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Sulzer Metco Thermal Spraying

Plasma spray - HVOF coating

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Page 1: Plasma spray - HVOF coating

Sulzer Metco

Thermal Spraying

Page 2: Plasma spray - HVOF coating

2Thermal Spray

Sulzer Metco

Page 3: Plasma spray - HVOF coating

Contents

3Thermal Spray

Sulzer Metco

B. Tanner/SulzerMetco

1 Introduction 31.1 Surface Properties 31.2 Coating Processes 4

2 Thermal Sprayed Coatings 52.1 Definition 52.2 Substrate Materials 52.3 Coating Materials 62.4 Thermal Spray Coating Processes 72.4.1 Conventional Flame Spray Process 82.4.2 Electric Arc Wire Spray 82.4.3 Plasma Spray 82.4.4 High Velocity Oxy-Fuel Spray (HVOF) 92.4.5 Process Comparison 92.4.6 Infrastructure (System Requirements) 112.5 Coating Structure 122.6 Coating Characteristics 132.6.1 Wear Protection 132.6.2 Corrosion Control 132.6.3 Insulative Coatings (Thermal / Electrical) 132.7 Post Processing 132.7.1 Mechanical Post Processing 132.7.2 Sealing 132.7.3 Post-Coating Heat Treatment 142.8 Coating Characterization 14

3 Applications 153.1 Production Applications 163.1.1 Hard Chrome Alternative 163.1.2 Medical Implants 163.1.3 Textile Machinery 163.1.4 Gas Turbines 173.1.5 Printing Industry 173.1.6 General Industrial Uses 173.1.7 Consumer Goods 173.1.8 Automotive Industry 183.1.9 Steel Industry 183.1.10 Paper Industry 183.1.11 Aerospace 183.2 Salvage and Restoration 19

4 Summary 21

5 Appendix5.1 Reference Tables 225.2 Literature References 23

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The necessary surface requirements for a com-ponent vary considerably depending on itsservice environment.

The range of surface requirements include suffi-cient protection against wear, corrosion resist-ance, thermal insulation, electrical insulation, andeven improved aesthetic appearance.

In practice, it is quite rare components are onlyexposed to a single condition. Usually a combi-nation is present; for example, abrasive wearcombined with high thermal stress. Wear andcorrosion resistance are the most frequent con-ditions the surface coating must withstand.

1.1 Surface Properties

In all sectors of industry today, the catchphrase“better, faster, cheaper” is a common and validphrase, as it seems that production demandsare ever-increasing. Highly demandingrequirements and aggressive service conditionsoften lead to the premature loss of function.

Shown in Figure 1a is a completely worn peltonturbine nozzle needle after some thousand hoursof actual service. If this service life is deemedunacceptable, either the entire component mustbe made of a more wear resistant material, orthe area where the wear occurs must beprotected. For cost reasons, the usual decisionis the latter. This leads to the use of surfacecoatings. Either the entire component can becoated or just the area prone to attack, whicheverbest fulfills the requirements.

1 Introduction

Figure 1b • Nozzle needle with a chrome oxide coating toprevent wear.

Figure 1a • Chrome plated, 13/4 steel pelton turbine nozzleneedle after service.

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Coating Typical Coating Coating Material Characteristics ExamplesProcess Thickness

PVD 1-5 µm (40-200 µin) Ti(C,N) Wear resistance Machine tools

CVD 1-50 µm (40-2000 µin) SiC Wear resistance Fiber coatings

Baked 1-10 µm (40-400 µin) Polymers Corrosion resistance, AutomobilePolymers aesthetics

Thermal 40- 3000 µm (0.0015-0.12 in) Ceramic and Wear resistance, BearingsSpray metallic alloys corrosion resistance

Hard Chrome 10-100 µm (40-4000 µin) Chrome Wear resistance RollsPlate

Weld Overlay 0.5-5 mm (0.02-0.2 in) Steel, Stellite Wear resistance Valves

Galvanize 1-5 µm (40-200 µin) Zinc Corrosion resistance Steel sheet

Braze Overlay 10-100 µm (40-4000 µin) Ni-Cr-B-Si alloys Very hard, dense Shaftssurface

Coating Thickness [µm]

Sub

stra

te T

emp

erat

ure

[°C

]

1000

800

600

400

200

00.1 1 10 100 1000 10000

Table 1a • Principal coating processes and characteristics

The coating process havingthe greatest range of coatingmaterials, coatingthicknesses and possiblecoating characteristics isthermal spray, which will befurther examined in moredetail.

are not suitable for certain coating materials; also, thenecessary coating thicknesses are not attainable withall methods. Beyond that, the equipment necessaryfor some processes can be quite complex and, therefore,costly. The use of cost analysis can determine whethera coating is a practical solution. Today’s regulationsrequire that ecological criteria of the respective coatingprocesses must also be examined, as not all methodsare environmentally equal.

Table 1b • Comparison ofcoating processes

1.2 Coating Processes

There are quite a number of processes to apply coatings,as well as a nearly unlimited number of coating materials.To select the correct combination for the respectiveapplication, the knowledge of specialists is usuallyrequired.

Table 1 lists principal coating processes, the typicalcoating thicknesses attainable, common coatingmaterials, and sample applications. Some processes

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The definition according to DIN 657 [ 1 ]*: "...applyingthese coatings takes place by means of special devices/ systems through which melted or molten spray materialis propelled at high speed onto a cleaned and preparedcomponent surface..." This definition does not suffi-ciently describe the thermal spray process.

Figure. 2 is a diagram showing the principle of thermalspray. The coating material is melted in a heat source. Thisliquid or molten material is then propelled by processgases and sprayed onto a base material, where it solidifiesand forms a solid layer. The individual aspects of a thermalsprayed coating follows.

2.2 Substrate Materials

Suitable substrate materials are those that can withstandblasting procedures to roughen the surface, generallyhaving a surface hardness of about 55 HRc or lower.Special processing techniques are required to preparesubstrates with higher hardnesses. Because theadhesion of the coating to the substrate predominantlyconsists of mechanical bonding, careful cleaning andpretreatment of the surface to be coated is extremelyimportant.

After the removal of surface impurities by chemical ormechanical methods, the surface is usually roughenedusing a blasting procedure. This activates the surfaceby increasing the free surface energy and also offersthe benefit of increased surface area for bonding ofthe sprayed particles.

The liquid or molten coating particles impact the surfaceat high speed. This causes the particles to deform andspread like "pancakes" on the substrate.

2 Thermal Sprayed Coatings

2.1 Definition

Spraying materialEnergy

Gas or other operating media

Preparedsurface

Spray plume

Thermal sprayed coating

Spray gun

Relative motion

Figure 2 • Principle of thermal spraying

Oxide particlePorosity

Unmelted particleSubstrate

Figure 3 •Schematic diagram of a thermal sprayed coating

* Translated from the German text.

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2.3 Coating Material

In principle, any material that does not decompose asit is melted can be used as a thermal spray coatingmaterial. Depending on the thermal spray process, thecoating material can be in wire or powder form.

In Table 2, some of the most frequently used classesof materials are listed, along with a typical example,characteristics and sample applications. Choosing acoating material that is suitable for a specific applicationrequires special knowledge about the serviceenvironment as well as knowledge about the materials.

Apart from the physical characteristics, such ascoefficient of expansion, density, heat conductivity andmelting point, additional factors, such as particle shape,particle size distribution and manufacturing process ofpowder material (i.e., agglomerated, sintered,composited) will influence coating performance. Asmost spraying materials are available as alloys or blends,this leads to a nearly unlimited number of combinationoptions, and only through many years of experienceand broad know-how can a proper selection be made.

Heat from the hot particles is transferred to the coolerbase material. As the particles shrink and solidify, theybond to the roughened base material. Adhesion of thecoating is therefore based on mechanical “hooking”.This procedure is represented schematically in Figures2 and 3. The amount of metallurgical bond caused bydiffusion between the coating particles and base materialis small and can be neglected for discussions aboutbonding mechanisms (exception: Molybdenum).

Surface roughening usually takes place via grit blastingwith dry corundum. In addition, other media, such aschilled iron, steel grit or SiC are used for someapplications. Besides the type of grit, other importantfactors include particle size, particle shape, blast angle,pressure and purity of the grit media.

Material Class Typical Alloy Characteristics Example Application

Pure metals Zn Corrosion protection Bridge construction

Self-fluxing Fe-Ni-B-Si High hardness, fused Shafts, bearingsalloys minimal porosity

Steel Fe-Cr13 Economical, Repairwear resistance

MCrAlY NiCrAlY High temperature Gas turbine bladescorrosion resistance

Ni-graphite Ni-25C Anti-fretting Compressoralloys inlet ducts

Oxides Al2O3 Oxidation resistance, Textile industryhigh hardness

Carbides WC-Co12 Wear resistance Shafts

Table 2 • Common classes of thermal spray powder materials

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Coating

Workpiece

Fuel gas

Powder

Nozzle

Oxygen

Coating

Workpiece

Fuel gasWire

Air cap

OxygenAir passage

Nozzle

Figure 4a • Schematic diagram of the wire flame spray process

There are several different processes used to apply athermal sprayed coating. They are:• Conventional flame spray,• Electric arc wire spray,

• Plasma spray and• High velocity oxy-fuel spray (HVOF).

Details of these processes follow. For an overview,please see reference [ 2 ].

2.4.1.1 Wire Flame Spray

With the wire flame spray process, thewire spray material is melted in agaseous oxygen-fuel flame.

The fuel gas can be acetylene, propaneor hydrogen.

The wire is fed concentrically into theflame, where it is melted and atomizedby the addition of compressed air anddirected towards the coating surface.

2.4.1.2 Powder Flame Spray

This coating process is based on thesame operational principle as thewire flame spray process, with thedifference that the coating material isa spray powder. Thus, a larger selectionof spray materials is available, as notall spray materials can be manufacturedin wire form.

2.4 Thermal Spray Coating Processes

2.4.1 Conventional Flame Spray Process

Figure 4b • Schematic diagram of the powder flame spray process

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Coating

Workpiece

Cathode

Plasma gas + current

Powder port

Water-cooled anode

Insulator

Coating

Workpiece

Compressed air

Wire guideWire feed control

Voltage

Figure 5 • Schematic diagram of the electric arc wire spray process

Figure 6a • Schematic diagram of the plasma spray process

2.4.2 Electric Arc Wire Spray

With electric arc wire spray, an arc isformed by contact of two oppositelycharged metallic wires, usually of thesame composition. This leads tomelting at the tip of the wire material.

Air atomizes the melted spray materialand accelerates onto the substrate.The rate of spray is adjusted byappropriate regulation of the wire feedas it is melted, so a constant arc canbe maintained.

2.4.3 Plasma Spray

The principle of plasma spraying isshown schematically in Figure 6a. Ahigh frequency arc is ignited betweenan anode and a tungsten cathode. Thegas flowing through between theelectrodes (i.e., He, H2, N2 or mixtures)is ionized such that a plasma plumeseveral centimeters in length develops.The temperature within the plume canreach as high as 16000° K. The spraymaterial is injected as a powder outsideof the gun nozzle into the plasmaplume, where it is melted, and hurledby the gas onto the substrate surface.

Figure 6b • VPS plasma spraying

For specialized applications, a variantof the process is to plasma spray in acontrolled, low pressure atmosphere.In contrast to coating in air(atmospheric plasma spraying, or APS),the melted particles oxidize far lesswith vacuum plasma spraying (VPS),resulting in coatings of considerablyhigher quality [ 3 ].

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Kinetic Energy

Th

erm

al E

ner

gy

Coating

Workpiece

OxygenFuel gas

Powder and carrier gas

Compressed air

Expansion nozzle

Diamond shockwaves

Figure 7 • Schematic diagram of the highvelocity oxy-fuel spray process (HVOF)

2.4.4 High Velocity Oxy-FuelSpray (HVOF)

The high velocity oxy-fuel spray (HVOF)process is a relatively recent additionto the family of thermal sprayprocesses. As it uses a supersonic jet,setting it apart from conventional flamespray, the speed of particle impact onthe substrate is much higher, resultingin improved coating characteristics.The mechanism differs from flamespraying by an expansion of the jet atthe exit of the gun (Figure 7). Fuel gasesof propane, propylene, acetylene,hydrogen and natural gas can be used,as well as liquid fuels such as kerosene.

The processes previously discussed differ fundamentallyby the thermal and kinetic energy imparted to the sprayparticles by each process. The thermal energy isdetermined by the attainable flame temperature andthe kinetic energy of the spray particle is a function ofgas velocity. An energy comparison of the sprayprocesses is represented in Figure 8. The hightemperature of plasma spraying is particularly suitablefor materials with a high melting point, such as ceramics.

Figure 8 • Energy comparisonof thermal spray processes

The HVOF process, having high kinetic energy andcomparatively low thermal energy, results in a positiveeffect on the coating characteristics and is favorablefor spray materials such as tungsten carbide coatings.The comparison of the processes is largely of interestin relation to the coatings that result. Table 3 lists someimportant coating characteristics, organized by materialclass.

2.4.5 Process Comparison

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Table 3 • Comparison of thermal spray process coating characteristics (approximate values)Table 3 • Comparison of thermal spray process coating characteristics (approximate values)Table 3 • Comparison of thermal spray process coating characteristics (approximate values)Table 3 • Comparison of thermal spray process coating characteristics (approximate values)

Characteristics Coating Type Powder HVOF Electric Arc Plasma

Flame Spray Spray Wire Spray Spray

Gas temperature [°C] 3000 2600 - 3000 4000 (Arc) 12000 - 16000

[°F] 5400 4700 - 5400 7200 (Arc) 21500 - 29000

Spray rate [kg/h] 2 - 6 1 - 9 10 - 25 2 – 10

[lb/h] 4.5 - 13 2 - 20 22 - 55 4.5 - 22

Particle velocity [m/s] up to 50 up to 700 approx. 150 up to 450

[ft/s] up to 160 up to 2300 approx. 500 up to 1500

Bond strength [MPa] Ferrous alloys 14 - 21 48 - 62 28 - 41 21 - 34

[psi] 2000 - 3000 7000 - 9000 4000 - 6000

[MPa] Non-ferrous alloys 7 - 34 48 - 62 14 - 48 14 - 48

[psi] 2000 - 5000 7000 - 9000 4000 - 7000 4000 - 7000

[MPa] Self-fluxing alloys 83+ (fused) 70 - 80 15 - 50 ---

[psi] 12000+ (fused) 10000 - 11500 2200 - 7200 ---

[MPa] Ceramics 14 - 34 --- --- 21 - 41

[psi] 4000 - 5000 --- --- 3000 - 6000

[MPa] Carbides 34 - 48 83+ --- 55 - 69

[psi] 5000 - 7000 12000+ --- 8000 - 10000

Coating thickness [mm] Ferrous alloys 0.05 - 2.0 0.05 - 2.5 0.1 - 2.5 0.4 - 2.5

[mil] 2 - 80 2 - 100 4 - 100 15 - 100

[mm] Non-ferrous alloys 0.05 - 5.0 0.05 - 2.5 0.1 - 5.0 0.05 - 5.0

[mil] 2 - 200 2 - 100 4 - 200 2 - 200

[mm] Self-fluxing alloys 0.15 - 2.5 0.05 - 2.5 --- ---

[mil] 6 - 100 2 - 100 --- ---

[mm] Ceramics 0.25 - 2.0 --- --- 0.1 - 2.0

[mil] 10 - 75 --- --- 4 - 80

[mm] Carbides 0.15 - 0.8 0.05 - 5.0 --- 0.15 - 0.8

[mil] 6 - 30 2 - 200 --- 6 - 30

Hardness [HRc] Ferrous alloys 35 45 40 40

(see Table A2 in Non-ferrous alloys 20 55 35 50

the Appendix) Self-fluxing alloys 30 - 60 30 - 60 --- 30 - 60

Ceramics 40 - 65 --- --- 45 - 65

Carbides 45 - 55 55 - 72 --- 50 - 65

Porosity [%] Ferrous alloys 3 - 10 < 2 3 - 10 2 - 5

Non-ferrous alloys 3 - 10 < 2 3 - 10 2 - 5

Self-fluxing alloys < 2 (fused) < 2 --- ---

Ceramics 5 - 15 --- --- 1 - 2

Carbides 5 - 15 < 1 --- 2 - 3

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Process Control Center

Control console

Gas Management Center

Powder feeder

Robot

Turntable

Plasmapowersupply

Spray gun

Electricalsupply cabinet

Heatexchanger

Water chiller

Spray cabin

Filter

Figure 9 • Typical coating facility

such as a turntable. Therefore, it is possible to applycoatings to very complex geometries. The ventilationsystem with its filtering unit is not to be forgotten, asthe so-called "overspray", i.e. the powder material thatdoes not stick to the component surface, can beexhausted and trapped in the filtering unit. The spraydust produced by some spray materials can ignite;hence, in these situations, the entire system must befire and explosion proof. Figure 24 on page 19 showsa modern, automated, high productivity coating facility.

2.4.6 Infrastructure (System Requirements)

Besides the principal item of a coating system, that ofthe spray gun, there are numerous other items necessaryto apply coatings in an industrial environment. Figure9 shows a coating system. The spray cabin serves asa shield for the sound and dust produced by the spraygun during spraying. The cabin has inlet ports for thepower, gas supply and the process monitoring andcontrol equipment. Usually, the gun is mounted on arobot, with movement programmed for the specificcomponents to be coated. The component to besprayed is usually mounted on a manipulation unit,

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Thermal sprayed coatings exhibit a certain amount ofprocess-dependant porosity. The highest porosityvalues develop for flame and electric arc spray. HVOFcoatings, however, produce very dense layers withporosity under 0.5 %. Typical plasma coatings haveapproximately one to two percent porosity.

The sprayed coating develops as the spray guntraverses repeatedly over the surface and applies thecoating in layers, bit by bit; with a typical layer thicknessof 10 to 20 µm (400 to 800 µin) . Oxides can form duringthe time between passes on the outer surface of thelayer. This oxidation can be minimized by spraying ina vacuum or inert atmosphere.

Fine dust from overspray and unmelted particles canbecome trapped in the coating. The dust is the resultof coating material that does not adhere to the workpieceduring spraying. Subsequent spray passes drag theseparticles towards the coating surface where theybecome trapped in the coating layer.

Figure 10 shows a photomicrograph of an arc sprayedcoating of X40 CR 13. One recognizes the laminatedstructure and existing porosity (the black regions). Thecircular particles are those that did not melt completelybefore resolidifying. The thickness of this coating canbe to up to several millimeters.

Figure 10 • Arc wire spray coating of X40Cr13 Figure 11 • HVOF spray coating of WC-(Co,Cr)12

2.5 Coating Structure

One can produce much denser coatings with the HVOFspray process. In Figure 11, a coating of WC (CoCr) isrepresented. There is hardly any porosity visible. Thebright regions consist of WC hard phase, which isembedded in a ductile matrix of cobalt and chrome.Here the typical coating thickness is with 0.2 to 0.3mm (0.008 to 0.012 inches).

Thermal sprayed coatings generally exhibit high internalstresses, which are attributable to the process ofsolidification and cooling. The hot particle contractsas it cools, which gives rise to the internal coatingstress.

If the ratio of the thermal expansion coefficients for thesubstrate material and the coating material are takeninto account, these stresses can be compensated forby producing compressive stresses. Temperature controlduring the coating process, therefore, plays an importantrole to determine if the substrate must be cooled orwarmed.

Sometimes, the adhesion of a ceramic coating on asubstrate does not meet the necessary requirementfor bond strength. In order to increase the bond strength,a bond coat is applied, usually composed of a NiAl orNiCr alloy, which acts as an intermediate layer betweenthe substrate and the ceramic coating. Suchintermediate coatings can also perform another

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2.6.2 Corrosion Protection

Low carbon, unalloyed steel and cast iron materialsare susceptible to rust and therefore often need constantsurface protection. This can be produced by flame

2.6 Coating Characteristics

As previously stated, the porosity of a thermal spraycoating is process-dependant, and exhibits an ansio-tropic, layered structure. These basic characteristicscan be modified within a wide range to suit the specificapplication.

2.6.1 Wear Protection

One of the most important uses of thermal sprayedcoatings is for wear protection [ 4 ]. In these applications,ceramics, and above all, carbide materials are used.The commonly used carbide materials are WC/Co orWC/CoCr. Here, the carbide hard phases (WC) exhibitexcellent resistance against abrasive and erosive wear,and are embedded in a ductile matrix of cobalt.

sprayed coatings of aluminum or zinc. The main areasof application are for bridges the offshore structures.For high temperature applications, protective coatingsof MCrAlY materials can be used. These are usuallyapplied using controlled atmosphere plasma spray.

2.6.3 Insulative Coatings (Thermal / Electrical)

Ceramic materials are excellent thermal and electricalinsulators. They also possess good oxidation and wearresistance. These characteristics are quite useful onengine and turbine components as thermal barriercoatings. The thermal barrier coating lowers the skintemperature of the substrate, thereby extending theuseable service life. On the other hand, efficiency isimproved as a result of reduced heat loss at the sameoperating temperature. These coating systems consistof a bond coat, which is usually an oxidation resistantMCrAlY material (M = Fe, Ni or Co) and a ceramic topcoat. An yttrium-stabilized zirconium oxide material isoften used for the top coat because of its good thermalshock characteristics.

2.7 Post Processing

Because many sprayed coatings have an inherentlyrough surface finish and porosity, it is frequentlynecessary to post process the surface. In addition,specification procedures can call for other methods,such as post-coating diffusion, nitrating, hot isostaticpressing or shot peening, as required.

2.7.1 Mechanical Post Processing

Thermal sprayed coatings possess a rough surfacethat is between 5 and 20 µm (see Table A1 in theAppendix). Therefore, it will often be necessary tomachine many components to achieve a final dimensionand surface finish. Depending on the coating applied,the surface can be worked by conventional machiningor can be ground and lapped to final dimension.

2.7.2 Sealing

Sealing sprayed coatings serves primarily to fill thepores and microcracks in the coating, which providesadditional protection against corrosive media that wouldotherwise penetrate to the base material.

When resin or wax sealants are used, those in a liquidcondition penetrate into the pores and then harden(usually with heating). If the sealant is sprayed or paintedon, the procedure may have to be repeated severaltimes to insure complete coverage.

Sealants can also be used to provide surfaces withnon-adhesive characteristics (PTFE based sealers).

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2.7.3 Post-Coating Heat Treatment

With thermal post treatments, one differentiates betweendiffusion to increase the bond between the base materialand the coating and fusing of "self-fluxing" alloys.

The self-fluxing alloys form a special class of spraymaterials in that after the spray coating is applied, theadditional step of melting the coating is employed. Thespray powders of these alloys are generally blends ofchrome, iron and nickel that contain a substantialamount of temperature suppressants, such as boronand silicon.

During the spray process, there is some, partial formationof intermetallic phases. Subsequent fusing of the coatingcauses a complete transformation of the materials andthe formation of hard silicide and boride phases.Diffusion into the substrate also occurs, improvingbonding, and porosity is nearly eliminated,with nointerconnecting porosity.

These coatings exhibit extremely good corrosionresistance as well as very high hardness. The commonmanual method used to melt the coating is through theuse of an acetylene torch. Fusing in a furnace, withlaser, electron beam or with induction heating is alsopossible. The temperature required to effect diffusion

In Figure 12, just such a coating of a NiCrBSi alloy isshown before and after fusing of the coating. Thehomogenization of the coating structure is clearlyrecognizable, as is the reduced porosity and densenature of the fused coating.

Aftercoating

Afterfusing

Apart from the coating characteristics that are importantwith respect to the application, there are somecharacteristics that can be determined with relativelylittle effort and can be accomplished in terms ofstandardized quality control measurements. These are:• Visual inspection• Coating thickness measurement• Surface finish measurement

If necessary, test pieces sprayed at the same time andunder the same conditions as the coating can beexamined to determine additional characteristics aboutcoating quality:• Cross-sectioning for the determination of precise

coating thickness, porosity and structure, as well asexamination of the microstructure for unmeltedparticles and oxide inclusion

• Microhardness measurement• Bond strength determination, using a special adhesive

and test equipment• Bend tests

The test measurements use standardized samplegeometries. Exact execution and interpretation is inaccordance with various standards [ 6 ]. Beyond that,there are many other possibilities. The characterizationof coatings in practice is quite complex, and there aremany different procedures that are not common.

In addition, the various methods for elemental analysiscan be included, as well as scratch testing, tribologicalinvestigations, stress analysis and corrosion andabrasion behavioral investigations. Since these are alldestructive examinations, they are not especially suitablefor production and are rarely employed on test pieces.Many end users have developed their own specificationsand test methods to characterize and judge the qualityof their coatings. In particular, the aerospace and spaceindustries have very strict guidelines.

2.8 Coating Characterization

Figure 12 • Self-fluxing coating

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30°

30°

2mm (0.08”)

5mm (0.2”) t3t>20mm

(0.75”)5mm (0.2”)

R>3tsimplified structure

t

50 - 80mm(2 - 3.2”)

with special spray gun,quality is reduced

>80mm (3.2”)

Not Feasible Feasible Preferred Configuration

Figure 13 • Favorable coating geometries for coating

3 Applications

In order to use thermal sprayed coatings to bestadvantage, the coating material has to be properlyselected, the coating process has to be chosen andthe process parameters developed. Also, the componentto be coated has to be correctly dimensioned forcoating.

The preferred geometries for coatings are disks, flatpanels and rotationally symmetrical components, asillustrated in Figure 13.

<50mm (2”)

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3.1 Production Applications

Figure 14 • Nose gear of an F5 Tiger with a WC/CoCrcoating

Figure 16 • Various textile machinery components

Figure 15 • Biocompatible SUME®PLANT titaniumcoating on a hip implant

For strong and durable anchoring of orthopedicimplants, such as artificial hip joints, surface finish isof great importance. Sulzer Metco SUME®PLANTcoatings, applied using the vacuum plasma process,are purposely sprayed with a very fissured surface thatallows the bone to grow into it. There are SUME®PLANTcoatings that act as a biocompatible titanium coating(Figure 15), or bioactive hydroxy apatite coatings, whichactively accelerates the growth of the natural bone intothe surface of the prosthesis.

3.1.2 Medical Implants

SUME®TEX coating systems were developed as theresult of many years of cooperation with textilemachinery manufacturers. These coatings arecharacterized by a precise definition of the morphologyproduced using various handling methods and thetopology of the surface. The surface texture is ofparticular importance for production components incontact with thread. In order to maximize fiberproduction, coatings of ceramic oxides are used, usuallywith a nickel bond coat that provides corrosionprotection. Sample applications are represented inFigure 16.

3.1.3 Textile Machinery

Because of growing requirements for environmentalprotection, plating shops are subject to ever tougherrestrictions. As an alternative to hard chrome plating,thermal spray coatings can be used to provide wearand corrosion protection. Both pure chrome and variouscarbide coatings can be used [ 5 ]. In order to achievecorrosion resistance as close as possible to that ofchrome plate, the high velocity oxy-fuel process isused. The characteristics of HVOF coatings, in part,exceed those of chrome plate, however, to obtain thereflective surface appearance of hard chrome platingthe coating can be ground and lapped. An exampleapplication where thermal spray is used to replace hardchrome plate is that of landing gear components forairplanes. Figure 14 shows a WC/CoCr coated nosegear of an F5 Tiger.

3.1.1 Hard Chrome Alternative

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Figure 17 • Coated gas turbine vanes

Figure 18 • Anilox printing roll with a laser engravedSUME®PRINT coating

Figure 19 • Bearing shaft with a babbitt coating

Coated rollers and cylinders are used extensively forprinting machinery. In partnership with customers fromthe paper and printing industry, several SUME®PRINTcoatings were developed. Plasma sprayed chromeoxide coatings for inking rollers exhibit very finemicrostructures, which can then be laser engraved witha very small and tight pattern (Figure 18).

3.1.5 Printing Industry

In both stationary and flight gas turbines, thermalsprayed coatings are used in many different placesand for many different functions. Protective coatingsfor high temperature corrosion resistance, thermallyinsulating coatings, clearance control coatings and therepair of superalloy components with coatings of similarcomposition are just some examples (see Figure 17).

3.1.4 Gas Turbines

The largest variety of applications is for machineryindustry. Figure 19 shows a bearing shaft coated witha babbitt coating used in cement plants.

This special, particularly porous coating is designedup for oil lubrication, providing a reservoir to preventseizure.

Other examples of applications are piston rings fordiesel engines, piston rods in compressors, pumpbearings, valve covers, etc.

3.1.6 General Industrial Uses

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Figure 20 • Coated household steam iron soleplate

Figure 21 • Dual-RotaPlasma®

3.1.9 Steel Industry

3.1.8 Automotive Industry

Next to the coating of numerous small parts, the newestbreak-through development for Sulzer Metco is coatingsfor aluminum engine blocks. The cylinder bores of theengines are coated by means of a special rotatingplasma gun manipulator (Figure 21), which can applythe coating to the interior of the small bores with awear resistant surface.

Although most uses for thermal spray coatings weredeveloped for very specialized components, there arealso applications within the consumer goods industry.An iron sole plate, on which a ceramic coating wasapplied as protection from wear is shown in Figure 20.A coating of an anti-stick material is subsequentlyapplied. Similar coatings are also applied to non-stickfrying pans.

3.1.7 Consumer Goods

Figure 22 • HVOF coating of a sink roll

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The rolls used in the steel working industry must handlevery heavy thermal loads of hot steel. In addition, slagfrom steel production must be reckoned with, and inzinc production, corrosive attack from the molten zinc.Several different SUME®STEEL coating systems havebeen qualified for use on both new parts and repairapplications. (Figure 22)

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3.1.10 Paper Industry

3.1.11 Aerospace

Besides those components already mentioned for gasturbines, there are additional coatings used on airplanes.Figure 24 shows a coating on the interior of a combus-tion chamber.

Figure 23 • SUME®CAL coating after superfinishing

Figure 24 • Combustion Chamber

Thermal spray can be used also in repair proceduresto restore components to their original dimensions. Thecoatings can be turned or ground to finished size.Ni- Cr, Ni-Al or Ni-Cr-Al are used as repair materialsfor alloyed steels.

3.2 Salvage and Restoration

Figure 25 • Repair procedure

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Rollers in the paper industry are subject to the mostdiverse of operating environments including wear,chemical attack from dyes, thermal stress on heatedrollers and mechanical stress from doctor blades. Atthe same time, they must exhibit a high surface finishover as long a length of time as possible. TheSUME®CAL coatings were developed to meet theserequirements, particularly for calendar rolls (Figure 23).

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Figure 26 • A modern LPPS high-volume production system for coating gas turbine blades

With thermal spray, probably more so than any othercoating process, there is almost no limitation in thenumber of options available for substrate and coatingmaterial combinations. As a result, thermal spray coat-ings lend themselves to a broad scope of applications,both for new component manufacture and for repair.The characteristics of the coatings can be varied withina wide range to suit specific application requirements.This presupposes, however, the many years of experi-ence and the know-how of specialists.

4 Summary

With our unsurpassed in-house knowledge in the designand construction of thermal spray systems, equipmentand materials, as well as many years of coating expe-rience for both prototype and production components,Sulzer Metco is the ideal partner for all thermal sprayneeds.

Please contact your Sulzer Metco account represent-ative for further information or visit us on the web atwww.sulzermetco.com.

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5 Appendix5.1 Reference Tables

Table A1 • Surface finish (approximate cross-reference values)

Table A2 • Hardness within the range HRc 80 to 20 (approximate cross-reference values)

Rockwell Vickers Brinell Tensile strengthHRc HV HB Rm [N/mm2]

80 186579 178778 171077 163376 155675 147874 140073 132372 124571 116070 107669 100468 94267 89466 85465 82064 78963 76362 74661 72060 69759 67458 653 620 218057 633 599 210556 613 580 203055 595 570 199554 577 551 192053 560 532 184552 544 515 178051 528 495 170050 513 485 1665

Rockwell Vickers Brinell Tensile strengthHRC HV HB Rm [N/mm2]

50 513 485 166549 498 475 163048 484 456 155547 471 447 152046 458 437 148545 446 423 145044 434 409 138543 423 399 135042 412 390 132041 402 380 129040 392 371 125539 382 361 122038 372 352 119037 363 340 115036 354 335 114035 345 330 111534 336 323 109533 327 314 106032 318 304 103031 310 295 99530 302 285 96529 294 280 95028 286 271 91527 279 266 90026 272 257 86525 266 252 85024 260 247 83523 254 242 82022 248 238 80021 243 233 78520 238 228 770

Surface Finish Ra in µm Ra in µin Rz in µmN0 0.0125 0.5N1 0.025 0.1 0.29N2 0.05 2 0.55N3 0.1 4 0.91N4 0.2 8 1.74N5 0.4 16 2.6N6 0.8 32 4.65N7 1.6 64 7.87N8 3.2 128 15.6N9 6.3 250 40N10 12.5 500 63N11 25 1000 100N12 50 2000 160

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5.2 Literature References

[1] DIN EN 657; Thermal Spray – Begriffe, Einteilung; Beuth-Verlag, Berlin (1994)[2] H.D. Steffens, J. Wilden: “Moderne Beschichtungsverfahren”, DGM-Verlag,

ISBN 3-88355-223-2, (1996)[3] P. Huber: “Vakuumplasmaspritzen”, oberfläche surface, 10 (1992), 8[4] H. Simon, M. Thoma: “Angewandte Oberflächentechnik für metallische Werkstoffe”,

Hanser-Verlag, München (1985)[5] E. Lugscheider. H. Reymann: “Hochgeschwindigkeitsflammgespritzte Chromschichten

zum Verschleiss-und Korrosionsschutz”, Schweissen und Schneiden, 50 (1998), 44[6] DIN 50600; Metallographische Gefügebilder, Beuth-Verlag, Berlin

DIN EN 582 Ermittlung der Haftzugfestigkeit, Beuth-Verlag, Berlin (1994)DIN EN 10109 Teil 1; Härteprüfung, Beuth-Verlag, Berlin (1995)

DVS 2310 Teil 2; Anleitung zur Schliffherstellung, DVS, Düsseldorf, (1989)

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Sulzer Metco

4. Issue • ©2008 Sulzer MetcoThermal Spraying

Perfect Solutions through Optimum Materials and Innovative Technologies

Sulzer Metco is a global leader in surface engineering solutions and services offering:

• A broad range of thermal spray, thin film and other advanced surface technology equipment, • Integrated systems and materials• Specialized coating and surface enhancement services• Manufactured components for the turbine, automotive and other industries• Customer support services

Sulzer Metco provides a comprehensive manufacturing, distribution and service network, catering to aerospace, power generation, automotive and other strategic growth industries.

To take control of your surface engineering challenges, contact your Sulzer Metco sales office, visit our website at www.sulzermetco.com or email us at [email protected]

www.sulzermetco.com • [email protected]

Information is subject to change without prior notice

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