Ceramic thermal-spray coatings
Ceramic spray feedstocks, deposition and microstructure, substrate preparation and bond coats, porosity/sealers, and application-specific coating qualification.
Tags: consumables, coatings, ceramics, thermal-spray
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Oerlikon lists 1,250°C maximum service temperature for its APS Metco 205NS coating with a properly selected and applied bond coat. Its separate Metcoseal AP-70 sealer is listed at 205°C continuous service. Qualify the complete deposited stack, including the substrate and bond coat, and check the sealer's own limits before combining products. Metco 205NS TDS, coating information Oerlikon sealer selection and application
Specify feedstock, spray process, preparation, bond coat and finishing. Verify the deposited thickness, phases, porosity, cracking, adhesion and functional properties separately from powder composition.
Feedstock identity is only the starting point
Ceramic powders may be fused/crushed, mechanically clad, or agglomerated and sintered or densified. Those forms influence feeding and deposition. Oerlikon's alumina–13% titania sheet illustrates the differences: Metco 130 is mechanically clad with irregular morphology and a nominal −53 +15 µm distribution; Metco 6221 is spheroidal, agglomerated/sintered, and −45 +15 µm. They belong to a related chemistry family but are not identical powder specifications. Oerlikon DSM-0258.2, ©2025, material tables.
Record the full grade and particle-size specification, not just “alumina,” “zirconia,” or “ceramic powder.” Stabilizer concentration matters for zirconia, and weight percent is not interchangeable with mole percent. The current retrieved HOSP yttria-stabilized zirconia sheet is DSM-0242.12, ©2026; it lists multiple grades designed for differing deposition characteristics, including dense or vertically cracked microstructures. Oerlikon HOSP 8% YSZ family sheet.
Deposition processes and coating structure
Thermal spraying heats and accelerates feedstock toward a prepared surface. In conventional molten-particle deposition, impacting droplets flatten into “splats” that build the coating. Particle temperature and velocity affect deposit formation. Thermal spray ordinarily transfers less heat to the substrate than fusion welding, but this does not remove the need to control the actual part temperature. Oerlikon TP-0011.1, ©2022, process principles.
Atmospheric plasma spray (APS) uses an ionized-gas jet and is especially useful for high-melting-point ceramics. Combustion powder spray is another option for selected oxide powders. HVOF supplies a high-velocity combustion stream and is widely used for carbide-containing wear systems; it is not a blanket replacement for a ceramic's specified plasma process. The feedstock and equipment must be selected together. Oerlikon thermal-spray introduction, May 2022; alumina–titania process recommendations.
The deposited layer can contain splat boundaries, pores, unmelted particles, and cracks. These features differ from a dense, sintered ceramic of the same nominal composition. The HOSP YSZ sheet, for example, describes a homogeneously porous, finely microcracked coating and a typical 8–20% porosity range. This family-level description does not certify a particular component's measured porosity. DSM-0242.12, coating information.
Preparation, bond coats, and geometry
Adhesion commonly relies strongly on mechanical anchoring to a roughened surface. Degreasing and removal of scale/oxide precede the qualified roughening procedure. Blast-media type, shape, size, cleanliness, pressure, and angle influence preparation; “grit blast” alone is an incomplete manufacturing instruction. Oerlikon thermal-spray introduction, substrate preparation.
Specify whether a metallic bond coat is required and its compatibility with both substrate and topcoat. For high-temperature zirconia systems, Oerlikon recommends suitable MCrAlY bond coats; the choice is part of the system rather than a universal underlayer for all ceramics. Its Metco 205NS sheet requires degreasing and grit removal of scale/oxidation before bond-coat application. Metco 205NS system recommendations.
Review spray access, masking, transitions, and finishing allowance. Sharp corners and recesses complicate deposition. Distinguish as-sprayed thickness from final dimensions. Oerlikon coating geometry guidance.
Match the microstructure to the function
| Intended function | What must be established |
|---|---|
| Wear surface | Wear mechanism, counterface, finish, hardness/toughness balance, and lubrication/environment. |
| Thermal barrier | Thermal conductivity, thickness, thermal cycling, bond-coat/substrate compatibility, and degradation in service. |
| Electrical insulation | Dielectric performance of the finished thickness and surface under the relevant moisture/contamination conditions. |
| Fluid or chemical barrier | Connected porosity, sealer compatibility, and resistance of the entire coating/substrate system. |
These functions can favor different designs. Oerlikon's alumina–titania sheet contrasts pure alumina's hardness/wear properties with the greater fracture toughness of 13% titania compositions. A wear grade should not be selected solely because a zirconia thermal barrier tolerates higher temperatures. DSM-0258.2 selection criteria.
Bounded thermal-barrier example: Metco 205NS
The DSM-0316.0 sheet, ©2021, describes a ceria–yttria-stabilized zirconia powder and reports these typical coating data:
| Property | Stated value and qualification |
|---|---|
| Recommended process | APS |
| Bond coat | Suitable high-temperature MCrAlY; named examples include Amdry 995C |
| Porosity | 5–10 vol.% by image analysis |
| Thermal conductivity | 0.9 W/(m·K), laser-flash method, as-sprayed condition |
| Maximum listed service temperature | 1,250 °C, with a properly selected/applied bond-coat system |
The sheet warns that conductivity changes with microstructure, porosity, service temperature, and time. It does not state a measurement temperature alongside that conductivity value. Do not treat it as a guaranteed hot-service value or infer a substrate-metal temperature limit from the ceramic's listed maximum. Metco 205NS TDS, coating information.
Porosity, sealing, and finishing
Porosity can retain lubricant in some wear applications, but connected pores can admit corrosive fluids or contaminants to the coating and substrate. Oerlikon's sealer sheet explains that moisture/contamination within ceramic pores can also create unwanted conductive paths. Sealing is therefore a separate functional choice, not merely cosmetic finishing. DSM-0230.9, ©2024, sealer principles.
Select the sealer for its own exposure, cure and temperature limits. Sealing before machining can keep contamination out of pores. Verify the surface after the actual sequence. Oerlikon sealer selection and application
Specify and verify the deposited system
Specify the feedstock, preparation, bond coat, equipment/parameters, thickness, finishing, and sealer. Oerlikon describes thickness/finish inspection and concurrently sprayed coupons for cross-sectional porosity/microstructure, hardness, and bond testing. Also verify the required functional performance; hardness alone cannot qualify thermal or electrical insulation. Oerlikon coating characterization guidance.