creep disk alloy.
Oxidation: Continuous to 1095°C; La-doping provides best-in-class cyclic-oxidation scale retention among wrought Co-base alloys.
Physical: ρ=9.09 g/cc, E20°C=214 GPa, CTE20–1000°C(mean)=16.8×10⁻⁶/K, non-magnetic FCC.
These data support material selection, FE thermal-stress input, and corrosion-allowance estimation for Haynes 188 (GH5188 / UNS R30188) components in aerospace propulsion, gas turbine exhaust, and high-temperature industrial furnace service.
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