Thermal Spraying

Thermal spraying processes (as classified in the EN 657 and ISO 14917 standards) offer a wide range of applications within modern surface technologies. Components made from a wide range of base materials can be coated with layers of high-melting-point metals or ceramics to protect them against wear and corrosion. Furthermore, thermally conductive or heat-insulating layers can be applied to highly thermally stressed components. Almost all coating materials that can be produced in powder or wire form can be processed in this way.

During thermal spraying, the coating materials are fed into — and melted by — an energetic heat source (fuel gas oxygen flames from combustible gas, arcs or plasmas of noble gases such as argon, hydrogen, nitrogen, helium). The particles, which are either softened or fully molten, are accelerated in the direction of the workpiece and collide with it at high speed (40–600 m/s). Once the heat has been transferred to the base material, the particles solidify and form a coating that consists of multiple layers. The desired thickness is achieved by repeated passes with the burner.

Base Materials Of Thermal Spraying

Almost any base material can be coated, including metals, ceramics, plastics, fiber composites or natural materials such as stone, wood, etc. Thermal spraying offers a great flexibility in terms of the possible material combinations.

Coating Thickness Of Coating

Achieving an optimal coating thickness — which may vary greatly depending on the application — is a prerequisite for good results. Depending on the material and process used, a coating thickness from a few tens of microns to several millimeters can be achieved. In the case of worn parts, for which the total thickness of the coating cannot be freely determined, the coating can be applied after a build-up layer.

Component Temperature During Coating

During the coating process, workpieces are usually heated to a maximum of 150°C and their surface temperature is monitored. Changes in the base material are largely excluded, with the exception of self-flowing alloys, which are subsequently fused at temperatures exceeding 1,000°C.

Pre-And Post-Processing From One Hand

To achieve the required surface quality, efficient finishing of the sprayed layers is just as important as selecting optimum materials of the necessary quality. For this reason, Nova Werke uses state-of-the-art facilities for turning, grinding, lapping, honing and polishing.

Quality Assurance For Materials, Equipment, Measuring Methods (Standards) And Personnel

Far from taking a "spray-and-pray" approach, our thermal spraying processes are based on consistent quality awareness on four M-levels: Material, Machine, Men and Measurement/Inspection. For comprehensive quality control, Nova Werke uses state-of-the-art test equipment for three-dimensional tolerance monitoring as well as a dedicated metallography lab, in which roughness measurements with track profile recording are carried out in addition to microsection analysis, hardness measurements and adhesion strength tests. These QA measures are coordinated with the customer on the basis of the applicable standards when the order is placed.

Thermal Spraying Processes At Nova Swiss:

Flame Spraying, Arc Spraying, High Velocity Flame Spraying (HVOF) And Plasma Spraying (APS)

The process to be used depends on the specific application. Economic considerations always play an important role here.

	Gas temperature [°C]	Particle velocity [m/s]	Adhesive pull strength	Porosity [Vol.-%]
Arc spraying	4,000	100	10–15	10
Flame spraying	3,100	40	10	10–15
High-velocity flame spraying	3,100	800	> 70	1-2
Plasma spraying	15,000	200	> 50	2–5

Coating Materials For Thermal Spraying And Their Features

Material Groups	Material	Melting point [°C]	Vickers Hardness [HV 0.3]*	Typical Properties	Application Areas
Pure Metals	Aluminum / Al	660	80	Soft	Corrosion protection for industrial and saltwater environments
	Copper / Cu	1080	120	Good thermal and electrical conductivity	Conductive layers, e.g. on non-conductors
	Molybdenum / Mo	2600	700	Good sliding and dry-running properties, hard, tough, good abrasion resistance, also suitable as corrosion protection. Extremely dense layers possible, good compressive strength	Sliding surfaces in general. Crankshafts, synchronizer and piston rings, pump parts, guides, diesel engine components, fit and press seats, prevention of fretting corrosion
	Zinc / Zn	420	30	Low melting point, good corrosion protection	Corrosion protection such as aluminum (often also as an Al/Zn alloy), in particular for bridge and crane structures as well as containers, etc.
	Tungsten / W	3400	300	High-melting-point element	Electrical contacts, electrodes

Material Groups	Material	Melting point [°C]	Vickers Hardness [HV 0.3]*	Typical Properties	Application Areas
Steel	Various alloys	1325 – 1536	160 – 600	Depending on the alloy: flexible to very hard, high fretting resistance, oxidation and acid-resistant	General repairs of heavily worn parts
	NiCr alloy	1400	350	Corrosion-resistant, very good adhesion, temperature-resistant.	Base and intermediate layers
	MCrAlY M = Ni, Co, Fe,	1360 – 1410	400 – 500	High melting point, corrosion-resistant	Base and adhesive layers
	Stellite	up to 1400	up to 700	Corrosion-resistant, abrasion-resistant	General wear resistance, steam turbine components
	Tribaloy (cobalt or nickel-based)	up to 1600	up to 650	Wear and corrosion-resistant. Good hot hardness	Resistant to fretting with good sliding properties

Material Groups	Material	Melting point [°C]	Vickers Hardness [HV 0.3]*	Typical Properties	Application Areas
Self-flowing alloys	NiCrBSi, NiCoBSi, CoCrNiMoBSi, CoCrNiWBSi	1000 – 1100	up to 800	Hard, tough, dense, high abrasion resistance. Fusing possible. Good hot hardness	General wear protection, especially for valve plating. Also used as corrosion protection. Fused layers are absolutely impervious

Material Groups	Material	Melting point [°C]	Vickers Hardness [HV 0.3]*	Typical Properties	Application Areas
Non-ferrous alloys	Aluminum bronze	1060	210	Hard, tough, pressure-resistant, corrosion-resistant, good dry-running properties	Fretting protection with very good dry-running properties
	Nickel aluminum / NiAl	1400	230	Very dense with good adhesion and resistance to thermal shock and corrosion	Base or intermediate layers Bearing seats

Material Groups	Material	Melting point [°C]	Vickers Hardness [HV 0.3]*	Typical Properties	Application Areas
Ceramics	Aluminum oxide pure / Al2O3	2050	up to 1000	Very hard, abrasion-resistant, but relatively brittle, good electrical insulator	Textile machine components, electrical and thermal insulation, highly wear-resistant, e.g. for mixer blades
	Aluminum oxide + titanium dioxide /Al2O3 – TiO2	1900	850	The titanium dioxide content improves the density, sliding properties and polishability, and also reduces the brittleness, however lower hardness values are achieved	Mechanical seals, shaft protection sleeves, textile machine parts, hydraulic parts, pressure rollers
	Chromium oxide / Cr2O3	2435	1200	Excellent corrosion resistance, hard, highly abrasion-resistant, very dense, smooth layers	Pump parts, plungers, shaft protection sleeves, seal seats, textile machine parts
	Zirconium dioxide / ZrO2 – Y2O3 stab. – MgO stab. – CaO stab.	up to 2680	up to 800	Thermal insulation layer, poorly wettable with molten metal, electrically conductive at high temperatures	Casting machine components, molds, high-temperature nozzles, combustion chambers, high-temperature heating elements (>2,000°C)

Material Groups	Material	Melting point [°C]	Vickers Hardness [HV 0.3]*	Typical Properties	Application Areas
Cermets	Composite materials made from ceramics and metals or metal alloys			These materials are usually a combination of two or more widely differing components.	Special applications and also suitable as intermediate layers
	Tungsten carbide + cobalt / WC-Co	(up to 1500)*	1450	Hard, high fretting resistance, corrosion, erosion and thermal shock-resistant. Very dense layers, very good adhesion	General wear protection against abrasion and erosion
	Tungsten carbide + cobalt-chromium / WC-CoCr	(up to 1500)*	1400	For properties, see WC-Co coatings	Corrosion-resistant in aqueous solutions
	Tungsten carbide + nickel / WC-Ni	(up to 1500)*	1450	Like tungsten carbide, highly wear-resistant in corrosive media and at high temperatures	Chemical plant components, linings, hydraulic valves, machines and tool parts of all kinds. Ideal wear protection for aluminum components

Material Groups	Material	Melting point [°C]	Vickers Hardness [HV 0.3]*	Typical Properties	Application Areas
Pseudo alloys	Nickel graphite	(up to 1450)*	44	Self-lubricating thanks to free graphite	Plain bearings Also suitable for dry running (depending on the application)
	Ceramic metal Ceramic plastic Metal plastic	-	-	No longer a homogeneous alloy, but often combines the properties of the two partner materials	Hard, abrasion protection (see "Cermets"), hard, non-wetting (foodstuffs/printing technology), e.g. Al-Si polyester run-in coating

[ ]* The Vickers hardness values [HV 0.3] are guideline values for thermal spary coatings.

( )* Instead of the melting point, the sintering temperature for the composite materials is given here.