Imp o ing he oxida ion esis ance o AlC N coa ings by ailo ing ch omium
ou -di usion
R. Escoba Galindo
a,
⁎, J.L. End ino
a
, R. Ma ínez
b
, J.M. Albella
a
a
Ins i u o de Ciencia de Ma e iales de Mad id, Consejo Supe io de In es igaciones Cien íficas, E-28049 Mad id, Spain
b
AIN-Cen o de Ingenie ía A anzada de Supe ficies, Co do illa, E-31191 Pamplona, Spain
abs ac a icle in o
A icle his o y:
Recei ed 10 June 2010
Accep ed 4 Sep embe 2010
A ailable online 16 Sep embe 2010
Keywo ds:
GDOES
AlC N
Oxida ion
Di usion ba ie
In his wo k, we ha e s udied he imp o emen on he oxida ion esis ance o AlC N-based coa ings by adding
a subsu ace i anium ni ide ba ie laye . Since oxida ion is in e ela ed wi h he inwa d di usion o oxygen
in o he su ace o Al
x
C
1−x
N (x=0.70) coa ings and he ou wa d di usion o C o he su ace, he oxida ion
beha iou o he aluminium- ich AlC N coa ings can be uned by designing he coa ing in an app op ia e
laye ed s uc u e. The bu ied dep h o he embedded laye and he oxida ion ime we e a ied, and he
changes in he AlC N/TiN dep h composi ion p ofiles and su ace oxida ion s oichiome y we e analysed by
means o Glow Discha ge Op ical Emission Spec oscopy (GDOES) and C oss Sec ional SEM (X-SEM) maps. I
was obse ed ha when a TiN di usion ba ie o 300 nm was deposi ed nea he op su ace (500 nm om
he su ace) he inhibi ion o he inwa d di usion o oxygen and o ma ion o beneficial alumina su ace laye s
was p omo ed and consequen ly an inc ease o he oxida ion esis ance is achie ed. This is explained in e ms
o a limi ed su plus o ch omium om he coa ing o he su ace. This was co obo a ed a e pe o ming
expe imen s using C N as embedded ba ie laye which esul ed in a con inuous su plus o ch omium o he
su ace and he o ma ion o C - ich oxides. GDOES, in combina ion wi h X-SEM elemen al maps, was p o ed
o be a as and accu a e echnique o moni o composi ion in-dep h changes du ing oxida ion, p o iding
unique in o ma ion ega ding he oxide s uc u e o ma ion.
© 2010 Else ie B.V. All igh s ese ed.
1. In oduc ion
Recen ly, Al–C –N based coa ings ha e ecei ed inc easingly
a en ion o esea che s and coa ing designe s due o hei excellen
mechanical p ope ies and supe io oxida ion esis ance compa ed
wi h Al–Ti–N based coa ings [1–6]. I has been p edic ed by he band
pa ame e s me hod ha he c i ical con en o Al in Al–C –N om B1
(NaCl- ype) o B4 (wu zi ic) is 77.2% in compa ison o only 65.3%
solubili y in Al–Ti–N[7]. This highe aluminium con en in a B1 cubic
phase allows o inc eased o ma ion o alumina-like ibofilms
wi hou sac ificing mechanical p ope ies such as ha dness. Alumina
based ibofilms ha e been shown o p o ec o ming and machining
ools by edi ec ing mo e hea owa ds he wo kpiece [8,9].
Ne e heless, inc easing aluminium con en in he p o ec i e coa ing
does no always gua an ee he o ma ion o alumina ibofilms since
he en halpy o o ma ion o C
2
O
3
is lowe han ha o Al
2
O
3
.
The oxida ion mechanism o AlC N hin films ha e been ex ensi ely
s udied in he li e a u e. In he ea ly 90's Ho mann [10] desc ibed his
p ocess in e ms o me al in e -di usion, o igina ing a ypical oxide
mul ilaye s uc u e. This mul ilaye is explained due o he di e en
di usi i y o he me al species. Al hough Al
2
O
3
is he mo e s able
compound, ch omium is he mo e mobile species and p e e en ially
o ms a su ace oxide. This ch omium oxide inhibi s he di usi i y o
aluminium, leading o a build-up o aluminium oxide benea h his laye .
In u n, he aluminium- ich laye educes he u he ou -di usion o
ch omium and leads o a sligh ly inc eased ch omium concen a ion
unde nea h. The e o e, a s uc u e wi h a mixed, C - ich, C /Al oxide
laye a he film su ace and an Al- ich, C /Al oxyni ide in he bulk is
o med. La ely, Banakh e al. [3] co obo a ed his model, sugges ing he
de-ni ida ion o he film and he o ma ion o a C /Al mixed oxide as he
oxida ion mechanism. Mo e ecen ly, Lin e al. s udied he oxida ion
p ocess o AlC N films by using di e en ial scanning calo ime y (DSC)
and he mog a ime ic analysis (TGA) [11]. They concluded ha , o he
oxida ion empe a u e anging om 700 o 1050 °C, he mal ene gy is
su ficien o acili a e ou wa d di usion o ni ogen a oms/ions owa ds
he film su ace (de-ni ida ion). A he same ime hey p oposed ha
he di usion o C and Al ions ou wa ds and a omic oxygen inwa ds will
p omo e he o ma ion o a (C , Al)
2
O
3
laye on he film su ace, ac ing as
a e ec i e di usion ba ie slowing down he inwa d di usion o
oxygen.
The e o e, i is well documen ed ha AlC N coa ings show high
sho - e m oxida ion esis ance up o 1100 °C due o he o ma ion o
C –Al oxides ha a e lub icious and ha e s ong di usion ba ie
p ope ies agains u he inwa d di usion o oxygen in o he films. In
Spec ochimica Ac a Pa B 65 (2010) 950–958
⁎Co esponding au ho . Tel.: +34 91 3721420x330.
E-mail add ess: [email p o ec ed] (R. Escoba Galindo).
0584-8547/$ –see on ma e © 2010 Else ie B.V. All igh s ese ed.
doi:10.1016/j.sab.2010.09.005
Con en s lis s a ailable a ScienceDi ec
Spec ochimica Ac a Pa B
jou nal homepage: www.else ie .com/loca e/sab
pa icula Al- ich Al
70
C
30
N coa ings p esen excellen oxida ion
esis ance due o he o ma ion o alumina a he su ace. Howe e ,
mo e demanding applica ions such as gas u bine engines, die cas ing
and moulding indus ies also equi e o long- e m oxida ion esis an
coa ings ha can wi hs and exposu e o oxygen and wa e apou
con aining en i onmen s o hei en i e se ice li es. Unde longe
exposu e imes in ai AlC N coa ings su e a pa ial deple ion o
aluminium a he su ace and a high di usion o ch omium is
p omo ed. In his case, he o ma ion o su ace alumina is inhibi ed
and ch omium- ich complex (Al, C )
2
O
3
oxide films a e o med due o
he solubili y o C
2
O
3
in alumina ma ix [12].
In his wo k we ha e s udied he inco po a ion o a subsu ace TiN
laye in he AlC N coa ings. This laye has been shown o ac as a
di usion ba ie in mic oelec onics [13–15] and can ac as an
excellen di usion ba ie o ch omium ions. He e, we demons a e
ha he TiN ba ie p omo es he o ma ion o aluminium- ich oxides
a he su ace o he coa ing, imp o ing he long- ime oxida ion
esis ance o he films. To achie e his goal, we ha e used Glow
Discha ge Op ical Emission Spec oscopy (GDOES) as a dep h
p ofiling echnique [16] due o i s excellen po en ial o accu a ely
moni o ing composi ion su ace and in-dep h changes du ing oxida-
ion. GDOES has been p e iously applied wi h success o s udy he
in e nal oxida ion o ca bu ized s eels [17], oxide scale o ma ion in
Fe–C alloys [18], and oxida ion esis ance o AlN/C N supe la ices
[19] and complex TiAlC SiYN coa ings [20]. In addi ion, we ha e
compa ed GDOES esul s on selec ed samples wi h C oss Sec ional
Scanning emission mic og aphs (X-SEM).
2. Expe imen al
2.1. Coa ing deposi ion
A on -loading Balze s' apid coa ing sys em (RCS) machine has
been employed o he deposi ion o he coa ings in his s udy. The
RCS machine is equipped wi h 6 ca hode a c sou ces posi ioned a wo
di e en heigh s. Two o he six sou ces con ained Ti a ge s and we e
used o deposi a 0.3 μm hick i anium ni ide adhesion laye as well
as o deposi a TiN subsu ace di usion ba ie . The emaining ou
sou ces con ained AlC (70:30) a ge s which we e employed o
deposi he main AlC N laye wi h a hickness o 3 μm in all he
samples. In his s udy, 20 mm-diame e cold wo k ool s eel coupons
we e used as subs a es. Du ing he deposi ion, he chambe was
back-filled wi h pu e eac i e ni ogen o a p essu e o 3.5 Pa and he
empe a u e o he subs a es was held a app oxima ely 450 °C. Also,
a subs a e bias ol age o −100 V was applied o he subs a es.
2.2. Mul ilaye cha ac e isa ion
GDOES dep h p ofile analysis o he coa ings was comple ed using
a Ho iba Jobin Y on RF GD P ofile equipped wi h a 4 mm diame e
coppe anode and ope a ing in a gon gas [21–23]. In p e ious wo ks
[24,25] Escoba Galindo e al. pe o med a comple e op imiza ion o
he ope a ing condi ions o he analysis using his GDOES sys em. By
applying a adio equency discha ge p essu e o 650 Pa and a o wa d
powe o 40 W mul ilaye s in he nanome e ange we e able o be
analyzed. The e o e in his s udy we ha e kep fixed hese ope a ion
se ings. The emission esponses om he exci ed spu e ed elemen s
we e de ec ed wi h a polych oma o o ocal leng h o 500 mm. The
op ical pa h o he spec ome e is ni ogen pu ged. The emission
lines used we e 130.21 nm o oxygen, 149.262 nm o ni ogen,
156.14 nm o ca bon, 371.99 nm o i on, 396.15 nm o aluminium
and 425.43 nm o ch omium. The chambe was cleaned by spu e ing
a silicon (100) sample o 20 min p io o he measu emen s. This
p ocedu e minimises he su ace con amina ion o he samples and
allows a as e s abilisa ion o he plasma [26]. No memo y e ec s
we e obse ed a e his p e-spu e ing p ocedu e. Be o e e e y
expe imen , he samples we e flushed wi h a gon du ing 60 s. This is a
ypical p ocedu e o emo e he con aminan s (ca bon, oxygen,
hyd ogen) om he inne walls o he anode p io o he analysis o
he sample and has been ex ensi ely applied by GDOES use s.
Molchan e al. ha e ecen ly p oposed [27] ha his p ocedu e can
be imp o ed by using a low-ene gy plasma (b5 W) o gen ly emo e
con aminan om he su ace o he sample. The high e ching a es
ob ained du ing GDOES analysis esul ed in e y sho expe imen al
imes (below 1 min o ope a ion). A collec ion a e o 200 poin s/
second was used o measu e all he samples. Quan ified p ofiles we e
ob ained au oma ically using he s anda d Jobin Y on QUANTUM
In elligen Quan ifica ion (IQ) so wa e. The se up was calib a ed
Fig. 1. GDOES p ofiles o AlC N coa ings wi hou TiN ba ie a e oxida ion in ai a
900 °C o a) 30 min, b) 1 h and c) 3 h.
951R. Escoba Galindo e al. / Spec ochimica Ac a Pa B 65 (2010) 950–958
using s anda d ma e ials o known composi ion. In o de o imp o e
he quan ifica ion o ni ogen, we ha e used a se ies o ch omium
ni ide coa ings deposi ed by magne on spu e ing in ou labo a o y
[28]. The composi ion o hese homemade s anda ds was assessed by
Ru he o d Backsca e ing Spec oscopy (RBS). A Veeco Dek ak 150
s ylus su ace p ofile was used o measu e he c a e dep hs.
Iso he mal oxida ion es s we e pe o med in ai , a 900 °C du ing
0.5, 1, 3 and 24 h wi h each specimen placed in an alumina c ucible.
Quali a i e c oss-sec ional ene gy-dispe si e X- ay spec oscopy
(EDX) elemen mapping and images we e ob ained using an INCAx-
sigh Field Emission Scanning Elec on Mic oscope (FE-SEM) wi h a
esolu ion o 136 eV when ope a ing a 5.9 keV.
3. Resul s and discussion
In Sec ion 3.1, we desc ibe he sho and long- e m oxida ion
kine ics o a single laye AlC N coa ings. La e in Sec ion 3.2,we
compa e hose esul s o he case o a mul ilaye AlC N/TiN/AlC N
sys em by a ying he bu ied dep h o he TiN di usion ba ie
(Sec ion 3.2.1) as well as he oxida ion ime (Sec ion 3.2.2). Finally in
Sec ion 3.3 we discuss he e ec i eness o TiN as a di usion ba ie by
s udying he oxida ion pe o mance o a AlC N/C N/AlC N mul ilaye
sys em.
3.1. Oxida ion pe o mance o AlC N
Fig. 1 shows he GDOES p ofiles o AlC N coa ing wi hou TiN
ba ie a e a) 30 min, b) 1 h and c) 3 h oxida ion a 900 °C. The
hicknesses o he oxide laye o med a e each oxida ion ime a e
epo ed in Table 1. Fo sho oxida ion imes (Fig. 1a), he e is a clea
pileup o ch omium nea he su ace e ealing he o ma ion o C -
ich oxide laye on op o he AlC N o iginal coa ing. Wi hin his
oxidised laye he a e age Al/C con en a io emains low (0.47) as
de ailed in Table 1. The p esence o Fe on he su ace o he coa ing is
obse ed e en a sho oxida ion imes, indica ing a mig a ion o
subs a e elemen s owa ds he su ace .A e inc easing he oxida ion
ime he e is a clea g ow h o he hickness o he oxide laye
(Fig. 1b–c). I can be also obse ed he p og essi e o ma ion o an
AlO
x
laye below he C O
x
(no e o example he “double peak”in he
Al p ofile wi hin he oxide laye o Fig. 1c). This beha iou can be
explained in e ms o he highe mobili y o ch omium o o m a C -
ich oxide laye . The di usi i y o aluminium is educed h ough his
ch omium oxide laye and an Al- ich oxide is g own unde nea h
gene a ing an oxide mul ilaye s uc u e as desc ibed by Ho mann
[10]. The o al Al/C a io sligh ly inc eases a e 1 and 3 h oxida ion o
0.54 and 0.68, espec i ely, bu he e is no e idence o he o ma ion
o a beneficial aluminium ich oxide on he su ace. A e oxida ion o
24 h he oxide laye was oo po ous and ough o be measu ed by he
GDOES echnique. In any case, he hickness o his g own scale can be
es ima ed o be o la ge han 4 μm by p ofilome y measu emen s. In
Fig. 2a, he oxygen p ofiles o he films wi hou oxida ion and a e
30 min, 1 h and 3 h oxida ion a e shown o compa ison. The inc ease
o he oxide laye hickness upon oxida ion can be clea ly obse ed
and compa ed wi h he sample con aining a TiN di usion ba ie (see
Fig. 2b) as discussed below in Sec ion 3.2.2.
3.2. Oxida ion pe o mance o AlC N/TiN/AlC N mul ilaye s
As p e iously s a ed, he main aim o his wo k is o con ol he
oxida ion beha iou o AlC N coa ings by he deposi ion o an
in e media e di usion ba ie o TiN. In Fig. 3, a GDOES p ofile and
X-SEM image and EDX elemen mapping o an as deposi ed AlC N/
TiN/AlC N mul ilaye a e shown. In his case, he di usion ba ie is
bu ied a a dep h o 700 nm om he su ace. In he ollowing sec ions
we s udy he influence on he mul ilaye oxida ion esis ance o a) he
dep h o he TiN embedded laye and b) he oxida ion ime.
3.2.1. E ec o bu ied dep h
A se o se en AlC N samples was deposi ed con aining an
in e media e TiN laye a di e en dep hs om he su ace (see
Table 2). The samples we e annealed in ai du ing 3 h a 900 °C. Fig. 4
shows ep esen a i e GDOES p ofiles o he oxidised samples o TiN
bu ied dep hs o a) 2.8 μm, b) 2.3 μm, c) 1.1 μm, d) 0.7 μm and e)
0.5 μm espec i ely. The fi s di e ence in compa ison o samples
Fig. 2. (Le ) GDOES oxygen p ofiles o AlC N coa ings wi hou TiN ba ie as deposi ed
and a e oxida ion in ai a 900 °C o 30 min, 1 h and 3 h. (Righ ) GDOES oxygen
p ofiles o AlC N/TiN coa ings wi h TiN ba ie bu ied a 0.6 μm as deposi ed and a e
oxida ion in ai a 900 °C o 30 min, 1 h, 3 and 24 h.
Table 1
Oxide Thickness and Al/C a io wi hin he oxide o AlC N samples oxidized a 900 °C
wi h no di usion ba ie and wi h TiN o C N ba ie s bu ied a a dep h o 0.6 μm. The
da a a e shown o di e en oxida ion imes.
Oxida ion Time (h) Di usion Ba ie Oxide Thickness (nm) Al/C oxide
0.5 No Ba ie 115±10 0.47±0.08
TiN 50±5 0.71±0.05
1 No Ba ie 190±20 0.54±0.10
TiN 85±10 0.77±0.20
3 No Ba ie 300±20 0.68±0.16
TiN 150±10 0.92±0.10
C N 280±20 0.66±0.08
24 No ba ie N4000 –
TiN 1100±50 1.00±0.20
952 R. Escoba Galindo e al. / Spec ochimica Ac a Pa B 65 (2010) 950–958
wi hou TiN ba ie (Fig. 1) is he hickness o he oxide laye o med.
Clea ly, he p esence o he TiN ba ie laye inc eases he o e all
oxida ion esis ance (app oxima ely by a ac o o 2) as can be
obse ed in Table 2. A e 3 h o oxida ion he scale g own on he
AlC N coa ing wi hou ba ie is o mo e han 300 nm hick, while o
he sample wi h he TiN is in he o de o 150 nm o he same
oxida ion ime, independen ly o he bu ied dep h. Mo eo e he e is
a s ong educ ion o he Fe signal on he su ace o he coa ings. This
indica es an inhibi ion o he mig a ion o subs a e elemen s owa ds
he su ace and unde sco es he benefi s o inco po a ing a TiN ba ie
laye on he AlC N coa ings.
The main obse a ion o samples wi h he TiN ba ie laye
deposi ed nea he subs a e (bu ied dep h N1μmFig. 4a–c) is he
o ma ion o an ex ensi e pile up o ch omium as in he case o he
coa ings wi hou TiN ba ie (Fig. 1c). P e ious XPS analysis e ealed
he o ma ion o a C - ich oxide laye (mainly C
2
O
3
[29,30]) on op o
he AlC N o iginal coa ing. Wi hin his oxidised laye he Al/C a io
o he sample wi h he ba ie a 2.8 μm is simila o he sample wi h
no ba ie (0.4) as de ailed in Table 2. Howe e , as he ba ie laye is
being deposi ed close o he su ace i can be obse ed he
p og essi e o ma ion o an AlO
x
laye below he C
2
O
3
(no e o
example he “double peak”in he Al p ofile wi hin he oxide laye o
Fig. 4b and cc). Consequen ly, he Al/C a io inc eases up o 0.5–0.6
o samples wi h he ba ie bu ied a dep hs be ween 2.3 and 1.1 μm
(see Table 2).
This mechanism d ama ically changes when he TiN laye is
deposi ed nea he su ace (bu ied dep h b1μm). In hese samples,
he e is a clea e idence o aluminium en ichmen a he su ace as
can be obse ed bo h in he GDOES p ofiles o Fig. 4c–d and in he
EDX-SEM c oss sec ional mapping o Fig. 5. The o med oxide laye s
a e hinne (100–120 nm) han o samples wi h he TiN close o he
subs a e. The highes Al/C a io in he oxidised laye (as high as
1.05) was ob ained o he sample wi h he TiN laye bu ied a 0.5 μm
(see Table 2). In pa icula , o his sample (see Fig. 4d), i is clea he
o ma ion o a 50 nm aluminium oxide film ollowed by a complex
AlC O
x
film. GDOES obse a ions a e suppo ed by XPS measu emen s
pe o med on his sample, whe e Al–O and Al–O–N bonds we e
p edominan [6]. Hence, he p esence o he TiN laye nea he su ace
Table 2
Oxide Thickness and Al/C a io wi hin he oxide o AlC N samples wi h TiN di usion
ba ie oxidized a 900 °C o 3 h.
Bu ied dep h (μm) Oxide hickness (nm) Al/C oxide
0.5 120±10 1.05±0.10
0.7 120±10 0.78±0.05
1.1 120±10 0.58±0.10
1.7 160±15 0.57±0.10
2.0 160±15 0.61±0.14
2.3 170±20 0.51±0.09
2.8 145±15 0.40±0.05
Fig. 3. GDOES p ofile ( op-le ) and c oss sec ional SEM image (bo om-le ) o as deposi ed AlC N/TiN coa ing wi h TiN ba ie bu ied a 0.6 μm. The do ed squa e a ea delimi a es
he zone whe e elemen al mapping was pe o med (see igh panels o C, Al, C , N, Ti, Fe and O).
953R. Escoba Galindo e al. / Spec ochimica Ac a Pa B 65 (2010) 950–958
p omo es he o ma ion o a hinne and Al- ich oxide wi h a highe
oxida ion esis ance due o he limi ed supply o C a oms o he
su ace.
3.2.2. Long- e m oxida ion
In he p e ious sec ion, we ha e es ablished he ole ha
deposi ing a TiN bu ied laye nea he su ace has on he oxida ion
p ocess o AlC N coa ings. In o de o s udy he kine ics o such
oxida ion mechanism, TiN/AlC N coa ings we e p epa ed by keeping
bo h he oxida ion empe a u e and he embedded dep h cons an a
900 °C and 0.6 μm, espec i ely, and a ying he oxida ion ime. He e
we pe o m a compa ison o samples wi h and wi hou a TiN ba ie
laye , p epa ed unde he same condi ions o oxida ion ime and
empe a u e as discussed in Sec ion 3.1.Table 1 summa ised he
samples s udied.
Fig. 6a shows he de ailed GDOES dep h p ofiles o he as
deposi ed AlC N coa ing wi h a TiN ba ie deposi ed a a fixed dep h
o 0.6 μm. The coa ing was hen subjec ed o oxida ion a 900 °C o
b) 30 min, c) 1 h, d) 3 h and e) 24 h. A e only 30 min oxida ion,
he e is he o ma ion o an oxide laye , wi h hickness o abou
50 nm. This oxide laye consis s o complex AlC O
x
(N) compound
(see Fig. 6b) and he Al/C a io is ma kedly highe (0.71) han o he
sample wi hou di usion ba ie (0.47) o he same oxida ion ime
(see Table 1). A his oxida ion ime, he e was no e idence o Fe
di usion owa ds he su ace. Inc easing he oxida ion ime o one
hou (see Fig. 6c) he oxide laye and he Al/C a io g ows up o
85 nm and 0.77, espec i ely. A e 3 h o oxida ion he ni ogen
con en o he oxide laye dec eases, wi h a inc easing mig a ion o
aluminium owa ds he su ace. As discussed in he p e ious sec ion,
he e is a clea sepa a ion o oxides wi h he o ma ion o a sub-
Fig. 4. GDOES p ofiles o AlC N/TiN coa ings a e oxida ion in ai a 900 °C o 3 h wi h TiN ba ie bu ied a a) 2.8 μm, b) 2.3 μm, c) 1.1 μm, d) 0.7 μm and e) 0.5 μm.
954 R. Escoba Galindo e al. / Spec ochimica Ac a Pa B 65 (2010) 950–958

s oichiome ic AlO
x
laye on op o he p e iously o med AlC O
x
(see
Fig. 6d). This is quan i a i ely e iden as he Al/C a io is much
highe (0.92) han he alue ob ained o he sample wi hou
di usion ba ie (0.68). A his s age, he e is some di usion o
i anium om he ba ie laye o he su ace and o i on om he
subs a e. Finally, a e an oxida ion ime o 24 h (Fig. 6e), he oxide
laye is hicke han 1 μm and he whole TiN bu ied laye disappea s,
mig a ing o he su ace. The oxide laye consis s o a s oichiome ic
alumina op laye (O/Al a io is 1.5) and a subsu ace AlC O
x
as can be
de i ed om he oscilla ions p esen in he C –Al p ofiles. The
solu ion o Fe inside he laye is now mo e e iden in acco dance
wi h obse a ions made by Ka esan o i on anspo ac oss alumina
scales [31]. This mul ilaye s uc u e is simila o he p edic ed by
Ho mann model [10] al hough in ou case he oxide op laye is
alumina and no ch omium oxide wi h he subsequen oxida ion
esis ance imp o emen . No e also he p ac ical disappea ance o
ni ogen a he su ace o his sample, in acco dance o he de-
ni ida ion model p oposed by Banakh e al. [3].InFig. 2b, he oxygen
p ofiles o he films wi hou oxida ion and a e 30 min, 1 h, 3 h and
24 h oxida ion a e shown o compa ison wi h hose ob ained
wi hou TiN ba ie laye (Fig. 2a).
3.3. Oxida ion pe o mance o AlC N/C N/AlC N mul ilaye s
In Sec ion 3.1 we ela ed he p esence o he TiN bu ied laye ,
close o he su ace, o he o ma ion o Al- ich oxides due o he
limi ed supply o C a oms o he su ace. In o de o co obo a e his
poin , a C N laye , which is a less e ec i e di usion ba ie , was
embedded in o he AlC N coa ing. By doing his, we assu e ha he
supply o C a oms o he su ace is no inhibi ed. The C N ba ie was
deposi ed a a dep h o 0.6 μm and he mul ilaye sample was
oxidised a 900 °C o 3 h. The e o e he esul s can be compa ed o
hose ob ained o AlC N/TiN/AlC N mul ilaye o Fig. 6d. Fig. 7 shows
he GDOES dep h p ofiles o a) he as deposi ed AlC N/C N/AlC N
sample and b) he sample a e 3 h o oxida ion. I is clea ha he
p esence o C N laye enhances he ch omium con en (Al/C a io is
0.66) and he hickness (280 nm) o he oxide scale as compa ed
wi h he sample con aining he TiN ba ie a simila dep h and
oxida ion empe a u e (see Table 1). Mo eo e , he C N laye
comple ely di uses o he su ace and he e is a seg ega ion o i on
ca bide om he subs a e a a dep h o 900 nm, comple ely
eplacing he ba ie laye . SEM EDX c oss sec ional mapping
(shown in Fig. 8) co obo a es he o ma ion o a su ace C - ich
oxide and a subsu ace FeC
x
laye .
Finally, in Fig. 9 we p esen , o compa ison pu poses, he wid h o
he g own oxide e sus he oxida ion ime o samples oxidised a
900 °C wi h a) no ba ie , b) TiN ba ie and c) C N ba ie . The
beneficial e ec o he p esence o he TiN di usion ba ie laye nea
he su ace can be clea ly obse ed. I significan ly educes he
oxygen inwa d di usion in o he laye and consequen ly esul s in an
inc ease in oxida ion esis ance a longe oxida ion imes. As can be
seen in he inse o Fig. 9, o sho oxida ion imes (up o 3 h) he
g own o he oxide ollows a pa abolic law,
x=B 1=2ð1Þ
whe e xis he hickness o he g owing oxide, Bis he pa abolic a e
cons an , and is he oxida ion ime [32]. I is e iden ha he a e o oxide
o ma ion is highe o samples wi h no ba ie (B=2.9±0.4nm s
−1/2
)
han when a TiN ba ie is p esen (B=1.6±0.1nm s
−1/2
). Mo eo e ,
al hough o samples wi h no ba ie he oxide s a g owing om e y
sho oxida ion imes, o samples wi h he TiN ba ie he e is an
incuba ion ime p io o he o ma ion o he scale (see he in e cep ion o
he fi ed line wi h he x-axis).
4. Conclusions
In his wo k we ha e s udied he oxida ion esis ance imp o e-
men o Al
70
C
30
N coa ings by ailo ing a mul ilaye s uc u e. To his
Fig. 5. C oss sec ional SEM image (le ) o as deposi ed AlC N/TiN coa ing wi h TiN ba ie bu ied a 0.7 μm. The do ed squa e a ea delimi a es he zone whe e elemen al mapping
was pe o med (see igh panels o C, Al, C , N, Ti, Fe and O).
955R. Escoba Galindo e al. / Spec ochimica Ac a Pa B 65 (2010) 950–958
pu pose we ha e employed GDOES and c oss sec ional SEM as
analy ical echniques. GDOES is a supe b ool o oxida ion
and di usion s udies hanks o i s high e osion a e (N2μm min
−1
),
sampling a e (N100 s
−1
) and p ecision (in he nanome e ange),
allowing he analysis o a la ge numbe o samples unde di e en
p epa a ion condi ions (i.e. oxida ion ime and empe a u e). In
combina ion wi h X-SEM elemen al maps, GDOES p o ides unique
in o ma ion ega ding he oxide s uc u e o ma ion due o i s supe b
accu acy o moni o in-dep h composi ional changes du ing
oxida ion.
GDOES and X-SEM esul s indica ed ha , upon oxida ion o an
AlC N single laye , C - ich oxides and oxyni ides a e o med due o
he high amoun o C a ailable o ou wa d di usion. Howe e , he
deposi ion o a di usion ba ie such as TiN embedded nea he
su ace (b1μm) imp o es he oxida ion esis ance o he AlC N-based
coa ings by:
 dec easing he ou wa d di usion a e o C .
 p omo ing he o ma ion o alumina a he han ch omium oxide.
 significan ly inc easing he Al a io wi hin he su ace oxidised
laye .
 educing he oxide inwa d di usion (up o 24 h oxida ion a 900 °C).
 inhibi ing he mig a ion o subs a e elemen s o he su ace.
Simila expe imen s ca ied ou using C N as embedded di usion
laye s did no esul in any oxida ion esis ance imp o emen . The
deposi ion o such laye s implies a con inuous C su plus o he
su ace and he e o e hey do no p e en C ou -di usion as in he
case o TiN laye s.
Fig. 6. GDOES p ofiles o AlC N/TiN coa ings wi h TiN ba ie bu ied a 0.6 μm, a) as deposi ed and a e oxida ion in ai a 900 °C o b) 30 min, c) 1 h, d) 3 h and e) 24 h.
956 R. Escoba Galindo e al. / Spec ochimica Ac a Pa B 65 (2010) 950–958
Acknowledgmen s
This wo k was financially suppo ed by he Spanish Minis y o
Science and Inno a ion (P ojec FUNCOAT, e . CSD2008-00023). REG
and JLE would like also o acknowledge he financial suppo om he
Ramon y Cajal p og amme.
Fig. 7. GDOES p ofiles o AlC N/C N coa ings wi h C N ba ie bu ied a 0.6 μm, a) as
deposi ed and b) a e oxida ion in ai a 900 °C o 3 h.
Fig. 8. C oss sec ional SEM image (le ) o AlC N/C N coa ing wi h C N ba ie bu ied a 0.6 μm a e oxida ion in ai a 900 °C o hou s. The do ed squa e a ea delimi a es he zone
whe e elemen al mapping was pe o med (see igh panels o Al, C , N, Fe, C and O).
Fig. 9. Oxide hickness e sus oxida ion ime o AlC N wi hou ba ie (open ci cles),
AlC N/TiN mul ilaye (closed ci cles) and AlC N/C N mul ilaye (closed squa e)
oxidized in ai a 900 °C. In he inse he oxide hickness is plo ed e sus he squa e
oo o he oxida ion ime o show he pa abolic oxide g ow h o sho oxida ion imes
(up o 3 h).
957R. Escoba Galindo e al. / Spec ochimica Ac a Pa B 65 (2010) 950–958
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