Ci a ion: Buch ík, M.; Bˇ ezina, M.;
M ˇna, L.; Palán, M.; Filipenský, J.;
Doležal, P.; Neˇcas, D.; F ýza, J.;
Kajánek, D.; Wasse baue , J.; e al.
E ec o Lase Remel ing o Fe-Based
The mally Sp ayed Coa ing on AZ91
Magnesium Alloy on I s S uc u al
and T ibological P ope ies. Coa ings
2023,13, 1033. h ps://doi.o g/
10.3390/coa ings13061033
Academic Edi o : Manuel An ónio
Pe al a E a is o
Recei ed: 12 May 2023
Re ised: 26 May 2023
Accep ed: 30 May 2023
Published: 2 June 2023
Copy igh : © 2023 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/).
coa ings
A icle
E ec o Lase Remel ing o Fe-Based The mally Sp ayed
Coa ing on AZ91 Magnesium Alloy on I s S uc u al and
T ibological P ope ies
Ma in Buch ík1,*, Ma ˇej Bˇ ezina 1, Libo M ˇna 2,3, Ma ek Palán4, Jan Filipenský5, Pa el Doležal 1,3 ,
Da id Neˇcas 3, Jose F ýza 3, Daniel Kajánek 6, Ja omí Wasse baue 1and Leoš Doskoˇcil 1
1Ma e ials Resea ch Cen e, Facul y o Chemis y, B no Uni e si y o Technology, Pu kyno a 464/118,
612 00 B no, Czech Republic; [email p o ec ed] (M.B.); [email p o ec ed].cz (P.D.);
[email p o ec ed] (J.W.); [email p o ec ed] (L.D.)
2Ins i u e o Scien i ic Ins umen s o he Czech Academy o Sciences, K alo opolska, 147,
612 64 B no, Czech Republic; [email p o ec ed]
3Facul y o Mechanical Enginee ing, B no Uni e si y o Technology, Technicka 2896/2,
602 00 B no, Czech Republic; [email p o ec ed] (D.N.); [email p o ec ed].cz (J.F.)
4Depa men o Ma e ials and Enginee ing Me allu gy, Facul y o Mechanical Enginee ing,
Uni e si y o Wes Bohemia, Uni e zi ni 22, 301 00 Plzen, Czech Republic; [email p o ec ed]
5PLASMAMETAL, L d., To a ni 917/1e, 643 00 B no, Czech Republic; [email p o ec ed]
6Resea ch Cen e, Uni e si y o Zilina, Uni e zi na 8215/1, 010 26 Zilina, Slo akia; [email p o ec ed]
*Co espondence: [email p o ec ed]; Tel.: +420-541-149-469
Abs ac :
An Fe-based coa ing was he mally sp ayed on o he su ace o AZ91 magnesium alloy ia
he High-Veloci y-Oxygen-Fuel (HVOF) me hod. The he mally sp ayed coa ing wi h a hickness
o 530
±
25
µ
m and a po osi y o 0.7
±
0.1% did no show any mac os uc u al de ec s and did no
cause any deg ada ion o he AZ91 alloy. Lase emel ing o he su ace laye o he sp ayed coa ing
esul ed in he ec ys alliza ion o he s uc u e and he disappea ance o p esen ed po es, spla
bounda ies, and o he de ec s. This led o an inc ease in he ha dness o he emel ed laye om he
o iginal 535
±
20 HV0.3 up o 625
±
5 HV0.3. Howe e , du ing he lase emel ing a a lase powe
o 1000 W, s ess c acking in he coa ing occu ed. The ibological p ope ies we e e alua ed by he
ball-on-pla e me hod unde d y condi ions. Compa ed o he uncoa ed AZ91 magnesium alloy, a
highe alue o ic ion coe icien (COF) was measu ed o he as-sp ayed coa ing. Howe e , he e
was a dec ease in wea a e and weigh loss. The emel ing o he su ace laye o he as-sp ayed
coa ing led o a u he dec ease in he wea a e and weigh loss. Based on he ob ained da a, i
has been shown ha he applica ion o lase - emel ed he mally sp ayed Fe-based coa ings on AZ91
Mg alloy imp o es ha dness and ibological p ope ies compa ed o ba e Mg alloy and as-sp ayed
Fe-based coa ings.
Keywo ds:
AZ91; magnesium alloy; HVOF coa ing; lase emel ing; ibological p ope ies; wea
beha io
1. In oduc ion
Magnesium alloys a e used in indus y, especially in he au omo i e indus y, he
ae ospace indus y, elec ical enginee ing, and elecommunica ions, due o hei low den-
si ies, which a e he lowes o any cu en ly known me allic cons uc ion ma e ials, and
due o hei high s eng h- o-weigh a ios [
1
–
4
]. Cu en applica ions in he au omo i e
indus y include hei use o componen s such as pedals, engine block cas ings, gea box
housings, sea ames, and some bodywo k componen s, e c. [
1
,
5
]. In indus ial enginee -
ing, such as in ex iles o p in ing, magnesium alloys a e used o componen s ope a ing a
high speeds and which he e o e need o be ligh weigh o minimize ine ial o ces [1,5].
Coa ings 2023,13, 1033. h ps://doi.o g/10.3390/coa ings13061033 h ps://www.mdpi.com/jou nal/coa ings
Coa ings 2023,13, 1033 2 o 16
Howe e , a common ea u e o all magnesium alloys is hei low esis ance o co o-
sion and wea [
1
,
6
–
9
]. These disad an ages can be a oided by he applica ion o p o ec i e
coa ings [
7
,
9
–
12
]. Many ypes o coa ings ha e been de eloped o inc ease he co osion
esis ance o magnesium ma e ials, o example, plasma elec oly ic oxida ion (PEO) coa -
ings [
13
], laye ed double hyd oxides (LDH), supe hyd ophobic coa ings [
14
,
15
], elec oless
coa ings o elec opla ed coa ings [
16
–
18
], phospha e coa ings o coa ings deposi ed ia
ho sp ay echnology [
3
,
19
–
21
]. Al hough hese coa ings inc ease co osion esis ance,
hey achie e low adhesion, ha dness and ab asion esis ance, which limi s hei p ac ical
applica ion [22,23].
In addi ion o he abo e-men ioned applica ions o p o ec i e coa ings, he addi ion o
alloying elemen s o he use o hea o mechanical ea men (e.g., sho peening [
24
–
26
],
lase sho peening [
27
], lase cladding [
28
] o ic ion s i welding [
29
] a e also used o
imp o e he su ace p ope ies o Mg alloys.
As epo ed in publica ions [
30
–
33
], he addi ion o an alloying elemen such as Nd,
Sc o Sm o AZ91 alloy esul ed in imp o ed co osion p ope ies and inc eased ha dness,
educed wea a e and inc eased s eng h. A sui able al e na i e could also be he appli-
ca ion o coa ings by mechanical alloying ollowed by lase cladding echnique [
28
]. The
applica ion o FeCoNiC Al/AlSi12-based composi e coa ings by he mechanical alloying
me hod can inc ease he ha dness and nanoha dness o he sample su ace. Subsequen
lase cladding o he FeCoNiC Al/AlSi12 coa ing esul ed in a u he signi ican inc ease
in ha dness. The coa ing exhibi ed a e ined and homogeneous mic os uc u e wi hou
s uc u al de ec s such as po es and c acks.
In ecen yea s, he mos p omising me hods o he p epa a ion o coa ings appea o
be he High-Veloci y-Oxygen-Fuel (HVOF) and Cold Sp ay (CS) me hods [
20
,
22
,
34
]. Bo h
HVOF and CS a e he mal sp aying echniques, allowing he deposi ion o dense, ha d,
and low po ous coa ings [
35
,
36
]. The HVOF echnique is sui able o he deposi ion o bo h
me al and me al–ce amic-based coa ings and allows he applica ion o ab asion- esis an
coa ings [
22
,
37
,
38
]. Ga cía-Rod íguez e al. [
39
] in es iga ed he applica ion o 316L-base
HVOF-sp ayed coa ings on ZE41 magnesium alloy and s udied he su ace p ope ies. I
was ound ha he applica ion o 316L-based coa ings educed he wea a e (a low wea
a es and lowe loads) by up o 93% compa ed o ba e ZE41 magnesium alloy. A he same
ime, he ha dness was inc eased mo e han six- old om 65 HV0.1 o 433 HV0.1 by he
applica ion o he coa ings. Koga e al. [
40
] epo ed ha he applica ion o amo phous
Fe60C 8Nb8B24 (a .%) HVOF-sp ayed coa ings can lead o a signi ican inc ease in su ace
ha dness, om 222
±
5 HV0.3 o s eel subs a e o 838
±
23 HV0.3 o amo phous coa ing.
As epo ed by he au ho s [
40
], he coa ings exhibi excellen ab asion p ope ies, mainly
due o he highe p opo ion o he amo phous phase. On he basis o wea measu emen s,
i was obse ed ha he wea a e o he amo phous coa ings was app oxima ely wo
o de s o magni ude lowe han ha o he s eel subs a e.
Wi h espec o s uc u al de ec s o HVOF he mally sp ayed coa ings (po es, mic oc-
acks, spla bounda ies, e c.), se e al me hods o pos - ea men ha e been s udied in he
pas o imp o e su ace p ope ies. Among hem, hea ea men and lase ea men ha e
been used o emo e hese s uc u al de ec s [
41
–
43
]. Such de ec s can ha e a nega i e
e ec on bo h he esul ing unc ional p ope ies and he beha io o he coa ed samples.
The lase emel ing p ocess can imp o e he p ope ies o he coa ings by elimina ing
hei de ec s (po es, c acks, e c.), which can lead o an inc ease in densi y, ha dness, wea
esis ance, s ess elie , e c.
The aim o his pape was o desc ibe he e ec o he lase emel ing o Fe-based
he mally sp ayed coa ings deposi ed on he su ace o AZ91 magnesium alloy. Using lase
powe s o 650 W and 1000 W, he e ec s o lase emel ing on he s uc u e, ha dness, and
ibological p ope ies o coa ings we e e alua ed. The lase emel ing p ocess can be a
use ul echnique o he pos - ea men o he mally sp ayed coa ings and o imp o ing
he pe o mance and ex ending he li e o he applied coa ing o coa ed pa . This issue has
no ye ecei ed su icien a en ion in he li e a u e. The expe imen al esul s showed ha
Coa ings 2023,13, 1033 3 o 16
he applica ion o lase - emel ed he mally sp ayed Fe-based coa ings on AZ91 Mg alloy
imp o es ha dness and ibological p ope ies compa ed o ba e Mg alloy and as-sp ayed
Fe-based coa ings.
2. Ma e ials and Me hods
2.1. Ma e ial
W ough AZ91 magnesium alloy was used as he subs a e o he deposi ion o he -
mally sp ayed coa ings. The elemen al composi ion o AZ91 alloy was (w %):
8.80 Al
;
0.81 Zn
;
0.32 Mn
; 0.04 Si; 0.01 Z ; balance Mg. The ma e ial was ecei ed as cas AZ91 mag-
nesium alloy shee s wi h he dimensions o 100
×
100
×
7 mm. Be o e he sp aying p ocess,
he su ace o each shee was co undum blas ed wi h F36 b own co undum (
500–600 µm
)
using a Hunzike ST 1403 (Hunzike , Die Cas Machine y, Waukegan, IL, USA) blas ing
uni a oom empe a u e unde a p essu e o 3 ba and hen d y ai -cleaned.
The su ace oughness o he blas ed samples (R
a
) was de e mined o be app oxima ely
5.2 µm using a con ocal mic oscope (Lex OLS 3000, Olympus, Tokyo, Japan).
The used eeds ock powde (Figu e 1) was a omized Fe-based powde o he mal
sp aying (Diamalloy 1010; Oe likon Me co, Lomm, The Ne he lands) wi h a nominal size
dis ibu ion o
−
45 + 16
µ
m. The chemical composi ion o he eeds ock powde speci ied
by he supplie was (w %): 28 C ; 16 Ni; 4.5 Mo; 1.5 Si; 1.75 C; balance Fe.
Coa ings 2023, 13, x FOR PEER REVIEW 3 o 17
a use ul echnique o he pos - ea men o he mally sp ayed coa ings and o imp o ing
he pe o mance and ex ending he li e o he applied coa ing o coa ed pa . This issue
has no ye ecei ed sufficien a en ion in he li e a u e. The expe imen al esul s showed
ha he applica ion o lase - emel ed he mally sp ayed Fe-based coa ings on AZ91 Mg
alloy imp o es ha dness and ibological p ope ies compa ed o ba e Mg alloy and as-
sp ayed Fe-based coa ings.
2. Ma e ials and Me hods
2.1. Ma e ial
W ough AZ91 magnesium alloy was used as he subs a e o he deposi ion o he -
mally sp ayed coa ings. The elemen al composi ion o AZ91 alloy was (w %): 8.80 Al; 0.81
Zn; 0.32 Mn; 0.04 Si; 0.01 Z ; balance Mg. The ma e ial was ecei ed as cas AZ91 magne-
sium alloy shee s wi h he dimensions o 100 × 100 × 7 mm. Be o e he sp aying p ocess,
he su ace o each shee was co undum blas ed wi h F36 b own co undum (500–600 µm)
using a Hunzike ST 1403 (Hunzike , Die Cas Machine y, Waukegan, IL, USA) blas ing
uni a oom empe a u e unde a p essu e o 3 ba and hen d y ai -cleaned.
The su ace oughness o he blas ed samples (Ra) was de e mined o be app oxi-
ma ely 5.2 µm using a con ocal mic oscope (Lex OLS 3000, Olympus, Tokyo, Japan).
The used eeds ock powde (Figu e 1) was a omized Fe-based powde o he mal
sp aying (Diamalloy 1010; Oe likon Me co, Lomm, The Ne he lands) wi h a nominal size
dis ibu ion o −45 + 16 µm. The chemical composi ion o he eeds ock powde speci ied
by he supplie was (w %): 28 C ; 16 Ni; 4.5 Mo; 1.5 Si; 1.75 C; balance Fe.
(a) (b)
Figu e 1. The su ace mo phology o eeds ock powde : (a) Diamalloy 1010 pa icles and (b) pa icle
de ail.
2.2. The mal Sp aying P ocess
The mally HVOF-sp ayed coa ings (sp ayed in 4 o ch passes) we e sp ayed on he
blas ed AZ91 magnesium alloy samples using a JP-5000 liquid- uel HVOF gun connec ed
o an IRB-2400/16 obo (ABB, Zü ich, Swi ze land), Figu e 2a. The o iginal 100 × 100 mm
blas ed samples (Figu e 2b) we e HVOF sp ayed along a s ip o 100 × 70 mm. The samples
we e ixed wi h s eel b acke s on each side o a dis ance o 15 mm.
Figu e 1.
The su ace mo phology o eeds ock powde : (
a
) Diamalloy 1010 pa icles and (
b
) pa i-
cle de ail.
2.2. The mal Sp aying P ocess
The mally HVOF-sp ayed coa ings (sp ayed in 4 o ch passes) we e sp ayed on he
blas ed AZ91 magnesium alloy samples using a JP-5000 liquid- uel HVOF gun connec ed
o an IRB-2400/16 obo (ABB, Zü ich, Swi ze land), Figu e 2a. The o iginal
100 ×100 mm
blas ed samples (Figu e 2b) we e HVOF sp ayed along a s ip o 100
×
70 mm. The samples
we e ixed wi h s eel b acke s on each side o a dis ance o 15 mm.
2.3. Lase T ea men P ocess
Lase ea men was pe o med on he HVOF-sp ayed coa ings. The coa ed magne-
sium samples we e i s p ehea ed o 200
◦
C o 30 min o educe he hea shock. The lase
beam powe ed by a YLS-2000 ibe lase sou ce (IPG, Ox o d, MA, USA) was led by a
100 µm- hick
ibe o a Fibe Rhino (A ges, Wacke sdo , Ge many) scanning head wi h an
S4LFT1330/328 - he a lens (Sill Op ics, Wendels ein, Ge many). The diame e o he beam
was 325
µ
m, and he lase powe s we e se a 650 W and 1000 W. The linea scanning speed
was 4 m
·
s
−1
wi h a line spacing o 60
µ
m. The lase ea men p ocessing pa e n was laid
down in he same way as in ou p e ious s udy [19].
Coa ings 2023,13, 1033 4 o 16
Coa ings 2023, 13, x FOR PEER REVIEW 4 o 17
(a) (b)
Figu e 2. The mal sp aying p ocess; (a) sample placemen o he mal sp aying and (b) sample
holde .
2.3. Lase T ea men P ocess
Lase ea men was pe o med on he HVOF-sp ayed coa ings. The coa ed magne-
sium samples we e i s p ehea ed o 200 °C o 30 min o educe he hea shock. The lase
beam powe ed by a YLS-2000 ibe lase sou ce (IPG, Ox o d, MA, USA) was led by a 100
µm- hick ibe o a Fibe Rhino (A ges, Wacke sdo , Ge many) scanning head wi h an
S4LFT1330/328 - he a lens (Sill Op ics, Wendels ein, Ge many). The diame e o he beam
was 325 µm, and he lase powe s we e se a 650 W and 1000 W. The linea scanning
speed was 4 m·s−1 wi h a line spacing o 60 µm. The lase ea men p ocessing pa e n was
laid down in he same way as in ou p e ious s udy [19].
2.4. Cha ac e iza ion
The eeds ock powde and he HVOF-sp ayed Fe-based coa ings we e cha ac e ized
by a JEOL JSM-7600 FESEM mic oscope equipped wi h an Ul im® Max ene gy-dispe si e
X- ay spec oscope (Ox o d Ins umen s plc, Abingdon, UK). The hicknesses o he di -
e en samples we e measu ed om a c oss-cu using he Sma SEM® Use In e ace scan-
ning elec on mic oscope so wa e. Measu emen s we e aken a h ee loca ions. EBSD
(Elec on backsca e diff ac ion) analysis o he coa ings was pe o med using a JEOL
JSM-7600 (JEOL) FESEM mic oscope equipped wi h a No dlys EBSD de ec o . The accel-
e a ing ol age o EBSD analysis was se o 20 kV in o de o achie e he bes signal:noise
a io and he s ep size was 0.5 µm. Fo he EBSD cha ac e iza ion, he samples we e ion
polished using IB-19500CP C oss Sec ion Polishe (JEOL). The po osi y was e alua ed by
means o image analysis using ImageJ so wa e.
The phase composi ions o AZ91 magnesium alloy, eeds ock powde , and as-
sp ayed coa ings we e de e mined using an Empy ean X- ay diff ac ion (XRD) spec om-
e e (Panaly ical, Mal e n, UK) wi h Cu Kα adia ion. The 2θ scan ange anged om 10
o 85°; he scan s ep size was 0.013°; he ime pe s ep was se o 39 s; he gene a o ol age
was 40 kV wi h he ube cu en 30 mA. HighSco e Plus so wa e was used o he e alu-
a ion o measu ed da a.
The Vicke s mic oha dness o all samples wi h he mally sp ayed coa ings and lase -
emel ed coa ings was measu ed unde an applied load o 300 g o a du a ion o 10 s
(AMH 55, LECO, S . Joseph, MI, USA) acco ding o ASTM E384.
T ibological measu emen s we e pe o med using he UMT T ibolab (B uke , Bille -
ica, MA, USA) uni e sal mechanical es e pla o m using he ball-on-pla e me hod ha
conside s ecip oca ing mo ion unde an applied no mal pin load o 20 N (Mean con ac
p essu e 1150 MPa). The du a ion was se o 600 s, wi h a o al sliding dis ance o 12 m a
a equency o 2 Hz, and a wo king dis ance (s oke leng h) o 10 mm. The sliding speed
was 20 mm·s−1. The d y sliding wea es s we e pe o med a labo a o y empe a u e on
Figu e 2.
The mal sp aying p ocess; (
a
) sample placemen o he mal sp aying and (
b
) sample holde .
2.4. Cha ac e iza ion
The eeds ock powde and he HVOF-sp ayed Fe-based coa ings we e cha ac e ized
by a JEOL JSM-7600 FESEM mic oscope equipped wi h an Ul im
®
Max ene gy-dispe si e X-
ay spec oscope (Ox o d Ins umen s plc, Abingdon, UK). The hicknesses o he di e en
samples we e measu ed om a c oss-cu using he Sma SEM
®
Use In e ace scanning
elec on mic oscope so wa e. Measu emen s we e aken a h ee loca ions. EBSD (Elec on
backsca e di ac ion) analysis o he coa ings was pe o med using a JEOL JSM-7600
(JEOL) FESEM mic oscope equipped wi h a No dlys EBSD de ec o . The accele a ing
ol age o EBSD analysis was se o 20 kV in o de o achie e he bes signal:noise a io
and he s ep size was 0.5
µ
m. Fo he EBSD cha ac e iza ion, he samples we e ion polished
using IB-19500CP C oss Sec ion Polishe (JEOL). The po osi y was e alua ed by means o
image analysis using ImageJ so wa e.
The phase composi ions o AZ91 magnesium alloy, eeds ock powde , and as-sp ayed
coa ings we e de e mined using an Empy ean X- ay di ac ion (XRD) spec ome e (Pan-
aly ical, Mal e n, UK) wi h Cu K
α
adia ion. The 2
θ
scan ange anged om 10 o 85
◦
;
he scan s ep size was 0.013
◦
; he ime pe s ep was se o 39 s; he gene a o ol age was
40 kV wi h he ube cu en 30 mA. HighSco e Plus so wa e was used o he e alua ion o
measu ed da a.
The Vicke s mic oha dness o all samples wi h he mally sp ayed coa ings and lase -
emel ed coa ings was measu ed unde an applied load o 300 g o a du a ion o 10 s
(AMH 55, LECO, S . Joseph, MI, USA) acco ding o ASTM E384.
T ibological measu emen s we e pe o med using he UMT T ibolab (B uke ,
Bille ica, MA, USA) uni e sal mechanical es e pla o m using he ball-on-pla e me hod
ha conside s ecip oca ing mo ion unde an applied no mal pin load o 20 N (Mean con-
ac p essu e 1150 MPa). The du a ion was se o 600 s, wi h a o al sliding dis ance o 12 m
a a equency o 2 Hz, and a wo king dis ance (s oke leng h) o 10 mm. The sliding speed
was 20 mm
·
s
−1
. The d y sliding wea es s we e pe o med a labo a o y empe a u e on
polished samples (Ra
≈
0.05
µ
m). The coun e -ball was Si
3
N
4
wi h a diame e o 7.5 mm.
A o al o 2 epe i ions we e pe o med o each sample.
3. Resul s and Discussion
3.1. S uc u al Cha ac e iza ion
Figu e 3a–c show he mic os uc u e o HVOF coa ings on AZ91 Mg alloy. F om he
mac oscopic poin o iew, i can be seen ha he as-sp ayed coa ing and he coa ing ea ed
by he 650 W lase powe we e homogeneous and ee o s uc u al de ec s (Figu e 3a,b). Fo
he 1000 W lase emel ed coa ing, ex ensi e c acks we e isible, ex ending o abou hal o
Coa ings 2023,13, 1033 5 o 16
he coa ing (Figu e 3c). As discussed in ou p e ious s udy [
19
], he p esence o hese c acks
can be explained by he high s esses in he coa ing associa ed wi h he olume change in
he emel ed laye . Du ing emel ing, po es, spla bounda ies and o he inhomogenei ies in
he su ace laye disappea ed. This led o ensile s esses and c ack o ma ion in he coa ing.
The e was no isible delamina ion, deadhesion, o isible oxida ion a he coa ing/Mg
subs a e in e ace in any o he coa ings, indica ing he po en ially high adhesion o he
coa ings o he Mg subs a e.
Coa ings 2023, 13, x FOR PEER REVIEW 5 o 17
polished samples (Ra ≈ 0.05 µm). The coun e -ball was Si3N4 wi h a diame e o 7.5 mm.
A o al o 2 epe i ions we e pe o med o each sample.
3. Resul s and Discussion
3.1. S uc u al Cha ac e iza ion
Figu e 3a–c show he mic os uc u e o HVOF coa ings on AZ91 Mg alloy. F om he
mac oscopic poin o iew, i can be seen ha he as-sp ayed coa ing and he coa ing
ea ed by he 650 W lase powe we e homogeneous and ee o s uc u al de ec s (Figu e
3a,b). Fo he 1000 W lase emel ed coa ing, ex ensi e c acks we e isible, ex ending o
abou hal o he coa ing (Figu e 3c). As discussed in ou p e ious s udy [19], he p esence
o hese c acks can be explained by he high s esses in he coa ing associa ed wi h he
olume change in he emel ed laye . Du ing emel ing, po es, spla bounda ies and o he
inhomogenei ies in he su ace laye disappea ed. This led o ensile s esses and c ack
o ma ion in he coa ing. The e was no isible delamina ion, deadhesion, o isible oxida-
ion a he coa ing/Mg subs a e in e ace in any o he coa ings, indica ing he po en ially
high adhesion o he coa ings o he Mg subs a e.
The hicknesses o as-sp ayed and lase emel ed coa ings was abou 500 µm. The
ha dness o he as-sp ayed coa ing was de e mined o be 535 ± 20 HV0.3. In he case o he
emel ed coa ing a a lase powe o 650 W, he e was an inc ease in he ha dness o he
30 µm-wide emel ed laye on he su ace o 610 ± 8 HV0.3. In he case o he emel ed
coa ing a a lase powe o 1000 W, he e was an inc ease in he ha dness o he 45 µm
wide emel ed laye on he su ace o 625 ± 5 HV. This inc ease in ha dness may be asso-
cia ed wi h he disappea ance o he spla bounda ies, po es, and o he mic os uc u al
de ec s. The indi idual coa ing hickness alues a e summa ized in Table 1.
The X- ay diff ac og am (Figu e 3d) o he subs a e (AZ91 alloy) showed he p es-
ence o wo main phases, namely he α-Mg ma ix phase (a solid solu ion o alloying ele-
men s in Mg), and he Mg17Al12 in e me allic phase. In he case o he eeds ock powde ,
he as-sp ayed coa ing, and he lase - emel ed coa ings, only wo phases we e always de-
ec ed, namely aus eni e and M7C3 ca bide, which is a mixed ca bide, whe e M = Fe, C ,
Mo [44,45]. Apa om hese peaks, no o he phases appea ed in he coa ings. Compa ed
o he peaks o he eeds ock powde , he indi idual peaks co esponding o he coa ings
ha e a lowe in ensi y, which is ela ed o he se e e plas ic de o ma ion o he pa icles
du ing he sp aying p ocess, and he p esence o amo phous a eas associa ed wi h he
impac o ully mel ed eeds ock powde pa icles on he Mg subs a e and hei apid
solidi ica ion [20,22].
(a) (b)
Coa ings 2023, 13, x FOR PEER REVIEW 6 o 17
(c) (d)
Figu e 3. Mic os uc u e o he mally sp ayed coa ings, (a) as-sp ayed, (b) lase - emel ed a 650 W,
(c) lase - emel ed a 1000 W. XRD pa e ns (d) o AZ91 alloy, eeds ock powde , and he mally
sp ayed coa ings.
As can be obse ed in Figu e 4, he mic os uc u e o he as-sp ayed coa ing consis ed
o non-mel ed, pa ially mel ed, and ully mel ed a eas. In Figu e 4a, he diffe en egions
a e clea ly dis inguishable and include spla bounda ies and po es. Figu e 4b shows a
non-mel ed pa icle sepa a ed om i s su oundings by spla bounda ies. As shown by
he XRD analysis (Figu e 3d), wo phases we e de ec ed in he coa ing, and hus in he
non-mel ed a ea–aus eni e and M7C3 ca bide. In he non-mel ed a ea, he dend i es o aus-
eni e (da ke egions) and ca bide (ligh e egions) we e well esol ed.
A diffe en mic os uc u e was obse ed o pa ially mel ed a eas and signi ican ly
de o med a eas (Figu e 4c). As can be seen in Figu e 4c, hese a eas we e composed o ine
ca bide pa icles and ca bides in he in e dend i ic space which did no o m a con inuous
ne wo k, as in he case o non-mel ed a eas. I appea s ha du ing he apid solidi ica ion
p ocess, he ca bide did no ha e ime o ully c ys allize. A high deg ee o plas ic de o -
ma ion is e iden compa ed o he non-mel ed egion (see Figu e 4a).
Fully mel ed a eas we e homogeneous. Acco ding o he li e a u e [22,40,46], such
ully mel ed a eas (Figu e 4c) can be assumed o be comple ely amo phous. These amo -
phous a eas we e p obably o med as a esul o he apid solidi ica ion o he ully mel ed
pa icle [22,47].
Table 1. Mic os uc u al and mechanical ea u es o he coa ings and Mg subs a e.
Sample Thickness (µm)
Thickness o
Remel ed Laye
(µm)
Ha dness HV0.3 Po osi y (%)
AZ91 alloy - - 85 ± 9 -
As-sp ayed
coa ing 530 ± 25 - 535 ± 20 0.7 ± 0.1
Lase - emel ed
650 W 517 ± 10 30 ± 5 610 ± 8 0.0 ± 0.0
Lase - emel ed
1000 W 515 ± 9 45 ± 5 625 ± 5 0.0 ± 0.0
Figu e 3.
Mic os uc u e o he mally sp ayed coa ings, (
a
) as-sp ayed, (
b
) lase - emel ed a 650 W,
(
c
) lase - emel ed a 1000 W. XRD pa e ns (
d
) o AZ91 alloy, eeds ock powde , and he mally
sp ayed coa ings.
The hicknesses o as-sp ayed and lase emel ed coa ings was abou 500
µ
m. The
ha dness o he as-sp ayed coa ing was de e mined o be 535
±
20 HV0.3. In he case o he
emel ed coa ing a a lase powe o 650 W, he e was an inc ease in he ha dness o he
30
µ
m-wide emel ed laye on he su ace o 610
±
8 HV0.3. In he case o he emel ed
coa ing a a lase powe o 1000 W, he e was an inc ease in he ha dness o he 45
µ
m wide
emel ed laye on he su ace o 625
±
5 HV. This inc ease in ha dness may be associa ed
wi h he disappea ance o he spla bounda ies, po es, and o he mic os uc u al de ec s.
The indi idual coa ing hickness alues a e summa ized in Table 1.

Coa ings 2023,13, 1033 6 o 16
Table 1. Mic os uc u al and mechanical ea u es o he coa ings and Mg subs a e.
Sample Thickness
(µm)
Thickness o
Remel ed Laye (µm)
Ha dness
HV0.3
Po osi y
(%)
AZ91 alloy - - 85 ±9 -
As-sp ayed coa ing 530 ±25 - 535 ±20 0.7 ±0.1
Lase - emel ed 650 W 517 ±10 30 ±5 610 ±8 0.0 ±0.0
Lase - emel ed 1000 W 515 ±9 45 ±5 625 ±5 0.0 ±0.0
The X- ay di ac og am (Figu e 3d) o he subs a e (AZ91 alloy) showed he p esence
o wo main phases, namely he
α
-Mg ma ix phase (a solid solu ion o alloying elemen s
in Mg), and he Mg
17
Al
12
in e me allic phase. In he case o he eeds ock powde , he
as-sp ayed coa ing, and he lase - emel ed coa ings, only wo phases we e always de ec ed,
namely aus eni e and M
7
C
3
ca bide, which is a mixed ca bide, whe e M = Fe, C , Mo [
44
,
45
].
Apa om hese peaks, no o he phases appea ed in he coa ings. Compa ed o he peaks
o he eeds ock powde , he indi idual peaks co esponding o he coa ings ha e a lowe
in ensi y, which is ela ed o he se e e plas ic de o ma ion o he pa icles du ing he
sp aying p ocess, and he p esence o amo phous a eas associa ed wi h he impac o ully
mel ed eeds ock powde pa icles on he Mg subs a e and hei apid solidi ica ion [
20
,
22
].
As can be obse ed in Figu e 4, he mic os uc u e o he as-sp ayed coa ing consis ed
o non-mel ed, pa ially mel ed, and ully mel ed a eas. In Figu e 4a, he di e en egions
a e clea ly dis inguishable and include spla bounda ies and po es. Figu e 4b shows a
non-mel ed pa icle sepa a ed om i s su oundings by spla bounda ies. As shown by
he XRD analysis (Figu e 3d), wo phases we e de ec ed in he coa ing, and hus in he
non-mel ed a ea–aus eni e and M
7
C
3
ca bide. In he non-mel ed a ea, he dend i es o
aus eni e (da ke egions) and ca bide (ligh e egions) we e well esol ed.
A di e en mic os uc u e was obse ed o pa ially mel ed a eas and signi ican ly
de o med a eas (Figu e 4c). As can be seen in Figu e 4c, hese a eas we e composed
o ine ca bide pa icles and ca bides in he in e dend i ic space which did no o m a
con inuous ne wo k, as in he case o non-mel ed a eas. I appea s ha du ing he apid
solidi ica ion p ocess, he ca bide did no ha e ime o ully c ys allize. A high deg ee o
plas ic de o ma ion is e iden compa ed o he non-mel ed egion (see Figu e 4a).
Fully mel ed a eas we e homogeneous. Acco ding o he li e a u e [
22
,
40
,
46
], such ully
mel ed a eas (Figu e 4c) can be assumed o be comple ely amo phous. These amo phous
a eas we e p obably o med as a esul o he apid solidi ica ion o he ully mel ed
pa icle [22,47].
The mic os uc u es o he lase - emel ed laye s a e shown in Figu e 5. The hicknesses
o he emel ed laye s a lase powe s o 650 W and 1000 W we e abou 30
µ
m and 45
µ
m,
espec i ely. A high-magni ica ion BSE SEM mic og aph (Figu e 5b,d) shows ha he
coa ing was p edominan ly c ys allized a e lase emel ing. This was also con i med
by he EBSD analysis (see Figu e 6a). This was due o he ac ha he HVOF coa ing
abso bed a la ge amoun o hea du ing he emel ing p ocess. The mic os uc u e in he
lase - emel ed laye consis ed o columna g ains wi h a subg ain dend i ic mic os uc u e.
Indi idual g ains we e o med by dend i es o aus eni e (da ke a eas) and M
7
C
3
ca bide
(ligh e a eas) in he in e dend i ic a ea (Figu e 5b,d). The e o e, emel ing did no esul
in he o ma ion o new phases. This was also con i med by he XRD analysis abo e
(Figu e 3d). As can be seen om he de ails in Figu e 5b,d, he dend i ic s uc u e in he
emel ed laye is simila o he dend i ic s uc u e o non-mel ed pa icles in he as-sp ayed
coa ing (Figu e 4b). As can be obse ed in Figu e 5d, in he case o he coa ing emel ed a
a lase powe o 1000 W, he aus eni e dend i es and ca bides in he emel ed laye we e
coa se han hose in he case o he coa ing emel ed a a lase powe o 650 W (Figu e 5b).
This may be due o he ac ha mo e hea was in oduced in o he coa ing du ing emel ing
wi h he highe lase powe , which esul ed in a longe cooling ime.
Coa ings 2023,13, 1033 7 o 16
Coa ings 2023, 13, x FOR PEER REVIEW 7 o 17
(a)
(b) (c)
Figu e 4. Highe magni ica ion mic og aph o as-sp ayed coa ing, (a) c oss-sec ion, (b) de ail o non-
mel ed pa icle, (c) de ail o mel ed, de o med and ully mel ed a ea.
The mic os uc u es o he lase - emel ed laye s a e shown in Figu e 5. The hick-
nesses o he emel ed laye s a lase powe s o 650 W and 1000 W we e abou 30 µm and
45 µm, espec i ely. A high-magni ica ion BSE SEM mic og aph (Figu e 5b,d) shows ha
he coa ing was p edominan ly c ys allized a e lase emel ing. This was also con i med
by he EBSD analysis (see Figu e 6a). This was due o he ac ha he HVOF coa ing ab-
so bed a la ge amoun o hea du ing he emel ing p ocess. The mic os uc u e in he
lase - emel ed laye consis ed o columna g ains wi h a subg ain dend i ic mic os uc-
u e. Indi idual g ains we e o med by dend i es o aus eni e (da ke a eas) and M7C3
ca bide (ligh e a eas) in he in e dend i ic a ea (Figu e 5b,d). The e o e, emel ing did
no esul in he o ma ion o new phases. This was also con i med by he XRD analysis
abo e (Figu e 3d). As can be seen om he de ails in Figu e 5b,d, he dend i ic s uc u e
in he emel ed laye is simila o he dend i ic s uc u e o non-mel ed pa icles in he as-
sp ayed coa ing (Figu e 4b). As can be obse ed in Figu e 5d, in he case o he coa ing
emel ed a a lase powe o 1000 W, he aus eni e dend i es and ca bides in he emel ed
laye we e coa se han hose in he case o he coa ing emel ed a a lase powe o 650 W
(Figu e 5b). This may be due o he ac ha mo e hea was in oduced in o he coa ing
du ing emel ing wi h he highe lase powe , which esul ed in a longe cooling ime.
As shown in Figu e 6, he as-sp ayed coa ing is p edominan ly non-c ys alline, as
e y ew diff ac ions we e obse ed. The EBSD esul s (Figu e 6b) sugges ed ha he black
a eas may be amo phous o po es and spla bounda ies, while he non-mel ed pa icles
and he pa ially mel ed and plas ically de o med pa icles e ained hei c ys allini y. Ad-
di ionally, i may be e y ine g ains/a eas ha a e smalle han he EBSD cha ac e iza ion
s ep size [48]. The e was an app oxima ely 5 µm- hick ansi ion band be ween he as-
Figu e 4.
Highe magni ica ion mic og aph o as-sp ayed coa ing, (
a
) c oss-sec ion, (
b
) de ail o
non-mel ed pa icle, (c) de ail o mel ed, de o med and ully mel ed a ea.
Coa ings 2023, 13, x FOR PEER REVIEW 8 o 17
sp ayed coa ing and he lase - emel ed laye (Figu e 6a,c). This was p obably he hea -
affec ed zone below he le el o he mel pools.
(a) (b)
(c) (d)
Figu e 5. Highe magni ica ion mic og aph o lase - emel ed coa ings, (a) coa ing emel ed a 650
W lase powe , (b) coa ing emel ed a 650 W lase powe –de ail, (c) coa ing emel ed a 1000 W
lase powe , (d) coa ing emel ed a 1000 W lase powe –de ail.
(a) (b)
Figu e 5.
Highe magni ica ion mic og aph o lase - emel ed coa ings, (
a
) coa ing emel ed a 650 W
lase powe , (
b
) coa ing emel ed a 650 W lase powe –de ail, (
c
) coa ing emel ed a 1000 W lase
powe , (d) coa ing emel ed a 1000 W lase powe –de ail.
Coa ings 2023,13, 1033 8 o 16
Coa ings 2023, 13, x FOR PEER REVIEW 8 o 17
sp ayed coa ing and he lase - emel ed laye (Figu e 6a,c). This was p obably he hea -
affec ed zone below he le el o he mel pools.
(a) (b)
(c) (d)
Figu e 5. Highe magni ica ion mic og aph o lase - emel ed coa ings, (a) coa ing emel ed a 650
W lase powe , (b) coa ing emel ed a 650 W lase powe –de ail, (c) coa ing emel ed a 1000 W
lase powe , (d) coa ing emel ed a 1000 W lase powe –de ail.
(a) (b)
Coa ings 2023, 13, x FOR PEER REVIEW 9 o 17
(c) (d)
Figu e 6. EBSD analysis o LT650W sample, (a) o e iew image o he lase - emel ed laye , ansi-
ion band, and non-affec ed HVOF coa ing, (b) de ail o lase - emel ed a ea, (c) de ail o (1) non-
affec ed as-sp ayed coa ing and (2) ansi ion band, (d) pole igu es o he emel ed a ea.
3.2. T ibological Beha iou
Figu e 7 summa izes he ic ion and wea esul s ob ained by he ball-on-pla e
me hod pe o med on AZ91 alloy, he as-sp ayed coa ing su ace, and lase - emel ed coa -
ings. I can be seen om Figu e 7a,b ha he lowes alue o ic ion coefficien (COF), 0.24
± 0.03, was measu ed o he uncoa ed AZ91 alloy. In he case o he coa ed alloy (as-
sp ayed coa ing), i was obse ed ha he COF was abou 0.45 a he beginning o he
es ing, bu as he sliding dis ance inc eased, he COF inc eased o app ox. 0.70. In he case
o he lase - emel ed coa ings a lase powe s o 650 and 1000 W, he COF alues we e
compa able—speci ically, 0.50 ± 0.05 and 0.48 ± 0.04, espec i ely. Figu e 7a shows ha
he COF can be conside ed cons an du ing he measu emen . The highe alues o he
COF o coa ings may be due o he highe p opo ion o ca bides in he coa ing and in
he lase - emel ed laye . These ca bides do no ha e good sliding p ope ies bu inc ease
wea esis ance [21,49]. In he case o he as-sp ayed coa ing, he g adual inc ease in he
ic ion coefficien can be caused by ab asi e and ibo-oxida i e wea , whe e debu ed
and oxidized pa icles and pa icles apped in he open po es o he coa ing and pi s can
inc ease he ic ion. The COF ends o inc ease due o he ex a ene gy in ol ed in d ag-
ging and pulling deb is ou o con ac be ween coun e -ball and wo n su ace; hus, he
wea ends o inc ease [50,51].
E en hough he lowes COF alue was ob ained o he uncoa ed AZ91 alloy, he
wea a e, pene a ion dep h, and weigh loss we e signi ican ly highe han o he coa ed
samples (Figu e 7c,d). The pene a ion dep h a e he wea es was app oxima ely 4–5
imes lowe o he coa ed samples han o he uncoa ed AZ91 alloy.
The weigh loss was also signi ican ly lowe o he coa ed samples. In he case o
AZ91 alloy, he weigh loss was de e mined o be 2.7 × 10−4 g, while in he case o he as-
sp ayed coa ing, he weigh loss was 1 × 10−4 g. In he case o lase - emel ed coa ings, he
weigh loss was e en lowe , a 3.3 × 10−5 g.
Figu e 6.
EBSD analysis o LT650W sample, (
a
) o e iew image o he lase - emel ed laye , ansi ion
band, and non-a ec ed HVOF coa ing, (
b
) de ail o lase - emel ed a ea, (
c
) de ail o (1) non-a ec ed
as-sp ayed coa ing and (2) ansi ion band, (d) pole igu es o he emel ed a ea.
As shown in Figu e 6, he as-sp ayed coa ing is p edominan ly non-c ys alline, as e y
ew di ac ions we e obse ed. The EBSD esul s (Figu e 6b) sugges ed ha he black a eas
may be amo phous o po es and spla bounda ies, while he non-mel ed pa icles and he
pa ially mel ed and plas ically de o med pa icles e ained hei c ys allini y. Addi ionally,
i may be e y ine g ains/a eas ha a e smalle han he EBSD cha ac e iza ion s ep
size [
48
]. The e was an app oxima ely 5
µ
m- hick ansi ion band be ween he as-sp ayed
coa ing and he lase - emel ed laye (Figu e 6a,c). This was p obably he hea -a ec ed zone
below he le el o he mel pools.
3.2. T ibological Beha iou
Figu e 7summa izes he ic ion and wea esul s ob ained by he ball-on-pla e me hod
pe o med on AZ91 alloy, he as-sp ayed coa ing su ace, and lase - emel ed coa ings. I can
be seen om Figu e 7a,b ha he lowes alue o ic ion coe icien (COF), 0.24
±
0.03, was
measu ed o he uncoa ed AZ91 alloy. In he case o he coa ed alloy (as-sp ayed coa ing), i
was obse ed ha he COF was abou 0.45 a he beginning o he es ing, bu as he sliding
dis ance inc eased, he COF inc eased o app ox. 0.70. In he case o he lase - emel ed
coa ings a lase powe s o 650 and 1000 W, he COF alues we e compa able—speci ically,
0.50
±
0.05 and 0.48
±
0.04, espec i ely. Figu e 7a shows ha he COF can be conside ed
cons an du ing he measu emen . The highe alues o he COF o coa ings may be due
o he highe p opo ion o ca bides in he coa ing and in he lase - emel ed laye . These
ca bides do no ha e good sliding p ope ies bu inc ease wea esis ance [
21
,
49
]. In he
case o he as-sp ayed coa ing, he g adual inc ease in he ic ion coe icien can be caused
by ab asi e and ibo-oxida i e wea , whe e debu ed and oxidized pa icles and pa icles
Coa ings 2023,13, 1033 9 o 16
apped in he open po es o he coa ing and pi s can inc ease he ic ion. The COF ends
o inc ease due o he ex a ene gy in ol ed in d agging and pulling deb is ou o con ac
be ween coun e -ball and wo n su ace; hus, he wea ends o inc ease [50,51].
Coa ings 2023, 13, x FOR PEER REVIEW 10 o 17
(a) (b)
(c) (d)
Figu e 7. Resul s o ibological es ing o indi idual samples: (a) eco d o he ic ion coefficien s
(COF), (b) COF alues, (c) pene a ion dep h alues, (d) weigh loss alues. In he case o Figu e (d),
he e o ba s a e no shown because he measu emen e o (weigh change) was close o ze o.
Wea acks and wea p o iles o he es ed samples a e shown in Figu e 8. The indi-
idual dimensions o he wea acks co ela e wi h he weigh loss esul s. As shown in
Figu e 8a, in he case o alloy AZ91, he pene a ion dep h o he wea ack a he lowes
poin was abou 30 µm. The wid h o he wea ack was app oxima ely 1200 µm a e he
wea es . The sp aying o he coa ing inc eased he wea esis ance o samples and hus
dec eased he pene a ion dep h. The pene a ion dep h was de e mined o be 5 µm in he
case o he as-sp ayed coa ing, and he wea ace wid h was de e mined o be 650 µm
(Figu e 8b). The emel ing o he he mally sp ayed (as-sp ayed) coa ing a a lase powe
o 650 o 1000 W led o a u he inc ease in wea esis ance. The pene a ion dep h a e
he wea es o he emel ed coa ings was de e mined o be app oxima ely 4 µm in bo h
cases, and he wid h o he wea acks was app oxima ely 430 µm (Figu e 8c,d).
(a)
(b)
Figu e 7.
Resul s o ibological es ing o indi idual samples: (
a
) eco d o he ic ion coe icien s
(COF), (
b
) COF alues, (
c
) pene a ion dep h alues, (
d
) weigh loss alues. In he case o Figu e (
d
),
he e o ba s a e no shown because he measu emen e o (weigh change) was close o ze o.
E en hough he lowes COF alue was ob ained o he uncoa ed AZ91 alloy, he wea
a e, pene a ion dep h, and weigh loss we e signi ican ly highe han o he coa ed sam-
ples (Figu e 7c,d). The pene a ion dep h a e he wea es was app oxima ely
4–5 imes
lowe o he coa ed samples han o he uncoa ed AZ91 alloy.
The weigh loss was also signi ican ly lowe o he coa ed samples. In he case o
AZ91 alloy, he weigh loss was de e mined o be 2.7
×
10
−4
g, while in he case o he
as-sp ayed coa ing, he weigh loss was 1
×
10
−4
g. In he case o lase - emel ed coa ings,
he weigh loss was e en lowe , a 3.3 ×10−5g.
Wea acks and wea p o iles o he es ed samples a e shown in Figu e 8. The
indi idual dimensions o he wea acks co ela e wi h he weigh loss esul s. As shown
in Figu e 8a, in he case o alloy AZ91, he pene a ion dep h o he wea ack a he lowes
poin was abou 30
µ
m. The wid h o he wea ack was app oxima ely 1200
µ
m a e he
wea es . The sp aying o he coa ing inc eased he wea esis ance o samples and hus
dec eased he pene a ion dep h. The pene a ion dep h was de e mined o be 5
µ
m in
he case o he as-sp ayed coa ing, and he wea ace wid h was de e mined o be 650
µ
m
(Figu e 8b). The emel ing o he he mally sp ayed (as-sp ayed) coa ing a a lase powe
o 650 o 1000 W led o a u he inc ease in wea esis ance. The pene a ion dep h a e
he wea es o he emel ed coa ings was de e mined o be app oxima ely 4
µ
m in bo h
cases, and he wid h o he wea acks was app oxima ely 430 µm (Figu e 8c,d).
Coa ings 2023,13, 1033 16 o 16
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