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AWS C2.23M/C2.23 Specification for the Application of Thermal Spray

Coatings (Metallizing) of Aluminum !inc an" Their Alloys an" Composites

for the Corrosion #rotection of Steel

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AWS C2.23M/C2.23 'ocument %nformation

Title

Specification for the Application of #hermal Spra! Coatin%s &Metalli'in%( of Aluminum)

*inc) an #heir Allo!s an Composites for the Corrosion Protection of Steel

American Wel"ing Society

#u$lication 'ate+an ,) 2--3

Scope

eneral.

#his stanar is a proceure for the application of metallic #hermal Spra! Coatin% SCs( of

aluminum) 'inc) an their allo!s an composites for the corrosion protection of steel.

equire equipment) application proceures) an inprocess qualit! control &0C( chec1points

are specifie. #his stanar ma! be use as a procurement ocument. Anne A presents a fill

intheblan1s moel procurement specification. #he flo ia%ram in 4i%ure , pro5ies ano5er5ie of the thermal spra! coatin% process presente in this stanar.

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6ot inclue in this stanar are requirements for esi%n an fabrication) thermal spra!

equipment qualification) coatin% selection) an operator an inspector certification. 4or

successful thermal spra! application) the steel structure an components shoul be esi%ne

an fabricate accorin% to 6AC7 Stanar P-,89. Aitional consieration shoul be

%i5en to elments hose o!fuel cut e%es ma! affect harness hich ma! preclue

aequate profile epth.

Safety.

#he basic precautions for thermal spra!in% are essentiall! the same as for elin% an cuttin%.

Information can be foun on Safet! in the Safet! Chapter in AWS Thermal Spraying:

Practice, Theory, and Application: A6SI *;ea an follo safet! precautions in the manufacturer?s equipment technical

instructions an manuals an the feestoc1 Material Safet! Data Sheet. #his stanar ma!

in5ol5e ha'arous materials) operations) an equipment. #his stanar oes not purport to

aress all of the safet! problems associate ith its use. It is the responsibilit! of the user ofthis stanar to establish appropriate safet! an health practices an etermine the

applicabilit! of re%ulator! limitations prior to use.

Potential thermal spra!in% ha'ars inclue eposure to 5apors) ust) fumes) %ases) noise &from

the spra! %un() an arc ultra5iolet &U@( raiation. Aitionall!) improperl! use thermal

spra! equipment can create potential fire an eplosion ha'ars from the fuel an carrier

%ases an a potential electrical shoc1 ha'ar from the electrical an electronic equipment an

char%e ire spools. #o minimi'e ha'ars) proper safet! precautions shall be folloe.

perators shall compl! ith the proceures in the safet! references) the manufacturer?s

technical manuals) an the material safet! ata sheets.

#hermal spra!in% can be a completel! safe process hen performe b! an operator ho

follos the recommene precautionar! measures) has a proper unerstanin% of thermal

spra!in% practices) an has 1nole%e) s1ill) an eercises care in usin% thermal spra!

equipment.

*nits of Measure

#his specification ma1es use of both the International S!stem Units &SI( of units an U.S.

Customar!. #he measurements are not eact equi5alents: therefore each s!stem must be use

inepenentl! of the other ithout combinin% in an! a!. #he specification C2.23M uses SIunits. #he specification ith the esi%nation C2.23 uses U.S. Customar! Units. #he latter are

shon in appropriate columns in tables or ithin parenthesis & ( hen use in the tet.

Suitable con5ersions encompassin% stanar si'es of both can be mae) hoe5er) if

appropriate tolerances are applie in each case.

=. AWS an A6SI stanars can be obtaine from Blobal 7n%ineerin%) ,= In5erness Wa!

7ast) 7n%leoo) C 9-,,2 =88>. #elephones &9--( 9=;8,8

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+ey,or"s

'inc/aluminum allo!

thermal spra! coatin%

Aluminum

steel protectionflame spra!

'inc

arc spra!

aluminum metal matri composite

A$out %&S

I"S &6$S7 I"S( is a leain% %lobal pro5ier of critical technical information) ecision

support tools an relate ser5ices in a number of inustries incluin% aerospace an efense)

automoti5e) construction)electronics) anener%!. I"S ser5es customers ran%in% from lar%e

%o5ernments an multinational corporations to smaller companies an technical professionals

in more than ,-- countries. I"S been in business for more than ;= !ears an emplo! morethan 2)3-- people aroun the orl.

Metal Coating

Man! ne materials ha5e been e5elope) but steel remains the principal construction

material for automobiles) appliances) an inustrial machiner!. ecause of steelEs

5ulnerabilit! to attac1 b! a%%ressi5e chemical en5ironments or e5en from simple atmospheric

oiation) metal coatin% is necessar! to pro5ie 5arious e%rees of protection) ran%in% from

hotippe an electroplate process to tou%h pol!mers an flamespra!e ceramics. In

%eneral) corrosi5e en5ironments contain more than one acti5e material) an the coatin% must

resist penetration b! a combination of oii'ers) sol5ents) or both. #hus) the best barrier is one

that resists FbroabanF corrosion.

Integrity of the Metal Coating in Use

Ph!sical inte%rit! of the metal coatin% is as important as its chemical barrier properties in

man! applications. 4or instance) metal coatin% on impellers that mi abrasi5e slurries can beabrae quic1l!: coatin%s on pipe Goints ill colflo aa! from a loae area if the creep

rate is not lo: an metal coatin% on flan%es an support brac1ets can be chippe or

penetrate urin% assembl! if impact stren%th is inaequate. Selectin% the best metal coatin%

for an application requires e5aluatin% all effects of the specific en5ironment) incluin%

thermal an mechanical conitions.

Zinc Metal Coating

ne of the most common an inepensi5e protection methos for steel is pro5ie b! metal

coatin% ith 'inc. *inccoate) or %al5ani'e) steel is prouce b! 5arious hotippin%techniques) but more steel companies toa! are mo5in% into electro%al5ani'in% so the! can

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pro5ie both. *inc or1s as a barrier metal coatin% an as a sacrificial metal coatin% to

pre5ent oiation. If the 'inc coatin% is scratche or penetrate) it continues to pro5ie

protection b! %al5anic action until the 'inc la!er is eplete. #his sacrificial action also

pre5ents corrosion aroun punche holes an at cut e%es.

#he %raes of 'inccoate steel commerciali'e in recent !ears ha5e been esi%ne too5ercome the rabac1s of traitional %al5ani'e steel) hich has been ifficult to el an

to paint to a smooth finish. #he neer metal coatin%s are intene specificall! for stampe

automoti5e components) hich are usuall! Goine b! spot elin% an hich require a

smooth) Class A painte finish.

Aluminum Metal Coating

#o t!pes of aluminumcoate steel are prouce) each for a ifferent 1in of corrosion

protection. #!pe , has a hotippe aluminumsilicon metal coatin% to pro5ie resistance to

both heat an corrosion. #!pe 2 has a hotippe metal coatin% of commerciall! pure

aluminum) hich pro5ies ecellent urabilit! an protection from atmospheric corrosion.

#!pe , aluminumcoate steel resists heat scalin% to ,)2=-H4 an has ecellent heat

reflecti5it! to

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7lectroless nic1el metal coatin%) in contrast to con5entional electroplatin%) operates

chemicall! instea of usin% an electric current to eposit metal. #he electroless metal coatin%

process eposits a uniform coatin% re%arless of substrate shape) o5ercomin% a maGor

rabac1 of electroplatin% the ifficult! of uniforml! platin% irre%ularl! shape

components. Conformin% anoes an comple fiturin% are unnecessar! in the electroless

process. Deposition thic1ness is controlle simpl! b! controllin% immersion time. #heeposition process is autocatal!tic) proucin% thic1nesses from -., to = mil. In %eneral) nic1el

coatin%s are noular. As coatin% thic1ness increases) noule si'e also increases. ecause the

columnar structure of the coatin% flees as the substrate mo5es) nic1elboron resists chippin%

an ear.

Metal Coating Co-deposition

Another tren in composite electroless metal coatin% appears to be toar coeposition of

particulate matter ithin a metal matri. #hese coatin%s are commerciall! a5ailable ith Gust

a fe t!pes of particulates iamon) silicon carbie) aluminum oie) an P#47 ith

iamon heain% the list in popularit!. #he coatin% can be applie to most metals) incluin%

iron) carbon steel) cast iron) aluminum allo!s) copper) brass) bron'e) stainless steel) an hi%h

allo! steels.

Conversion Metal Coatings

7lectroless metal coatin%s are more accuratel! escribe as con5ersion coatin%s) because the!

prouce a protecti5e la!er or film on the metal surface b! means of a chemical reaction.

Another con5ersion process) the blac1 oie finish) has been ma1in% pro%ress in applications

ran%in% from fasteners to aerospace. lac1 oie is %ainin% in popularit! because it pro5ies

corrosion resistance an aesthetic appeal ithout chan%in% part imensions.

n a chemical le5el) blac1 oiin% occurs hen the iron ithin the steelEs surface reacts to

form ma%netite &4e3;(. Processors use inor%anic blac1enin% solutions to prouce the

reaction. ii'in% salts are first issol5e in ater) then boile an hel at 29- to 29=H4. #he

prouct surface is cleane in an al1aline soa1 an then rinse before immersion in the

blac1enin% solution. After a secon rinse) the finish is seale ith rust pre5entati5es) hich

can prouce finishes that 5ar! from sli%htl! oil! to har an r!.

lac1 oiin% prouces a microporous surface that reail! bons ith a topcoat. 4or eample)

a supplemental oil topcoat can be ae to boost saltspra! resistance to the same le5el as that

of 'inc plate ith a clear chrome coatin% &,-- to 2-- hr(.

lac1 oie can be use ith mil steel) stainless steel) brass) bron'e) an copper. As lon% as

parts are scale free an o not require pic1lin%) the finish ill not prouce h!ro%en

embrittlement or chan%e part imensions. peratin% temperatures ran%e from cr!o%enic to

,)---H4.

Metal Coating by Sputtering

4ormerl! use primaril! to prouce inte%ratecircuit components) metal coatin% b!

sputterin% has mo5e on to lar%e) prouctionline Gobs such as coatin% of automoti5e trim

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parts. #he metal coatin% sputterin% process eposits thin) aherent films in a plasma

en5ironment on 5irtuall! an! substrate.

Metal coatin% b! sputterin% offers se5eral a5anta%es to automoti5e manufacturers for an

economical replacement for con5entional chrome platin%. Sputterin% lines are less epensi5e

to set up an operate than platin% s!stems. An because sputtere metal coatin%s are uniformas ell as thin) less coatin% material is require to prouce an acceptable finish. Also)

pollution controls are unnecessar! because the process oes not prouce an! effluents. Metal

coatin% b! sputterin% requires less ener%! than con5entional platin% s!stems. Metal coatin% b!

sputterin% is the onl! eposition metho that oes not epen on meltin% points an 5apor

pressures of refractor! compouns such as carbies) nitries) silicies) an bories. As a

result) films of these materials can be sputtere irectl! onto surfaces ithout alterin%

substrate properties.

Much of the research in metal coatin% b! sputterin% is aime at proucin% solifilm

lubricants an har) earresistant refractor! compouns. #here is interest in these

tribolo%ical applications because metal coatin% can be sputtereposite ithout a biner)ith stron% aherence) an ith controlle thic1ness on cur5e an compleshape surfaces

such as %ears an bearin% retainers) races) an balls. Also) because metal coatin% b! sputterin%

is not limite b! thermo!namic criteria) unli1e most con5entional processes that in5ol5e heat

input) film properties can be tailore in a!s not a5ailable ith other eposition methos.

esearch on sputtere solilubricant metal coatin% has been one mainl! ith MoS2. ther

metal coatin% that has been one ith sputterin% inclues tun%sten carbie) titanium nitrie)

lea oie) %ol) sil5er) tin) lea) inium) camium) P#47) an pol!imie. f these coatin%s)

%olcolore titanium nitrie coatin%s are most prominent. #i6 coatin%s are chan%in% both the

appearance an performance of hi%hspeesteel metal cuttin% tools. ife of #i6coate tools)

accorin% to proucersE claims) increases b! as much as tenfol) metalremo5al rates can be

ouble) an more re%rins are possible before a tool is iscare or rebuilt.

Metal Coating by Ion Plating

#he basic ifference beteen metal coatin% b! sputterin% an b! ion platin% is that sputtere

material is %enerate b! impact e5aporation an transferre b! a momentum transfer process.

In ion platin%) the e5aporant is %enerate b! thermal e5aporation. Ion platin% combines the

hi%h throin% poer of electroplatin%) the hi%h eposition rates of thermal e5aporation) an

the hi%h ener%! impin%ement of ions an ener%etic atoms of sputterin% an ionimplantation

processes.

#he ecellent aherence of ionplate metal coatin% is attribute to the formation of a %rae

interface beteen the film an substrate) e5en here the to materials are incompatible. #he

%rae interface also stren%thens the surface an subsurface 'ones an increases fati%ue life.

"i%h throin% poer an ecellent aherence ma1es possible metal coatin% of comple

threeimensional confi%urations such as internal an eternal tubin%) %ear teeth) ball

bearin%s) an fasteners. Bears for space applications) for eample) ha5e been ion plate ith

-.,2 to -.2 Jm of %ol for lubrication an to pre5ent col elin% of the %ear pitch line. Ion

platin% has also been use) on a prouction basis) to plate aluminum on aircraft lanin%%ear

components for corrosion protection.

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Metal Coating by hermal Spraying

Metal coatin% b! arc spra!in%) a thermal form of spra!in% of metals) is one to metal surface

usin% a ire arc %un. #he coatin% metal is in the form of to ires that are fe at rates that

maintain a constant istance beteen their tips. An electric arc liquefies the metal) an an air

spra! propels it onto the substrate. ecause particle 5elocit! can be 5arie consierabl!) theprocess can prouce a ran%e of metal coatin% finishes from a fine to a coarse teture.

Arc spra!e metal coatin% is somehat porous) bein% compose of man! o5erlappin%

platelets. Use in applications here appearance is important) thermall! spra!e metal

coatin% can be seale ith pi%mente 5in!l copol!mers or paints) hich usuall! increase the

life of the metal coatin%. Arc spra!e metal coatin% is thic1er than those applie b! hot

ippin%) ran%in% from 3 to = mil for li%htut!) lotemperature applications to 8 to ,2 mil for

se5ere ser5ice.

ecause 'inc an aluminum are) uner most conitions) more corrosion resistant than steel)

the! are the most iel! use metals use in arc spra!e metal coatin%. In aition) since

both metals are anoic to steel) the! act %al5anicall! to protect ferrous substrates. In %eneral)

aluminum is more urable in aciic en5ironments) an 'inc performs better in al1aline

conitions. 4or protectin% steel in %as or chemical plants) here temperatures mi%ht reach

;--H4) an aluminum metal coatin% is recommene. A 'inc metal coatin% is preferre for

protectin% steel in fresh) col ater. In aqueous solutions abo5e ,=-H4) aluminum metal

coatin% is the usual choice.

4or ser5ice to ,)---H4) a thermall! spra!e aluminum coatin% shoul be seale ith a

siliconealuminum paint. eteen ,)--- an ,)>=-H4) the aluminum coatin% fuses an reacts

ith the steel base metal) formin% a coatin% that) ithout bein% seale) protects the structurefrom an oii'in% en5ironment. An) for continuous ser5ice to ,)9--H4) a nic1elchrome allo!

is use) sometimes folloe b! aluminum.

In 7urope) here thermall! spra!e metal coatin%s for corrosion protection ha5e been far

more iel! use than in the U.S.) man! structures such as bri%es are still in %oo conition

after as lon% as ;- !ears) ith minimum maintenance. ther applications inclue ehaust %as

stac1s) boat hulls) masts) an man! outoor structures.

Metal coatin% b! thermal spra!in% has become much more than a process for rebuilin% orn

metal surfaces. #han1s to sophisticate equipment an precision control) it is no factore

into the esi%n process) proucin% uniform metal coatin% onto metal an ceramic. With someprocesses e5en %raient coatin%s can be applie. #his is one b! coatin% the substrate ith a

material that pro5ies a %oo bon an that has compatible epansion characteristics) then

sitchin% %rauall! to a secon material to prouce the require surface qualit! such as ear

resistance) solerabilit!) or thermalbarrier characteristics.

Metal Coating by Plasma Spraying

Plasma spra! metal coatin% relies on a hot) hi%hspee plasma flame &nitro%en) h!ro%en) or

ar%on( to melt a poere material an spra! it onto the substrate. A irectcurrent arc is

maintaine to ecite %ases into the plasma state. #he hi%hheat plasma &in ecess of ,=)---H4(enables this process to hanle a 5ariet! of metal coatin% materials as ell as ceramics)

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carbies an plastics. Althou%h most coatin% materials are heate to ell be!on their meltin%

points) substrate temperatures commonl! remain belo 2=-H4.

#he plasma spra! metal coatin% process has foun ie acceptance in the aircraft inustr!.

Plasmaspra!e metal coatin%s protect turbine blaes from corrosion) an spra!e ceramics

pro5ie thermalbarrier protection for other en%ine parts.

efinements in plasma spra! metal coatin% technolo%! inclue a ear resistance coatin%

material that lens itself to formin% amorphous/microcr!stalline phases hen plasma spra!e.

#he resultant coatin% pro5ies ecellent corrosion resistance ith minimal oiation at hi%her

temperatures. #his promises to eliminate problems of or1harene cr!stalline coatin%s that

chip or elaminate in response to stress) hich ha5e pre5iousl! been ta1en care of b!

epensi5e allo!in% elements.