ma e ials
A icle
S uc u e and P ope ies o Cas Ti-Al-Si Alloys
Anna Knaislo á1, Pa el No ák1,* , Jiˇ íLinha 1, I o Szu man 2, Ka eˇ ina Sko nico á2, Jan Juˇ ica 2and
Tomᚡ
Cegan 2


Ci a ion: Knaislo á, A.; No ák, P.;
Linha , J.; Szu man, I.;
Sko nico á, K.; Juˇ ica, J.; ˇ
Cegan, T.
S uc u e and P ope ies o Cas
Ti-Al-Si Alloys. Ma e ials 2021,14,
813. h ps://doi.o g/10.3390/
ma14040813
Academic Edi o : Sa a Biamino
Recei ed: 22 Decembe 2020
Accep ed: 2 Feb ua y 2021
Published: 8 Feb ua y 2021
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
1Depa men o Me als and Co osion Enginee ing, Uni e si y o Chemis y and Technology, P ague,
Technická5, 166 28 P ague 6, Czech Republic; [email p o ec ed] (A.K.); [email p o ec ed] (J.L.)
2Depa men o Non-Fe ous Me als, Re ining and Recycling, Facul y o Ma e ials Science and Technology,
VSB—Technical Uni e si y o Os a a, 17. lis opadu 15, 708 33 Os a a-Po uba, Czech Republic;
[email p o ec ed] (I.S.); [email p o ec ed] (K.S.); [email p o ec ed] (J.J.);
[email p o ec ed] (T. ˇ
C.)
*Co espondence: [email p o ec ed]
Abs ac :
In e me allic compounds based on Ti-Al- (Si) a e a ac i e ma e ials wi h good he mal
s abili y and low densi y. Howe e , he p oduc ion o hese ma e ials is qui e complica ed. Pa ially
modi ied con en ional me hods o mel ing me allu gy a e mos o en used due o a ailabili y,
possible high p oduc i i y, and ela i ely low p oduc ion cos s. The e o e, some echnologies o he
p oduc ion o in e me allics based on Ti-Al a e cu en ly a ailable, bu wi h ce ain disad an ages,
which a e caused by poo cas ing p ope ies o ex eme eac i i y o he mel wi h c ucibles. Some
sho comings can be elimina ed by modi ying he mel ing echnology, which con ibu es o inc easing
he cos o he p ocess. The wo k deals wi h he p epa a ion o Ti-Al-Si in e me allic compounds
wi h di e en con en s o aluminum and silicon, which we e p oduced by cen i ugal cas ing in an
induc ion acuum u nace Linn Supe cas -Ti an. This p ocess could con ibu e o he comme cial
use o hese alloys in he u u e. Fo his esea ch, he TiAl15Si15(in w .%) alloy was selec ed, which
ep esen s a balanced a io o aluminides and silicides in i s s uc u e, and he TiAl35Si5 alloy, which
due o he lowe silicon con en allows be e mel ing condi ions, especially wi h ega d o he mel ing
empe a u e. This alloy was also in es iga ed a e HIP (“Ho Isos a ic P essing”) ea men .
Keywo ds: in e me allics; cas ing; Ti-Al based alloys
1. In oduc ion
Ex ensi e es ing o alloys based on in e me allic compounds o he Ti-Al sys em,
which has been ca ied ou since he 1980s, has enabled hei comme cial applica ion in he
ae ospace and au omo i e indus ies. TiAl alloys a e cu en ly used comme cially, mainly
o he p oduc ion o u bocha ge s and ai c a engine blades [1–3].
Fou classes o alloys based on in e me allic compounds o he Ti-Al sys em a e p e-
sen ed in [
4
]. The i s gene a ion is based mainly bina y alloys wi h di e en aluminum
con en s in he ange o 42–48 a .%. These alloys show e y low duc ili y and educed
esis ance o c eep and oxida ion a high empe a u es [
1
,
4
]. In o de o imp o e he p op-
e ies, second gene a ion TiAl alloys ha e been de eloped. Rep esen a i es o his class
include TiAl48Mn2Nb2 and TiAl48C 2Nb2 alloys, which a e s ill comme cially applied
oday o he blades o low-p essu e pa s o a combus ion u bine. Addi ionallyincluded
ones a e TiAl47W2Si0.5 alloy and modi ied TiAl47W2Si0.5B0.5 alloy. Du ing he de elop-
men o second-gene a ion TiAl alloys, he posi i e e ec o bo on on he alloy s uc u e
was demons a ed. Bo on alloying has p o en o be an e ec i e me hod o p e en ing
he uncon ollable g ow h o indi idual alloy g ains du ing hea ea men and he mal
exposu e du ing se ice [
1
,
4
]. Due o he pe sis ing limi a ion in e ms o duc ili y, a hi d
gene a ion o TiAl alloys has been de eloped. This gene a ion o alloys has been de eloped
p ima ily o ho o ming echnology. These TiAl-based alloys a e highly alloyed mainly
wi h niobium and small amoun s o ca bon and bo on. Due o hei excellen mechanical
Ma e ials 2021,14, 813. h ps://doi.o g/10.3390/ma14040813 h ps://www.mdpi.com/jou nal/ma e ials
Ma e ials 2021,14, 813 2 o 14
p ope ies and esis ance o high empe a u e oxida ion and c eep up o 800
◦
C, hey
become sui able ma e ials o a ious componen s in gas u bines, je and au omobile
engines [
3
,
4
]. Due o he g owing demands on hese alloys wi h ega d o ae ospace com-
ponen s, which should be able o wi hs and e e -inc easing empe a u es, he la es ou h
gene a ion o TiAl-based alloys is being de eloped, ep esen ed by Ti46Al8Ta (a .%) alloy.
This compound is alloyed wi h an alum, which signi ican ly educes he di usion in he
ma e ial o i s s eng hening, e en a low cooling a es [4].
Mo e han en yea s ago, TiAl48Nb2C 2 alloy was i s comme cially applied o he
GEnx engine’s low-p essu e u bine blades. The lowe cen i ugal load o he ligh e
TiAl blades educes he o al weigh o he disc, which con ibu es o a signi ican pa o
he sa ing o he o al weigh o he mo o , up o 100 kg. Ob ained knowledge om he
ope a ion show ha he GEnx engine deli e s a 20% educ ion in uel consump ion, a 50%
educ ion in noise and an 80% educ ion in NO
X
emissions compa ed o p e ious engines
in he same se ies, which use con en ional nickel alloy blades. Today, app oxima ely
190 000 TiAl blades a e applied o he low-p essu e pa s o combus ion u bines i ed
o Boeing 787-s and 747-8s ai c a engines. Fu he mo e, his applica ion o TiAl alloy
is also planned o new LEAP engines [
1
–
3
]. In addi ion o he GEnx engines al eady
men ioned, he applica ion o s abilized
β
-TiAl alloy o he p oduc ion o LPT blades o
PW1100 G engines has now expanded. Rolls-Royce has also announced he applica ion o
TiAl blades o low p essu e combus ion u bine pa s o i s u u e engines. Fu he mo e,
he applica ion o TiAl alloys is conside ed o co e s and blade holde s and u bine
dampe s. To da e, howe e , he TiAl blades o he low-p essu e pa s o he combus ion
u bine o he GEnx engine a e he only la ge-scale comme cial applica ion in he ae ospace
indus y [1,2].
One o he mos success ul applica ions o TiAl alloys om he poin o iew o he au-
omo i e indus y is he p oduc ion o u bocha ge s o he Japanese au omo i e company
Mi subishi Mo o s Inc. These u bocha ge s a e success ully used o Mi subishi Lance
p oduc ion ca s. In 2002, o ged exhaus al es o in e nal combus ion engines made o
γ
-
TiAl alloy we e applied o Fo mula 1 ca s, which oday do no mee he equi ed s anda ds
and he e o e had o be wi hd awn. Due o he a o able p ope ies o alloys, such as low
densi y, high s eng h and a igue esis ance, he e is an e o o modi y he p oduc ion
echnology and e-applica ion o exhaus al es o he au omo i e indus y [5,6].
The abo e comme cial and u u e applica ions show a s ong in e es in he u he
de elopmen and subsequen applica ion o hese alloys in he ae ospace and au omo-
i e indus ies. Ex ensi e esea ch in o TiAl-based alloys aims o educe engine weigh
and imp o e engine pe o mance. The cu en s a e o p oduc ion echnology o TiAl
in e me allics is he esul o se e al decades o signi ican esea ch and de elopmen
in academia and indus y a ound he wo ld. Today, esea ch is mainly conce ned wi h
imp o ing he alloy i sel and p oduc ion echnologies o achie e he equi ed p ope ies
adap ed o speci ic applica ions, and TiAl-based alloy componen s will be mo e compe i i e
in he u u e and hei po en ial can be ully exploi ed [2,7].
The p ocessing echnologies o in e me allics, which a e conside ed o al eady applied
in indus ial p axis, include mos commonly he me hods o mel ing me allu gy. Fo he
p ocessing o in e me allics, he ExoMel p ocess had been de eloped [
8
], es ed o Fe-Al
in e me allics and could be applicable also o he p ocessing o Ti-Al based alloys. This
p ocess comp ises a me hod o cha ging ini ial componen s in he u nace in o de o u ilize
he hea gene a ed by he eac ions be ween he aluminum and ansi ion me als, which
o m he in e me allics. O he wise, acuum induc ion mel ing has become a s anda d in
p ocessing o Ti-Al based in e me allics [
9
–
14
]. The ma e ial solu ion o he mel ing c ucible
is also a p oblem in he case o Ti-based in e me allics due o ex eme eac i i y o he
mel s [
15
]. The ce amics based on y ia (y ium oxide) is widely applied [
16
], bu e en in
such a case he mel could be con amina ed by y ium. Calcium zi cona e c ucibles could
be a solu ion [
17
]. Howe e , se e al eams succeeded wi h using g aphi e as he c ucible
ma e ial o Ti-based in e me allics [
18
,
19
]. Due o a poo cas abili y o hese ma e ials,
Ma e ials 2021,14, 813 3 o 14
cen i ugal cas ing is o en applied [
20
–
22
]. In o de o heal he in e nal po osi y o he
cas ings, ho isos a ic p essing (HIP) is equi ed in some cases [23,24].
This wo k deals wi h he addi ion o silicon in o he TiAl alloys. Silicon is a sui able
alloying elemen ha imp o es he esis ance o in e me allics TiAl o oxida ion and c eep
a high empe a u es. I has a e y low solubili y in he gi en in e me allic and he e o e
o ms a s able silicide Ti
5
Si
3
wi h i anium. I is an in e me allic phase wi h a high mel ing
poin (2130
◦
C) and a low speci ic g a i y. Fu he mo e, silicon has a posi i e e ec on
he o ma ion o an adhesi e and compac oxide laye , which in he case o in e me allics
based on Ti-Al-Si consis s o a mix u e o TiO
2
and Al
2
O
3
and SiO
2
, which heals unwan ed
po es. Fo hese easons, in e me allics a e esis an e en a highe empe a u es [
25
–
28
].
Recen ly de eloped Ti-Al-Si alloys ha e been p epa ed by powde me allu gy p ocesses,
especially eac i e sin e ing [
26
,
29
] and he echnology consis ing o mechanical alloying
and spa k plasma sin e ing [
30
]. Howe e , hese me hods, e en hough hey enable apid
p epa a ion and almos ee choice o he chemical composi ion o he p oduc , a e no
so sui able o mass indus ial p oduc ion. This pape aims o es he acuum induc ion
mel ing wi h cen i ugal cas ing as he p ocessing ou e o hese ma e ials and desc ibes
he p ope ies o he p oduc .
2. Ma e ials and Me hods
Expe imen al alloys TiAl15Si15 and TiAl35Si5 (w .%) we e p epa ed by acuum
induc ion mel ing wi h cen i ugal cas ing (CC). Fo he p epa a ion, he Linn Supe cas -
Ti an de ice was used. The mel ing ope a ions we e pe o med a VSB-Technical uni e si y
o Os a a, depa men o Non- e ous me als, e ining and ecycling. As aw/inpu
ma e ials, Ti (g ade 2, ound ba , diame e 10 mm, heigh up o 60 mm), Al (99.99 w .%,
pieces up o 20 mm
×
20 mm
×
20 mm) and Si (99.99 w .%, pieces up o 10 mm
×
10 mm
×
10 mm) we e used. The o al olume o he mel was 100 cm
3
. Used g aphi e c ucible
was made o isos a ic p essed g aphi e—SGV5-G B 527 XN. Fo each alloy, a sepa a e
c ucible was used. G aphi e cas ing o m (inne diame e 20 mm, heigh 225 mm) wi h
no-p ehea ing was used. P io o mel ing, he de ice was e acua ed se e al imes and illed
wi h A (99.9999%). Mel ing was ealized unde low p essu e o p o ec i e gas. Ro a ing
speed du ing cas ing was 400 pm. By his way, cylind ical samples we e ob ained. The
selec ed TiAl35Si5 alloy was also subjec ed o ho isos a ic p essing (HIP), which ook place
in a u nace a a empe a u e o 1260
◦
C and a p essu e o 190 MPa o 4 h wi h hea ing a
10
◦
C/min. This echnology was chosen o minimizing he in e nal po osi y o he cas ing.
Cas alloys TiAl15Si15 and TiAl35Si5 we e subjec ed o X- ay di ac ion analysis using
a di ac ome e PANaly icalX’Pe P o ((PANaly ical, Almelo, Ne he lands) ollowed by
e alua ion in X’Pe HighSco e 3.0 so wa e package (PANaly ical, Almelo, Ne he lands)
using PDF-2 2018 da abase o iden i y he phase composi ion. Me allog aphic cu s we e
p epa ed o s udy he mic os uc u e o expe imen al alloys. Samples we e e ched by K oll’s
agen (5 mL HNO
3
, 10 mL HF, 85 mL H
2
O) due o he obse ing o he mic os uc u e wi h
a Nikon Eclipse MA200 ligh mic oscope (Nikon, Tokyo, Japan) using he NIS Elemen s
(Labo a o y Imaging, P ague, Czech Republic) p og am. The indi idual phases and
chemical composi ion we e examined using a TESCAN VEGA 3LMU scanning elec on
mic oscope in backsca e ed elec ons egime (TESCAN, B no, Czech Republic) wi h an
Ox o d Ins umen s X-max 20 mm
2
EDS analyze (Ox o d Ins umen s, High Wycombe,
UK). The po osi y o he alloys was de e mined by he image analysis o he op ical
mic og aphs by ImageJ 1.53 so wa e.
F om he mechanical es s, Vicke s ha dness wi h a load o 5 kg (HV 5) was mea-
su ed om 10 inden ion in each sample. Tes s o comp essi e s eng h we e conduc ed by
he means o he uni e sal es ing de ice LabTes 5.250SP1-VM (p oduced by Labo Tech,
Opa a, Czech Republic). Values o ul ima e ensile s eng h in comp ession we e de e -
mined om he measu ed loading cu es. T ibological p ope ies was de e mined by
he TRIBO es e ball-on-disc ibome e (T ibo echnic, Clichy, F ance) wi h subsequen
e alua ion in he TRIBO echnic p og am. The wea es s ook place a a load o 5.0 N, wi h
Ma e ials 2021,14, 813 4 o 14
a o al pa h o 20,000 mm and a displacemen speed o 15 mm/s, which was pe o med by
a sphe ical body o Al
2
O
3
wi h a diame e o 6 mm as he s a ic pa ne . The eccen ici y o
he de ice was se o 5 mm and o his eason he ab asion a ea on he sample eached a
leng h o 10 mm. The whole measu emen ook place a oom empe a u e and he esul
was he measu ed wea a e o he sample and he a e age coe icien o ic ion. The
esul ing wea acks we e subsequen ly examined using he scanning elec on mic oscope
wi h he EDS analyze desc ibed abo ein o de o app oach he wea mechanism.
High- empe a u e p ope ies o alloys we e in es iga ed by cyclic oxida ion es s a
800
◦
C and 1000
◦
C o a o al leng h o 400 h. The leng h o one oxida ion cycle was 50 h
(8 cycles pe 50h). A he end o each cycle, he samples we e emo ed om he u nace.
A e spon aneous cooling in ai , hey we e weighed by an analy ical scale Pionee Plus
(Ohaus, Pa sippany, NJ, USA) wi h an accu acy o 0.0001 g and placed back in he u nace a
he se es empe a u e. The oxida ion a e was de e mined as he weigh gain ha esul ed
om he o ma ion o an oxide laye on he su ace o he indi idual expe imen al alloys.
The phase composi ion o he o med oxide laye s was de e mined by X- ay di ac ion
analysis using a PANaly icalX
´
Pe P o di ac ome e and he mic os uc u e o he oxide
laye s was examined using SEM-EDS.
3. Resul s
3.1. Mic os uc u e and Phase Composi ion
Mic os uc u e o bo h es ed alloys consis s o i anium silicide (Ti
5
Si
3
) pa icles in
i anium aluminide (TiAl) ma ix, see Figu es 1and 2. In addi ion o hese phases, g aphi e
was also de ec ed in TiAl15Si15 alloy (Figu e 1) as a esul o equi ed o e hea ing o his
high-silicon alloy and co esponding in e ac ion o g aphi e wi h he mel . The size (equi -
alen diame e ) o silicide pa icles eaches app oxima ely 50 and 10 in cas TiAl35Si5 and
TiAl15Si15 alloys, espec i ely. The silicide pa icles exhibi mos ly sha p-edged mo phol-
ogy in bo h alloys in as-cas s a e. Ho isos a ic p essing o he TiAl35Si5 cas ing led o
pa ial sphe oidiza ion o he Ti
5
Si
3
pa icles, leading o ound shape o he silicide. The
po osi y o all es ed alloys de e mined by image analysis is e y low. As-cas alloys each
he po osi y o abou 1 ol. %, a e HIP he po osi y dec eased o 0.7 ol. %.
Ma e ials 2021, 14, x FOR PEER REVIEW 5 o 15
Figu e 1. XRD pa e ns o he es ed alloys.
Figu e 2. Op ical mic og aphs o he es ed alloys: (a) TiAl15Si15 in as-cas s a e, (b) TiAl35Si5in as-cas s a e, (c)
TiAl35Si5 a e ho isos a ic p essing (HIP).
Figu e 1. XRD pa e ns o he es ed alloys.
Ma e ials 2021,14, 813 5 o 14
Ma e ials 2021, 14, x FOR PEER REVIEW 5 o 15
Figu e 1. XRD pa e ns o he es ed alloys.
Figu e 2. Op ical mic og aphs o he es ed alloys: (a) TiAl15Si15 in as-cas s a e, (b) TiAl35Si5in as-cas s a e, (c)
TiAl35Si5 a e ho isos a ic p essing (HIP).
Figu e 2.
Op ical mic og aphs o he es ed alloys: (
a
) TiAl15Si15 in as-cas s a e, (
b
) TiAl35Si5in as-cas s a e, (
c
) TiAl35Si5 a -
e ho isos a ic p essing (HIP).
3.2. Mechanical and T ibological P ope ies
The ha dness o he Ti-Al-Si alloys inc eases wi h he amoun o silicon (Table 1).
TiAl15Si15 alloy eaches a highe ha dness han TiAl35Si5 alloy. Ho isos a ic p essing has
no had an e ec on he ha dness o he ma e ial, TiAl35Si5 alloy has he same ha dness
be o e HIP and a e HIP. Values o ul ima e comp essi e s eng h inc ease wi h he amoun
o aluminum and HIP has no an e ec on hese alues. TiAl35Si5 alloys ha e he highes
alues due o i s s uc u e, which is la gely o med by ela i ely oughe aluminides TiAl.
Table 1. Mechanical p ope ies o es ed alloys.
Mechanical P ope ies TiAl15Si15
(CC)
TiAl35Si5
(CC)
TiAl35Si5
(CC + HIP)
Ha dness HV 5 459 ±15 375 ±16 374 ±7
Ul ima e comp essi e s eng h [MPa] 1205 ±80 1867 ±75 1801 ±47
T ibological p ope ies we e es ed unde he condi ions o a d y sliding wea agains
alumina as he s a ic ic ion pa ne . The esul s indica e ha he ic ion coe icien , as
well as he wea a e, a e in luenced by he amoun s o silicon and aluminum in he alloy.
The high-silicon ma e ial (TiAl15Si15) exhibi s he highes ic ion coe icien (Table 2) and
wea a e. Obse a ion o he wea ack by scanning elec on mic oscope in backsca e ed
elec ons egime e ealed ha his alloy ends o a s ong emo al o he silicide pa icles

Ma e ials 2021,14, 813 6 o 14
om he su ace due o hei b i le na u e (Figu e 3a). This phenomenon can be seen also
in he case o he low-silicon (FeAl35Si5) ma e ial, bu in much lowe ex en (Figu e 3b,c).
The wea a all o he es ed ma e ials is mos ly ab asi e, whe e he ex ac ed ha d silicide
pa icles ac as ab asi e. The e a e no isible signs o oxida ion o he ma e ial in he wea
ack. The in luence o HIP p ocessing on he ic ion coe icien , wea a e, and mechanism
o he wea damage is almos negligible.
Table 2. T ibological p ope ies o es ed alloys.
T ibological P ope ies TiAl15Si15 (CC) TiAl35Si5 (CC) TiAl35Si5
(CC + HIP)
ic ion coe icien [–] 0.555 ±0.006 0.453 ±0.004 0.462 ±0.003
wea a e [mm3m−1N−1] (4.17 ±0.09) ×10 −4(1.25 ±0.02) ×10 −4(1.21 ±0.04) ×10 −4
Ma e ials 2021, 14, x FOR PEER REVIEW 7 o 15
Figu e 3. Mo phology o he wea acks (SEM-BSE) on: (a) TiAl15Si15 in as-cas s a e, (b) TiAl35Si5 in as-cas s a e, (c)
TiAl35Si5 a e HIP.
3.3. High-Tempe a u e P ope ies
The oxida ion a e was de e mined om he weigh gain ob ained due o he o -
ma ion o oxides on he su ace o he base ma e ial du ing he mal exposu e. The weigh
gain can be obse ed on he kine ic cu es in Figu e 4 o 800 °C and in Figu e 5 o 1000
°C, when he s udied alloys we e weigh ed, including scaled-o (delamina ed) oxides.
Fo a mo e de ailed iew o he delamina ion o oxide laye s, kine ic cu es we e gene -
a ed only o delamina ed oxides, in Figu e 6 o 800 °C, and in Figu e 7 o 1000 °C.
Figu e 3.
Mo phology o he wea acks (SEM-BSE) on: (
a
) TiAl15Si15 in as-cas s a e, (
b
) TiAl35Si5 in as-cas s a e,
(c) TiAl35Si5 a e HIP.
Ma e ials 2021,14, 813 7 o 14
3.3. High-Tempe a u e P ope ies
The oxida ion a e was de e mined om he weigh gain ob ained due o he o ma ion
o oxides on he su ace o he base ma e ial du ing he mal exposu e. The weigh gain can
be obse ed on he kine ic cu es in Figu e 4 o 800
◦
C and in Figu e 5 o 1000
◦
C, when
he s udied alloys we e weigh ed, including scaled-o (delamina ed) oxides. Fo a mo e
de ailed iew o he delamina ion o oxide laye s, kine ic cu es we e gene a ed only o
delamina ed oxides, in Figu e 6 o 800 ◦C, and in Figu e 7 o 1000 ◦C.
Ma e ials 2021, 14, x FOR PEER REVIEW 8 o 15
Figu e 4. Dependence o o al weigh gain o Ti-Al-Si alloys (including delamina ed oxides) on cy-
clic oxida ion du a ion (800 °C; 400 h).
Figu e 5. Dependence o o al weigh gain o Ti-Al-Si alloys (including delamina ed oxides) on cy-
clic oxida ion du a ion (1000 °C; 400 h).
Figu e 4.
Dependence o o al weigh gain o Ti-Al-Si alloys (including delamina ed oxides) on cyclic
oxida ion du a ion (800 ◦C; 400 h).
Ma e ials 2021, 14, x FOR PEER REVIEW 8 o 15
Figu e 4. Dependence o o al weigh gain o Ti-Al-Si alloys (including delamina ed oxides) on cy-
clic oxida ion du a ion (800 °C; 400 h).
Figu e 5. Dependence o o al weigh gain o Ti-Al-Si alloys (including delamina ed oxides) on cy-
clic oxida ion du a ion (1000 °C; 400 h).
Figu e 5.
Dependence o o al weigh gain o Ti-Al-Si alloys (including delamina ed oxides) on cyclic
oxida ion du a ion (1000 ◦C; 400 h).
Ma e ials 2021,14, 813 8 o 14
Ma e ials 2021, 14, x FOR PEER REVIEW 9 o 15
Figu e 6. Dependence o he weigh o delamina ed oxides o Ti-Al-Si alloys on he ime o cyclic
oxida ions (800 °C; 400 h).
Figu e 7. Dependence o he weigh o delamina ed oxides o Ti-Al-Si alloys on he ime o cyclic
oxida ions (1000 °C; 400 h).
Cyclic oxida ion es s a 800 °C showed good oxide laye adhesion o all alloys. The
highes inc ease in oxida ion a e was shown by he TiAl15Si15 alloy a bo h p ocess
empe a u es. This alloy con ained la ge sha p-edged silicide pa icles in i s s uc u e
and in pa icula i was con amina ed by ca bon. A e cyclic oxida ion es s o his alloy,
he e was mos likely a be e oxygen pe meabili y o he base ma e ial du ing exposu e
due o he di usion o ca bon om he s uc u e a a highe empe a u e. Fo his eason,
he e was a cons an g ow h o he oxide laye and con inuous oxida ion o he whole
ma e ial, which was demons a ed o his alloy a e cyclic oxida ion es s a a empe -
a u e o 1000 °C, when he whole base ma e ial was comple ely oxidized. The esul ing
oxide laye is po ous, bu e en a a empe a u e o 1000 °C i did no unde go massi e
delamina ion (Figu e 7). In he case o cas alloys TiAl35Si5 and TiAl35Si5 a e HIP, he
esul s o cyclic oxida ion es s a 800 °C showed he o ma ion o a hin and
well-adhe ing oxide laye , which p o ec ed he base ma e ial om subsequen oxida ion.
The weigh gain was p ac ically ze o h oughou he oxida ion es s (see Figu e 4). The
Figu e 6.
Dependence o he weigh o delamina ed oxides o Ti-Al-Si alloys on he ime o cyclic
oxida ions (800 ◦C; 400 h).
Ma e ials 2021, 14, x FOR PEER REVIEW 9 o 15
Figu e 6. Dependence o he weigh o delamina ed oxides o Ti-Al-Si alloys on he ime o cyclic
oxida ions (800 °C; 400 h).
Figu e 7. Dependence o he weigh o delamina ed oxides o Ti-Al-Si alloys on he ime o cyclic
oxida ions (1000 °C; 400 h).
Cyclic oxida ion es s a 800 °C showed good oxide laye adhesion o all alloys. The
highes inc ease in oxida ion a e was shown by he TiAl15Si15 alloy a bo h p ocess
empe a u es. This alloy con ained la ge sha p-edged silicide pa icles in i s s uc u e
and in pa icula i was con amina ed by ca bon. A e cyclic oxida ion es s o his alloy,
he e was mos likely a be e oxygen pe meabili y o he base ma e ial du ing exposu e
due o he di usion o ca bon om he s uc u e a a highe empe a u e. Fo his eason,
he e was a cons an g ow h o he oxide laye and con inuous oxida ion o he whole
ma e ial, which was demons a ed o his alloy a e cyclic oxida ion es s a a empe -
a u e o 1000 °C, when he whole base ma e ial was comple ely oxidized. The esul ing
oxide laye is po ous, bu e en a a empe a u e o 1000 °C i did no unde go massi e
delamina ion (Figu e 7). In he case o cas alloys TiAl35Si5 and TiAl35Si5 a e HIP, he
esul s o cyclic oxida ion es s a 800 °C showed he o ma ion o a hin and
well-adhe ing oxide laye , which p o ec ed he base ma e ial om subsequen oxida ion.
The weigh gain was p ac ically ze o h oughou he oxida ion es s (see Figu e 4). The
Figu e 7.
Dependence o he weigh o delamina ed oxides o Ti-Al-Si alloys on he ime o cyclic
oxida ions (1000 ◦C; 400 h).
Cyclic oxida ion es s a 800
◦
C showed good oxide laye adhesion o all alloys.
The highes inc ease in oxida ion a e was shown by he TiAl15Si15 alloy a bo h p ocess
empe a u es. This alloy con ained la ge sha p-edged silicide pa icles in i s s uc u e and
in pa icula i was con amina ed by ca bon. A e cyclic oxida ion es s o his alloy, he e
was mos likely a be e oxygen pe meabili y o he base ma e ial du ing exposu e due o
he di usion o ca bon om he s uc u e a a highe empe a u e. Fo his eason, he e
was a cons an g ow h o he oxide laye and con inuous oxida ion o he whole ma e ial,
which was demons a ed o his alloy a e cyclic oxida ion es s a a empe a u e o
1000
◦
C, when he whole base ma e ial was comple ely oxidized. The esul ing oxide laye
is po ous, bu e en a a empe a u e o 1000
◦
C i did no unde go massi e delamina ion
(Figu e 7). In he case o cas alloys TiAl35Si5 and TiAl35Si5 a e HIP, he esul s o
cyclic oxida ion es s a 800
◦
C showed he o ma ion o a hin and well-adhe ing oxide
laye , which p o ec ed he base ma e ial om subsequen oxida ion. The weigh gain was
p ac ically ze o h oughou he oxida ion es s (see Figu e 4). The o ma ion o a s able
oxide laye wi h p o ec i e e ec s esul s in a dec ease in he oxida ion a e due o he
slowing down o he di usion o oxygen h ough he oxide laye . In he cyclic oxida ion
Ma e ials 2021,14, 813 9 o 14
es s, which ook place a a empe a u e o 1000
◦
C, he e was al eady an inc ease in he
oxide laye wi h insu icien p o ec i e e ec , and he e o e a massi e delamina ion o
his laye ollowed in bo h TiAl35Si5 alloys, which allowed u he oxida ion o he base
ma e ial. Poo adhesion o he p o ec i e laye can be de ec ed in Figu e 5. Alloys show
epe i i e pa abolic g ow h o he oxide laye . Due o he insu icien p o ec ion o he base
ma e ial by he espec i e su ace oxides, he oxida ion a e is con olled by he chemical
eac ion o oxygen wi h he su ace o he ma e ial. The non-compac ness o he laye
du ing his exposu e is pa ly due o he insu icien amoun o silicon in he alloys.
The phase composi ion o he o med oxide laye s o he s udied Ti-Al-Si alloys was
de e mined a e cyclic oxida ion es s by X- ay di ac ion analysis. The p esence o
TiO2 and Al2O3 oxides, which o med he majo componen s o he su ace oxide laye ,
was p o ed in all alloys. A e he mal exposu e a 800
◦
C (Figu e 8), he p esence o
i anium silicide was u he p esen ed in Ti-Al-Si alloys p oduced by cen i ugal cas ing.
In he case o TiAl15Si15 (CC) alloy, a highe TiSi
2
silicide was de ec ed on he su ace, in
con as o TiAl35Si5 (CC) alloys, whe e he b i le phase o Ti
5
Si
3
silicide was p esen . The
su ace laye o TiAl35Si5 (CC) and TiAl35Si5 (CC+HIP) alloys was u he supplemen ed
wi h a Ti
2
AlN phase, which o ms an in e media e laye be ween he base ma e ial and
he esul ing oxide laye and u he inc eases i s adhesion. A e he mal exposu e a
1000
◦
C (Figu e 9), he e was no signi ican change in he phase composi ion o he cas
Ti-Al-Si alloys compa ed o he p e ious esul s. In he case o he TiAl35Si5 (CC) alloy, he
AlN and TiN phases we e u he de ec ed, in which he same e ec can be expec ed as
in he men ioned Ti
2
AlN phase. In he cas HIP- ea ed TiAl35Si5 alloy, he p esence o a
highe i anium aluminide TiAl
3
was de ec ed, which was p obably due o he inc eased
concen a ion o aluminum in he su ace laye o he alloy du ing he mal exposu e.
Ma e ials 2021, 14, x FOR PEER REVIEW 10 o 15
o ma ion o a s able oxide laye wi h p o ec i e e ec s esul s in a dec ease in he oxi-
da ion a e due o he slowing down o he di usion o oxygen h ough he oxide laye .
In he cyclic oxida ion es s, which ook place a a empe a u e o 1000 °C, he e was al-
eady an inc ease in he oxide laye wi h insu icien p o ec i e e ec , and he e o e a
massi e delamina ion o his laye ollowed in bo h TiAl35Si5 alloys, which allowed
u he oxida ion o he base ma e ial. Poo adhesion o he p o ec i e laye can be de-
ec ed in Figu e 5. Alloys show epe i i e pa abolic g ow h o he oxide laye . Due o he
insu icien p o ec ion o he base ma e ial by he espec i e su ace oxides, he oxida ion
a e is con olled by he chemical eac ion o oxygen wi h he su ace o he ma e ial. The
non-compac ness o he laye du ing his exposu e is pa ly due o he insu icien
amoun o silicon in he alloys.
The phase composi ion o he o med oxide laye s o he s udied Ti-Al-Si alloys was
de e mined a e cyclic oxida ion es s by X- ay di ac ion analysis. The p esence o TiO2
and Al2O3 oxides, which o med he majo componen s o he su ace oxide laye , was
p o ed in all alloys. A e he mal exposu e a 800 °C (Figu e 8), he p esence o i anium
silicide was u he p esen ed in Ti-Al-Si alloys p oduced by cen i ugal cas ing. In he
case o TiAl15Si15 (CC) alloy, a highe TiSi2 silicide was de ec ed on he su ace, in con-
as o TiAl35Si5 (CC) alloys, whe e he b i le phase o Ti5Si3 silicide was p esen . The
su ace laye o TiAl35Si5 (CC) and TiAl35Si5 (CC+HIP) alloys was u he supplemen ed
wi h a Ti2AlN phase, which o ms an in e media e laye be ween he base ma e ial and
he esul ing oxide laye and u he inc eases i s adhesion. A e he mal exposu e a
1000 °C (Figu e 9), he e was no signi ican change in he phase composi ion o he cas
Ti-Al-Si alloys compa ed o he p e ious esul s. In he case o he TiAl35Si5 (CC) alloy,
he AlN and TiN phases we e u he de ec ed, in which he same e ec can be expec ed
as in he men ioned Ti2AlN phase. In he cas HIP- ea ed TiAl35Si5 alloy, he p esence o
a highe i anium aluminide TiAl3 was de ec ed, which was p obably due o he in-
c eased concen a ion o aluminum in he su ace laye o he alloy du ing he mal ex-
posu e.
Figu e 8. Phase composi ion o he su ace oxide laye o Ti-Al-Si alloys a e cyclic oxida ion a
800°C.
Figu e 8.
Phase composi ion o he su ace oxide laye o Ti-Al-Si alloys a e cyclic oxida ion a
800 ◦C.