surface engineering part 1(1)

7/21/2019 Surface Engineering Part 1(1)

1/71

Surface Engineering Part 1Surface Engineering Part 1

Dr Zhu LiuDr Zhu Liu

Corrosion and Protection CentreCorrosion and Protection Centre

School of MaterialsSchool of Materials

The University of ManchesterThe University of Manchester

MATS 64532: Surface Engineering and Materials DesignMATS 64532: Surface Engineering and Materials Design


2/71

Lecture ArrangementLecture Arrangement

L1 Surface Engineering I Introduction to SE

Hot-dipping Electroplating Chemical plating Thermal spray Overlay coating

Cold spray Diffusion coating

L3 Surface Engineering III

Introduction to LSE Heat-treatment Surface re-melting Surface alloying Cladding Shock-peening

L2 Surface Engineering IIhysical vapour deposition Chemical vapour deposition Ion implantation Sol-gel coating

L4 Surface Engineering I

Surface te!turing Surface modification of

polymers Surface finishing


3/71

Definiti!n !f Surface EngineeringDefiniti!n !f Surface Engineering

1" Treatment of the surface and near-surface regions of

a material to allo# the surface to perform functions

that are distinct from those functions demanded from

the $ulk of the material %defined $y &S' hand$ook(

2" The design of a surface and a su$strate together as a

system) to give a cost effective performance of #hich

neither is capa$le alone %defined $y CEST(


4/71

Surface EngineeringSurface Engineering

Surface "r!#ertiesSurface "r!#erties

I!roved corrosion resistanceI!roved corrosion resistance

I!roved "ear resistanceI!roved "ear resistance

I!roved theral insulationI!roved theral insulation

I!roved high#te!erature o$idation resistanceI!roved high#te!erature o$idation resistance

I!roved adhesion %for !olyers&I!roved adhesion %for !olyers&

I!roved "etta'ility %'oth !olyers and etals&I!roved "etta'ility %'oth !olyers and etals&

Ec!n!mic $enefitsEc!n!mic $enefits


5/71

%lassificati!n !f Surface Engineering

%&anging surface

metallurg'

%&anging surface

c&emistr'

Adding

c!atings

I!n

im#lantati!n

Laser surface

all!'ing

Localised surface

hardening* +lame)

Induction) Laser and

Electron-$eam

,apid solidification*

Laser surface melting

Shot peeningLaser shock peening

Hot-dip coatingElectroplatingChemical platingDiffusion coatingThermal sprayOverlay coatingCold sprayhysical vapour

depositionChemical vapour

depositionSol-gelLaser Cladding

%&anging surface

structure

Laser surface

te(turing

)#atterning

)structuring


6/71

(or a!!lications of corrosion !rotection)(or a!!lications of corrosion !rotection)

Metallic coatingsMetallic coatings

*nodic coating*nodic coating

Cathodic coatingCathodic coating

+eutral coating+eutral coating

Ceraic, !olyer coatingsCeraic, !olyer coatings

%lassificati!n !f %!atings%lassificati!n !f %!atings


7/71

An!dicAn!dic%!atings%!atings

Coating material is less no'elthan the su$strate to $e protected"

Cathodic or sacrificial protection

& $arrier to the environment

E!amples* inc-coatings on steel .galvanised steel/

(eatures) at $reaks or pores

or cut edges the coating

corrodes preferentially andprovides sacrificial protection

to the underlying steel

su$strate"http*00###"gordonengland"co"uk0corrosion"htm
http://www.gordonengland.co.uk/corrosion.htmhttp://www.gordonengland.co.uk/corrosion.htmhttp://www.gordonengland.co.uk/corrosion.htm


8/71

%at&!dic%at&!dic%!atings%!atings

Coatings is ore no'leto the su$strate to $e protected

E!amples* nickel-coatings on steel) copper-coating on steel

Liitation) the coating

must provide a complete$arrier to the su$strate from

the environment1 other#ise)

at $reaks) pores or cut edges

the steel #ill corrode)

causing severe pitting

$ecause the anodes #ill $e

small #hile the cathode area

is much larger"

http*00###"gordonengland"co"uk0corrosion"htm
http://www.gordonengland.co.uk/corrosion.htmhttp://www.gordonengland.co.uk/corrosion.htmhttp://www.gordonengland.co.uk/corrosion.htm


9/71

Arrangement !f metals in *al+anic SeriesArrangement !f metals in *al+anic Series

rotection of car$on steels*rotection of car$on steels*

An!dic c!atingsAn!dic c!atings

2n2n&l .e!ceptional cases/&l .e!ceptional cases/

CdCd

'g .too reactive/'g .too reactive/

%at&!dic c!atings%at&!dic c!atings

TinTin

3ickel3ickel

CopperCopper

Corrosive End %*nodic or less no'le&

------------------------------------------------

Magnesium

,inc

Aluminium%admium

Ir!n)steel

Stainless steel -acti+e.

Tin

/ic0el

%!##er

Stainless steel -#assi+e.

*!ld

Protective End %Cathodic or ost no'le&


10/71

!tdi##ed %!atings!tdi##ed %!atings

Definiti!n* & metallic coating o$tained $y dipping the su$strate

metal into a molten metal"4 coating #ith lo#er melting temperature

Stages:

5/ re-treatment* degreasing) descaling and rinsing

6/ +lu!ing* #etting

7/ Dipping*

8/ ost-treatment* annealing) or rolling) or rapid coling

T'#ical &!tdi##ing #r!cesses:

9alvanied steel

http*00###"youtu$e"com0#atch:v;c6n?hS$s
http://www.youtube.com/watch?v=c2J07n5hSbshttp://www.youtube.com/watch?v=c2J07n5hSbs


11/71

T'#ical Surface A##earance !f *al+anied SteelT'#ical Surface A##earance !f *al+anied Steel

Surface appearance* 5==@ 2n A $right) polycrystalline structure #ith

visi$le crystalline grains of inc) some times several centimetres in

sie"


12/71

T'#ical Micr!structure !f *al+anied SteelT'#ical Micr!structure !f *al+anied Steel

utla'er -23 m.* 5==@ 2nMetallurgical !nding* various 2n-+e intermetallics

,n7e intermetallics is rittleA limited additional shaping


13/71

t&er ,incased %!atingst&er ,incased %!atings

To improve f!rmailit' and ductilit'of coatings $y addition of other elements into the molten inc $ath"

8*alfan8 -,n59Al.:

Continuous coil-coating) much improved ductility

Better corrosion resistance than 2n coating

Similar function of sacrificial protection

8*al+alume -,n559Al.:

Continuous coil-coating) much improved ductility

Even $etter corrosion resistance than 2n-?@&l coatingLimited sacrificial protection

8*al+anneal8:

+ull 2n-+e intermetallic layer $y heat-treatment

Similar function of sacrificial protection


14/71

%!rr!si!n "r!tecti!n !f *al+anied Steels%!rr!si!n "r!tecti!n !f *al+anied Steels

,n

Steel

,n #r!+ides:

"&'sical arrier .corrosion rate of 2n

is ?-5=@ that of steel/* hen e!posed

to the atmosphere) inc reacts #ith

o!ygen to form inc o!ide) #hich further reacts #ith #ater

molecules in the air to form inc hydro!ide" +inally inc hydro!ide reacts #ith car$on dio!ide in the atmosphere to

yield a thin) impermea$le) tenacious and uite insolu$le dull

grey layer of inc car$onate #hich adheres e!tremely #ell to

the underlying inc) so protecting it from further corrosion"

%at&!dic #r!tecti!n: 2inc coatings prevent corrosion of the

protected metal $y forming a physical $arrier) and $y acting as a

sacrificial anode if this $arrier is damaged"


15/71

9alvanied Steel

9uard ,ail System

9alvanied

steel pipe

9alvanied

Steel $ucket

A##licati!ns !f *al+anied SteelsA##licati!ns !f *al+anied Steels

Lifetime of galvanied steel* up to ?= years

E!tended lifetime $y duple! system* up to >? years"
http://www.galvanizeit.org/resources/files/AGA%20PDFs/Duplex%20Systems.pdfhttp://www.galvanizeit.org/resources/files/AGA%20PDFs/Duplex%20Systems.pdfhttp://www.galvanizeit.org/resources/files/AGA%20PDFs/Duplex%20Systems.pdf


16/71

Electr!de#!siti!n)Electr!#lating

rinciples A ho# it #orks

Consist of* anode) cathode)

aueous-metal solution and

po#er supplier

Corrosion process in reverse

E!ample* 3i plating

&node* 3i 3i6E

6e-

Cathode* 3i6E 6e-3i

.6HE 6e-H6/


17/71

Surface "re#arati!n and Electr!#latingSurface "re#arati!n and Electr!#lating

ProcedureDegreasing

Etching0chemical pre-treatment

ashing0rinsing

re-plating or other surface treatmentashing0rinsing

lating

ashing0rinsing

ost-treatments .annealing) polishing) passivating) etc"/

I!ortance of surface cleanliness) In real #orld) surface

preparation is more crucial than plating to ensure good

adhesion and surface uality


18/71


Structure of !lating

Epita!ial gro#th for a fe#hundred atomic layer

.clean and o!ide-free surface/

Coating thic-nessroportional to the current density

and length of deposition time) leading

to one of the maFors dra#$acks in

electroplating A ina$ility of achieving uniform deposition forirregular shaped components

4 Thro"ing !o"er) a'ility of a !lating solution to !roduce a

unifor etal distri'ution on an irregular sha!ed o'.ect/


19/71


Ma.or dra"'ac-s

oor thickness uniformity on comple! components Hydrogen em$rittlement for steels

3ot applica$le to insulating su$strates

Possi'le environental concerns "ith !lating 'aths

*dvantages)Lo# temperature treatment .G 5== C/ A no distortion and

no metallurgical changesCoatings are dense #ith e!cellent adhesion to the su$strate

3o technical limitation to coating thickness - thick layers possi$leSelective deposition possi$le $y applying masks&pplica$le to a #ide range of metal su$strates

Lo# cost


20/71

A##licati!ns !f S#ecific %!ating S'stemsA##licati!ns !f S#ecific %!ating S'stems

+ic-el !lating* corrosion protection) undercoat forelectroplating chromium for decorative purpose of

automotive) consumer products and office furniture

Chroiu !lating) Chromium easily passivated A cannot $e

used as solu$le anode" Decorative .tarnish-resistant/) hard)#ear-resistance coatings .al#ays need nickel as undercoat/"

3ote a pro$lem #ith cracks and pores #ithin the chromium

coating) leading to limited corrosion protection"

Cadiu and Zinc !lating) Cadmium for marineenvironment) and inc .G m/ for industrial environment"

Tin !lating* for non-aggressive environment) tin coating

.="?-5 m/ is reuired) such as tin plated steel cans"


21/71

A##licati!ns !f S#ecific %!ating S'stems

Micr! and /an!c!m#!site %!atings'etal 'atri! Composite .''C/ A Ceramic particles

.car$ides) o!ides/ in metal matri! .cermet/

Sie of ceramic particles* a fe# micron) su$micron) or nano-"

Ceramic particles suspendingin an electrolyte

Co-deposit ceramic particlesinto metal matri!


22/71

A##licati!n E(am#les !f Electr!de#!siti!nA##licati!n E(am#les !f Electr!de#!siti!n

Mild steel c!re and

electr!#lated ;it& %u

9old plating

olished electroplated chrome or multi-layer Environmental concerns

Chromium Coating for

Superior 'etalrotection


23/71

%&emical "lating

Cheical !lating* deposition of metal on su$strate

#ithout applying e!ternal current"

T"o fors

-1. Immersi!n #latingCu6E +e ; +e6E Cu

-2. Electr!less #lating

3i6E

6HO6-

; 3i H6 6O6-

Mec&anisms* Electrochemical in nature) involving

$oth o!idation and reduction reactions


24/71

Immersi!n "lating

Immersion plating

O!idation* 2n 2n6 6e-) anodic) E= ; ="> J

,eduction* Cu6 6e-Cu) cathodic) E=; ="78 J

------------------------------------------------------------------------------

Overall reaction* 2n Cu62n6 Cu E= ; 5"5 J

& simply displacement reaction $et#een an anodic su$strate

and a more no$le metal ion in solution #ith the deposition

reaction driven $y local dissolution of the su$strate

Limited plating thickness .5m/* Displacement processcontinues until almost the entire su$strate is covered #ith

copper"


25/71

Electr!less "lating

Electroless plating

,eduction* 3i6E 6e-3i E=;-6? mJ

O!idation* H6O6- H6O H6O7- 6HE 6e- E=; ?= mJ

------------------------------------------------------------------------------

3i6E

H6O6-

H6O 3i H6O7-

6HE

E=

; 6? mJ

0 Sustaina'le o$idation reaction

&utocatalytic mechanism

lating thicker coating layers


26/71

%&emical %!ating)Electr!less #lating%&emical %!ating)Electr!less #lating

*dvantages)

Lo# temperature treatment 'ore corrosion resistant than electrodeposited Cr

Can coat comple! shapes uniformly

Hard particles can $e incorporated to increase Hv

T+E can $e incorporated to reduce friction

Can coat most metals and some insulators

Disadvantages'ore e!pensive than electroplated Cr

eattreatment

is needed t! de+el!# !#timum #r!#erties


27/71

T&ermal S#ra' %!atingsT&ermal S#ra' %!atings


28/71

T&ermal S#ra' %!atingsT&ermal S#ra' %!atings

A c!mm!n feature !f all t&ermal s#ra' c!atings is t&eir

lenticular !r lamellar grain structureresulting fr!m t&e

ra#id s!lidificati!n !f small gl!ules? flattened fr!m

stri0ing a c!ld surface at &ig& +el!cities

http*00###"gordonengland"co"uk0


29/71

T&ermal S#ra' %!atings: $!nding

T&ermal S#ra' %!ating $!nding Mec&anisms:

1. Mec&anical 0e'ing !r interl!c0ing

6/ Diffusion $onding or 'etallurgical $onding

7act!rs affecting !nding and suse@uent uild u# !f

c!ating:

5/Cleanliness1 6/Surface area 7/Surface topography or

profile1 8/Temperature . thermal energy/1 ?/Time .reaction

rates K cooling rates etc" /1 /Jelocity . kinetic energy /1 >/

hysical K chemical properties1 /hysical K chemical

reactions"


30/71

T&ermal S#ra' %!atings

%!ating structure

Lamellar !r flattened grains? !(ide inclusi!ns!utlining t&e grains !r #article !undaries

"!r!sit': 1259

L!; im#act energ' - unmelted #articles ) l!;

+el!cit' .

S&ad!;ing effects - unmelted #articles ) s#ra'angle .

S&rin0age and stress relie+e effects


31/71

ari!us t&ermal s#ra' c!ating #r!cesses

L!;energ' #r!cesses:

%!musti!n ;ire t&ermal s#ra'

%!musti!n #!;der t&ermal s#ra'

Arc ;ire t&ermal s#ra'

ig&energ' #r!cesses:

"lasma t&ermal s#ra'

7 t&ermal s#ra'


32/71

%!musti!n T&ermal S#ra' -7lame S#ra'.

%!ating Material in #!;der? !r ;ire f!rm

7lame -!('acet'lene !r &'dr!gen m!st c!mm!n.

7lame +el!cit': 5 m)s and Tem#erature ac&ie+ed B 3 C%

L!; #erf!rmance c!atings -&ig& #!r!sit'? #!!r !nding.

http*00###"gordonengland"co"uk0


33/71

ig& el!cit' ('gen 7uel -7. T&ermal S#ra'

Similar t! c!musti!n t&ermal s#ra'? ut ;it& s#ecial

design !n t!rc&

7lame +el!cit' u# t! su#ers!nic +alues


34/71

"lasma S#ra'

7!rmati!n !f #lasma

Material in t&e f!rm !f #!;der inected int! a +er' &ig&

tem#erature #lasma flame ra#idl' &eated and accelerated

t! a &ig& +el!cit'

ig& +el!cit' and &ig& tem#erature -u# t! 55 C%.


35/71

%!m#aris!n !f ari!us T&ermal S#ra' "r!cesses

T&ermal

#r!cess

el!cit'

m)s

Tem#era

ture? C%

Ma(> s#ra'

rate? 0g)&

"!r!sit'?

9

$!nding

%!musti!n

#!;der

3 22 62 #!!r

7 6115 31 14 B >5 ;ellad&erent

"lasma

s#ra'

24 55 5 B 2 ;ell

ad&erent


36/71

A##licati!ns !f T&ermal S#ra'ed Al %!atings

T&ermal s#ra' metallic c!atings? ;it& and ;it&!ut sealersT&ermal s#ra' metallic c!atings? ;it& and ;it&!ut sealersand t!#c!ats? as a means t! #re+ent c!rr!si!n !f steeland t!#c!ats? as a means t! #re+ent c!rr!si!n !f steel

surfaces>surfaces>

T'#es !f metallic c!atings included are #ure inc? #ureT'#es !f metallic c!atings included are #ure inc? #ure

aluminum? and inc)aluminum all!'? F59 inc)159aluminum? and inc)aluminum all!'? F59 inc)159aluminum ' ;eig&t>aluminum ' ;eig&t>

A##licati!nsA##licati!ns

ig& tem#erature resistantig& tem#erature resistant

E(cellent resistance t! #!lluted and marine en+ir!nmentsE(cellent resistance t! #!lluted and marine en+ir!nments

7!rms !(ide la'er7!rms !(ide la'er

Geduces c!rr!si!nGeduces c!rr!si!n

E l f T& l S % ti


37/71

E(am#les !f T&ermal S#ra' %!atings

E(am#le 1:Metal Matri$ Co!osite %MMC& Coatings

''C coatings) comprised of a hard ceramic phase

em$edded in a metallic matri!) are increasingly $eing

applied for many industrial components in the petrochemical

industry) po#er generation and offshore applications toprovide cost effective protection against #ear and corrosion"

Ty!ical e$a!les)

C CoCrC 3iCrBSi

Cr6C7 3iCr

Ty!ical coating techniue) HJO+

E l f T& l S % ti


38/71


3anoparticles cannot $e sprayed directly1

,econstitution of 3s into spherical micro-sied granules

3ano-C0Co feedstock po#der

Conventional C0Co feedstock po#der

Coating !ro!erties)

Hardness of n-C0Co

coating is higher than that ofthe conventional one"

Corrosion resistance of n-

C0Co coating is higher than

that of the conventional one"

Potential !ro'les)

De-car$uriation of Cdue to higher surface to

volume ratio"


39/71


E(am#le 2:E(am#le 2:Plasa s!rayed theral 'arrier coatingsPlasa s!rayed theral 'arrier coatings

Coating material* M6O7-2rO6 .56=-6?=

m/) plus metallic $ond-coat .?=-56= m/

Coating characteristics*orosity .interconnected/) microcracks

and layered-structure

High-temperature corrosion $ehaviour*

enetration of corrosive gas) fuel and

liuid through the inter-connected pores

to get contact #ith metallic su$strate A

o!idation A spallation of coatings


40/71

A##licati!ns !f T&ermal S#ra' %!atings

HJO+ spraying Tungsten Car$ide 0 Co$alt Chromium Coating

.C05=Co8Cr/ onto ,oll for the aper 'anufacturing Industry

&tt#:));;;>'!utue>c!m);atc&=+H0T"$m&s3M

&tt#:));;;>'!utue>c!m);atc&=+H,g0SJF&J4
http://www.youtube.com/watch?v=k-T_PBmhs3Mhttp://www.youtube.com/watch?v=ZgkSY8hYbH4http://www.youtube.com/watch?v=ZgkSY8hYbH4http://www.youtube.com/watch?v=k-T_PBmhs3M


41/71

A##licati!n E(am#les !f Surface EngineeringA##licati!n E(am#les !f Surface Engineering

2as tur'ine 'lades2as tur'ine 'lades

Environment* High-temperature) corrosive"

Coatings* Ceramic coatings as thermal $arrier

Bond coat* 'Cr&lM alloy
http://doc.tms.org/servlet/ProductCatalog?container=JOM+2005+January


42/71

T'#ical A##licati!ns !f T&ermal S#ra' %!atings

"lasma s#ra': %eramic? metal?

caride c!atings t! s!l+e

industrial #r!lems and ;ear?

arasi!n? c!rr!si!n? t&ermal

arriers>

7: Ser+ing all industriesre@uiring e(treme ;ear resistant?

dense caride and metal c!atings

l % i


43/71

+erla' %!atings+erla' %!atings

Melting!f a la'er !f material !n t&e sustrate t!

f!rm a c!ating

eating s!urce: ;elding t!rc&? arc? #lasma?

electr!neam>

$!nding: metallurgical fusi!n

Main a##licati!ns:

ardfacing: engine +al+e seats

%!rr!si!n #r!tecti!n

Ge#airing !f damaged c!m#!nents


44/71

%!m#ared ;it& t&ermal s#ra' c!atings

%!m#aris!n +erla' c!atings T&ermal s#ra'

T&ic0ness 26 mm /!rmall' B 1

mm/umer !f

la'ers%an e multi

la'ers/!rmal single

la'er

$!nding 7usi!n Mec&anical

interl!c0ing

Micr!structure S!lidificati!n Laminar and#anca0e li0e

% ld S -Ki ti S .


45/71

%!ld S#ra' -Kinetic S#ra'.

"!;der sie: 1 5"!;der sie: 1 5 mm

"!;der #article +el!cit':"!;der #article +el!cit': 45 1 m)s -su#ers!nic.45 1 m)s -su#ers!nic.

"!;der im#inging !n t&e sustrate in s!lid f!rm at"!;der im#inging !n t&e sustrate in s!lid f!rm at

tem#erature ;ell el!; melting tem#eraturetem#erature ;ell el!; melting tem#erature

!; %!ld s#ra' %!ating $uilds


46/71

!; %!lds#ra' %!ating $uilds

Stage 5* Su$strate cratering and first

layer $uilt up of particles .initialcratering) deformation of su$strate)

spat formation) fracturing of surface

o!ides on metal particles and

su$strates and first particle layer

formation

Stage 6* article deformation and

realignment .multilayer coating

$uild-up/

Stage 7* 'etallic $ond formation

$et#een particle0particle and void

reduction

Stage 8* +urther densification and

#ork hardening of the coatingJan Steenkiste) T"H") et al) Surface and Coatings

Technology 5?8 .6==6/ 67>-6?6"


47/71

Im#!rtant "arameters !f %!ld S#ra' "r!cess

A critical +alue !f #!;der #article +el!cit' -c.

Determining fact!rs f!r #!;der #article +el!cit':

gas tem#erature

#article sie

m!lecular ;eig&t !f gas

-L!;er gas m!lecular

;eig&t? t&e faster t&e#!;der #article +el!cit'.


48/71

Micr!structural %&aracteristics !f

%!lds#ra' %!atings

T!# la'er:

#!r!usmicr!structure

Inner la'er:

densermicr!structure

Tam#ing effect

Ti on steel su$strate

Jan Steenkiste) T"H") et al) Surface and Coatings Technology 5?8 .6==6/ 67>-6?6"


49/71

Diffusi!n %!atings

'etals and alloys are used at high-temperature environment"

Protection echanis* rotective elements lead to

formation of chromia) alumina and silica scales respectively)

for o!idation and corrosion protection"

Process) & protective element .or elements/) like%r? Al !rSi) is deposited on the surface of the $ase metal) and diffused

into the $ase metal at high temperature

Diffusion coatings !rocesses)

&luminiing1

Chromiing1

&$ove-the-pack or out-of-pack chemical vapour deposition

Aluminising


50/71

Aluminising

"r!cess* carried out $y a pack cementation process"

"ac0* &l or &l alloy po#der)

halide salt .activator/) e"g" 3H8Cl) to form metal halide

#ith high vapor pressure

inert filler .alumina/Tem#erature re@uired* a$ove ?= to 55==C for several hours

ack

Su$strate to $e

coated

Aluminising


51/71

Aluminising

%&emical reacti!ns and diffusi!n*

on heating* activator reacts #ith the metallic component of the

pack to form metal halides) e"g"

3H8Cl N 3H7 HCl

HCl &l N &lCl! H6

&lCl!has high vapour pressure #hich diffuse through the pack)

to form &l deposit on the su$strate) then diffuse into the

su$strate to form +e-&l .or 3i-&l/ intermetallics

T'#ical micr!structures !f aluminised car!n steels: layers

of -+e6&l?) P-+e&l and0or +e7&l along the depth"

Aluminising


52/71

Aluminising

Acti+it' !f aluminising #r!cess depends on* the amount

and type of &l source alloy) the amount and type of

halide activator) the amount of inert o!ide and process

temperature"

7!r aluminising !f /i ase all!'s:

ig&acti+it' aluminising* high concentration ofaluminium-rich vapour at the surface of the part

and coatings gro# mainly $y in#ard diffusion of

aluminium

L!;acti+it' aluminising* the coatings are formedmainly $y out#ard diffusion of nickel1 the

formation of higher aluminide phases is suppressed"

L!;acti+it' aluminiing


53/71


The pack contains aluminium alloy po#der " The concentration of aluminium-rich vapor is lo#" The coatings gro# mainly ' !ut;ard diffusi!n !f nic0el" The processing temperature is 5===-55?=C) i"e" the high end" 'icrostructure* 3i&l) no post-coating heat treatment reuired The coatings have coarse-grained columnar microstructures

#ith limited ductility" The coatings thickness is less than high-activity coating

thickness"

T&e effect !f sustrate materials !n aluminiing: e>g>

1./i

2./i%r -+ariati!n !f %r c!ntent.



54/71


Aluminising !n #ure /i sustrate

Originalinterface Kirkendall

porosity

Nidiusion

Inclusions

5/ Coating gro#s out#ard

6/ Original surface

7/ 3i diffuses out#ard faster

than &l diffuses in#ard Aformation of Qirkendall

porosity at the interface"

8/ +ormation of inclusions $y

trapping pack particles in

the coating"



55/71


Aluminising !n /i%r sustrate

Originalinterface Kirkendall

porosity

Nidiusion

Inclusions

,egion $elo# the original

surface*

5/ Depletion of 3i

6/ Enrichment of Cr

+or 3i-5=Cr alloy*

Cr is still in solid solution

+or 3i-6=Cr alloy*

Cr precipitates out of the solid

solution to form RCr .reduce

ductility/"

ig&acti+it' aluminiing


56/71

ig& acti+it' aluminiing The pack contains pure aluminium po#der" The concentration of aluminium-rich vapour is high"

The coatings gro# mainly ' in;ard diffusi!n !f aluminium" The processing temperature is >== - ==C" The coatings is then heat-treated) typically 8h at 5=?=-55==C)

to convert $rittle aluminium-rich phases) such as -3i&l7and -

3i6&l

7) to P-3i&l"

High-activity aluminiing is more common than lo#-activity

aluminiing"

%!m#aris!n et;een l!; and &ig&


57/71

# g

acti+it' aluminiing

%!m#aris!n !f t&e f!ll!;ing as#ects:

5" Original surface

6" Diffusion direction .3i) &l/

7" 'icrostructures* Qirkendall porosity) em$edded pack particles)

8" 'echanical properties

Aluminising /i%r su#erall!'

f!r gas turine engines

%&r!mising


58/71

g

"r!cess* carried out $y a pack cementation process"

"ac0* Cr po#der) ammonium chloride and inert alumina filler

Micr!structures:

L!;car!n steels: t&e c&r!mium de#!sits !n t&e surface t! f!rm a s!lid

s!luti!n all!' !f ferritic ir!nc&r!mium

Medium&ig& car!n steels: tend t! result in t&e f!rmati!n !f a la'er !f

c&r!miumir!n caride #re+enting %r diffusi!n #r!cess>

Tem#erature re@uired* typically to 55?=C for several hours1

eight@Chr

omium

Temperature)

oC??

56

=

58==

==

= 56

a/ $/

Distance into su$strate

eight @ Chromium

+e-Cr euili$rium diagram

R

te

A!+et&e#ac0 #r!cesses


59/71

# #

Su$strate to $e coated is positioned a$ove the pack in a retort

9as-phase process &luminising or Chromising

Ad+antages !+er #ac0 #r!cesses:

a$ility to uniformly coat internal passages and holes

coating #ithout pack particle entrapment .no direct contact

#ith the pack/

$etter mechanical properties in terms of lo#er transition

temperature .3i&l/

ut!f#ac0 c&emical +a#!ur de#!siti!n


60/71

# # #

%&amer* a gas mi!ture of aluminium chloride and hydrogen .&lCl7is

created e!ternally $y passing HCl or Cl6gas over &l/

%&emical reacti!ns and diffusi!n*

HCl 6&l --- 6&lCl7 7H61

6&lCl7 8&l --- &lCl

&lCl 3i 7H6 --- 3i&l HCl .g/

Tem#erature:5=== C for 8 hours

L!; aluminium acti+it'* microstructure

is similar to lo#-activity pack aluminising"

The use of molten aluminium is to increase

aluminium activity $y forming lo#er

chlorides of aluminium #hen passing the

inlet gas mi!ture over liuid aluminium"


61/71

%!m#aris!n !f +a#!ur#&ase aluminising

;it& #ac0 cementati!n aluminising

a#!ur#&ase aluminiing is m!re c!stl'

In large ret!rts? +ariati!ns in t&e c!ncentrati!ns !f +a#!ur

#&ase reactants can result in n!nunif!rm c!ating t&ic0ness

a#!ur#&ase aluminiing is effecti+e f!r c!ating c!m#le(

s&a#ed #arts? and dust &aards ass!ciated ;it& &andling

large am!unts !f #!;der are a+!ided>

T'#ical A##licati!ns !f "ac0 %ementati!n


62/71

'aFority of aero-engine tur$ine

$lade aerofoils are aluminised to

improve their resistance to hightemperature o!idation or surface

preparation prior to deposition of TBC"

M!dified Diffusi!n %!atings


63/71


Adding %rint! aluminide c!atings t! im#r!+e resistance

t! T'#e II &!t c!rr!si!n? T !(idati!n and ductilit'> Deposition of Cr-enriched layer prior to aluminising and

then aluminising of chromium coated su$strate

ack containing &l and Cr po#ders

Adding Siint! aluminied c!atings t! im#r!+e resistance

t! T'#e II &!t c!rr!si!n? and &ig& tem#erature !(idati!n>

Deposition of metallic Si layer prior to aluminising

Silicon-containing coatings are suscepti$le to $asic flu!ing) i"e" $y 3a6O)

leading to Type I hot corrosion) $ut have good resistance to sulphidation" In

addition) it may $e prone to cracking during thermal cycling due to the formation

of $rittle intermetallics"



64/71


Adding "tint! aluminised c!atings

1. t! im#r!+e resistance t! !(idati!n and t'#e I &!tc!rr!si!n ut 2.resistance t! t'#e II &!t c!rr!si!n is

marginall' etter t&an c!n+enti!nal aluminides> In additi!n?

3.resistance t! c'clic !(idati!n is #!!r as "t aluminides are

less ductile t&an !rdinar' aluminides>

Depositing a layer of t .?-5= Um/) and follo#ed $y

diffusion heat treatment) and then aluminiing

Micr!structure: a matri! of nickel aluminide #ith t present

in solid solution %.3i)t/&l() and as intermetallic phases) .t&l6

or t6&l7near the outer surface/"VV continue



65/71

g

"r!tecti!n mec&anism* to promote formation of pure alumina scale and reduce scale

gro#th rate to act as a phase sta$iliser and prevent the detrimentalconvertion from to W on thermal cycling to improve alumina scale adherence) including mechanical

keying) as a possi$le mechanism due to the formation of anirregular o!ide-alloy interface1 to improve self-healing of the alumina scale after modest

spalling to suppress interfacial void formation to tie up &l as t-&l compounds) thus lo#ering &l activity) in

turn) to reduce the driving force for the diffusion of 3i from the

su$strate into the coating1

4 During service) t&l6can transform to t&l to cause cracking and void formation"

7ailure !f Metallic c!atings


66/71

g

Defects in t&e c!ating !r at t&e c!ating)sustrate interface

L!ss !f #r!tecti+e elements fr!m t&e c!ating in ser+ice:

$y spallation of scale"

$y vaporiation into a gaseous atmosphere) e"g" Cr6O7can

$e further o!idied a$ove 5===C to $ecome volatile CrO7"

$y dissolution into molten salt deposits* 'olten salt has

3a6O reacting #ith &l6O7 O6$ecome 3a&lO7.aluminate/



67/71

g

%!atingsustrate interacti!ns in ser+ice -interdiffusi!n.-c!m#!siti!nal difference et;een c!ating and sustrate

#r!+ides dri+ing f!rce at &ig& tem#erature.>

5/ +ormation of detrimental phases #ithin the coating) e"g"$rittle intermetallics reduces ductility of the coating"

6/ Dilution of the coating in the protective elements) e"g" 'o

and J from alloy su$strate migrate to the coating) leading

to reduction of resistance to hot corrosion"7/ Qirkendall porosity at the coating0su$strate interface

reduces the adhesive strength) leading to spallation of the

coatings"



68/71

g

%!atingsustrate interacti!ns in ser+ice -interdiffusi!n.:

8/ Loss of &l to the su$strate $y interdiffusion1 and Diffusion

of refractory elements from the superalloy into the coating)

leading to degradation of o!idation resistance of protective

aluminide coatings on high temperature superalloy

components"

%!ating -2 4 at9. Al

Su#erall!'-5 1 at9 Al.

Cr) Ta)) 'o

Al



69/71

E(am#le 1: Aluminied /ic0elase su#erall!'s

A$ 2 &!urs at 1!% in air>

$% 5 &!urs at 12!% in air

7ailure mec&anism:

&l6O7scale tends to spall easily in service1

Interdiffusion $et#een the coating and the su$strate

leads to dilution of the coating in aluminium" If &l is

less than a critical value) it is no longer protective"

3ote the effect of temperature in service"

g

&

B

C

Time

eightgain



70/71

E(am#le 2: %&r!mied car!n steels? n!te t&e effect !f %

L!; car!n steel l!ss !f c&r!mium due t!:

s#allati!n !f %r23scale? diffusi!n !f c&r!mium

int! t&e steel sustrate and +!latiliati!n !f %r3

ig& car!n steel f!rms a l!t !f %r23%6#reci#itates

during c&r!miing t&ese are an effecti+e s!urce !fc&r!mium? t&ere' increasing t&e time t! rea0a;a'!(idati!n t&at arises fr!m l!ss !f c&r!mium fr!m t&e

c!ating>

Im#r!+ing lifetimes !f c!ating)sustrate


71/71

Inc!r#!rating a arrier la'er et;een c!ating

and sustrate: to reduce the rates of interdiffusion

$et#een coating and su$strate"

43i-Hf compound) t-Hf compound used at interface of

superalloy0aluminide coating

Inc!r#!rating a reacti+e element? suc& as J !r

%e? int! t&e c!ating: to improve scale adhesion on

thermal cycling .needs to understand the effect of

Diffusion

$arrier layer

&luminide coating

Superalloy

&lumina scale

surface engineering part 1(1)

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