nickel-superalloys

name	nickel-superalloys
description	Nickel superalloys — Inconel, Waspaloy, Hastelloy, René alloys; high-temperature properties, creep, oxidation, coating systems, gas turbine applications, processing.
metadata	{"priority":7,"promptSignals":{"phrases":["nickel superalloy","Inconel","Waspaloy","Hastelloy","high temperature alloy","gas turbine material","creep resistant"],"minScore":3}}

Nickel Superalloys — Complete Skill

Classification

Solid Solution Strengthened

Strengthened by: Mo, W, Cr, Co in FCC matrix Hastelloy X: 47Ni-22Cr-18Fe-9Mo; used to 1200°C oxidation; sheet metal fabrication Hastelloy C276: excellent corrosion resistance; chemical plant Inconel 625: 58Ni-21Cr-9Mo-3.6Nb; weld overlay, pressure vessels, seawater

Precipitation Strengthened (γ' or γ'' precipitates)

γ' (Ni₃Al): primary strengthener in most turbine alloys; coherent with matrix; resists cutting by dislocations γ'' (Ni₃Nb): in 718 (metastable, transforms at ~650°C)

Waspaloy: 58Ni-20Cr-14Co-4Mo-3Ti-1.4Al; turbine discs up to 760°C Inconel 718: 52Ni-19Cr-18Fe-5Nb-3Mo-1Ti-0.5Al; most widely used (disk, rings, cases); good weldability René 88DT: powder metallurgy disc alloy; higher γ' fraction → higher temperature capability CMSX-4: single-crystal casting alloy; turbine blades (1050-1100°C capability) IN738LC: conventionally cast blades; moderate temperature, oxidation resistant TMS-238: 3rd gen single crystal; latest Toshiba/NIMS; T_cap ≈ 1140°C

Properties at Temperature

Inconel 718 (Most Common)

Room temp: S_y = 1035 MPa, S_u = 1240 MPa, El = 12% At 540°C: S_y = 965 MPa, S_u = 1170 MPa At 650°C: S_y = 862 MPa, S_u = 1000 MPa

Max service temperature: 650-700°C (γ'' coarsens/dissolves) Fatigue: endurance limit R=-1 ~750 MPa (room temp); decreases with temperature

Waspaloy

RT: S_y = 795 MPa, S_u = 1275 MPa 700°C: S_y = 690 MPa; 760°C: S_y = 620 MPa Use: turbine discs, rings to 760°C

CMSX-4 (Single Crystal)

RT: S_y = 1000 MPa; Su = 1340 MPa 1000°C: excellent creep resistance (key property) Larson-Miller parameter at 1000°C, 150 MPa: log t_r ≈ 3.5

Creep Behavior

Larson-Miller: LMP = T(K) × (log t_r + C) × 10⁻³; C ≈ 20 for most superalloys Power-law creep: ε̇ = A σ^n exp(-Q/RT); n ≈ 3-5 for dislocation creep Rafting (single crystals): γ' coarsens under stress at high T → directional morphology Positive misfit: γ' rafts perpendicular to tensile stress (unfavorable) Negative misfit: parallel rafts (beneficial — preferred direction in CMSX alloys)

Oxidation Resistance

Al₂O₃ former: Al > 6% → slow-growing, protective scale (used in blades with coating) Cr₂O₃ former: Cr > 15% → protective at intermediate temperature Breakaway oxidation: rapid attack when protective scale spalls

Thermal Barrier Coating (TBC) System

Bond coat: MCrAlY (M = Ni, Co): forms thermally grown oxide (TGO) for TBC adhesion TBC (8YSZ): 7-8 wt% Y₂O₃ stabilized ZrO₂; k ≈ 2 W/mK; 100-300 μm thick Temperature drop: ΔT = q_flux × t_TBC / k_TBC ≈ 150-300°C → enables higher gas T TBC life limit: TGO growth → buckling/spallation; typical life 10,000-40,000 hours

Processing

Powder Metallurgy (PM) Disc Alloys

Inert gas atomization → screened powder → hot isostatic press (HIP) + forge Advantages: fine uniform grain, no segregation, higher γ' fraction possible René 88DT, LSHR, Alloy 10: PM disc alloys for modern turbines

Directional Solidification and Single Crystal

DS: grains aligned with solidification direction (columnar; better creep in blade length direction) SX: single grain eliminated grain boundaries → no grain boundary creep; highest capability Investment casting with crystal selectors or seed crystal orientation

Post-Weld Heat Treatment

Inconel 718: 955°C/1hr + 720°C/8hr + 620°C/8hr (SHT + double age) Waspaloy: 1080°C SHT + 845°C/4hr + 760°C/16hr

Applications

Component	Alloy	Temperature
Turbine disc	IN718, Waspaloy	To 650-760°C
1st stage blade	CMSX-4, René N5	To 1100°C
Combustor liner	Hastelloy X, IN617	To 1200°C
Nozzle guide vane	IN738, TBC	900-1050°C
Exhaust casing	Inconel 625	To 700°C
Chemical reactor	Hastelloy C276	Corrosion

Output

Provide: alloy recommendation for service temperature and environment, S_y and S_u at operating temperature [MPa], creep life from Larson-Miller [hrs], TBC temperature drop [°C], oxidation protection strategy, processing method recommendation (cast/wrought/PM).