ORIGINAL RESEARCH ARTICLE
Lase -Assis ed Su ace Modi ica ion o TRIP S eels:
Chemical and Mic os uc u al E olu ion, Residual
S esses, and Mic omechanical P ope ies
G. RIU-PERDRIX, S. SLAWIK, O. GAVALDA-DIAZ, J.A. TRAVIESO-RODRIGUEZ,
G. FARGAS, ANTONIO MATEO, F. MU
¨CKLICH, and J.J. ROA
The use o new ligh weigh design s a egies is implemen ed in he au omo i e indus y, o
applica ions whe e high ic ion o ces a e p esen and lub ica ion sys ems need o be implemen ed.
Mic o- opog aphy modifica ion h ough lase ex u ing is an ad an ageous manu ac u ing
echnique ha is cu en ly being used by he indus y. Combining bo h ideas, his manusc ip
aims o analyze he effec o su ace modifica ion lase - ex u ing p ocess on a
TRans o ma ion-Induced Plas ici y s eel. Residual s esses, supe ficial chemis y, mic os uc u e,
and mechanical p ope ies a he submic ome ic leng h scale a e in es iga ed. Resul s show ha he
in ensi y and he numbe o pulses s ongly modi y he pa e n geome y. Also, he pa e n dis ance
affec s he esidual s ess s a e, changing om ensile o comp essi e s esses o dis ances highe
han 20 lm. Chemical and mic os uc u al changes a he icini y o he lase may be associa ed o
he as cooling o he sublima ed ma e ial a ound he pa e n induced du ing he lase -assis ed
su ace modifica ion he mal p ocess. Fu he mo e, he ha dness emains s able, and no changes a e
e iden in he bulk ma e ial. Howe e , a ha dness educ ion o a ound 95 pc in he aus eni ic alue is
e iden in he pile-up zone a ound he lase pa e n due o (1) he mic opo osi y and de ec s confined
inside he pile-up egion and (2) due o he esidual chemical composi ion c ea ed du ing he
solidifica ion p ocess, which is ich in i on, ch omium, nickel, and manganese and poo in oxygen.
h ps://doi.o g/10.1007/s11663-024-03330-9
The Au ho (s) 2024
I. INTRODUCTION
Gi en he ac ual egula ions de eloped o educe he
ca bon dioxide emission and he financial penal ies ha
b ing along, uel economy and he educ ion o he
emissions ha e become key ac o s o he au omo i e
indus y. Bo h ac o s a e clea ly ela ed o p oduce
ligh weigh ehicles.
[1]
Bu beside ligh weigh , good
o mabili y, high mechanical s eng h, and capaci y o
ene gy abso p ion a e he main equi emen s o he
au omo i e indus y, which also equi es applicabili y a
high p oduc ion a es and low cos .
In his sense, he me as able aus eni ic s ainless s eels,
and in pa icula TRans o ma ion-Induced Plas ici y
(TRIP) s eels, a e he pe ec op ion conce ning c ash
beha io p ope ies, due o hei high ene gy abso p ion
po en ial. These s eels p esen an aus eni ic ( ace-cen-
e ed cubic— cc) phase which is no he modynamically
s able a oom empe a u e. Then, when plas ically
de o med, aus eni e (c) expe iences ma ensi ic phase
ans o ma ion ha can p oduce wo diffe en ypes o
ma ensi e: ewhich has a hexagonal close packed (hcp)
s uc u e and a¢wi h a body-cen e ed cubic (bcc)
s uc u e. Typically, he phase ans o ma ion can be
defined h ough wo diffe en eac ions, di ec ly o
indi ec ly.
[2]
In he fi s case, cfia¢,
[3,4]
while o he
second case, whe e a¢is gene a ed passing h ough an
in e media e s a e, he ema ensi e, which ans o ms
almos immedia ely in a¢as ollows: cfiefia¢.
[5,6]
The
diffe ence in packing densi y be ween cand a¢p o ides a
olume expansion o ~3 pc ,
[7]
inducing an in e nal
comp essi e esidual s ess ha enhances he mechanical
p ope ies in e ms o ha dness and a igue beha io .
G. RIU-PERDRIX, G. FARGAS, A. MATEO, and J.J. ROA a e
wi h he Cen e o S uc u al In eg i y, Reliabili y and
Mic omechanics o Ma e ials (CIEFMA), Depa men o Ma e ials
Science and Enginee ing/Ba celona Resea ch Cen e in Mul iscale
Science and Enginee ing, Escola d’Enginye ia de Ba celona Es ,
Uni e si a Poli e
`cnica de Ca alunya, 08019 Ba celona, Spain.
Con ac e-mail: an onio.manuel.ma [email protected] S. SLAWIK and F.
MU
¨CKLICH a e wi h he Func ional Ma e ials, Depa men o
Ma e ials Science and Enginee ing, Saa land Uni e si y, 66123
Saa b uecken, Ge many. O. GAVALDA-DIAZ is wi h he
Depa men o Ma e ials, Cen e o Ad anced S uc u al Ce amics,
Impe ial College London, London SW7 2AZ, UK. J.A. TRAVIESO-
RODRIGUEZ is wi h he Mechanical Enginee ing Depa men ,
Escola d’Enginye ia de Ba celona Es , Uni e si a Poli e
`cnica de
Ca alunya, 08019 Ba celona, Spain.
Manusc ip submi ed Ma ch 9, 2022; accep ed Oc obe 5, 2024.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Unde se ice condi ions (e.g., a igue, wea , e c.), he
ailu e o hese s eels is usually ini ia ed a he su ace.
The e o e, su ace modifica ion has become a key ac o
o ake in o conside a ion o inc easing hei li e ime.
This can be done h ough su ace modifica ions such as
nano ex u ing, in o de o enhance he mechanical and
ibological esponse unde diffe en complex s ess
fields. In his ega d, se e al echniques (i.e., g inding,
sho peening, lase pa e ning, among o he s
[8–11]
)ha e
been used o mic os uc u ally change he supe ficial
p ope ies and, as a consequence, he esidual s ess
s a e.
[12,13]
Cu en ly, sho peening is he mos employed
echnique o enhance he a igue esis ance. The com-
p essi e esidual s esses induced by sho peening
inc ease he amoun o ma ensi ic phase a he su ace,
eaching alues up o 20 o 30 pc .
[14]
Despi e his
achie emen , his echnique has limi a ions, like inaccu-
acy o he ep oducibili y, induced de ec s (i.e., olds,
mic o-, and submic ome ic c acks, e c.), among o he s.
Fo o e coming hese p oblems, du ing he las decade,
he lase su ace ex u ing (LST) echnique has been
widely s udied o supe ficially induce mic o- ex u ing.
LST is conside ed a echnique ha p ecisely con ols he
ene gy o lase beams o c ea e pa e ns a diffe en
leng h scales on s eel su aces.
[15]
In pa icula , he
pa ame e s ha influence he final p ope ies include
su ace chemis y (e.g., chemical composi ion), opog-
aphy (e.g., oughness), su ace ene gy, cha ge, and
po en ial. I is wo h o men ion ha la ge amoun o
wo k on lase su ace ex u ing has been ca ied ou
mainly o modi y seals, pis on ings, and h us bea ings
in o de o enhance he ibological p ope ies.
[16–22]
Howe e , sca ce in o ma ion on his subjec is p esen in
he li e a u e ela ed o TRIP s eels. In his sense, du ing
he las yea s, Rezaya e al.
[15,23–27]
in es iga ed he
effec o lase su ace ex u ing on linea pa e ns
conduc ed on TRIP s eels. Changes in mic os uc u e,
mechanical p ope ies, g ain cha ac e is ics, and he
main mechanical p ope ies a he s a ic s a e ha e been
epo ed. These di e se s udies p esen in he li e a u e
con ibu e o he ad ancemen o p ecise º and eliable
su ace oughness measu emen s pa icula ly by lase
con ocal mic oscopy as well as o be e unde s and he
chemical, mic os uc u al, and mechanical supe ficial
effec induced by a nanosecond (ns-) lase on TRIP
s eels a he edges o he pa e ns. While some p elim-
ina y s udies ha e shown p omising esul s in selec ing
he employed ex u ing pa ame e s o con ol he
su ace oughness om nano- up o mic ome ic leng h
scale on linea pa e ns,
[28,29]
mo e esea ch is needed o
demons a e p ac ical applica ions o ns-lase su ace
ex u ing o diffe en pa e ning geome ies o eal-
wo ld indus ial applica ions on TRIP s eels.
Wi hin his con ex , he main goal behind his
esea ch is o unde s and he in e ac ion lase /ma e-
ial—in e ms o esidual s esses, chemical composi ion,
mic os uc u e, and mechanical p ope ies—on supe fi-
cially modified TRIP s eels by using lase -assis ed
modifica ion. In o de o achie e his aim, i is necessa y
o op imize he lase wo king pa ame e s: in ensi y,
equency, numbe o pulses, and dis ance be ween
pa e ns. A e wa d, he e e ence and he supe ficially
modified samples will be in es iga ed om a chemically,
mic os uc u ally, and mechanically poin - iew o ge a
deepe unde s anding o he lase - ex u ing in e ac ion
on TRIP s eels.
II. MATERIALS AND METHODS
A. Ma e ial
The ma e ial was a comme cial AISI 301LN s ainless
s eel (co esponding o Eu opean s anda d EN 1.4318)
p o ided by Ou okumpu (Finland). I was supplied as
1.5-mm- hick shee s wi h a duplex mic os uc u e
(a ound 92 pc o he c-phase, while he es co esponds
o a¢-phase, in ag eemen wi h he da a p esen ed in
Re e ence 22). I s chemical composi ion is summa ized
in Table I.
P io o su ace modifica ion, he specimens we e
sequen ially polished un il a mi o -like su ace, by
using he ollowing diamond suspensions: 30, 6, and
3lm. Finally, hey we e chemo-mechanically polished
by using a neu al suspension o alumina (20 o 45 nm o
a e age pa icle size). Subsequen ly, in o de o emo e
he wo k ha dening laye , as well as he a¢-phase induced
du ing he polishing p ocess, samples we e elec o-chem-
ically polished a oom empe a u e by using a Buehle
PoliMa 2 (Mik on) a a cons an ol age o a ound
11.6 V o 15 seconds.
B. Su ace Modifica ion
Su ace modifica ion was ca ied ou using a nanosec-
ond pulsed lase (Spec a Physics, One Explo e 346-120)
wi h Nd:YLF solid-s a e medium and 346 nm o
wa eleng h. The wo king condi ions we e op imized
by using a Design o Expe imen s (DoE), aking in o
conside a ion he ollowing pa ame e s: equency (Hz),
pulse in ensi y (A), numbe o pulses, and spacing
be ween pa e ns. Mo e in o ma ion ela ed wi h he
DoE is a ailable in Re e ence 30.
C. Mic os uc u al Cha ac e iza ion
The lase pa e n gene a ed was obse ed wi h a
con ocal lase scanning mic oscope (LSCM, LEXT
OL31000) and in mo e de ail wi h a Field Emission
Scanning Elec on Mic oscopy (FESEM, Ca l Zeiss
Neon 40), in o de o cha ac e ize he induced opog-
aphy. The supe ficial esidual s esses ( ) induced
du ing he LST p ocess was measu ed by using he
x- ay diff ac ion (XRD) echnique. The equipmen used
was PANaly ical Empy ean, which has been ope a ed
wi h C ube (40 kV and 40 mA). A polycapilla y op ics
(x- ay lens) wi h c oss ape u e 1 91 mm and V-fil e
METALLURGICAL AND MATERIALS TRANSACTIONS B
(p ima y side) and a pa allel pla e collima o wi h Xe
p opo ional de ec o (seconda y side) we e employed.
The 220 peak ound a 2h=126 deg was used o he
s ess calcula ions, a 8 Chi angles om 0 o + 70 deg.
S ess analysis was pe o med by using he PANaly ical
X’Pe S ess plus so wa e using he sin
2
wand by using
X- ay elas ic cons an s o S1=1.50 TPa
1
and 1/2
S2 = 6.50 TPa
1
.
Damage induced as well as he mic os uc u al
changes due o he lase pa e ning we e in es iga ed
by ocused ion beam (FIB) milling o c oss sec ion and
scanning elec on mic oscopy (SEM) inspec ion. I was
done by using a dual-beam wo ks a ion, Zeiss Neon 40
wi h a Ga+ ion sou ce a a ol age o 30 kV. The final
polishing p ocess o he c oss sec ion was pe o med a a
cu en o 500 pA and 30 kV o accele a ion ol age.
D. Chemical Cha ac e iza ion
Elec on p obe x- ay mic oanalysis (EPMA), using
wa eleng h-dispe si e spec ome y (WDS), was con-
duc ed in a small a ea, whe e se e al lase pa e ns we e
included using a JEOL JXA-8230 mic op obe. The
x- ay maps we e eco ded in high- esolu ion mode,
using a channel wid h o 1 eV. Elec on cu en s we e
selec ed o ensu e ha coun ing a es we e less han 10
4
coun s/s. Mo e in o ma ion abou he p o ocol ollowed
o conduc his analysis can be ound elsewhe e.
[31,32]
X- ay pho oelec on spec oscopy (XPS) expe imen s
we e pe o med in wo diffe en samples: he e e ence
and he supe ficially modified one o compa ison
pu poses. PHI 5500 Mul i echnique Sys em ( om Phys-
ical Elec onics) wi h a monoch oma ic X- ay sou ce
(AlKaline o 1486.6 eV ene gy and 350 W) was placed
pe pendicula o he analyze axis and calib a ed using
he 3d5/2 line o Ag wi h a ull wid h a hal maximum
(FWHM) o 0.8 eV. The analyzed a ea was a ci cle o
0.8 mm in diame e , and he selec ed esolu ion o he
spec a was 187.5 eV o Pass Ene gy and 0.1 eV/s ep o
he spec a o he diffe en elemen s. All measu emen s
we e made in an ul a-high acuum (UHV) chambe a a
p essu e be ween 5 910
9
and 5 910
8
To .
To s udy he mo phology and elemen dis ibu ion
a ound abla ed pa e ns, elec on anspa en samples
o ansmission elec on mic oscopy (TEM) we e p e-
pa ed using a FIB li -ou echnique (Helios NanoLab
SEM, FEI). These samples whe e cha ac e ized a 200
kV using TEM b igh -field (BF) imaging, scanning
ansmission elec on mic oscopy (STEM), and
ene gy-dispe si e x- ay spec oscopy (EDS) wi h a
TEM/STEM a 200 kV (JEM-2100F, Jeol) equipped
wi h an EDS de ec o (X-Max de ec o STEM-EDS,
Ox o d Ins umen s).
E. Mechanical Cha ac e iza ion a he Submic ome ic
Leng h Scale
Mechanical p ope ies a he mic ome ic leng h scale,
mainly ha dness (H) and elas ic modulus (E), we e
de e mined by means o nanoinden a ion o bo h he
non-modified ( e e ence ma e ial) and he modified
TRIP s eel. These mic omechanical es s we e pe -
o med wi h a Nanoinden e XP (MTS) uni , equipped
wi h a Be ko ich diamond ip inden e and a con inuous
s iffness measu emen mode (CSM), allowing a dynamic
de e mina ion o he mechanical p ope ies du ing he
inden a ion p ocess by he Oli e and Pha
me hod
[33,34]
and subsequen ly applying he Ulm e al.
me hod
[35–38]
(mo e in o ma ion abou his me hodol-
ogy is a ailable in Appendix A1). A o al o 400 imp in s
(20 by 20) we e pe o med unde displacemen con ol
mode a 200 nm o maximum displacemen in o su ace.
The dis ance be ween imp in s was kep cons an a
10 lm, in o de o a oid any o e lapping effec . S ain
a e was held cons an a 0.05 s
1
and he inden e
shape was ca e ully calib a ed o ue inden a ion dep h
as small as 25 nm by inden ing used silica s anda d o
known Young’s modulus o 72 GPa.
[33]
III. RESULTS AND DISCUSSION
A. DoE Analysis—Op imiza ion o he Nanosecond
Pulsed Lase
Design o Expe imen s (DoE) is defined as a planned
app oach o de e mining cause and effec ela ion-
ships.
[39]
This me hod consis s o (1) educing he
numbe o needed expe imen s, (2) e i ying all ac o s
ha affec an expe imen , and (3) defining a s a egy o
ob ain eliable solu ions a e a se o expe imen s.
This me hodology has been used, ollowing a ull
ac o ial app oach, o op imize he lase pa ame e s
looking o he lowes su ace oughness as well as he
highes ensile esidual s esses. A schema ic ep esen-
a ion o he diffe en s eps aken in o conside a ion is
summa ized in Figu e 1.
The c i ical pa ame e s o ake in o conside a ion o
his analysis a e as ollows: lase beam in ensi y, e-
quency, and numbe o pulses. A e ha , he h ee
diffe en oughness pa ame e s (Ø
,Ø
wp
, and h, defined
as he o al diame e which includes he pa e n as well
as he abla ion pile-up, he pa e ning inne diame e
wi hou aking in o accoun he abla ion pile-up, and
he maximum dep h eached du ing he lase pa e ning
p ocess, espec i ely) we e measu ed o each condi ion
by LSCM echnique, as shown in Figu es 2(a) and (b).
As i is e iden , hdoes no depend o he diffe en lase
pa ame e s in es iga ed he e. On one hand, bo h Ø
and
Ø
wp
linea ly inc ease wi h he lase in ensi y and he
numbe o pulses. On he o he hand, he equency is
no a key ac o as he diffe en mo phological pa am-
e e s in es iga ed emain cons an . Acco ding o he
diffe en measu emen s by LSCM conduc ed on he
diffe en in es iga ed pa e ns, he op imal pa ame e s
a e as ollows: equency o 1000 Hz (being his he
minimum equency employed in his s udy), a lase
Table I. Chemical Composi ion o AISI 301LN
Elemen C Ni Mn Si N Mo C Fe
W . Pc 17.6 6.5 1.13 0.42 0.17 0.04 0.02 bal.
METALLURGICAL AND MATERIALS TRANSACTIONS B
in ensi y o 4 A, and a cons an numbe o pulses o 20
spo s a he same egion (as shown in Figu e 2(b), he
numbe o pulses does no modi y he h). In his
pa icula s udy, 20 was chosen because i was he
minimum numbe o pulses, which was able o p oduce
pe ec pa e ns wi h he minimum pile-up a ound he
desi ed pa e n.
Once he lase pa ame e s ela ed o beam in ensi y,
equency, and numbe o pulses we e op imized, he
dis ance be ween he lase pa e ns was also e alua ed.
In o de o op imize his dis ance, ou diffe en (x,y)
alues we e in es iga ed (20/20, 50/50, 100/100, and 150/
150 lm) (see Figu e 2(c)) in o de o see he effec o he
lase spo on he esidual s esses, and he e o e be able
o choose he dis ance which p oduces less comp essi e
esidual s esses. In his sense, he esidual s esses we e
measu ed by means o XRD by using he sin
2
Wme hod
in he
11
and
22
di ec ions (see Figu e 2(c)) o hose
ou dis ances be ween spo s. The esul ing da a a e
summa ized in Table II. Finally, by using hese op i-
mized lase pa ame e s, he desi ed pa e ns in es iga ed
p esen he ollowing dimensions: abou 26.02 ±
0.98 lm in diame e wi h pile-up (Ø
as depic ed in
Figu e 2) and abou 32.2 ±4.8 lm in dep h.
Fig. 1—Schema ic diag am o he pa ame e op imiza ion s eps o p oduce he final lase - ex u ed specimens.
Fig. 2—(a) Schema ic ep esen a ion o he mo phological pa ame e s employed o op imize he main lase pa ame e s h ough DoE analysis. (b)
Va ia ion o he dep h and/o wid h as a unc ion o he lase in ensi y, equency, and numbe o pulses and (c) op ical image showing he
diffe en lase pa e ns using he op imized lase condi ions a diffe en dis ances (20, 50, 100, and 150 lm). The
11
(longi udinal) and
22
( ans e sal) o e lapped o he op ical image deno e he di ec ion measu emen o he esidual s esses by using he sin
2
Wme hod.
METALLURGICAL AND MATERIALS TRANSACTIONS B
I is well known ha a he mal p ocess, such as lase ,
will induce ensile esidual s esses, while a mechanical
p ocess (i.e., sho peening, g inding, e c.) will induce
comp essi e esidual s esses, as ound in Re e ence 40.
In iew o he esul s ob ained in e ms o esidual
s esses in bo h di ec ions (
11
and
22
) as a unc ion o
he dis ance be ween each pa e n, ha dis ance was
chosen o be 20 lm due o wo diffe en easons: (1) o
smalle dis ances be ween pa e ns he amoun o
abla ed ma e ial a ound he pa e n is highe and he
in e ac ion lase /ma e ial is mo e e iden , and (2) he
esidual s esses a e ensile and sca ce in o ma ion is
a ailable on TRIP s eels wi h his kind o s esses. Bo h
easons will lead o be e unde s anding o he
lase /ma e ial in e ac ion on TRIP s eels. Wi h all his
in o ma ion, a homogeneous lase pa e ning was con-
duc ed a 1000 Hz, 4 A, 20 pulses, and he dis ance
be ween pa e ns was kep cons an and equal o 20 lm
( om now labeled as SM 20).
B. Mic os uc u al Cha ac e iza ion
The su ace modifica ion p ocess induces chemical,
mic os uc u al, and mechanical changes. In his ega d,
a he e ogeneous laye is c ea ed du ing he lase
abla ion pa e ning p ocess, as depic ed in s aw ones
in he LSCM mic og aph (Figu e 3(a)). When he
dis ance be ween he diffe en spo s is small, his effec
p o ides mo e he mal impac and, as a consequence, a
change in physical/chemical and mechanical p ope ies
o he su ace. Also, he oughness is inc eased.
Figu e 3(b) shows he SEM gene al mic og aph o he
lase - ex u ed su ace wi h a cons an dis ance o
~20 lm. Fu he mo e, as i is e iden in Figu e 3(c),
he su ace seems o be pa ially mel ed. The affec ed
mol en ma e ial (spa e ) has been ejec ed om he lase
pa e n due o he high ene gy and long pulse du a ion
and appea s deposi ed a he icini y o he spo o ming
a o pile-up, as depic ed in Figu e 3(d). This abla ed
ma e ial is he e ogeneously e-deposi ed pulse by pulse
along he lase - ex u ing p ocess. This p ocess can be
assimila ed o a local he mal shock, including a
con inuous p ocess o mel ing and solidifica ion. Also,
be ween each abla ed laye a he mal-affec ed zone
co-exis s, gene a ing some de ec s (i.e., c acks, olds,
chemical and mic os uc u al he e ogenei ies, e c.) along
he pile-up (see whi e a ow in Figu e 3(e)).
C. Chemical Cha ac e iza ion
Aiming o ex ac mo e de ailed in o ma ion a ound
he lase pa e n and in be ween, he su ace chemis y
o bo h in es iga ed samples was obse ed by punc ual
analysis ho ough EPMA echnique. Fi e diffe en
poin s, he e ogeneously dis ibu ed, we e measu ed o
a omically (a . pc ) quan i y he main cons i u i e
elemen s. The esul s a e summa ized in Table III.In
addi ion, composi ional maps o a small a ea o he
TRIP lase - ex u ed su ace we e ob ained (Figu e 4).
Th ee diffe en zones wi h a he e ogeneous chemical
composi ion dis ibu ion could be dis inguished (see
ma ks in Figu e 4labeled as 1, 2, and 3, co esponding
o he diffe en egions o he base ma e ial, deposi ed
laye a e he lase -pa e ning p ocess, and he pile-up
zone, espec i ely) om he diffe en composi ion maps.
Regions 1 and 3 p esen ed simila chemical composi ion
o he main cons i u i e alloy elemen s, while in egion 2
he a . pc con en o Fe, C , and Ni was lowe han in
he o he in es iga ed egions. On he o he hand, he O
chemical composi ion map (Figu e 4) in be ween he
diffe en pa e n’s p esen oxygen he e ogeneously dis-
ibu ion, highligh s he possibili y o gene a e a hin
oxide laye . On he o he hand, a ound he lase pa e n
(pile-up egion), lowe con en o oxygen is p esen ,
highligh ing he possibili y o c ea e an in e me allic
ma e ial due o he as - he mal cooling p ocess induc-
ing jus a e he abla ion p ocess gene a ed by he
nanosecond lase . This ac ema ks ha he su ace
laye gene a ed in he egion be ween he diffe en
lase - ex u ing pa e s ( egion 1 and 2 in Figu e 4) was
an oxide laye . The chemical analysis p esen ed in
Figu e 4and summa ized in Table III does no p esen
significan diffe ences be ween he e e ence and he
su ace-modified specimens. This ac mani es s ha he
induced laye is so hin ha his echnique is no
sui able o p ecisely de e mine hei chemical composi-
ion. Thus, o he hin laye gene a ed du ing he
lase - ex u ing p ocess, he da a ob ained by means o
his echnique only could p o ide a quali a i ely s udy.
This may be a ibu ed o he ac ha elec on/sample
in e ac ion is oo deep and mainly confined in he bulk
ma e ial o he egion o s udy, being impossible o
accu a ely de e mine he chemical composi ion o he
supe ficial laye induced du ing he lase - ex u ing
p ocess and co ec ly iden i y and quan i y he chemical
composi ion o he su ace laye gene a ed du ing he
local he mal abla ion p ocess induced du ing he
lase - ex u ing p ocess.
To ge a deepe knowledge ela ed o he chemical
composi ion o he hin laye induced du ing he
lase - ex u ing p ocess, an analysis a he su ace le el
(fi s nm) by means o XPS echnique was done.
Figu es 5(a) and 5(b) exhibi gene al XPS spec a o
he e e ence and lase - ex u ed specimens, espec i ely.
As can be seen o he lase - ex u ed specimen (Fig-
u e 5(b)), he XPS spec um highligh s he p esence o
Zn (no p esen in he e e ence specimen—Figu e 5(a))
as well as he inc ease o he Ni con en o he
lase - ex u ed specimen as summa ized in Table IV.
Compa ing hese da a wi h hose de e mined by
Table II. Summa y o he Residual S esses De e mined in
11
and
22
Di ec ions o he Diffe en Lase Dis ances
In es iga ed (20, 50, 100, and 150 lm)
Dis ance (lm)
11
(MPa)
22
(MPa)
Re e ence 15.7 ±18.9 24.8 ±15.6
20 45.5 ±15.8 67.4 ±12.1
50 71.5 ±5.5 20.0 ±16.1
100 59.7 ±18.4 57.1 ±15.8
150 177.5 ±15.7 113.5 ±19.4
The lase beam in ensi y, equency, and numbe o pulses we e
held cons an and equals o 4 A, 1000 Hz, and 20 pulses, espec i ely.
METALLURGICAL AND MATERIALS TRANSACTIONS B
SEM-EDS and epo ed o he e e ence ma e ial in
Table I, Zn does no appea in he chemical composi ion
o he comme cial TRIP s eel, so i is likely o be below
he de ec ion limi , in he o m o aces in he e e ence,
o he SEM-EDS echnique. The p esence o Zn in he
lase - ex u ed specimen can be due because pe haps
lase abla ion ola ilizes and e-deposi s his elemen on
he su ace, gene a ing a new in e me allic-based Zn
compound wi h he o he elemen s.
Figu es 5(c) h ough (h) summa ize he XPS spec a
o he induced laye o each majo i y elemen o he
e e ence ( o compa ison pu poses) and lase - ex u ed
(induced du ing he as - he mal cooling p ocess) spec-
imens, le and igh spec a, espec i ely. The e e ence
XPS spec a o he Ni elemen a e e y noisy (see
Figu e 5(h)), highligh ing ha he con en p esen on he
e e ence sample is a he de ec ion limi sensi i i y o
he XPS equipmen . In his sense, i is no possible o
decon olu e his peak and be able o quan i y he
con en o Ni p esen on he e e ence sample.
Fu he mo e, he Si-spec a o he e e ence and
lase - ex u ed specimen p esen a diffe en c ys allo-
g aphic s a e (see Figu e 5( )), which p esen ed a double
peak dis ibu ion o he lase - ex u ed specimen ( igh )
and a monomodal peak dis ibu ion o he e e ence
sample (le ). This phenomenon may be ela ed o he
ac ha silica (SiO
2
) p esen s an allo opic phase
ans o ma ion a high empe a u e (being he mos
common phase; qua z, c is obali e and idymi e
[41]
)
and each one o hem p esen s a low and high a omic
o de phase (a-and b-, espec i ely
[1]
). So, he peaks
p esen ed in he XPS spec a may be ela ed o a- and
b-Si. Fu he mo e, XPS analysis ga e quali a i e in o -
ma ion on he chemical composi ion o he hin laye
gene a ed du ing lase - ex u ing p ocess.
In an a emp o ge mo e de ail knowledge o he
abla ion pile-up, as well as on he laye induced du ing
he lase -pa e ning p ocess, and on he bimodal SiO
2
peak dis ibu ion, a TEM lamella was ex ac ed by FIB
om he egion o in e es . I was di ec ly ex ac ed
om he whi e dash line p esen ed in Figu e 6(a).
A TEM obse a ion o he pile-up abla ed zone is
p esen ed in Figu e 6(b). The TEM analysis in Fig-
u e 6(c) shows he p esence o some c ys alline and
amo phous egions. Fu he mo e, his TEM mic o-
g aph displayed a complex mic os uc u e, like mic o-
g ains, po es, and holes among o he s. The de ec s
obse ed hough TEM inspec ion and confined in he
abla ion pile-up egion ag ee wi h hose epo ed in
Re e ence 26. This phenomenon highligh s ha he
solidifica ion p ocess p esen s wo diffe en egions: one
phase o low and o he o high a omic o de , in
ag eemen wi h he da a ob ained by XPS and p esen ed
in Figu e 5( ) ( igh side). The EDS maps o he TEM
mic og aph p esen ed in Figu e 6(c) show a homoge-
neous dis ibu ion o he main elemen s wi hin he TRIP
s eel. F om his TEM analysis, i is concluded ha he
abla ed and also he laye induced du ing he lase - ex-
u ing p ocess p esen a homogeneous chemical compo-
si ion. In his sense, u he chemical assays by using
Fig. 3—Mic os uc u al analysis o he TRIP lase su ace specimen. (a) LSCM mic og aph showing he diffe en he e ogenei ies induced du ing
he abla ion p ocess; (b) SEM mic og aphs showing he homogeneous a ay o pa e ns; (c) SEM magnifica ion mic og aph o a pa e n showing
he pile-up as well as he edeposi ion effec induced du ing he abla ion p ocess a he icini y o he pa e n; (d) il ed-SEM mic og aph in
o de o highligh he pile-up effec induced du ing he abla ion p ocess; and (e) SEM mic og aph showing he de ec s p esen in he pile-up
egion.
METALLURGICAL AND MATERIALS TRANSACTIONS B
a omis ic leng h scale echniques, like a om p obe
omog aphy may be done in o de o quan i y and
de e mine he hickness o his in e me allic laye .
D. Mechanical Cha ac e iza ion
A emp ing o obse e he ene gy/ma e ial in e ac ion
in e ms o mechanical p ope ies (mainly ha dness, H),
nanoinden a ion echnique was used o e alua e he
ha dness o he e e ence and lase - ex u ed specimens
and, in pa icula , o de e mine he in insic ha dness o
he s aw laye om Figu e 3(a).
In o de o measu e he mechanical p ope ies o he
su ace and be able o co ela e he mic os uc u e and
he mechanical p ope ies, p io and a e he lase - ex-
u ing p ocess, o each cons i u i e phase (c,a¢as well
as he c/a¢-in e phase), 400 imp in s we e conduc ed a 2
mN o maximum applied load. P io using he me hod-
ology explained in Appendix A1 i is necessa y o
de e mine he igh bin size. This pa ame e leads o
quali a i ely dis inguish how many phases a e p esen in
he in es iga ed ma e ial, as shown in Figu e 7(a). Fo a
cons an bin size o a ound 1 GPa, only one peak is
clea ly isible, while h ee diffe en peaks a e disce nible
Table III. Chemical Analysis (W Pc ) by EPMA Tes o Two Diffe en Samples
Sample Fe C Ni Mn O
Re e ence 73.72 ±0.28 17.82 ±0.12 6.54 ±0.11 1.20 ±0.02 0.09 ±0.01
SM 20 73.73 ±0.14 17.82 ±0.06 6.38 ±0.08 1.17 ±0.01 0.08 ±0.01
Fig. 4—EPMA analysis pe o med on a TRIP lase - ex u ed specimen. (a) Quali y SEM mic og aph o he analyzed egion, (b) i on—Fe, (c)
ch omium—C , (d) nickel—Ni, (e) manganese—Mn, and ( ) oxygen—O.
METALLURGICAL AND MATERIALS TRANSACTIONS B
educing his pa ame e up o 0.25 GPa. Figu e 7(b)
exhibi s he ha dness his og am o e lapped o he
Gaussian simula ion cu es o each cons i u i e phase.
Th ee mean peaks we e obse ed o he TRIP s eel. The
highes and he lowes alue peaks, cen e ed a 7.67 ±
0.75 and 5.74 ±0.74 GPa we e a ibu ed o he a¢and c
phases, espec i ely, while he in e media e peak cen-
e ed a 6.27 ±0.87 GPa co esponded o he c/
a¢-in e phase.
The ha dness o he laye gene a ed du ing he
ex u ing p ocess was de e mined ollowing he same
p o ocol me hodology p esen ed in Appendix A1 and
also explained in Figu e 7 o he e e ence sample. In
his sense, om he da a ob ained h ough he s a is ical
me hod, he alue o in insic ha dness o he hin laye
induced du ing he lase - ex u ing p ocess was
decon olu ed by implemen ing es ablished hin film
models. The use o hin film models is expec ed o yield
easonable alues o ha dness and he la e al s iffness is
conside ed low in compa ison o he no mal s iffness,
due o he la ge opening angle o he Be ko ich inden e
ip. In his s udy, he models o Ko sunsky e al.
[42]
and
Puchi-Cab e a e al.
[43]
we e used o ex ac he in insic
ha dness o he base Zn in e ace. They a e desc ibed
by Eqs. [1] and [2], espec i ely, as ollows:
HC¼HSþH Hs
1þkb2½1
whe e H
C
(lase - ex u ing laye + TRIP bulk ma e-
ial), H
(lase - ex u ing laye ), and H
S
(TRIP bulk
ma e ial) a e he composi e, film, and subs a e
x 104
5
10
15
20
25
30
35
40
45
50
CPS
900 600 300 0
Binding Ene gy (eV)
(Si)
(N)
(O)
(C)
(C )
(Mn)
(Fe)
(Ni)
(Zn)
(C)
(N)
(O)
(Si)
(C )
(Mn)
(Fe)
(Ni)
Gene al spec a Oxygen I on
(a)
(b) (c) (d) (e)
Ch omium
Silicon Ni ogen Nickel
(g)( ) (h)
Fig. 5—XPS spec a. (a) Re e ence sample, (b) lase - ex u ed specimen wi h a cons an pa e ning dis ance o 20 lm, (c) O-spec a, (d)
Fe-spec a, (e) C -spec a, ( ) Si-spec a, (g) N-spec a, and (h) Ni-spec a. The le and igh spec a o (c) h ough (h) co espond o he XPS
spec a o he e e ence and lase - ex u ed specimen.
METALLURGICAL AND MATERIALS TRANSACTIONS B
ha dness, espec i ely, while bis he ela i e inden a-
ion dep h and kis a cons an ela ed o he film hick-
ness.
HC¼HSþH HS
ðÞeðkbnÞ;½2
whe e kand n ep esen ma e ial pa ame e s ha cha -
ac e ize he change in ha dness as he inden e passes
om he lase - ex u ed film o he subs a e. As a
esul , an in insic ha dness o he lase - ex u ed coa -
ing was calcula ed and summa ized in Table V. The
lowe alues ob ained, compa ed o hose o hose o
he e e ence sample, showed a so ening in e ms o
ha dness when i is measu ed in he abla ion pile-up.
This ha dness educ ion may be ela ed o wo diffe -
en effec s ha ake place a he same ime: (1) om a
chemical poin o iew, he abla ion pile-up is a egion
ich o in e me allic elemen s and (2) om a
mic os uc u al poin o iew, he p esence o submi-
c ome ic po osi y as p esen ed in he TEM mic o-
g aph (Figu e 6(b)) and also epo ed in Re e ence 26
p oduces a dissipa ion o he plas ic s ess field
induced du ing he inden a ion p ocess and as a di ec
consequence a educ ion o hei ha dness. This ac
e eals ha he supe ficial chemical composi ion o he
abla ion pile-up has changed and does no co espond
o he gene a ion o an oxide. In his sense, hese find-
ings fi wi h he da a p esen ed in Sec ion III–C.
IV. CONCLUSIONS
The esul s shown in his con ibu ion ha e demon-
s a ed ha he lase -assis ed su ace modifica ion o
TRIP s eels supe ficially changes he mic os uc u e, he
chemical composi ion o he abla ed ma e ial obse ed
a ound he pa e ns in o ms o pile-up, and he
mechanical p ope ies a he su ace le el. The ollowing
conclusions can be d awn:
1. The DoE analysis highligh s ha he lase in ensi y
and he numbe o pulses change he final shape o
he pa e n, in e ms o diame e and dep h. Fu -
Table IV. Chemical Analysis (A . Pc ) De e mined by XPS Tes o he Re e ence and Lase -Tex u ed Specimens
Sample O Fe C Si N Ni
Re e ence E ching 46.254 6.339 3.387 2.193 0.911 DL
SM 20 E ching 47.553 9.287 3.278 2.628 2.096 0.318
P io he chemical composi ion analysis, he su ace o bo h analyzed specimens was e ched wi h a gon in o de o educe he con amina ion and
be able o inc ease he me allic peaks in ensi y. DL means de ec ion limi —i means he spec a a e noisy and canno be decon olu ed o co ec ly
de e mine he Ni con en p esen on he e e ence sample.
Fig. 6—(a) SEM mic og aph o he egion o s udy. The whi e dash line shows he egion, whe e TEM lamellae was ex ac ed, (b) TEM
mic og aph in b igh -field (BF) mode showing he mic os uc u e in he pile-up abla ed zone, and (c) EELS chemical composi ion maps o he
main cons i u i e elemen s p esen in TRIP s eels.
METALLURGICAL AND MATERIALS TRANSACTIONS B
