Why Thermal Spray Is Growing Across Industries
Thermal spray coatings — deposited by accelerating molten or semi-molten particles of metal, ceramic, carbide, or composite materials onto a substrate surface to form a coating whose composition and microstructure can be engineered independently of the underlying component material — provide a uniquely flexible surface engineering capability that is finding growing commercial application across an expanding range of industries whose common need is the improvement of surface properties without replacing the component whose substrate material provides the required bulk mechanical properties. The commercial logic of thermal spray is compelling in the economic context of modern industrial equipment: the components whose surfaces experience the most severe wear, corrosion, thermal, and erosion environments are frequently the most expensive and most difficult to replace, and the application of a thermal spray coating that dramatically extends the service interval between replacements — or that makes a worn component serviceable again through dimensional restoration — generates returns on coating investment measured in multiples of coating cost through avoided component replacement cost and reduced equipment downtime.
The thermal spray technology family encompasses several distinct processes whose particle temperature and velocity — and consequently the microstructure and properties of the deposited coating — differ substantially. High velocity oxy-fuel (HVOF) spraying — in which fuel combustion at high pressure produces a supersonic gas jet that accelerates spray powder particles to very high velocities before impact — produces dense, well-bonded coatings of WC-Co and other hard metal carbide compositions whose wear resistance and adhesion properties are superior to earlier thermal spray processes and that have become the standard coating technology for wear-resistant coating applications in aerospace, oil and gas, and industrial equipment. Plasma spraying — using a plasma torch at temperatures above 10,000 Kelvin to melt the spray particles — is the process of choice for the thermal barrier coatings that protect nickel superalloy turbine components from the combustion gas temperatures of jet engines and industrial gas turbines, because the plasma process can melt high-melting-point ceramics including yttria-stabilised zirconia that fuel combustion processes cannot reach.
Aerospace: The Premium Application Driving Technology Development
The aerospace application of thermal spray coatings — thermal barrier coatings on turbine blades and vanes, abradable coatings in engine compressor and turbine tip clearance seals, and wear and corrosion protection coatings on a range of airframe and landing gear components — has been the primary driver of thermal spray technology development and represents the highest-specification and highest-value segment of the thermal spray coatings market. The thermal barrier coating on the high-pressure turbine blades of jet engines — whose ceramic topcoat insulates the underlying nickel superalloy from combustion gas temperatures that would otherwise exceed the alloy's melting point — is among the most technically critical coatings in any engineering application, because coating failure in service creates turbine blade oxidation, thermal fatigue, and potential structural failure whose consequences in an operating aircraft engine are severe.
The development of next-generation thermal barrier coating compositions — beyond the yttria-stabilised zirconia that has been the industry standard for 40 years — is one of the most actively researched areas in aerospace materials science, driven by the engine manufacturers' desire to increase turbine inlet temperatures beyond the limits of YSZ's phase stability and sintering resistance. The rare earth zirconate and pyrochlore oxide compositions being evaluated as YSZ successors offer better high-temperature stability and lower thermal conductivity at the temperatures of advanced engine designs, but their deposition by thermal spray requires process parameter optimisation and quality assurance development that is being conducted in parallel with the materials science research at the engine manufacturers and their coating suppliers. The commercial market for advanced aerospace thermal barrier coating development is consequently growing not only with the volume of engines being produced but with the R&D investment that next-generation engine temperature targets require.
Power Generation and Industrial Turbines
The power generation gas turbine market — industrial gas turbines used for electricity generation at utility and industrial scale — represents the largest volume application for thermal spray thermal barrier coatings outside aerospace and is growing with both the expansion of gas turbine-based power generation and the increasing firing temperatures of advanced gas turbine designs whose efficiency improvements require the thermal protection that barrier coatings provide. The industrial gas turbine coating market differs from the aerospace market in its component sizes — industrial turbine blades and vanes are larger than aero engine equivalents — and in the greater accessibility of industrial turbine components for coating maintenance and replacement during scheduled outages, creating a more active refurbishment coating market alongside the OEM coating of new components. The growing adoption of hydrogen co-firing in gas turbines — burning blends of natural gas and green hydrogen as a decarbonisation pathway for gas turbine power generation — is creating new coating requirements, because the higher flame temperature and different combustion chemistry of hydrogen co-firing affects coating durability in ways that require coating system adaptation and qualification.
The wear and corrosion protection coating market in industrial applications — coating pump components, valve seats, hydraulic cylinder rods, printing rolls, paper mill rolls, and the range of industrial equipment whose surface-critical components experience severe wear and corrosion — is the largest volume segment of the thermal spray market by coating area applied and the one with the most geographically distributed commercial activity. The HVOF and plasma spray coating of tungsten carbide, chromium carbide, and ceramic oxide compositions on industrial wear components is a well-established commercial service whose value proposition is demonstrated through decades of application experience across industries including oil and gas, pulp and paper, steel production, food processing, and mining. The growth of this market reflects the expansion of industrial production activity, the increasing cost of precision-machined components that coating extends, and the growing awareness among maintenance engineers of thermal spray as a cost-effective alternative to component replacement whose payback period in maintenance cost reduction typically falls within months of initial coating application.
Additive and HVAF Technologies: The Process Innovation Front
The thermal spray technology market's innovation front is the development of high velocity air-fuel (HVAF) spraying — a variant of HVOF that uses air rather than oxygen as the combustion oxidant, reducing process gas cost and allowing higher particle velocities with lower substrate thermal input than conventional HVOF. The HVAF process produces coatings with density and adhesion comparable to or exceeding those of HVOF at lower operating cost, and is gaining commercial adoption in the hard chrome replacement market — where environmental and health concerns about hexavalent chromium have created regulatory pressure to replace hard chrome electroplating with alternative coating technologies including HVOF and HVAF WC-Co coatings that provide equivalent wear and corrosion protection without the hexavalent chromium waste streams of the plating process. The cold spray process — in which particles are deposited at temperatures below their melting point by supersonic gas jet acceleration, allowing deposition of highly sensitive materials without the thermal damage or oxidation of conventional thermal spray — is growing in commercial application for additive repair of metallic components including turbine blades, aerospace structural components, and the dimensional restoration of worn shafts and bores whose repair by cold spray avoids the metallurgical changes that welding or high-temperature thermal spray would introduce.