High Entropy Alloys Coatings Deposited by Laser Cladding: A Review of Grain Boundary Wetting Phenomena



Ci a ion: S aumal, B.B.; Klinge , L.;
Kuzmin, A.; Lopez, G.A.; Ko ne a,
A.; S aumal, A.B.; Ve shinin, N.;
Go nako a, A.S. High En opy
Alloys Coa ings Deposi ed by Lase
Cladding: A Re iew o G ain
Bounda y We ing Phenomena.
Coa ings 2022,12, 343. h ps://
doi.o g/10.3390/coa ings12030343
Academic Edi o s: Ionelia Voiculescu
and Julia Claudia Mi za-Rosca
Recei ed: 27 Decembe 2021
Accep ed: 1 Ma ch 2022
Published: 6 Ma ch 2022
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coa ings
Re iew
High En opy Alloys Coa ings Deposi ed by Lase Cladding: A
Re iew o G ain Bounda y We ing Phenomena
Bo is B. S aumal 1,2,*, Leonid Klinge 3, Alexei Kuzmin 4, Gab iel A. Lopez 5, Anna Ko ne a 6,
Alexande B. S aumal 1, Nikolai Ve shinin 1and Alena S. Go nako a 1
1Osipyan Ins i u e o Solid S a e Physics o he Russian Academy o Sciences, 142432 Che nogolo ka, Russia;
[email p o ec ed] (A.B.S.); [email p o ec ed] (N.V.); [email p o ec ed] (A.S.G.)
2Che nogolo ka Scien i ic Cen e o he Russian Academy o Sciences, 142432 Che nogolo ka, Russia
3Depa men o Ma e ials Science and Enginee ing, Technion—Is ael Ins i u e o Technology,
Hai a 3200003, Is ael; [email p o ec ed]
4Ins i u e o Solid S a e Physics, Uni e si y o La ia, LV-1063 Riga, La ia; [email p o ec ed]
5Physics Depa men , Uni e si y o he Basque Coun y UPV/EHU, 48940 Leioa, Spain;
[email p o ec ed]
6Ins i u e o Me allu gy and Ma e ials Science, Polish Academy o Sciences, 30059 C acow, Poland;
[email p o ec ed]
*Co espondence: [email p o ec ed]u
Abs ac :
High-en opy alloys (HEAs) a e called also alloys wi hou a main componen o mul i-
p incipal alloys. They consis o i e, six o mo e componen s in mo e o less equal p opo ions and
possess unique p ope ies. Se e al dozens o housands o publica ions ha e al eady been de o ed o
bulk HEAs, while HEA coa ings a e jus beginning o de elop. Mo e han hal o he wo ks on he
deposi ion o HEA coa ings a e de o ed o lase cladding. In he lase cladding p ocess, a mix u e
o powde s on a subs a e is mel ed in a ocused lase beam, which sequen ially scans he subs a e.
In he hea ed zone, he powde mix u e mel s. A he end o he c ys alliza ion p ocess, a solidi ied
polyc ys al and a small amoun o esidual mel a e ound in he hea ed zone. I is possible ha he
g ain bounda ies (GBs) in he solidi ied polyc ys al a e incomple ely o ully we ed by his liquid
phase. In his way, he GB we ing wi h a mel de e mines he mo phology and mic os uc u e o
HEAs coa ings. This e iew analyzes GB we ing in single-phase HEAs, as well as in HEAs con aining
wo o mo e phases. We analyze how he HEAs’ composi ion, lase scanning speed, lase beam
powe , ex e nal magne ic ield o ul asonic impac a ec he mic os uc u e and GB we ing. I is
also shown how he mic os uc u e and GB we ing change o e he hickness o he a he hick as
well as mul ilaye coa ings deposi ed using a lase cladding.
Keywo ds:
lase cladding; coa ings; high-en opy alloys; g ain bounda y we ing; phase ansi ions;
phase diag ams
1. In oduc ion
Lase cladding is a mode n coa ing echnology o su ace s eng hening and epai [
1
].
The powde o a cladding ma e ial apidly mel s and solidi ies unde he lase i adia ion.
Due o he high empe a u e g adien , he ough and ine-g ained coa ing o ms on he
subs a e wi h a good me allu gical bond wi h i . The mos equen ly used lase cladding
schemes a e he coaxial and p eplaced powde sys ems (see schemes in Figu e 1). In he
i s a ian he lase beam i adia es he su ace o he subs a e. As a esul i o ms a
liquid mel pool. The p essu e o a ca ie gas in he nozzle ejec s he powde o be mel ed
om his nozzle o he liquid mel pool. The lase beam mel s he powde in o a cladding
laye . The lase beam mo es synch onously wi h he powde eeding nozzle and scans he
subs a e “line-by-line”. The second case is a p eplaced powde sys em. In his sys em he
subs a e is al eady co e ed by he cladding ma e ial. The lase beam scans he p eplaced
Coa ings 2022,12, 343. h ps://doi.o g/10.3390/coa ings12030343 h ps://www.mdpi.com/jou nal/coa ings
Coa ings 2022,12, 343 2 o 22
powde . I mel s and apidly cools down, hus o ming a cladding laye . The coa ed sample
usually con ains he ollowing ou zones: zone o cladding (CZ), zone o in e ace (IZ),
zone in luenced by he hea ing (HAZ) and he subs a e zone (SUB).
Coa ings 2022, 12, x FOR PEER REVIEW 2 o 23
scans he p eplaced powde . I mel s and apidly cools down, hus o ming a cladding
laye . The coa ed sample usually con ains he ollowing ou zones: zone o cladding
(CZ), zone o in e ace (IZ), zone in luenced by he hea ing (HAZ) and he subs a e
zone (SUB).
Figu e 1. Scheme showing he lase cladding sys ems o coaxial (le ) and p eplaced ( igh ) pow-
de cases. Rep in ed wi h pe mission om Re . [1]. Copy igh 2021 Else ie .
The idea o high en opy alloys (HEAs) o alloys wi hou main componen o mul-
ip incipal alloys has been i s p oposed by P o . B ian Can o wi h cowo ke s om he
Uni e si y o Ox o d [2] and P o . Jien-Wei Yeh wi h his eam om NTHU, Taiwan [3].
They checked nume ous alloys wi h 6 o 12 and mo e componen s in equia omic p o-
po ions and disco e ed many composi ions whe e he uni o m diso de ed solid solu-
ion is o med. I was he as onishing and ully coun e -in ui i e disco e y. I is because
such alloys con aining a high numbe o di e en elemen s in mo e o less equal
amoun s ha e a high mixing en opy. This ac would lead, gene ally speaking, o
amo phiza ion. Ne e heless, he no el HEAs ha e high ha dness [4,5] and a easonable
s eng h a high empe a u es [6]; hey can also possess excellen oxida ion [7], wea [8],
and co osion esis ance [9]. The idea soon appea ed o deposi ing coa ings o HEAs on
he su ace o he usual ma e ials. This gi es he possibili y o combine in such a way he
ad an ages o coa ings and subs a es. Recen ly, he ocus o in e es in HEA in es iga-
ions shi ed om one-phase homogeneous solid solu ions o he e ogeneous HEAs con-
aining mo e ha one phase, he inhomogeneous dis ibu ion o componen s and o he
elemen s o inhomogenei y. F equen ly, such non-homogeneous s uc u es can be suc-
cess ully explained based on he concep o g ain bounda y (GB) phase ans o ma ions.
The GB phase ans o ma ions include GB we ing by a second liquid o solid phase, and
also o ma ion o di e en hin GB phases [10–13].
Lase cladding is he mos equen ly used echnology o he manu ac u ing o
HEA coa ings [14–16]. HEA coa ings can also be deposi ed by plasma cladding [17,18],
plasma sp ay [19–26], he mal sp ay [27], magne on spu e ing [28–37], elec ic a c
deposi ion [38], elec on beam physical apo deposi ion [39], and acuum a c deposi-
ion [40–44]. The solidi ica ion o mel ed pool du ing lase cladding and he esul ing
mic os uc u e can be s ongly a ec ed by comple e o incomple e GB we ing. GB we -
ing phenomena caused by lase cladding o HEA coa ings is he opic o his e iew. GB
we ing phenomena in o he HEA coa ings will be discussed elsewhe e.
Figu e 1.
Scheme showing he lase cladding sys ems o coaxial (
le
) and p eplaced (
igh
) powde
cases. Rep in ed wi h pe mission om Re . [1]. Copy igh 2021 Else ie .
The idea o high en opy alloys (HEAs) o alloys wi hou main componen o mul i-
p incipal alloys has been i s p oposed by P o . B ian Can o wi h cowo ke s om he
Uni e si y o Ox o d [
2
] and P o . Jien-Wei Yeh wi h his eam om NTHU, Taiwan [
3
]. They
checked nume ous alloys wi h 6 o 12 and mo e componen s in equia omic p opo ions and
disco e ed many composi ions whe e he uni o m diso de ed solid solu ion is o med. I
was he as onishing and ully coun e -in ui i e disco e y. I is because such alloys con ain-
ing a high numbe o di e en elemen s in mo e o less equal amoun s ha e a high mixing
en opy. This ac would lead, gene ally speaking, o amo phiza ion. Ne e heless, he
no el HEAs ha e high ha dness [
4
,
5
] and a easonable s eng h a high empe a u es [
6
];
hey can also possess excellen oxida ion [
7
], wea [
8
], and co osion esis ance [
9
]. The idea
soon appea ed o deposi ing coa ings o HEAs on he su ace o he usual ma e ials. This
gi es he possibili y o combine in such a way he ad an ages o coa ings and subs a es.
Recen ly, he ocus o in e es in HEA in es iga ions shi ed om one-phase homogeneous
solid solu ions o he e ogeneous HEAs con aining mo e ha one phase, he inhomoge-
neous dis ibu ion o componen s and o he elemen s o inhomogenei y. F equen ly, such
non-homogeneous s uc u es can be success ully explained based on he concep o g ain
bounda y (GB) phase ans o ma ions. The GB phase ans o ma ions include GB we ing
by a second liquid o solid phase, and also o ma ion o di e en hin GB phases [10–13].
Lase cladding is he mos equen ly used echnology o he manu ac u ing o HEA
coa ings [
14
–
16
]. HEA coa ings can also be deposi ed by plasma cladding [
17
,
18
], plasma
sp ay [
19
–
26
], he mal sp ay [
27
], magne on spu e ing [
28
–
37
], elec ic a c deposi ion [
38
],
elec on beam physical apo deposi ion [
39
], and acuum a c deposi ion [
40
–
44
]. The
solidi ica ion o mel ed pool du ing lase cladding and he esul ing mic os uc u e can be
s ongly a ec ed by comple e o incomple e GB we ing. GB we ing phenomena caused
by lase cladding o HEA coa ings is he opic o his e iew. GB we ing phenomena in
o he HEA coa ings will be discussed elsewhe e.
2. G ain Bounda y We ing Phase T ansi ions
Usually, HEAs con ain a leas i e di e en componen s, and espec i e equilib ium
phase diag ams should be cons uc ed in a leas 5 dimensions. Ne e heless, we can
discuss he mos impo an ea u es o GB we ing phase ansi ions [
45
] using he simples
wo-dimensional scheme o bina y alloys. Such a schema ic phase diag am o wo
componen s in he sys em is shown in Figu e 2. Bold lines o he bulk phase ansi ions
Coa ings 2022,12, 343 3 o 22
a e liquidus, solidus, sol us and eu ec ic line. Thin lines a T
wmin
and T
wmax
show he
ie-lines o he GB ansi ions. Du ing he cooling, he alloy is i s in he liquid a ea L and
hen c osses he liquidus line, en e ing he L +
α
wo-phase a ea. In his L+
α
, he liquid
phase, L, is in equilib ium wi h he solid phase, α(s ic ly speaking i is he solid solu ion
based on componen A). By dec easing empe a u e, he po ion o mel L dec eases and
ha o solid solu ion
α
inc eases. The composi ion o solidi ying
α
-phase ollows he
solidus line. I means ha he i s po ions o
α
-phase a e ee om componen B, and
a e wa ds he concen a ion o B inc eases. I he concen a ion o B is low (see lines
a,b,c,d in Figu e 3e), he solidi ica ion inishes a he solidus line. As a esul he solid alloy
con ains only α-phase, bu he las solidi ied po ions a e en iched by he componen B.
Coa ings 2022, 12, x FOR PEER REVIEW 3 o 23
2. G ain Bounda y We ing Phase T ansi ions
Usually, HEAs con ain a leas i e di e en componen s, and espec i e equilib-
ium phase diag ams should be cons uc ed in a leas 5 dimensions. Ne e heless, we
can discuss he mos impo an ea u es o GB we ing phase ansi ions [45] using he
simples wo-dimensional scheme o bina y alloys. Such a schema ic phase diag am o
wo componen s in he sys em is shown in Figu e 2. Bold lines o he bulk phase ansi-
ions a e liquidus, solidus, sol us and eu ec ic line. Thin lines a Twmin and Twmax show
he ie-lines o he GB ansi ions. Du ing he cooling, he alloy is i s in he liquid a ea L
and hen c osses he liquidus line, en e ing he L + α wo-phase a ea. In his L+α, he liq-
uid phase, L, is in equilib ium wi h he solid phase, α (s ic ly speaking i is he solid
solu ion based on componen A). By dec easing empe a u e, he po ion o mel L de-
c eases and ha o solid solu ion α inc eases. The composi ion o solidi ying α-phase
ollows he solidus line. I means ha he i s po ions o α-phase a e ee om compo-
nen B, and a e wa ds he concen a ion o B inc eases. I he concen a ion o B is low
(see lines a,b,c,d in Figu e 3e), he solidi ica ion inishes a he solidus line. As a esul
he solid alloy con ains only α-phase, bu he las solidi ied po ions a e en iched by he
componen B.
Figu e 2. Scheme explaining he GB we ing phenomena in a bina y A–B phase diag am. The bulk
phase ans o ma ions a e shown by he hick lines. The ie-lines a Twmin and Twmax a e o he GB
we ing by he liquid phase and a e shown by he hin lines. On he igh -hand side o he diag am
he mic og aphs a e shown o he mic os uc u e o Al–Mg samples. Case (a) is o he alloy an-
nealed abo e Twmax (in his sample all GBs we e comple ely we ed). Case (b) is o he alloy an-
nealed be ween Twmin and Twmax (in his sample se e al GBs a e ully we ed and he o he GBs a e
incomple ely we ed). Case (c) is o he alloy annealed below Twmin (no comple ely we ed GBs a
all). The mic og aphs a e ep in ed wi h pe mission om Re . [46].
In mul icomponen HEAs, he GB we ing ansi ions a e no so simple. Fo exam-
ple, i HEA con ains six componen s i needs o i s desc ip ion he phase diag am in six
dimensions. In such a case an alloy s a ing o solidi y by cooling om he mel , L, may
in e sec se e al mul iphase a eas (and no jus one wo-phase egion, α + L) un il i be-
comes comple ely solid, α. In such mul iphase egions mo e han one liquid and one
solid phase(s) may coexis . The polyc ys al in he wo-phase egion, α + L, con ains he
GBs as well as bounda ies be ween he α-phase and he mel L called in e phase bound-
a ies (IBs). Le us conside now he iple junc ions (TJs) be ween wo IBs and GB. He e
GB con ac s wi h he mel (see schemes on he le -hand side o Figu e 2).
Figu e 2.
Scheme explaining he GB we ing phenomena in a bina y A–B phase diag am. The bulk
phase ans o ma ions a e shown by he hick lines. The ie-lines a T
wmin
and T
wmax
a e o he
GB we ing by he liquid phase and a e shown by he hin lines. On he igh -hand side o he
diag am he mic og aphs a e shown o he mic os uc u e o Al–Mg samples. Case (a) is o he
alloy annealed abo e T
wmax
(in his sample all GBs we e comple ely we ed). Case (b) is o he alloy
annealed be ween T
wmin
and T
wmax
(in his sample se e al GBs a e ully we ed and he o he GBs
a e incomple ely we ed). Case (c) is o he alloy annealed below T
wmin
(no comple ely we ed GBs
a all). The mic og aphs a e ep in ed wi h pe mission om Re . [46].
Coa ings 2022, 12, x FOR PEER REVIEW 4 o 23
Figu e 3. SEM mic og aphs o Mo0, Mo0.15, Mo0.20 and Mo0.25 HEA coa ings (a) Mo0; (b)
Mo0.15; (c) Mo0.20; (d) Mo0.25. The ed poin s and le e s A and B ma k he loca ions o composi-
ion measu emen s. (e) Scheme wi h he bina y phase diag am o he explana ion o espec i e
GB we ing p ocesses. The do ed ed a ows show he cooling ajec o ies co esponding o he
mic og aphs (a–d). Mic og aphs (a–d) a e ep in ed wi h pe mission om Re . [47]. Copy igh
2021 Else ie .
Le us suppose ha he GB ene gy, σGB, is less han he ene gy o he wo sol-
id/liquid IBs, 2σSL (see lowe scheme in Figu e 2). The GB and IBs o m in his case he
con ac angle, θ > 0, a his TJ, and he GB we ing is called pa ial (o incomple e). I σGB
> 2σSL (see uppe scheme in Figu e 2) hen θ = 0. In his case, he solid α-g ains would be
sepa a ed by a hick liquid laye . This is he case o comple e GB we ing by he mel . I
is desc ibed o many bina y alloys. In his case he con ac angle θ usually dec eases
wi h g owing empe a u e and can each ze o a a ce ain empe a u e, Tw [46,48–50]. A
Tw he incomple e GB we ing changes o he comple e one. Tw is he empe a u e o he
GB we ing phase ans o ma ion. The GB we ing phase- ansi ion can be o he i s o
second o de as o con en ional bulk phase ans o ma ions [51–53]. I he GB we ing
ans o ma ion is o a i s -o de , hen he i s de i a i e o θ, wi h espec o empe a-
u e, dθ/dT has a discon inui y a Tw [46,51,52]. In his case, exhibi s dθ/dT d ops sud-
denly om a ce ain ini e alue o 0 [46,51,52]. I he GB we ing phase ansi ion is con-
inuous (o o a second-o de ), hen dθ/dT con inuously dec eases wi h inc easing T and
eaches ze o dθ/dT = 0 a Tw [51,52]. We ha e o unde line he e ha he σGB alue de-
pends on he GB miso ien a ion angle, χ, as well as on he GB inclina ion angle, ψ [54].
The σGB(χ) and σGB (ψ) dependences possess sha p cusps a ce ain χ and ψ [55]. The e-
o e, he in e al o σGB alues can be e y b oad. The highe is σGB, he smalle is he θ
alue a he GB TJ wi h he mel [56,57]. In o he wo ds, he θ alues in a wo-phase
polyc ys al could be e y di e en a each ixed empe a u e. Wi h inc easing empe a-
u e, hese θ alues o di e en GBs would dec ease wi h di e en a es. This is he
eason why he spec um o Tw empe a u es in a polyc ys al can be e y wide.
Typical examples o such wo-phase polyc ys als mic os uc u es a e shown in
Figu e 2 o he bina y Al–Mg alloys. Thus, ega ding he GB we ing phase ansi ions,
he bulk phase diag am becomes wo addi ional GB ie-lines. The Twmin ie-line co e-
sponds o he GBs we ing ansi ion om pa ial o comple e we ing o he g ain
bounda ies ha ing highes ene gy σGB. Unde Twmin one canno obse e in he alloy any
ully we ed GB. The polyc ys al unde Twmin con ains only pa ially we ed GBs wi h θ >
0. Fi s , comple ely we ed GBs appea wi h he hea ing o he alloy abo e Twmin. Abo e
Twmin, he po ion o ully we ed GBs inc eases wi h inc easing empe a u e. A Twmax i
eaches uni y. Ano he ie-line shows he empe a u e Twmax. Abo e Twmax all GBs con ain
he mel ed laye and a e, he e o e, comple ely we ed. In his case each g ain is com-
ple ely su ounded by he mel . I canno con ac o he abu ing g ains. This is because
he non-we ed GBs a e he modynamically disad an ageous abo e Twmax. In o he
Figu e 3.
SEM mic og aphs o Mo0, Mo0.15, Mo0.20 and Mo0.25 HEA coa ings (
a
) Mo0; (
b
) Mo0.15;
(
c
) Mo0.20; (
d
) Mo0.25. The ed poin s and le e s A and B ma k he loca ions o composi ion
measu emen s. (
e
) Scheme wi h he bina y phase diag am o he explana ion o espec i e GB we ing
p ocesses. The do ed ed a ows show he cooling ajec o ies co esponding o he mic og aphs
(a–d). Mic og aphs (a–d) a e ep in ed wi h pe mission om Re . [47]. Copy igh 2021 Else ie .
Coa ings 2022,12, 343 4 o 22
In mul icomponen HEAs, he GB we ing ansi ions a e no so simple. Fo example,
i HEA con ains six componen s i needs o i s desc ip ion he phase diag am in six
dimensions. In such a case an alloy s a ing o solidi y by cooling om he mel , L, may
in e sec se e al mul iphase a eas (and no jus one wo-phase egion,
α
+ L) un il i
becomes comple ely solid,
α
. In such mul iphase egions mo e han one liquid and one
solid phase(s) may coexis . The polyc ys al in he wo-phase egion,
α
+ L, con ains he GBs
as well as bounda ies be ween he
α
-phase and he mel L called in e phase bounda ies
(IBs). Le us conside now he iple junc ions (TJs) be ween wo IBs and GB. He e GB
con ac s wi h he mel (see schemes on he le -hand side o Figu e 2).
Le us suppose ha he GB ene gy,
σGB
, is less han he ene gy o he wo solid/liquid
IBs, 2
σSL
(see lowe scheme in Figu e 2). The GB and IBs o m in his case he
con ac angle,
θ
> 0, a his TJ, and he GB we ing is called pa ial (o incomple e). I
σGB
> 2
σSL
(see uppe scheme in Figu e 2) hen
θ
= 0. In his case, he solid
α
-g ains would
be sepa a ed by a hick liquid laye . This is he case o comple e GB we ing by he mel .
I is desc ibed o many bina y alloys. In his case he con ac angle
θ
usually dec eases
wi h g owing empe a u e and can each ze o a a ce ain empe a u e, T
w
[
46
,
48
–
50
]. A
T
w
he incomple e GB we ing changes o he comple e one. T
w
is he empe a u e o he
GB we ing phase ans o ma ion. The GB we ing phase- ansi ion can be o he i s o
second o de as o con en ional bulk phase ans o ma ions [
51
–
53
]. I he GB we ing
ans o ma ion is o a i s -o de , hen he i s de i a i e o
θ
, wi h espec o empe a u e,
d
θ
/dThas a discon inui y a T
w
[
46
,
51
,
52
]. In his case, exhibi s d
θ
/dTd ops suddenly
om a ce ain ini e alue o 0 [
46
,
51
,
52
]. I he GB we ing phase ansi ion is con inuous
(o o a second-o de ), hen d
θ
/dTcon inuously dec eases wi h inc easing Tand eaches
ze o d
θ
/dT= 0 a T
w
[
51
,
52
]. We ha e o unde line he e ha he
σGB
alue depends on he
GB miso ien a ion angle,
χ
, as well as on he GB inclina ion angle,
ψ
[
54
]. The
σGB
(
χ
) and
σGB
(
ψ
) dependences possess sha p cusps a ce ain
χ
and
ψ
[
55
]. The e o e, he in e al
o
σGB
alues can be e y b oad. The highe is
σGB
, he smalle is he
θ
alue a he GB
TJ wi h he mel [
56
,
57
]. In o he wo ds, he
θ
alues in a wo-phase polyc ys al could be
e y di e en a each ixed empe a u e. Wi h inc easing empe a u e, hese
θ
alues o
di e en GBs would dec ease wi h di e en a es. This is he eason why he spec um o
Tw empe a u es in a polyc ys al can be e y wide.
Typical examples o such wo-phase polyc ys als mic os uc u es a e shown in Figu e 2
o he bina y Al–Mg alloys. Thus, ega ding he GB we ing phase ansi ions, he bulk
phase diag am becomes wo addi ional GB ie-lines. The T
wmin
ie-line co esponds o he
GBs we ing ansi ion om pa ial o comple e we ing o he g ain bounda ies ha ing
highes ene gy
σGB
. Unde T
wmin
one canno obse e in he alloy any ully we ed GB. The
polyc ys al unde T
wmin
con ains only pa ially we ed GBs wi h
θ
> 0. Fi s , comple ely
we ed GBs appea wi h he hea ing o he alloy abo e T
wmin
. Abo e T
wmin
, he po ion o
ully we ed GBs inc eases wi h inc easing empe a u e. A T
wmax
i eaches uni y. Ano he
ie-line shows he empe a u e T
wmax
. Abo e T
wmax
all GBs con ain he mel ed laye and
a e, he e o e, comple ely we ed. In his case each g ain is comple ely su ounded by
he mel . I canno con ac o he abu ing g ains. This is because he non-we ed GBs
a e he modynamically disad an ageous abo e T
wmax
. In o he wo ds, abo e T
wmax
all
solid c ys alli es a e de ached om hei neighbo s by he skins o a liquid phase. Thus, a
con en ional bina y phase diag am becomes he new GB ie-lines in he
α
+ L a ea. Such
new ie-lines a e due o he GB we ing phase ansi ions. The con en ional phase diag ams
suppose ha all bulk phases a e single c ys als and igno e he GBs and GB phenomena.
3. GB We ing in he HEA Coa ings Con aining One Phase
In Re . [
47
] he FeNiCoC Mo
x
(wi h a omic a io x= 0, 0.15, 0.20, 0.25) HEA coa ings
we e p epa ed by lase cladding on 316 s ainless s eel subs a e. The coa ings we e named,
espec i ely, Mo0, Mo0.15, Mo0.20 and Mo0.25. The p eplaced powde sys em was used.
The X- ay di ac ion (XRD) pa e ns show ha wi h inc easing concen a ions o Mo he
high en opy alloy coa ings s ill ha e a single-phase ace-cen e ed cubic ( cc) s uc u e.
Coa ings 2022,12, 343 5 o 22
The XRD pa e ns con ain no di ac ion peaks excep o (111), (200), (220), (311) and
(222) cc solid solu ion di ac ion peaks. They only shi a li le due o he change o la ice
pe iod. Scanning elec on mic oscopy (SEM) mic og aphs o hese coa ings a e shown in
Figu e 3a–d. The composi ion was locally measu ed by he ene gy dispe si e spec ome y
(EDS). Figu e 3e shows he scheme wi h he bina y phase diag am o he explana ion o
he espec i e GB we ing p ocesses. The do ed ed a ows show he cooling ajec o ies
co esponding o he mic og aphs (a)–(d). As men ioned abo e, i he ajec o ies (a)–(d)
do no in e sec he line o eu ec ic ans o ma ion, he Mo-poo dend i es solidi y i s ,
and las en iched po ions o he mel be ween dend i es solidi y a he end. We can see
ha dend i e g ains do no g ow oge he du ing he solidi ica ion, hey do no o m
GBs “dend i e/dend i e”. Thus, hese GBs we e ully we ed by he Mo-en iched mel .
Ne e heless, a e solidi ica ion he FeNiCoC Mo
x
HEAs con ained one cc phase, bu
wi h di e en composi ion in bulk and in GBs.
The compa able beha io o GB we ing ook place also in he CoC
2
FeNiMo
x
HEA
wi h changing Mo con en x= 0, 0.1, 0.2, 0.3, 0.4 [
58
]. In Re . [
59
] he AlCoC FeNiSi
x
HEAs
wi h x= 0, 0.1, 0.2, 0.3, 0.4, and 0.5 ha e been deposi ed by lase cladding. The coa ings
always con ain he single cc phase, as in Re . [
47
]. Howe e , he ansi ion be ween
comple e and incomple e GB we ing ook place wi h inc easing Si con en [
59
]. This means
ha he T
wmin
and T
wmax
ie-lines (see scheme in Figu e 3e) a e posi ioned highe , and wi h
inc ease o Si con en he solidi ica ion ajec o ies come o he a ea below T
wmin
be o e
he solidi ica ion is inished. One can ind ano he pu e example o he comple e we ing
p ocess o he cc/ cc GBs by he inal po ions o solidi ying mel in he C FeNiNbTi
alloy [
60
]. The small amoun o equiaxial Fe
2
Ti p ecipi a es does no dis u b he pe ec
pic u e o a GB we ing. In Re . [
61
] he CoC Cu
1-x
FeNi
x
HEA con ains only one cc phase
a all s udied x alues (namely, x= 0, 0.1, 0.3 and 0.5). Howe e , he we ing condi ions
change, simila o [
59
]. Namely, a x= 0 almos all g ain bounda ies in he ace-cen ed
cubic ma ix phase a e comple ely we ed by he Cu- ich cc phase. When xinc eases, he
po ion o pa ially we ed GBs inc eases as well.
4. GB We ing in he HEA Coa ings Con aining Two Phases
Re . [
62
] gi es ano he example when he solidi ied HEA con ains wo di e en phases,
namely he cc and bcc (base cen e ed cubic) phases. In ha s udy, he AlCoC FeNiTi
0.5
coa ing was manu ac u ed by lase cladding wi h p eplaced powde sys em om pu e
(>99.5 w %) Al, Co, C , Fe, Ni and Ti elemen al powde s wi h pa icle size anging om
48
µ
m o 75
µ
m. The XRD pa e n o he coa ing demons a ed ha i was composed o
majo cc and mino bcc phases. The di ac ion peaks o he cc phase we e in acco dance
wi h he peaks o AlNi
2
Ti (PDF #65–432) o AlCo
2
Ti (PDF #65–4682), and he bcc phase
co esponded o he Fe–C phase (PDF #34–0396). In Figu e 4, he ma ix cc phase is
called dend i e egion (DR1). I s g ains a e su ounded by he laye s o in e dend i e bcc
phases (IR1 and IR2). I is clea ly isible ha he bcc phase comple ely we s all cc/ cc GBs
(Figu e 4a).
TEM pe mi ed de ailed analysis o he s uc u e o bulk and GB phases. Figu e 5
con ains he b igh ield (BF) images o he DR and IR egions. Figu e 5b–d a e he
co esponding selec ed a ea di ac ion pa e ns (SADP) o a ea A ( he phase appea s
ligh -g ey), a ea B ( he phase appea s da k-g ey), and a ea C ( he phase appea s black),
espec i ely. The phase appea ing ligh -g ey is he DR one, while he o he wo phases
appea ing black and ligh -g ey a e he GB IR ones. The indexed SADP in Figu e 5b shows
ha he DR s uc u e is ace-cen ed cubic wi h a la ice pa ame e o 0.5761 nm, which is
close o he alues o 0.5848 nm (AlNi
2
Ti, PDF #65–0432) and 0.5865 nm (AlCo
2
Ti, PDF
#65–4682). Bo h GB phases (da k-g ey and black) a e bcc ones. The SADP in Figu e 5c
o da k-g ey IR phase is in acco dance wi h he bcc s uc u e o Fe–C (PDF#34–0396,
0.2876 nm). The SADP in Figu e 5d o black IR phase is in acco dance wi h he bcc
C 13Fe35Ni3Ti7s uc u e (PDF#16–0443, 0.8856 nm).

Coa ings 2022,12, 343 6 o 22
Coa ings 2022, 12, x FOR PEER REVIEW 6 o 23
e dend i e bcc phases (IR1 and IR2). I is clea ly isible ha he bcc phase comple ely
we s all cc/ cc GBs (Figu e 4a).
Figu e 4. (a) The mic os uc u e o he c oss-sec ion o an AlCoC FeNiTi0.5 coa ing. (b) Local mag-
ni ied iew o do ed ame in (a). (c) Schema ic phase diag am wi h GB we ing ie-lines. The
do ed ed a ow shows he cooling ajec o y co esponding o he mic og aphs (a,b). Mic o-
g aphs (a,b) a e ep in ed wi h pe mission om Re . [62]. Copy igh 2021 Else ie .
TEM pe mi ed de ailed analysis o he s uc u e o bulk and GB phases. Figu e 5
con ains he b igh ield (BF) images o he DR and IR egions. Figu e 5b–d a e he co -
esponding selec ed a ea di ac ion pa e ns (SADP) o a ea A ( he phase appea s
ligh -g ey), a ea B ( he phase appea s da k-g ey), and a ea C ( he phase appea s black),
espec i ely. The phase appea ing ligh -g ey is he DR one, while he o he wo phases
appea ing black and ligh -g ey a e he GB IR ones. The indexed SADP in Figu e 5b
shows ha he DR s uc u e is ace-cen ed cubic wi h a la ice pa ame e o 0.5761 nm,
which is close o he alues o 0.5848 nm (AlNi2Ti, PDF #65–0432) and 0.5865 nm (Al-
Co2Ti, PDF #65–4682). Bo h GB phases (da k-g ey and black) a e bcc ones. The SADP in
Figu e 5c o da k-g ey IR phase is in acco dance wi h he bcc s uc u e o Fe–C
(PDF#34–0396, 0.2876 nm). The SADP in Figu e 5d o black IR phase is in acco dance
wi h he bcc C 13Fe35Ni3Ti7 s uc u e (PDF#16–0443, 0.8856 nm).
Figu e 5. TEM mic og aphs o he AlCoC FeNiTi0.5 coa ing: (a) b igh ield image o DR and IR
phases, (b) SADP o bulk a ea A, (c) SADP o GB a ea B, (d) SADP o GB a ea C. Rep in ed wi h
pe mission om Re . [62]. Copy igh 2021 Else ie .
The schema ic bina y phase diag am in Figu e 4c shows he possible a angemen
o GB we ing ie-line(s) as well as liquidus and eu ec ic lines. In con as o he p e ious
example gi en in Sec ion 2, he solidi ica ion ajec o y (do ed ligh - ed a ow) does no
inish in he α-a ea bu c osses he ho izon al line o eu ec ic ansi ion L → α + β. Fo
Figu e 4.
(
a
) The mic os uc u e o he c oss-sec ion o an AlCoC FeNiTi
0.5
coa ing. (
b
) Local
magni ied iew o do ed ame in (
a
). (
c
) Schema ic phase diag am wi h GB we ing ie-lines. The
do ed ed a ow shows he cooling ajec o y co esponding o he mic og aphs (
a
,
b
). Mic og aphs
(a,b) a e ep in ed wi h pe mission om Re . [62]. Copy igh 2021 Else ie .
Coa ings 2022, 12, x FOR PEER REVIEW 6 o 23
e dend i e bcc phases (IR1 and IR2). I is clea ly isible ha he bcc phase comple ely
we s all cc/ cc GBs (Figu e 4a).
Figu e 4. (a) The mic os uc u e o he c oss-sec ion o an AlCoC FeNiTi0.5 coa ing. (b) Local mag-
ni ied iew o do ed ame in (a). (c) Schema ic phase diag am wi h GB we ing ie-lines. The
do ed ed a ow shows he cooling ajec o y co esponding o he mic og aphs (a,b). Mic o-
g aphs (a,b) a e ep in ed wi h pe mission om Re . [62]. Copy igh 2021 Else ie .
TEM pe mi ed de ailed analysis o he s uc u e o bulk and GB phases. Figu e 5
con ains he b igh ield (BF) images o he DR and IR egions. Figu e 5b–d a e he co -
esponding selec ed a ea di ac ion pa e ns (SADP) o a ea A ( he phase appea s
ligh -g ey), a ea B ( he phase appea s da k-g ey), and a ea C ( he phase appea s black),
espec i ely. The phase appea ing ligh -g ey is he DR one, while he o he wo phases
appea ing black and ligh -g ey a e he GB IR ones. The indexed SADP in Figu e 5b
shows ha he DR s uc u e is ace-cen ed cubic wi h a la ice pa ame e o 0.5761 nm,
which is close o he alues o 0.5848 nm (AlNi2Ti, PDF #65–0432) and 0.5865 nm (Al-
Co2Ti, PDF #65–4682). Bo h GB phases (da k-g ey and black) a e bcc ones. The SADP in
Figu e 5c o da k-g ey IR phase is in acco dance wi h he bcc s uc u e o Fe–C
(PDF#34–0396, 0.2876 nm). The SADP in Figu e 5d o black IR phase is in acco dance
wi h he bcc C 13Fe35Ni3Ti7 s uc u e (PDF#16–0443, 0.8856 nm).
Figu e 5. TEM mic og aphs o he AlCoC FeNiTi0.5 coa ing: (a) b igh ield image o DR and IR
phases, (b) SADP o bulk a ea A, (c) SADP o GB a ea B, (d) SADP o GB a ea C. Rep in ed wi h
pe mission om Re . [62]. Copy igh 2021 Else ie .
The schema ic bina y phase diag am in Figu e 4c shows he possible a angemen
o GB we ing ie-line(s) as well as liquidus and eu ec ic lines. In con as o he p e ious
example gi en in Sec ion 2, he solidi ica ion ajec o y (do ed ligh - ed a ow) does no
inish in he α-a ea bu c osses he ho izon al line o eu ec ic ansi ion L → α + β. Fo
Figu e 5.
TEM mic og aphs o he AlCoC FeNiTi
0.5
coa ing: (
a
) b igh ield image o DR and IR
phases, (
b
) SADP o bulk a ea A, (
c
) SADP o GB a ea B, (
d
) SADP o GB a ea C. Rep in ed wi h
pe mission om Re . [62]. Copy igh 2021 Else ie .
The schema ic bina y phase diag am in Figu e 4c shows he possible a angemen
o GB we ing ie-line(s) as well as liquidus and eu ec ic lines. In con as o he p e ious
example gi en in Sec ion 2, he solidi ica ion ajec o y (do ed ligh - ed a ow) does no
inish in he
α
-a ea bu c osses he ho izon al line o eu ec ic ansi ion L
→α
+
β
. Fo he
s udied AlCoC FeNiTi
0.5
coa ing [
62
],
α
in he scheme co esponds o he majo cc phase
and
β
is o he mino bcc phase(s). A a la e solidi ica ion s age, he las po ions o he
mel comple ely we all cc/ cc GBs and hen decompose acco ding he eac ion L
→α
+
β
.
Ano he pe ec example o wo-phases HEA is he FeNiCoC Ti
0.6
Nb
0.4
alloy whe e he
La es phase comple ely we s he bcc/bcc GBs in he ma ix [63].
5. GB We ing in he HEA Coa ings in Case o T ansi ion om One Phase o Two Phases
We will nex discuss he example o GB we ing in HEAs whe e he ansi ion om
one phase o wo phases akes place wi h changing composi ion. In Re [
64
], he HEA
coa ings Al
x
C FeCoNiCu (x: mola a io, x= 0, 0.1, 0.3, 0.5, 0.7, 0.8, 1.0, 1.2, 1.5, 1.8, o 2.0)
we e p epa ed ia lase cladding wi h he p eplaced powde sys em. I can be seen ha
he Al concen a ion a ied ac oss a b oad in e al o 11 di e en concen a ion alues.
The XRD pa e ns (Figu e 6a) show ha he samples wi h x= 0, 0.1, 0.3 con ain only one
cc phase. Thei mic os uc u e (Figu e 7a– ) is e y simila o ha shown in Figu e 3. The
composi ion has been measu ed in he poin s DR 1,2,3 and 4 inside he dend i es and in
Coa ings 2022,12, 343 7 o 22
he poin s IR 1, 2, 3 and 4 be ween he dend i es. The coa ing in all IR poin s was s ongly
en iched by coppe and in he IR 2, 3 and 4 i was en iched by Al. In o he wo ds, a he las
s age o c ys alliza ion he solid g ains we e comple ely isola ed om hei neighbo s by
he Cu- and Al- ich mel be o e solidi ica ion. I means ha in he schema ic phase diag am
(Figu e 8g) he samples ollowed he ajec o ies (0, 0.1, 0.3) shown by ed a ows. In o he
wo ds, du ing solidi ica ion in he
α
+L a ea he samples we e abo e he T
wmax
ie-line
and all cc/ cc GBs we e ully we ed by he liquid phase. In he sample wi h x= 0.5, a
small amoun o bcc1 phase appea ed (Figu e 6a), bu he mic os uc u e o his sample
(Figu e 7d) was s ill e y simila o he samples wi h x= 0, 0.1, 0.3 (Figu e 7a–c). I means
ha he solidi ica ion ollowed he ajec o y “0.5” in he scheme Figu e 8g.
Coa ings 2022, 12, x FOR PEER REVIEW 7 o 23
he s udied AlCoC FeNiTi0.5 coa ing [62], α in he scheme co esponds o he majo cc
phase and β is o he mino bcc phase(s). A a la e solidi ica ion s age, he las po ions
o he mel comple ely we all cc/ cc GBs and hen decompose acco ding he eac ion L
→ α + β. Ano he pe ec example o wo-phases HEA is he FeNiCoC Ti0.6Nb0.4 alloy
whe e he La es phase comple ely we s he bcc/bcc GBs in he ma ix [63].
5. GB We ing in he HEA Coa ings in Case o T ansi ion om One Phase o Two
Phases
We will nex discuss he example o GB we ing in HEAs whe e he ansi ion om
one phase o wo phases akes place wi h changing composi ion. In Re [64], he HEA
coa ings AlxC FeCoNiCu (x: mola a io, x = 0, 0.1, 0.3, 0.5, 0.7, 0.8, 1.0, 1.2, 1.5, 1.8, o 2.0)
we e p epa ed ia lase cladding wi h he p eplaced powde sys em. I can be seen ha
he Al concen a ion a ied ac oss a b oad in e al o 11 di e en concen a ion alues.
The XRD pa e ns (Figu e 6a) show ha he samples wi h x = 0, 0.1, 0.3 con ain only one
cc phase. Thei mic os uc u e (Figu e 7a– ) is e y simila o ha shown in Figu e 3.
The composi ion has been measu ed in he poin s DR 1,2,3 and 4 inside he dend i es
and in he poin s IR 1, 2, 3 and 4 be ween he dend i es. The coa ing in all IR poin s was
s ongly en iched by coppe and in he IR 2, 3 and 4 i was en iched by Al. In o he
wo ds, a he las s age o c ys alliza ion he solid g ains we e comple ely isola ed om
hei neighbo s by he Cu- and Al- ich mel be o e solidi ica ion. I means ha in he
schema ic phase diag am (Figu e 8g) he samples ollowed he ajec o ies (0, 0.1, 0.3)
shown by ed a ows. In o he wo ds, du ing solidi ica ion in he α+L a ea he samples
we e abo e he Twmax ie-line and all cc/ cc GBs we e ully we ed by he liquid phase. In
he sample wi h x = 0.5, a small amoun o bcc1 phase appea ed (Figu e 6a), bu he mi-
c os uc u e o his sample (Figu e 7d) was s ill e y simila o he samples wi h x = 0,
0.1, 0.3 (Figu e 7a–c). I means ha he solidi ica ion ollowed he ajec o y “0.5” in he
scheme Figu e 8g.
Figu e 6. XRD pa e ns o AlxC FeCoNiCu HEA coa ings. (a) coa ings wi h low Al con en , (b)
coa ings wi h medium-Al con en . Rep in ed wi h pe mission om Re . [64]. Copy igh 2021 Else-
ie .
Figu e 6.
XRD pa e ns o Al
x
C FeCoNiCu HEA coa ings. (
a
) coa ings wi h low Al con en , (
b
) coa -
ings wi h medium-Al con en . Rep in ed wi h pe mission om Re . [64]. Copy igh 2021 Else ie .
Coa ings 2022, 12, x FOR PEER REVIEW 7 o 23
he s udied AlCoC FeNiTi0.5 coa ing [62], α in he scheme co esponds o he majo cc
phase and β is o he mino bcc phase(s). A a la e solidi ica ion s age, he las po ions
o he mel comple ely we all cc/ cc GBs and hen decompose acco ding he eac ion L
→ α + β. Ano he pe ec example o wo-phases HEA is he FeNiCoC Ti0.6Nb0.4 alloy
whe e he La es phase comple ely we s he bcc/bcc GBs in he ma ix [63].
5. GB We ing in he HEA Coa ings in Case o T ansi ion om One Phase o Two
Phases
We will nex discuss he example o GB we ing in HEAs whe e he ansi ion om
one phase o wo phases akes place wi h changing composi ion. In Re [64], he HEA
coa ings AlxC FeCoNiCu (x: mola a io, x = 0, 0.1, 0.3, 0.5, 0.7, 0.8, 1.0, 1.2, 1.5, 1.8, o 2.0)
we e p epa ed ia lase cladding wi h he p eplaced powde sys em. I can be seen ha
he Al concen a ion a ied ac oss a b oad in e al o 11 di e en concen a ion alues.
The XRD pa e ns (Figu e 6a) show ha he samples wi h x = 0, 0.1, 0.3 con ain only one
cc phase. Thei mic os uc u e (Figu e 7a– ) is e y simila o ha shown in Figu e 3.
The composi ion has been measu ed in he poin s DR 1,2,3 and 4 inside he dend i es
and in he poin s IR 1, 2, 3 and 4 be ween he dend i es. The coa ing in all IR poin s was
s ongly en iched by coppe and in he IR 2, 3 and 4 i was en iched by Al. In o he
wo ds, a he las s age o c ys alliza ion he solid g ains we e comple ely isola ed om
hei neighbo s by he Cu- and Al- ich mel be o e solidi ica ion. I means ha in he
schema ic phase diag am (Figu e 8g) he samples ollowed he ajec o ies (0, 0.1, 0.3)
shown by ed a ows. In o he wo ds, du ing solidi ica ion in he α+L a ea he samples
we e abo e he Twmax ie-line and all cc/ cc GBs we e ully we ed by he liquid phase. In
he sample wi h x = 0.5, a small amoun o bcc1 phase appea ed (Figu e 6a), bu he mi-
c os uc u e o his sample (Figu e 7d) was s ill e y simila o he samples wi h x = 0,
0.1, 0.3 (Figu e 7a–c). I means ha he solidi ica ion ollowed he ajec o y “0.5” in he
scheme Figu e 8g.
Figu e 6. XRD pa e ns o AlxC FeCoNiCu HEA coa ings. (a) coa ings wi h low Al con en , (b)
coa ings wi h medium-Al con en . Rep in ed wi h pe mission om Re . [64]. Copy igh 2021 Else-
ie .
Figu e 7.
The mic os uc u e o coa ings wi h low Al con en . (
a
) FeCoNiC Cu. (
b
) is he enla ged im-
age o Figu e 7a. (
c
) Al
0.1
C FeCoNiCu. (
d
) is he enla ged image o Figu e 7c. (
e
) Al
0.3
C FeCoNiCu.
(
) is he enla ged image o Figu e 7e. (
g
) Al
0.5
C FeCoNiCu. (
h
) is he enla ged image o Figu e 7g.
DR1, 2, 3 and 4 show he poin s o concen a ion measu emen s inside he dend i es. IR1, 2, 3 and 4
show he poin s o concen a ion measu emen s be ween he dend i es. Rep in ed wi h pe mission
om Re . [64]. Copy igh 2021 Else ie .
The samples x= 0.7, 0.8, 1.0 con ained no only he cc phase bu wo addi ional bcc1
and bcc2 phases (Figu e 6b). The espec i e mic os uc u es a e shown in Figu e 8. They
a e qui e di e en om hose in Figu e 7and ha e some simila i y wi h mic os uc u es
shown in Figu e 4In o he wo ds, he ma ix g ains ha e cc s uc u e, and he las po ions
o he mel a e decomposed in he cc + (bcc1,bcc2) mix u e. These po ions o Al- ich
mel also we ed he cc/ cc GBs, bu he we ing was no as pe ec as in Figu e 7a–c o
x= 0, 0.1, 0.3. Some g ains o he ma ix cc phase o med he GBs wi h each o he and,
he e o e, he GB we ing was only pa ial o hem. This can be schema ically explained
wi h ajec o ies “0.7, 0.8, 1.0” in Figu e 8g. Namely, jus be o e he eu ec ic line, he samples
we e below he T
wmax
ie-line (and maybe e en below he T
wmin
ie-line) and, he e o e,
no all GBs we e comple ely we ed. Mo eo e , we can see ha amoun o comple ely
we ed GBs dec eases when he Al concen a ion inc eases om 0.7 o 1.0. Mos p obably,
Coa ings 2022,12, 343 8 o 22
his is because he schema ic bina y phase diag am in Figu e 8g is oo simple o he six-
componen Al
x
C FeCoNiCu HEAs. I does no ake in o accoun ha indeed no wo
α
+
β
bu h ee solid phases cc + (bcc1,bcc2) we e p esen in he s udied samples.
Coa ings 2022, 12, x FOR PEER REVIEW 8 o 23
Figu e 7. The mic os uc u e o coa ings wi h low Al con en . (a) FeCoNiC Cu. (b) is he enla ged
image o Figu e 7a. (c) Al0.1C FeCoNiCu. (d) is he enla ged image o Figu e 7c. (e)
Al0.3C FeCoNiCu. ( ) is he enla ged image o Figu e 7e. (g) Al0.5C FeCoNiCu. (h) is he enla ged
image o Figu e 7g. DR1, 2, 3 and 4 show he poin s o concen a ion measu emen s inside he
dend i es. IR1, 2, 3 and 4 show he poin s o concen a ion measu emen s be ween he dend i es.
Rep in ed wi h pe mission om Re . [64]. Copy igh 2021 Else ie .
Figu e 8. The mic os uc u e o coa ings wi h medium Al con en . (a) Al0.7C FeCoNiCu. (b) is he
enla ged image o Figu e 8a. (c) Al0.8C FeCoNiCu. (d) is he enla ged image o Figu e 8c. (e)
Al1.0C FeCoNiCu. ( ) is he enla ged image o Figu e 8e. (g) Schema ic phase diag am wi h GB
we ing ie-lines. The do ed ed a ows wi h Al concen a ions on he op show he cooling a-
jec o ies co esponding o he mic og aphs in Figu es 7 and 8. Mic og aphs (a– ) a e ep in ed
wi h pe mission om Re . [64]. Copy igh 2021 Else ie .
The samples x = 0.7, 0.8, 1.0 con ained no only he cc phase bu wo addi ional
bcc1 and bcc2 phases (Figu e 6b). The espec i e mic os uc u es a e shown in Figu e 8.
They a e qui e di e en om hose in Figu e 7 and ha e some simila i y wi h mic o-
s uc u es shown in Figu e 4. In o he wo ds, he ma ix g ains ha e cc s uc u e, and
he las po ions o he mel a e decomposed in he cc + (bcc1,bcc2) mix u e. These po -
ions o Al- ich mel also we ed he cc/ cc GBs, bu he we ing was no as pe ec as in
Figu e 7a–c o x = 0, 0.1, 0.3. Some g ains o he ma ix cc phase o med he GBs wi h
each o he and, he e o e, he GB we ing was only pa ial o hem. This can be sche-
ma ically explained wi h ajec o ies “0.7, 0.8, 1.0” in Figu e 8g. Namely, jus be o e he
eu ec ic line, he samples we e below he Twmax ie-line (and maybe e en below he Twmin
ie-line) and, he e o e, no all GBs we e comple ely we ed. Mo eo e , we can see ha
amoun o comple ely we ed GBs dec eases when he Al concen a ion inc eases om
0.7 o 1.0. Mos p obably, his is because he schema ic bina y phase diag am in Figu e
8g is oo simple o he six-componen AlxC FeCoNiCu HEAs. I does no ake in o ac-
coun ha indeed no wo α+β bu h ee solid phases cc + (bcc1,bcc2) we e p esen in
he s udied samples.
The in e es ing example o he ansi ion om one-phase o wo-phase coa ings was
obse ed in he HEA CoC FeNiAlxMn(1−x) so-called dual-phase coa ings [65]. The Al
con en x in hese alloys inc eased om ze o o 0.8 (x = 0, 0.2, 0.4, 0.6, and 0.8). A low x <
0.5 he alloy con ains only cc phase. A x > 0.5 he bcc phase appea s. The bcc phase
comple ely we s some cc/ cc GBs and incomple ely we s he es o he cc/ cc GBs. In
he AlxCoC Fe2Ni (x = 0.3, 0.7, 1.0) HEAs he mic os uc u e a x = 0.3 is simila o he
one-phase case shown in Figu e 7, he mic os uc u e a x = 1.0 is simila o he
wo-phase one shown in Figu e 4, bu a he in e media e concen a ion x = 0.7 no indi-
Figu e 8.
The mic os uc u e o coa ings wi h medium Al con en . (
a
) Al
0.7
C FeCoNiCu. (
b
) is
he enla ged image o Figu e 8a. (
c
) Al
0.8
C FeCoNiCu. (
d
) is he enla ged image o Figu e 8c.
(
e
) Al
1.0
C FeCoNiCu. (
) is he enla ged image o Figu e 8e. (
g
) Schema ic phase diag am wi h
GB we ing ie-lines. The do ed ed a ows wi h Al concen a ions on he op show he cooling
ajec o ies co esponding o he mic og aphs in Figu es 7and 8. Mic og aphs (
a
–
) a e ep in ed
wi h pe mission om Re . [64]. Copy igh 2021 Else ie .
The in e es ing example o he ansi ion om one-phase o wo-phase coa ings was
obse ed in he HEA CoC FeNiAl
x
Mn
(1−x)
so-called dual-phase coa ings [
65
]. The Al
con en xin hese alloys inc eased om ze o o 0.8 (x= 0, 0.2, 0.4, 0.6, and 0.8). A low
x< 0.5
he alloy con ains only cc phase. A x> 0.5 he bcc phase appea s. The bcc phase
comple ely we s some cc/ cc GBs and incomple ely we s he es o he cc/ cc GBs. In
he Al
x
CoC Fe
2
Ni (x= 0.3, 0.7, 1.0) HEAs he mic os uc u e a x= 0.3 is simila o he
one-phase case shown in Figu e 7, he mic os uc u e a x= 1.0 is simila o he wo-phase
one shown in Figu e 4, bu a he in e media e concen a ion x= 0.7 no indica ions o GB
we ing a e p esen a all [
66
]. In he FeCoNiTiAl
x
alloys he inc ease o Al con en om
ze o h ough 0.5 o 1 p omo ed he ansi ion om cc (a x= 0) o bcc (a x= 1) phase [
14
].
In wo-phase cc+bcc alloys a x= 0.5 some ma ix bcc/bcc GBs we e ully we ed and
o he s we e pa ially we ed by he cc phase.
HEA coa ings can also con ain mo e han wo phases as, o example, in AlC Co
NiFeCTa
x
HEAs wi h x= 0, 0.5 and 1.0 [
64
], TiZ AlNbCo HEAs [
67
], ce amic pa icle
ein o ced FeCoNiC MnTi HEA wi h La es phase, bcc-phase and TiN in he cc/ cc GB
we ing laye s [
68
], and CoC
2
FeNb
0.5
NiSi coa ing wi h cc, La es and ch omium oxide
phases [
69
]. In hese cases he mic os uc u es and GB we ing-dewe ing phenomena a e
e en mo e complica ed.
6. In luence o Lase Scanning Speed on GB We ing in HEA Coa ings
This sec ion will look a how lase scanning speed can a ec he GB we ing in HEA
coa ings. In Re . [
70
] he Al
16.80
Co
20.74
C
20.49
Fe
21.28
Ni
20.70
HEAs we e ab ica ed by lase
cladding wi h di e en lase scanning speeds. The hickness o he powde laye was 1 mm.
Lase cladding was ca ied ou by IPG YLS-5000 ibe sys em wi h a p o ec i e gas and lase
powe 3000 W. The lase scanning speeds we e 7, 9, 11, 13, 15, 17, 19 and 21 mm/s o eigh
Coa ings 2022,12, 343 9 o 22
HEA coa ings named as V7, V9, V11, V13, V15, V17, V19 and V21. The XRD pa e ns show
ha he as-deposi ed Al
16.80
Co
20.74
C
20.49
Fe
21.28
Ni
20.70
HEAs con ain he majo phase wi h
bcc la ice and mino phase wi h cc la ice. Figu e 9shows he SEM mic og aphs o hese
coa ings deposi ed wi h di e en lase scanning speeds. A low speeds o 7 and 9 mm/s, he
5–7
µ
m hick laye s o cc phase (appea s b igh in SEM mic og aphs) comple ely we ed he
GBs be ween bcc ma ix g ains (appea da k). Mo eo e , he slow o ma ion a e o HEA
coa ings allowed he g ow h o Widmans ä en pla es o cc phase om he GBs in o he
bulk o he bcc ma ix. Only a ew cc nanopa icles p ecipi a ed in he bulk. A 11 mm/s
he Widmans ä en pla es disappea ed. Only a hick “coa ” o cc p ecipi a es co e s he
bcc/bcc GBs. A speeds o 13, 15, 17 and 19 mm/s, he po ion o nanop ecipi a es inc eased
and he hickness o cc GB laye s con inuously inc eased. Ne e heless, all bcc/bcc GBs
we e s ill comple ely we ed by he hin cc laye s. Howe e , a he highes s udied speed
o 21 mm/s, only abou one hal o bcc/bcc GBs we e comple ely we ed, while he o he
hal con ained sepa a ed pa icles o cc-phase. These GBs we e pa ially we ed. Thus, he
inc easing speed o he lase scanning is equi alen o he shi o T
wmin
alue o highe
empe a u es (see he do ed ed a ow in he scheme a Figu e 4c) and no all bcc/bcc GBs
become comple ely we ed by he las po ion o he mel be o e eu ec ic c ys alliza ion.
Coa ings 2022, 12, x FOR PEER REVIEW 9 o 23
ca ions o GB we ing a e p esen a all [66]. In he FeCoNiTiAlx alloys he inc ease o Al
con en om ze o h ough 0.5 o 1 p omo ed he ansi ion om cc (a x = 0) o bcc (a x
= 1) phase [14]. In wo-phase cc+bcc alloys a x = 0.5 some ma ix bcc/bcc GBs we e ully
we ed and o he s we e pa ially we ed by he cc phase.
HEA coa ings can also con ain mo e han wo phases as, o example, in
AlC CoNiFeCTax HEAs wi h x = 0, 0.5 and 1.0 [64], TiZ AlNbCo HEAs [67], ce amic
pa icle ein o ced FeCoNiC MnTi HEA wi h La es phase, bcc-phase and TiN in he
cc/ cc GB we ing laye s [68], and CoC 2FeNb0.5NiSi coa ing wi h cc, La es and ch o-
mium oxide phases [69]. In hese cases he mic os uc u es and GB we ing-dewe ing
phenomena a e e en mo e complica ed.
6. In luence o Lase Scanning Speed on GB We ing in HEA Coa ings
This sec ion will look a how lase scanning speed can a ec he GB we ing in HEA
coa ings. In Re . [70] he Al16.80Co20.74C 20.49Fe21.28Ni20.70 HEAs we e ab ica ed by lase
cladding wi h di e en lase scanning speeds. The hickness o he powde laye was 1
mm. Lase cladding was ca ied ou by IPG YLS-5000 ibe sys em wi h a p o ec i e gas
and lase powe 3000 W. The lase scanning speeds we e 7, 9, 11, 13, 15, 17, 19 and 21
mm/s o eigh HEA coa ings named as V7, V9, V11, V13, V15, V17, V19 and V21. The
XRD pa e ns show ha he as-deposi ed Al16.80Co20.74C 20.49Fe21.28Ni20.70 HEAs con ain he
majo phase wi h bcc la ice and mino phase wi h cc la ice. Figu e 9 shows he SEM
mic og aphs o hese coa ings deposi ed wi h di e en lase scanning speeds. A low
speeds o 7 and 9 mm/s, he 5–7 μm hick laye s o cc phase (appea s b igh in SEM mi-
c og aphs) comple ely we ed he GBs be ween bcc ma ix g ains (appea da k). Mo eo-
e , he slow o ma ion a e o HEA coa ings allowed he g ow h o Widmans ä en
pla es o cc phase om he GBs in o he bulk o he bcc ma ix. Only a ew cc nanopa -
icles p ecipi a ed in he bulk. A 11 mm/s he Widmans ä en pla es disappea ed. Only a
hick “coa ” o cc p ecipi a es co e s he bcc/bcc GBs. A speeds o 13, 15, 17 and 19
mm/s, he po ion o nanop ecipi a es inc eased and he hickness o cc GB laye s con-
inuously inc eased. Ne e heless, all bcc/bcc GBs we e s ill comple ely we ed by he
hin cc laye s. Howe e , a he highes s udied speed o 21 mm/s, only abou one hal o
bcc/bcc GBs we e comple ely we ed, while he o he hal con ained sepa a ed pa icles
o cc-phase. These GBs we e pa ially we ed. Thus, he inc easing speed o he lase
scanning is equi alen o he shi o Twmin alue o highe empe a u es (see he do ed
ed a ow in he scheme a Figu e 4c) and no all bcc/bcc GBs become comple ely we ed
by he las po ion o he mel be o e eu ec ic c ys alliza ion.
Figu e 9. SEM mic og aphs o Al16.80Co20.74C 20.49Fe21.28Ni20.70 HEA coa ings deposi ed wi h di e en
lase scanning speeds: (a,b) a e he coa ings named as V7 and V9. They con ain Widmans ä en
side pla e and nanop ecipi a es; (c–h) he coa ings named as V11–V21 con ain only nanop ecipi-
a es, wi hou Widmans ä en pla e. Rep in ed wi h pe mission om Re . [70]. Copy igh 2021
Else ie .
7. In luence o Lase Beam Powe on GB We ing in HEA Coa ings
Figu e 9.
SEM mic og aphs o Al
16.80
Co
20.74
C
20.49
Fe
21.28
Ni
20.70
HEA coa ings deposi ed wi h di e -
en lase scanning speeds: (
a
,
b
) a e he coa ings named as V7 and V9. They con ain Widmans ä en
side pla e and nanop ecipi a es; (
c
–
h
) he coa ings named as V11–V21 con ain only nanop ecipi a es,
wi hou Widmans ä en pla e. Rep in ed wi h pe mission om Re . [70]. Copy igh 2021 Else ie .
7. In luence o Lase Beam Powe on GB We ing in HEA Coa ings
The lase beam powe can also in luence he GB we ing condi ions in HEA coa ings. In
e . [
71
] he ((CoC FeNi)
95
Nb
5
)
100-x
Mo
x
HEA coa ings wi h x= 1, 1.5 and 2 we e ab ica ed
unde di e en lase powe o 800, 1000 and 1200 W. A low Mo con en o x= 1 and 1.5, he
coa ing con ained only one cc phase (see XRD pa e ns in Figu e 10a). The mic os uc u e
o hese coa ings a cons an lase beam powe o 800 W demons a es he comple e we ing
o Mo-deple ed g ains wi h he Mo- ich mel (Figu e 10 b,c). This s uc u e is simila o
ha shown in Figu es 3and 7whe e he solidi ica ion ajec o ies do no c oss he line o
eu ec ic ansi ion (do ed ed a ows a,b,c,d in Figu e 3e, as well as do ed ed a ows 0,
0.1, 0.3 in Figu e 8g). A x= 2 he small amoun o second phase (La es phase, Figu e 10a)
appea s. Howe e , he ew p ecipi a es o La es phase do no dis u b he comple e GB
we ing o cc/ cc GBs by he las po ions o solidi ied mel (see Figu e 10d). This si ua ion
is simila o ha shown in Figu e 6g,h (mic og aphs) and do ed ed a ow “0.5” in he
scheme o Figu e 8g.
Coa ings 2022,12, 343 16 o 22
we ing laye s is di e en in he i s and second laye . This may be due o he highe Mg
concen a ion in he i s laye due o he pa ial mel ing o a subs a e.
Coa ings 2022, 12, x FOR PEER REVIEW 16 o 23
Figu e 19. SEM mic og aph e ealing he mo phologies on he bo h side o he e-mel ed bounda-
y be ween 1s and 2nd laye s o he AlCoC CuFeNi HEA coa ing (deno ed by he line). Rep in ed
wi h pe mission om Re . [94]. Copy igh 2019 Else ie .
In Re . [95], he double laye AlCoC FeNiSi-based HEA coa ing ein o ced in si u
by Ti(C, N) was ab ica ed on he H13 s eel subs a e using lase cladding wi h coaxial
powde eeding di ec lase deposi ion sys em equipped wi h an y e bium ibe lase .
The equia omic CoC FeNi HEA powde s we e mixed wi h high-pu i y Ti and C pow-
de s gi ing he mola a io o CoC FeNi, Al, Si, Ti o C powde as 8:1:1:1:1. Conside ing
he dilu ion o mel ed subs a e in he HEA mol en pool, a double-laye g adien coa ing
is ab ica ed on he subs a e. The e o e, he coa ing has he unc ional g adien s uc u e
(see Figu e 20). F om he dep hs o he i e zones shown in Figu e 20, i can be deduced
ha zone I and zone II cons i u e he second laye , and zone IV is he i s laye . Zone III
is he ansi ion egion be ween i s laye and second laye , while zone V is he ansi-
ion egion be ween i s laye and H13 subs a e.
Figu e 20. The HEA g adien coa ing: he ha dness dep h p o ile. The mic os uc u es a e placed
a co esponding dep h. The meaning o Zones I o V is explained in he ex . Rep in ed wi h pe -
mission om Re . [95]. Copy igh 2021 Else ie .
Figu e 19. SEM mic og aph e ealing he mo phologies on he bo h side o he e-mel ed bounda y
be ween 1s and 2nd laye s o he AlCoC CuFeNi HEA coa ing (deno ed by he line). Rep in ed wi h
pe mission om Re . [94]. Copy igh 2019 Else ie .
In Re . [
95
], he double laye AlCoC FeNiSi-based HEA coa ing ein o ced in si u
by Ti(C, N) was ab ica ed on he H13 s eel subs a e using lase cladding wi h coaxial
powde eeding di ec lase deposi ion sys em equipped wi h an y e bium ibe lase .
The equia omic CoC FeNi HEA powde s we e mixed wi h high-pu i y Ti and C powde s
gi ing he mola a io o CoC FeNi, Al, Si, Ti o C powde as 8:1:1:1:1. Conside ing he
dilu ion o mel ed subs a e in he HEA mol en pool, a double-laye g adien coa ing is
ab ica ed on he subs a e. The e o e, he coa ing has he unc ional g adien s uc u e (see
Figu e 20). F om he dep hs o he i e zones shown in Figu e 20, i can be deduced ha
zone I and zone II cons i u e he second laye , and zone IV is he i s laye . Zone III is he
ansi ion egion be ween i s laye and second laye , while zone V is he ansi ion egion
be ween i s laye and H13 subs a e.
In zone I he bcc solid-solu ion ma ix is o med wi h i anium disilicide TiSi
2
laye s
in GBs (Figu e 20). The i anium disilicide TiSi
2
(appea ing whi e in Figu e 21b) comple ely
we s abou 80% o GBs in he bcc phase in Zone I (appea ing blue in Figu e 21b). The
i anium ca boni ide Ti(CN) (appea s ed in Figu e 21c) has a shape o isola ed ound
pa icles and does no “pa icipa e” in GB we ing. I is supposed in [
95
] ha he i anium
di usion in o ca bon powde pa icles leads o he nuclea ion o TiC ca bide pa icles in
he mel . A e wa ds, he TiC ca bide pa icles g ow du ing solidi ica ion. In Re . [
95
],
he ni ogen played he ole o shielding gas o he lase cladding. The ni ogen a oms
dissol ed in he mol en pool and eplaced some ca bon a oms allowing he p ecipi a ion
o Ti(C,N) pa icles. The highes a e age ha dness was in he zone I wi h a dep h o ~100
µ
m (see Figu e 20). Wi h he inc easing dep h, he ha dness g adually dec eased om
934
±
65HV o abou 800HV. In he deepe laye II (see Figu e 20) he amoun o ma ix
bcc phase inc eased and ha o he TiSi
2
and Ti(CN) phases dec eased. Ne e heless, he
laye s o TiSi
2
phase comple ely we almos all bcc/bcc GBs (see Figu e 20). In he Zones III
and IV he TiSi
2
and Ti(CN) phases disappea and he o de ed Al-Ni-Ti B2 phase appea s
ins ead. In his wo-phase mix u e no GB we ing is p esen . The e o e, he dilu ion o a
H13 s eel subs a e in he i s mel ed laye du ing lase cladding, indeed, modi ies no
only composi ion, bu also he GB we ing condi ions.

Coa ings 2022,12, 343 17 o 22
Coa ings 2022, 12, x FOR PEER REVIEW 16 o 23
Figu e 19. SEM mic og aph e ealing he mo phologies on he bo h side o he e-mel ed bounda-
y be ween 1s and 2nd laye s o he AlCoC CuFeNi HEA coa ing (deno ed by he line). Rep in ed
wi h pe mission om Re . [94]. Copy igh 2019 Else ie .
In Re . [95], he double laye AlCoC FeNiSi-based HEA coa ing ein o ced in si u
by Ti(C, N) was ab ica ed on he H13 s eel subs a e using lase cladding wi h coaxial
powde eeding di ec lase deposi ion sys em equipped wi h an y e bium ibe lase .
The equia omic CoC FeNi HEA powde s we e mixed wi h high-pu i y Ti and C pow-
de s gi ing he mola a io o CoC FeNi, Al, Si, Ti o C powde as 8:1:1:1:1. Conside ing
he dilu ion o mel ed subs a e in he HEA mol en pool, a double-laye g adien coa ing
is ab ica ed on he subs a e. The e o e, he coa ing has he unc ional g adien s uc u e
(see Figu e 20). F om he dep hs o he i e zones shown in Figu e 20, i can be deduced
ha zone I and zone II cons i u e he second laye , and zone IV is he i s laye . Zone III
is he ansi ion egion be ween i s laye and second laye , while zone V is he ansi-
ion egion be ween i s laye and H13 subs a e.
Figu e 20. The HEA g adien coa ing: he ha dness dep h p o ile. The mic os uc u es a e placed
a co esponding dep h. The meaning o Zones I o V is explained in he ex . Rep in ed wi h pe -
mission om Re . [95]. Copy igh 2021 Else ie .
Figu e 20. The HEA g adien coa ing: he ha dness dep h p o ile. The mic os uc u es a e placed a
co esponding dep h. The meaning o Zones I o V is explained in he ex . Rep in ed wi h pe mission
om Re . [95]. Copy igh 2021 Else ie .
Coa ings 2022, 12, x FOR PEER REVIEW 17 o 23
In zone I he bcc solid-solu ion ma ix is o med wi h i anium disilicide TiSi2 laye s
in GBs (Figu e 20). The i anium disilicide TiSi2 (appea ing whi e in Figu e 21b) com-
ple ely we s abou 80% o GBs in he bcc phase in Zone I (appea ing blue in Figu e 21b).
The i anium ca boni ide Ti(CN) (appea s ed in Figu e 21c) has a shape o isola ed
ound pa icles and does no “pa icipa e” in GB we ing. I is supposed in [95] ha he
i anium di usion in o ca bon powde pa icles leads o he nuclea ion o TiC ca bide
pa icles in he mel . A e wa ds, he TiC ca bide pa icles g ow du ing solidi ica ion. In
Re . [95], he ni ogen played he ole o shielding gas o he lase cladding. The ni o-
gen a oms dissol ed in he mol en pool and eplaced some ca bon a oms allowing he
p ecipi a ion o Ti(C,N) pa icles. The highes a e age ha dness was in he zone I wi h a
dep h o ~100 μm (see Figu e 20). Wi h he inc easing dep h, he ha dness g adually de-
c eased om 934 ± 65HV o abou 800HV. In he deepe laye II (see Figu e 20) he
amoun o ma ix bcc phase inc eased and ha o he TiSi2 and Ti(CN) phases dec eased.
Ne e heless, he laye s o TiSi2 phase comple ely we almos all bcc/bcc GBs (see Figu e
20). In he Zones III and IV he TiSi2 and Ti(CN) phases disappea and he o de ed
Al-Ni-Ti B2 phase appea s ins ead. In his wo-phase mix u e no GB we ing is p esen .
The e o e, he dilu ion o a H13 s eel subs a e in he i s mel ed laye du ing lase
cladding, indeed, modi ies no only composi ion, bu also he GB we ing condi ions.
Figu e 21. The mic os uc u es wi h EBSD and EDS esul s o in he zone I (see Figu e 12), (a)
EBSD band con as (BC) map, (b) EBSD phase map, (c– ) EDS elemen dis ibu ion maps o Si,
Ti, N and C. Rep in ed wi h pe mission om Re . [95]. Copy igh 2021 Else ie .
Thus, o he deposi ion o coa ings using lase cladding, he p epa a ion o mul-
i-pass hick coa ings by he o e lay p ocessing is e y impo an . This p ocess allows
p oduc ion o he g adien unc ional s uc u e on he coa ed su ace [96]. The cladding
laye always includes he pa ially mel ed subs a e in i s bo om pa in he in e ace
dilu ion egion [97]. In case o mul i-pass hick coa ings no he subs a e bu he p e i-
ous pa ially emel ed and solidi ied HEA laye is included ins ead. One can expec ,
he e o e, ha he po ions wi h less p onounced GB we ing (like Zones IV and V in
Figu e 20) would be excluded om he mul ilaye HEA coa ings and only pe iodically
epea ed laye s wi h good GB we ing simila o Zones I and II (see Figu e 20) would be
p esen . Such a s uc u e could p e en unwan ed c acking h ough he whole mul i-
laye coa ing [98]. The emel ing akes place also in he o e lapping neighbo ing lase
line scans [90–92,98]. The e o e, he la e al shi o he scan acks o e en hei axial o-
Figu e 21.
The mic os uc u es wi h EBSD and EDS esul s o in he zone I (see Figu e 12), (
a
) EBSD
band con as (BC) map, (
b
) EBSD phase map, (
c
–
) EDS elemen dis ibu ion maps o Si, Ti, N and
C. Rep in ed wi h pe mission om Re . [95]. Copy igh 2021 Else ie .
Thus, o he deposi ion o coa ings using lase cladding, he p epa a ion o mul i-pass
hick coa ings by he o e lay p ocessing is e y impo an . This p ocess allows p oduc ion
o he g adien unc ional s uc u e on he coa ed su ace [
96
]. The cladding laye always
includes he pa ially mel ed subs a e in i s bo om pa in he in e ace dilu ion egion [
97
].
In case o mul i-pass hick coa ings no he subs a e bu he p e ious pa ially emel ed
and solidi ied HEA laye is included ins ead. One can expec , he e o e, ha he po ions
wi h less p onounced GB we ing (like Zones IV and V in Figu e 20) would be excluded
om he mul ilaye HEA coa ings and only pe iodically epea ed laye s wi h good GB
we ing simila o Zones I and II (see Figu e 20) would be p esen . Such a s uc u e could
p e en unwan ed c acking h ough he whole mul ilaye coa ing [
98
]. The emel ing
Coa ings 2022,12, 343 18 o 22
akes place also in he o e lapping neighbo ing lase line scans [
90
–
92
,
98
]. The e o e, he
la e al shi o he scan acks o e en hei axial o a ion o he subsequen coa ing laye s
could addi ionally imp o e he wea p ope ies [
99
] o p e en he c acking o a ha d
coa ing [100,101].
10. Conclusions
This e iew analyzes he g ain bounda y (GB) we ing in he high-en opy alloys
(HEAs) coa ings deposi ed by lase cladding. I an HEA con ains only one phase, his
means ha du ing solidi ica ion, he HEAs in e sec only he liquidus and solidus lines
in he phase diag am. In his case, he mel en iched wi h 1–3 componen s we s he GBs
in he solid phase, poo in hese componen s, and hen solidi ies, o ming a phase wi h
he same c ys al la ice as he ma ix. HEAs can also con ain wo o mo e phases. In his
case, du ing solidi ica ion, he HEA c osses he liquidus line, and hen he line o eu ec ic
ans o ma ion. In his ins ance, he las po ions o he mel , which comple ely o pa ially
we he GBs, decompose in o a mix u e o wo o mo e solid phases. Then, in he solid s a e,
he second, hi d, and u he phases o m in e laye s in GBs. They sepa a e he c ys alli es
in he ma ix phase om hei neighbo s. The ansi ion om comple e o incomple e
GB we ing occu s, as a ule, when he lase beam powe o he scanning speed inc eases.
The mic os uc u e and GB we ing can also be in luenced by he HEAs composi ion, he
ex e nal magne ic ield o ul asonic impac . The mic os uc u e and GB we ing also
change signi ican ly o e he hickness o he ( a he hick) coa ings deposi ed by he lase
cladding. Especially in e es ing is he phenomenon o emel ing o HEAs in neighbo ing
acks o double and mul ilaye coa ings. In his case, he composi ion g adien in he
dep h can also modi y he condi ions o GB we ing.
11. Pa en s
This sec ion is no manda o y bu may be added i he e a e pa en s esul ing om he
wo k epo ed in his manusc ip .
Au ho Con ibu ions:
Concep ualiza ion, B.B.S., A.B.S., G.A.L. and A.K. (Anna Ko ne a); me hodol-
ogy, A.K. (Anna Ko ne a), A.B.S., A.K. (Alexei Kuzmin), B.B.S., A.B.S. and N.V.; o mal analysis, A.K.
(Anna Ko ne a), A.K. (Alexei Kuzmin), A.B.S., A.S.G. and N.V.; w i ing—o iginal d a p epa a ion,
A.K. (Anna Ko ne a), A.K. (Alexei Kuzmin), A.B.S., L.K. and N.V.; w i ing— e iew and edi ing,
B.B.S.; supe ision, B.B.S. and A.K. (Anna Ko ne a); p ojec adminis a ion, B.B.S. and A.K. (Anna
Ko ne a); unding acquisi ion, A.K. (Anna Ko ne a), and B.B.S. All au ho s ha e ead and ag eed o
he published e sion o he manusc ip .
Funding:
This esea ch was unded by he Russian Minis y o Science and Highe Educa ion
(con ac no. 075-15-2021-945 g an no. 13.2251.21.0013) Suppo om he Uni e si y o he Basque
Coun y unde he GIU19/019 p ojec is also acknowledged.
Ins i u ional Re iew Boa d S a emen : No applicable.
In o med Consen S a emen : No applicable.
Da a A ailabili y S a emen :
All he da a equi ed o ep oduce hese expe imen s a e p esen in
he a icle.
Acknowledgmen s:
This e iew was w i en du ing he p epa a ion o M-e a.Ne ull p oposal
“G ain bounda ies in mul icomponen alloys wi hou p incipal componen ” (A.Ko., A.Ku., G.A.L.
and L.K., applica ion No 9345). The Ins i u e o Solid S a e Physics, Uni e si y o La ia, as a
cen e o excellence, has ecei ed unding om he Eu opean Union’s Ho izon 2020 F amewo k
P og amme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 unde g an ag eemen no. 739508,
p ojec CAMART2.
Con lic s o In e es : The au ho s decla e no con lic o in e es .
Coa ings 2022,12, 343 19 o 22
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