The Coating Between the Turbine and Its Operating Temperature
A modern gas turbine operates at combustion temperatures that would melt the nickel superalloy blades and vanes at its hot section if those components were not protected by a ceramic thermal barrier coating whose insulating properties allow the metal substrate to operate at temperatures hundreds of degrees below the gas temperature passing over it. The turbine inlet temperature is the single parameter most directly correlated with thermodynamic efficiency, and the ability to increase turbine inlet temperature without destroying hot section components is the engineering challenge that thermal barrier coating development has been advancing for fifty years. The yttria-stabilised zirconia that forms the standard thermal barrier coating material can sustain a temperature differential of more than one hundred degrees Celsius across a coating of one hundred to three hundred micrometres thickness, allowing turbine designers to increase firing temperature, reduce cooling air requirements, and improve cycle efficiency without the metal temperature increase that would reduce component life. The economic consequence of this coating capability, measured in fuel savings across the operating life of a large industrial gas turbine, is orders of magnitude larger than the cost of the coating that enables it.
Thermal spray coating is the deposition process that applies thermal barrier coatings and a range of other functional coatings to gas turbine components during manufacture and repair. The plasma spray process, which generates a plasma jet at temperatures exceeding ten thousand degrees Celsius that melts coating powder and propels it toward the substrate where it solidifies into a dense, adherent coating, is the primary deposition method for thermal barrier coatings in both new component manufacture and component repair. High velocity oxygen fuel spraying, which accelerates coating powder particles to supersonic velocities in a combustion gas jet before impact with the substrate, produces denser coatings with lower porosity and higher bond strength than plasma spray, making it the preferred method for wear-resistant and corrosion-resistant coatings on compressor components and other applications where coating density and adhesion are more important than the thermal insulation that the columnar or lamellar porosity of plasma-sprayed thermal barrier coatings provides.
The Repair Market and Its Commercial Scale
The industrial gas turbine repair and overhaul market is where thermal spray coating generates the greatest commercial volume relative to new component manufacture. A large industrial gas turbine operating in power generation or mechanical drive service undergoes major maintenance at intervals of typically twenty-five thousand to fifty thousand operating hours. At each major overhaul, hot section components including first and second stage turbine blades and vanes are removed, inspected, and either replaced or repaired through processes that include thermal barrier coating removal, substrate restoration, and reapplication of thermal barrier and bond coat systems. The economics of blade and vane repair through thermal spray recoating rather than replacement with new components are compelling at the component values that advanced nickel superalloy turbine blades represent. A repaired blade that returns to service with restored thermal barrier coating and a remaining metal substrate whose thickness is within acceptance limits has recovered most of its original design life at a fraction of the new component cost, and the thermal spray coating technology is the enabling process that makes this repair economically viable.
The commercial scale of the gas turbine repair market served by thermal spray coating encompasses the full installed base of industrial gas turbines in power generation, oil and gas compression, and industrial mechanical drive applications globally, plus the military and commercial aviation engine fleets whose thermal spray coating requirements are technically demanding and commercially valuable per component. The concentration of high-value turbine component repair at a relatively small number of licensed repair and overhaul facilities whose thermal spray capability is a primary differentiating asset creates commercial relationships between turbine OEMs and their authorised repair networks that are commercially durable because the technical validation of the repair process to OEM specifications is a multi-year investment that creates switching costs for both the repair facility and the turbine operator.
Emerging Applications Beyond Gas Turbines
The thermal spray coating technology developed for gas turbine applications is finding commercially growing applications in the hydrogen economy, where components exposed to hydrogen in fuel cells, electrolysers, and hydrogen processing equipment require corrosion protection and functional surface engineering that thermal spray processes can provide. The solid oxide fuel cell market uses plasma-sprayed electrolyte and electrode coatings whose deposition quality directly determines cell performance and durability. Electrolyser components for alkaline and PEM electrolysis require corrosion-resistant and catalytically active coatings whose application by thermal spray processes is being developed as an alternative to the conventional electroplating and physical vapour deposition methods that current electrolyser manufacturing uses. The emerging market for thermal spray coatings in hydrogen equipment represents the most commercially significant new application domain for the technology's established industrial base.
Top 10 Companies in Thermal Spray Coatings Globally
- Oerlikon Metco: Largest thermal spray coating company globally with thermal spray equipment, coating materials, and contract coating services; its position as both the equipment supplier and materials supplier to the thermal spray industry and its contract coating centres serving aerospace and industrial gas turbine customers create the vertically integrated market position that no other thermal spray company matches.
- Linde (Praxair Surface Technologies): Thermal spray coating services company with a global network of coating service centres for aerospace and industrial gas turbine components; its technical approval from major turbine OEMs for specific coating processes and its gas supply infrastructure create the commercial integration that makes it the primary coating service provider for the most demanding aerospace and turbine applications.
- Bodycote: Global heat treatment and surface technology services company with thermal spray coating capability at multiple sites; its broad industrial customer base and its geographic reach create the coating service capacity that industrial gas turbine operators and aerospace manufacturers use for both new component coating and repair.
- Sulzer: Swiss industrial services company with turbine component repair and thermal spray coating services for power generation and oil and gas customers; its gas turbine blade and vane repair programmes using thermal spray recoating create the cost-effective component life extension that turbine operators depend on for maintenance cost management.
- Chromalloy: Gas turbine component manufacturer and repair company with thermal spray coating capability integrated into its component repair programmes; its OEM-approved repair processes for major gas turbine manufacturers and its broad geographic repair centre network create the commercial position in the gas turbine aftermarket whose value is proportional to the installed turbine fleet it serves.
- Flame-Spray Industries: US thermal spray coating materials and equipment company with a long history in gas turbine coating materials development; its coating powder portfolio and its application engineering expertise create the materials foundation that contract coating companies use to build OEM-approved coating processes.
- Southwest United Industries: US aerospace thermal spray coating service provider with OEM approvals for multiple engine platforms; its aerospace focus and its proximity to major aircraft engine manufacturing and MRO operations in the US create the customer relationship depth that aerospace thermal spray qualification programmes require.
- Plasma-Therm: Thermal spray equipment manufacturer whose plasma spray systems are used in research, development, and production coating operations globally; its equipment technology and its application development laboratory support create the technical foundation for new thermal spray coating process development by coating service companies and research institutions.
- Sprayon Coatings: Thermal spray coating materials and services company with specialty coatings for wear, corrosion, and thermal protection in industrial equipment; its position in the non-aerospace industrial thermal spray market creates the commercial diversification from the gas turbine focus that characterises most premium thermal spray companies.
- APS Materials: US thermal spray powder manufacturer producing ceramic, metallic, and cermet coating materials for thermal spray deposition; its powder metallurgy capability and its custom powder development services create the materials innovation that enables next-generation coating process development by thermal spray service companies.