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 melted on or fused, 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 via repeated passes with the burner.

Thermal Spraying

Base Materials

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 deal of flexibility in terms of the possible material combinations.

Coated Base Materials

Coating Thickness

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 μm 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 initially applied layer by layer.

Metallography

Component Temperature

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 melted down or remelted at temperatures exceeding 1,000°C.

Component Temperature at Nova Swiss

Finishing

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.

Finishing of the Sprayed Layers

Quality Assurance

Far from taking a "spray-and-pray" approach, our thermal spraying processes are based on consistent quality awareness on four levels: Material, Machine, Personnel 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.

Quality Assurance

Thermal Spraying at Nova Swiss®

The process to be used depends on the specific application. Profitability 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

Material
Groups
Material Melting point
[°C]
Vickers Hardness
[HV 0.3]*
Typical Properties Application Areas
Pure
Metals
Aluminum / Al 660 80 Smooth Corrosion protection
for industrial and saltwater environments
  Copper / Cu 1080 120 Good thermal and electrical conductivity Sliding surfaces in general. Crankshafts, synchronizer and piston rings, pump parts, guides, diesel engine components, fit and press seats, prevention of frictional corrosion
  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 Conductive layers,
e.g. on non-conductors
  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, rust 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 /
WC-CoCr
(up to 1500)* 1450 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 (initial layers)

[ ]* The Vickers hardness values [HV 0.3] are guideline values for the thermally sprayed layers.  

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

Coating materials from NOVA SWISS®

Contact

  • Dr. Stephan Siegmann (Manager Division Surface Technology / Sales, Member of the Executive Management)

    Dr. Stephan Siegmann
    Manager Division Surface Technology / Sales, Member of the Executive Management
    Tel: +41 52 354 16 07
    Fax: +41 52 354 16 91
    stephan.siegmann@novaswiss.com

  • Marco Schade (Chief Executive Officer)

    Marco Schade
    Chief Executive Officer
    Tel: +41 52 354 16 10
    Fax: +41 52 354 16 05
    marco.schade@novaswiss.com