Metco 204 is Oerlikon Metco's workhorse yttria-stabilized zirconia family — the ceramic topcoat sprayed onto combustor liners, transition pieces, and turbine airfoils in virtually every commercial aero and industrial gas turbine running today.

The chemistry is 7-8 wt% Y₂O₃ in ZrO₂, manufactured by the HOSP (Hollow Oven Spherical Powder) process that combines fused-and-crushed density with spray-dried flow. That morphology is why Metco 204 variants — 204NS, 204B-NS, 204C-NS, 204F, 204NS-G, 204D — show up on OEM-approved vendor lists from GE, Pratt & Whitney, Rolls-Royce, Siemens, and Mitsubishi.

The numbers that matter: thermal conductivity around 1 W/m·K (about 1/11th of the superalloy beneath it), engineered porosity 8-20%, typical topcoat thickness 10-15 mils on combustor hardware and 8-20 mils on blades and vanes. Always over an Amdry 386-family MCrAlY bond coat at 5-8 mils. The bond coat is not optional — YSZ does not adhere to bare superalloy.

Under turbine duty, that sandwich drops metal-substrate temperature 150-300°C. That's how modern engines push flame temperatures past 1,600°C without melting blades.

Watch for: spallation at the bond-coat interface, CMAS attack above 1,200°C. Send us the part, the duty cycle, and the OEM spec — we'll match the right Metco 204 grade and bond coat together.

Technical data

Hardness: As-sprayed 450-600 HV typical for HOSP 8YSZ coatings (Rockwell C 30±5 on the ground coating); hardness is a QC check, not the spec — YSZ is bought for insulation and strain tolerance, not wear resistance
Bond strength: ~2,200-3,000 psi (15-21 MPa) tensile against a properly deposited MCrAlY bond coat; failures cleave at the bond-coat/topcoat interface, not within the ceramic
Max service temp: ~2,200°F coating surface for long-life duty; ~2,400°F short-excursion; substrate metal kept under ~1,800°F by the insulating layer (industry rule of thumb: 100-300°F drop per 10 mils of YSZ)
Max service temp: ~1,200°C coating surface for long-life TBC duty (the t′ phase-stability ceiling for 7-8 wt% yttria); ~1,300°C for short excursions; metal substrate typically held at 950-1,050°C
As-sprayed porosity: 8-20% engineered porosity depending on grade and spray parameters — Metco 204NS family runs 10-18%, Metco 204F can be sprayed dense (4-8%) or with vertical segmentation cracks; porosity is the strain-tolerance mechanism, not a defect
Typical thickness: 10-15 mils (250-380 µm) topcoat on combustor liners and transition pieces; 8-20 mils on turbine blades and vanes; up to 40 mils on thick industrial hot-section hardware
Density: ~5.6-5.9 as-sprayed (theoretical ZrO₂ ~6.1; engineered porosity accounts for the difference)

Where it earns its keep

HOSP (Hollow Oven Spherical Powder) morphology delivers high deposition efficiency and consistent spray behavior — less overspray waste, more predictable coating builds than fused-and-crushed YSZ
Approved to many OEM aircraft and industrial gas turbine specifications — Metco 204NS, 204B-NS, 204C-NS, 204F, 204NS-G, and 204D variants cover the full range of particle-size and coating-architecture needs
Thermal conductivity 1.0-1.1 W/m·K drops metal-substrate temperature 150-300°C under turbine duty — the reason jet engines push flame temperatures past 1,600°C without melting blades
Engineered 8-20% porosity is the strain-tolerance mechanism that lets the ceramic survive thousands of thermal cycles from cold-start to takeoff without spalling off the metal
Forty-plus years of flight history traceable to Stephan Stecura and Curt Liebert's original NASA Lewis (now Glenn) work on 7-8 wt% Y₂O₃-ZrO₂ in the 1970s

Where it doesn't

Metco 204 is thermal insulation — do not specify it where the duty is sliding wear, abrasion, or hard contact. For that you want WC-Co, Stellite, or Cr₃C₂-NiCr
The MCrAlY bond coat is not optional. Spec the Amdry 386 / 365 / 962 family bond coat and the Metco 204 topcoat together, or don't spec either — YSZ does not bond directly to superalloy
Grade selection matters: 204F for dense or segmentation-cracked architectures, 204NS / 204B-NS / 204C-NS for conventional porous TBC, 204NS-G for premium OEM aerospace work. Particle-size distribution drives crack density and porosity
CMAS attack above 1,200°C is the durability ceiling for standard 7-8 wt% YSZ — Middle East and Pacific Rim operating environments accelerate failure. Rare-earth-doped or pyrochlore topcoats are the path forward above that line
Failure mode is spallation, not wear. Inspect for edge lift, segmentation cracking, and TGO thickness at overhaul — a single flaked zone on a turbine blade is a return-to-service issue

Sources

Data points on this page draw on the following published references. Nothing here replaces a material-specific review by our process engineers — but it's the working starting point.

Oerlikon Metco DSMTS-0001.8 — HOSP 8% Yttria-Stabilized Zirconia Powders
“Covers Metco 204C-NS Premium, 204NS-G Premium, 204D, 204E, 204NS, 204B-NS, 204AF, Amdry 204NS-1, 204C-NS, 204F, 204NS-G, 204NS-AP, SPM 2000, SPM 2000-1. ZrO₂ balance, Y₂O₃ 7.0-8.0 wt%; HOSP process combines pre-alloyed fused-and-crushed properties with spray-dried flowability; used as TBC top coat on combustion liners, transition pieces, afterburners, heat shields, and turbine airfoils for thermal protection to ~900°C component metal.”
Oerlikon Metco — Understanding Thermal Barrier Coatings
“Metco 204 yttria-stabilized zirconia (ZrO₂-8Y₂O₃) family plasma-sprayed as ceramic topcoat on MCrAlY bond coats (Amdry 386 family, NiCoCrAlSiHfY) for decades of in-service performance; turbine inlet temperatures have risen ~500°C over four decades while material limits only ~220°C, with components running past 1,500°C.”
DOE OSTI — Combustion Control and Diagnostics Sensor Testing (NETL Report)
“Metco-204 (ZrO₂ − 8% Y₂O₃) thermal barrier coating applied 250-380 µm (0.010-0.015 in.) thick over Praxair NI-171 NiCoCrAlY bond coat 125-200 µm (0.005-0.008 in.) thick on combustor liner; applied by plasma spray.”
Med-Lab — Metco 204B-NS 8% YSZ (OMAT 3/185A) Powder Data
“Spherical free-flowing partially stabilized 7-8% yttria zirconia; produces excellent high-temperature thermal barrier coatings resistant to thermal cycling stresses; average particle size 75±44 µm; RC 30±5 powder hardness; as-sprayed coating hardness 450-600.”
Oerlikon Metco — YSZ TBC Solutions Using Cascaded-Arc Gun Technology
“Metco 204F (D50 20-30 µm, −45 +15 µm nominal) achieves the highest segmentation crack density ~3.3 cracks/mm; Metco 204NS-G (D50 50-57 µm) and Metco 204C-NS (D50 68-77 µm) for conventional porous architectures; 204C-NS demonstrates 64% deposition efficiency at 40 g/min.”
NASA NTRS — Thermal Barrier Coating Life Prediction Model Development (NASA Lewis/Glenn)
“NASA ceramic TBC system: two-layer with Ni-16Cr-6Al-0.6Y bond coat and ZrO₂-Y₂O₃ ceramic topcoat; tested by industrial and governmental organizations for aeronautical, marine, and ground-based gas-turbine engine applications; seven tests evaluated thermal protection and durability, five others determined thermal conductivity, vibratory fatigue, and corrosion resistance.”
MDPI Coatings — Revisiting the Birth of 7YSZ TBCs: Stephan Stecura
“7-8 wt% Y₂O₃-ZrO₂ is the industry-standard TBC composition, established through NASA Lewis (now Glenn) plasma-sprayed TBC studies, most notably component and engine tests championed by Curt Liebert as far back as 1972.”
European Turbine Network — A Practical Guide for TBCs in Gas Turbines
“Industry-standard 7-8 wt% YSZ APS topcoats 250-500 µm over MCrAlY bond coats 100-200 µm; bond strength 15-25 MPa tensile; operating surface temperature ceiling 1,200°C for long-life duty; failure by spallation at TGO interface; CMAS attack the modern durability limit.”
npj Materials Degradation — CMAS Corrosion Attack on Thermally Sprayed TBCs
“Molten CMAS infiltrates porous TBC microstructure by capillary action, destabilizes YSZ by thermochemical reaction, solidifies on cooling, stiffens the coating (Young's modulus ~250 GPa CMAS-infiltrated vs ~40 GPa non-infiltrated), drives premature spallation.”

Material data on this page is provided as a general reference and can vary by lot, substrate, and application. Contact HTS to confirm the right material and specification for your specific part.

Metco 204

Technical data

Where it earns its keep

Where it doesn't

Typical applications

Wear modes addressed

Industries

Substrates

Sources

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