What is Thermal Spraying and When Should You Use It?
Wear of industrial components starts at the surface. A pump casing, a boiler tube, a hydraulic cylinder rod the core material may be perfectly sound, but once the surface degrades under constant wear, corrosion or erosion, the entire component is compromised. Replacing it outright is expensive, slow, and in many cases unnecessary. Thermal spraying exists to solve exactly this problem: applying a protective or restorative layer to a component’s surface without replacing the component itself.
Laserbond has offered thermal spraying since 1992, when the company was founded as HVOF Australia and brought liquid fuel High Velocity Oxygen Fuel (HVOF) spraying to the Australian market for the first time. Today, Laserbond operates the full range of thermal spraying processes and applies them across mining, power generation and fluid handling applications throughout Australia. This article explains what thermal spraying is, how each process works, and how to decide whether it is the right solution for your application.
What is Thermal Spraying?
The thermal spraying process
Thermal spraying is a surface engineering process in which a coating material, metal, ceramic or composite is heated to a molten or semi-molten state and then propelled at high velocity onto a prepared component surface. When the particles strike the surface, they flatten, cool rapidly and interlock mechanically to form a dense, adherent coating layer.
Unlike laser cladding, which creates a metallurgical bond by fusing the coating material to the substrate, thermal spraying adheres by a mechanical bond. The coating adheres strongly to the surface, HVOF coatings achieve bond strengths exceeding 80 MPa but remains a distinct layer rather than becoming part of the parent material. This distinction matters for some applications and is irrelevant for others, which is why understanding the process differences helps in choosing the right one.
The substrate is not melted during thermal spraying. This is one of the process’s most important practical advantages: because no significant heat is introduced to the component, there is no heat-affected zone, no risk of distortion, and no change to the mechanical properties of the underlying material. parent materials that cannot tolerate the heat input of welding-based processes can typically be thermal sprayed without concern of any metallurgical changes.
The Thermal Spraying Processes Laserbond Offers
Thermal spraying is not a single process, it is a family of techniques, each with its own heat source, particle velocity, coating characteristics and cost profile. Laserbond offers all thermal spraying processes covered by the international standard ISO 14917, with the exception of cold gas spraying.
HVOF and HVAF — High Velocity Oxygen Fuel and High Velocity Air Fuel Spraying
HVOF is a high-kinetic thermal spraying process and the one Laserbond has specialised in longest. It uses a pressurised combustion chamber and a converging-diverging nozzle to accelerate powder particles to supersonic velocities up to 1,000 metres per second. The result is an exceptionally dense coating with very low porosity (typically below 1%), high bond strength (exceeding 80 MPa) and low oxide content. Tungsten carbide is the most widely used HVOF coating material in demanding wear applications, but the process is also used with nickel and cobalt-based alloys for wear and corrosion protection.
HVOF is the preferred process when the application demands the tightest coating quality, hard chrome replacement, valve seat protection, and wear-intensive mining and fluid handling components are all well-suited to HVOF.
HVAF replaces oxygen with air as the oxidant, reducing operating temperatures while maintaining the high particle velocities that give HVOF its performance advantage. With optimal spray parameters a HVAF coating can be more ductile at higher hardness, due to the lower temperature and less formation of brittle phases in the coating.
Arc Spraying
Arc spraying uses an electric arc between two consumable wire electrodes to melt the coating material, which is then atomised and propelled onto the surface by a compressed air jet. It is one of the most cost-effective thermal spraying processes for large surface areas and is widely used for about 100 years for coating and remanufacturing of engineering components and applying zinc and aluminium alloys for atmospheric corrosion protection of steel structures, bridges and wind turbine towers exposed to marine and atmospheric corrosion.
Arc spraying is faster and uses simpler equipment than HVOF, making it practical for manual and on-site applications where portability matters. The coating posses higher porosity than HVOF, so in some corrosive environments a sealer needs to be applied.
Atmospheric Plasma Spraying (APS)
Plasma spraying uses an electrical plasma arc to generate temperatures high enough to melt oxide -ceramics that cannot be processed by other thermal spraying techniques. This makes APS the process of choice for thermal barrier coatings the ceramic layers applied to gas turbine blades and combustion components to insulate the underlying metal from extreme operating temperatures.
APS coatings tend to have higher porosity than HVOF coatings, which is a disadvantage for wear and corrosion applications but is actually beneficial for thermal barrier coatings, where micro-porosity improves insulating performance.
Flame Spraying
Flame spraying is the original thermal spraying process, using a combustion flame as the heat source. It can be used to apply a range of coating materials in the form of powder or wire, including ceramics, although ceramic coatings produced by flame spraying are generally lower in quality than those applied using atmospheric plasma spraying (APS). Flame-sprayed coatings typically have higher porosity and lower bond strength than HVOF or plasma-sprayed coatings, but the process remains a practical and cost-effective option where performance requirements are moderate and simplicity or cost is a key consideration.
When to Choose Thermal Spraying
Thermal spraying is the right choice in several situations.
When you need to protect a large surface area cost-effectively, thermal spraying, particularly arc spraying or flame spraying covers ground faster and at lower cost per square metre than laser cladding. Conveyor components, structural surfaces and large-bore pump casings are typical examples.
When the component cannot tolerate heat input, the absence of a heat-affected zone makes thermal spraying preferable to any welding-based process. Thin-walled components, non-metallic substrates and components requiring a very thin coating benefit from the low thermal load of thermal spraying.
When you need a ceramic coating, APS, and to some degree flame spraying, is the only practical option. Thermal barrier coatings for turbine blades and bioactive coatings for medical implants both require the extreme temperatures that only plasma spraying can achieve.
When hard chrome replacement is the goal, HVOF in particular is a well-established alternative. It eliminates the toxic hexavalent chromium used in electroplating, matches or exceeds hard chrome’s wear performance, and has been qualified as a hard chrome replacement for aerospace landing gear applications under standard AMS2447 since 1998.
When Laser Cladding is the Better Choice
Thermal spraying is not always the right answer. When the application demands the absolute highest bond strength one that cannot delaminate under impact or cyclic loading laser cladding’s metallurgical bond offers a level of integrity that thermal spraying cannot match. And for dimensional restoration of more than 1mm, rebuilding a worn component back to its original dimensions before returning it to service laser cladding and the full remanufacturing process are typically more appropriate than thermal spraying alone.
The practical guidance: if your component is not mobile and requires coating application in field , thermal spraying is likely the more cost-effective choice. If your component requires a thick coating, laser cladding or full remanufacturing should be considered.
Thermal Spraying Across Industries
In mining, HVOF coatings are used to protect components exposed to severe abrasive and erosive wear, including slurry pump components, hydraulic components and other high-wear equipment where surface protection can extend service life. Arc spraying can also provide corrosion protection for structural components exposed to mine site water and harsh atmospheric conditions.
In power generation, atmospheric plasma spraying applies thermal barrier coatings to gas turbine blades and combustion liners, protecting the underlying superalloy from operating temperatures that would otherwise cause rapid degradation. Thermal spraying also protects boiler tubes in coal-fired, waste-to-energy and biomass boilers from erosive fly ash and corrosive combustion gases, extending tube life and reducing the risk of premature failure.
In fluid handling, HVOF coatings protect pump impellers, casings, valve seats and pipework components from the combined wear of cavitation, erosion and corrosive process media. HVOF coatings can also provide an alternative to hard chrome for hydraulic cylinder rods used across mining, civil and industrial applications.
Choosing the Right Thermal Spraying Partner
Thermal spray coating quality is highly process-dependent. The same coating material applied by different operators using different equipment and process parameters can produce dramatically different results in coating density, bond strength and service life. Choosing a partner with demonstrated process control, an on-site materials testing capability, and proven application experience in your specific industry is as important as choosing the right process.
Laserbond has operated thermal spraying equipment since 1992, holds extensive experience across HVOF, HVAF, arc spraying, plasma spraying and flame spraying applications, and maintains an on-site metallurgy laboratory to support both process development and quality verification. To discuss which thermal spraying process is right for your component and application, contact the Laserbond team directly.
ES 
EN 
JA 
AR 
HI 
BN 
ZH 
PT 
IT 
FR 
DE