Phase dependence o he he mal memo y e ec in polyc ys alline ibbon
and bulk Ni
55
Fe
19
Ga
26
Heusle alloys
A. Vidal-C espo
a
, A.F. Manch´
on-Go d´
on
b,**
, J.M. Ma ín-Olalla
a
, F.J. Rome o
a
,
J.J. Ipus
a
, M.C. Galla do
a
, J.S. Bl´
azquez
a,*
, C.F. Conde
a
a
Dp o. Física de la Ma e ia Condensada, ICMSE-CSIC, Uni e sidad de Se illa, P.O. Box 1065, 41080, Se illa, Spain
b
Ins i u o de Ciencia de Ma e iales de Se illa, ICMSE CSIC-Uni e sidad de Se illa, C. Am´
e ico Vespucio 49, Se illa, 41092, Spain
ARTICLE INFO
Keywo ds:
Ma ensi ic ans o ma ion
The mal memo y e ec
Shape memo y alloys
Ni-Fe-Ga Heusle alloys
Ul aslow calo ime y
ABSTRACT
The he mal memo y e ec , TME, has been s udied in Ni
55
Fe
19
Ga
26
shape memo y alloys, ab ica ed as ibbons
ia mel -spinning and as pelle s ia a c-mel ing, o e alua e i s dependence on he ma ensi ic s uc u e and he
mac os uc u e o he samples. When he e e se ma ensi ic ans o ma ion is in e up ed, a kine ic delay in he
subsequen comple e ans o ma ion is only e iden in he ibbon samples, whe e he 14M modula ed s uc u e is
he dominan phase. In con as , deg ada ion o he modula ed s uc u e o he p esence o he γ phase signi -
ican ly educes he obse ed TME. In such cases, he magni ude o he TME app oaches he de ec ion limi s o
comme cial calo ime e s, and only high- esolu ion calo ime e a e y low hea ing a e (40 mK h
−1
) can show
he e ec . Following he kine ic a es and subsequen cooling, he e e se ma ensi ic ans o ma ion was
comple ed a se e al hea ing a es o con i m he a he mal na u e o he phenomenon.
1. In oduc ion
The p ope ies o shape memo y alloys, SMAs, ha e a ac ed
conside able in e es making hem p omising o inno a i e enginee ing
and mechanical applica ions, p ima ily due o hei unique shape
memo y e ec , SME, and supe elas ici y, SE [1]. These dis inc cha ac-
e is ics a ise om he ma ensi ic ans o ma ion, MT, ha hese ma-
e ials exhibi : a solid-s a e, i s -o de phase ansi ion. MT in ol es he
coo dina ed mo emen o a conside able numbe o a oms, achie ing a
g ow h eloci y simila o sound wa es [2]. On cooling, a
high- empe a u e aus eni e phase wi h high symme y ans o ms in o a
low- empe a u e ma ensi e phase wi h educed symme y. The hea ing
ans o ma ion is hus called e e se MT. In gene al, he
low- empe a u e ma ensi e phase exhibi s a mul idomain mic os uc-
u e, esul ing om he dis o ion o he c ys al la ice. This s uc u al
dis o ion accoun s o many o he dis inc i e cha ac e is ics o hese
ans o ma ions.
In addi ion o showcasing SME o SE, SMAs ha e demons a ed hei
capaci y o ecall no only speci ic shapes bu also he empe a u es a
which he e e se MT was in en ionally hal ed [3,4]. Unlike he
well-unde s ood SME, he called he mal memo y e ec , TME, is less
clea , and di e en scena ios ha e been p oposed encompassing he
edis ibu ion o accumula ed s ess [5,6] o he impac o geome ical
cons ic ions [7]. In his phenomenon, when an in en ional a es
occu ed a a s op empe a u e Ts op be ween aus eni e s a , As, and
aus eni e inish empe a u es, A , i.e. Ts op ∈(As,A ), he ollowing
comple e e e se MT shows a kine ic pause close o Ts op. I has been
p e iously labeled as he mal a es memo y e ec [8], o as a e e sible
s ep-wise ans o ma ion om ma ensi e o aus eni e [9].
In ecen yea s, a ious heo e ical app oaches ha e been p oposed
o explain his phenomenon, wi h pa icula emphasis on he ela ion-
ship be ween TME and ac o s such as disloca ions [10], in e ace in-
e ac ions [11], elas ic de o ma ion o he ma ensi e pla es [3,8], and
he con inuous dis ibu ion o s o ed elas ic ene gy, which elaxes du -
ing pa ial hea ing cycles [12]. Howe e , he e is no consensus
ega ding he o igin o hese e ec s, and hei physical in e p e a ion
emains con o e sial. This unce ain y a ises p ima ily because local
s ess e olu ion canno be easily measu ed, making i di icul o assess
i s impac on ans o ma ion beha io . This is a signi ican echnological
challenge, especially since mos eal SMA ac ua o s ypically expe ience
only pa ial ans o ma ion cycles unde wo king condi ions [13]. Mo e
ecen ly, in-si u neu on di ac ion expe imen s ha e p o ided a
* Co esponding au ho .
** Co esponding au ho .
E-mail add esses: [email p o ec ed] (A.F. Manch´
on-Go d´
on), [email p o ec ed] (J.S. Bl´
azquez).
Con en s lis s a ailable a ScienceDi ec
In e me allics
jou nal homepage: www.else ie .com/loca e/in e me
h ps://doi.o g/10.1016/j.in e me .2025.108695
Recei ed 15 No embe 2024; Recei ed in e ised o m 27 Janua y 2025; Accep ed 1 Feb ua y 2025
In e me allics 180 (2025) 108695
A ailable online 9 Feb ua y 2025
0966-9795/© 2025 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license ( h p://c ea i ecommons.o g/licenses/by-
nc-nd/4.0/ ).
comp ehensi e desc ip ion o e olu ion o he moelas ic s ains occu -
ing in SMAs du ing pa ial he mal ans o ma ion. As a esul , TME is
expec ed in mul i-domain c ys als unde going s uc u al i s -o de
phase ansi ions, whe e accommoda ion p ocesses lead o s ain dis-
ibu ion among domains [14].
While he TME was ini ially obse ed in Ni-Ti alloys [8], i has also
been de ec ed in Ni-Mn-Ga [15,16] and Ni-Fe-Ga [17,18] Heusle alloys.
In he la e case, he MT occu s be ween an aus eni e phase wi h a B2 o
o de ed L2
1
s uc u e o ei he a modula ed (se en-laye , 14M, o
i e-laye , 10M) o a non-modula ed (L1
0
e agonal) ma ensi ic
s uc u e. The speci ic s uc u e depends on ac o s such as he compo-
si ion and he he mal and mechanical his o y [19,20]. The γ-phase
p ecipi a es a e usually o med in con en ionally p oduced samples,
esul ing in enhanced mechanical p ope ies. These p ecipi a es can be
also easily induced by he mal ea men s in monophasic mel -spun
ibbons [21]. This duc ile phase does no pa icipa e in he ma ensi ic
phase ansi ion, and i s p esence weakens he SME. As he amoun o
he duc ile phase inc eases, i hinde s he mo emen o ma ensi e
a ian s, educing he ma e ial’s abili y o eco e s ain. In his sense,
po osi y can a ec he ans o ma ion a o ing he mo emen o he
win bounda ies due o a highe ee su ace, as epo ed o Ni-Mn-Ga
[22]. This phenomenon is enhanced in oams [23]. The e o e, he
di e se a ay o mic os uc u es in which MT can be obse ed calls o
an examina ion o hei in luence on he TME.
This s udy sys ema ically explo es he TME a ising om in e up ing
e e se MT in di e en samples o Ni
55
Fe
16
Ga
26
Heusle alloys ab i-
ca ed as ibbon-shaped specimens, using mel -spinning, and as pelle -
shaped samples, using a c-mel ing. The s udy encompassed he execu-
ion o ei he a single in e up ion o he e e se MT o a se ies o
in e up ed p ocesses wi h se e al s op empe a u es. The main goal was
o compa e how he ma ensi ic s uc u e and he mac os uc u e o he
sample in luences he TME. The indings p esen ed in his s udy com-
ple e p e ious wo ks by some o he au ho s on Ni-Fe-Ga SMAs,
explo ing a ious aspec s: i) he in luence o p essu e on he phase s a-
bili y and magne os uc u al ansi ion o ibbons [20], ii) dis inc ions
in s uc u al and magne ic p ope ies be ween ibbon and bulk samples
[21], iii) he kine ics [24] and iso he mal/a he mal na u e [18] o he
MT in ibbons, and i ) he iden i ica ion o a alanches du ing he MT in
bulk samples using ul aslow calo ime y [25].
2. Expe imen al
The ma e ial analyzed in his s udy is an alloy wi h a nominal
composi ion o Ni
55
Fe
19
Ga
26
(a . %) ab ica ed using bo h mel -spinning
and a c-mel ing echniques. Comp ehensi e de ails ega ding he
p epa a ion p ocedu es and a ho ough mic os uc u al and magne ic
cha ac e iza ion o bo h samples a e a ailable in Re . [21]. Mo eo e ,
de ailed insigh s in o he ma ensi ic s uc u e a oom empe a u e
(RT), he MT p ocess, and he chemical composi ion o he Ni
55
Fe
16
Ga
26
samples u ilized in his s udy can be also ound in ou ea lie publica ion
[21].
The mal p ope ies o he samples we e assessed using wo dis inc
ins umen s: a comme cial di e en ial scanning calo ime e (DSC)
Pe kinElme DSC7 (Pe kinElme , No walk, CT, USA) and a home-made
conduc ion calo ime e able o pe o m high- esolu ion DTA analysis (1
nW) [26,27].
DSC was employed unde A low and equipped wi h a cooling sys-
em. Va ious hea ing a es, β, ( anging om 5 o 40 K min
−1
) we e
applied. To ake in o accoun he impac o he a ying β on he
measu ed empe a u e, he mel ing empe a u e o In s anda d (429.75
K) was u ilized (e o s below 0.5 K) when he cooling sys em was ac i e,
and he mel ing poin o Pb (600.65 K) was used o he wise.
Fo he ibbons, an ini ial s ep hea ing up o 473 K was applied o
elimina e he in luence o he e ogenei ies due o s ain ields ha migh
be p esen in he sample du ing i s p ocessing, he eby ensu ing con-
sis ency and epe i i eness in subsequen measu emen s. Mo eo e , o
mi iga e po en ial a ia ions in he cha ac e is ic pa ame e s o he
o wa d and e e se MT caused by cycling and inhomogenei ies [24],
he same ibbon pieces we e consis en ly used o he same se ies o DSC
measu emen s. Gi en he small mass o an indi idual piece ela i e o
he c ucible dimensions o he equipmen , mul iple pieces o ibbons
we e included in each expe imen o achie e a mass compa able o ha
o he u ilized s anda ds. Fo sake o compa ison, a consis en p o ocol
was applied o he bulk sample, bu using a single piece o all
expe imen s.
In TME expe imen s using DSC, samples we e ini ially hea ed a β =
20 K min
−1
un il Ts op ∈(As,A )was eached and he empe a u e was
hal ed o 10 min. This ime was chosen om ou p e ious esul s [18]
ha show ha iso he mal ea men s in hese samples equi e 10 min o
dwell ime o s abilize he ans o med phase ac ion. The e o e, a e
10 min, we expec ha empe a u e will be homogeneous and a he mal
p ocesses a e comple ed. Then, he samples we e cooled below M a
cons an β =-20 K min
−1
. In he subsequen s ep, he samples we e
ehea ed abo e A a a cons an a e, while employing a ying a es
om 5 o 40 K min
−1
o he second hea ing s ep o in es iga e he ki-
ne ics o he p ocess. Addi ionally, di e en Ts op alues we e u ilized. To
cla i y he ollowed p ocess, Fig. 1 illus a es he empe a u e- ime
cu e o a comple e DSC expe imen , including an iso he mal dwell
conduc ed a 381 K, in e up ed a e 10 min, as an illus a i e example.
The inclusion o an iso he mal s ep is necessa y o achie e uni o m
empe a u e dis ibu ion wi hin he c ucible, pa icula ly because mul-
iple pieces o ibbons a e p esen . The ma ked zone co esponds o ha
in which he hea ing a e has been modi ied o di e en expe imen s.
The inal empe a u e o second hea ing, which exceeds A , ensu es he
elimina ion o any esidual memo y e ec s, as he sample is ully
ans o med in o he aus ene phase. S a ing he hea ing p ocess a e
s abiliza ion o he calo ime e below M con i ms ha he sample is
ini ially in he ma ensi ic s a e.
The mal p ope ies we e also s udied in he conduc ion calo ime e
capable o cap u ing high- esolu ion DTA aces. De ailed in o ma ion
abou he equipmen and i s unc ionali y can be ound in Re s. [26,27].
Due o he subs an ial he mal ine ia o he equipmen , scanning a es
a y om a ew kel ins pe hou (slow a e ange) o a ew millikel ins
pe hou (ul aslow a e ange), signi ican ly slowe han hose used in
comme cial calo ime e s. The sample was a pa allelepiped piece wi h
dimensions 9.0 mm ×9.57 mm ×2.35 mm (leng h x wid h x heigh ) and
Fig. 1. Illus a ion o a comp ehensi e he mal ea men conduc ed in com-
me cial DSC expe imen s o examine he he mal memo y e ec in he in es-
iga ed NiFeGa ibbon samples. In he ini ial hea ing s ep (β =20 K min
−1
), he
e e se ma ensi ic ans o ma ion was hal ed a a speci ic empe a u e, 381 K,
and o a du a ion o 10 min in he epo ed case (1). Subsequen ly, he sample
unde wen cooling below ma ensi e inish empe a u e and was hen ehea ed
o 473 K a di e en hea ing a es (2). The shaded a ea ep esen s he he mal
ea men in which TME should be e lec ed.
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
2
1.5987(1) g in mass.
Su ace obse a ions o he specimens we e pe o med using a FEI
Teneo scanning elec on mic oscope (SEM) ope a ing a 20 kV. Be o e
SEM imaging, he su ace o bulk and ibbon samples was mechanically
polished using a se ies o sandpape s wi h a ying g i sizes, ollowed by
polishing wi h ab asi e pas es.
3. Resul s
In his s udy, we ha e analyzed six di e en samples, namely he as-
spun ibbon (AS-R), he mally ea ed ibbon (TT-R), p essu e ea ed
ibbon (PT-R), pul e ized ibbon (powde ), as-p epa ed bulk (AP-B),
and he mally ea ed bulk (TT-B). Table 1 p esen s he key ansi ion
empe a u es, encompassing he aus eni e s a , As, and inish, A ,
empe a u es, along wi h he ma ensi ic s a , Ms, and inish, M ,
empe a u es. Fu he mo e, he espec i e s uc u e o each sample a
RT de e mined by X- ay di ac ion echnique is ou lined.
The s uc u e o he AS-R sample displays a monophasic ma ensi e
wi h a modula ed 14M s uc u e a RT. Howe e , when he ibbon is
c ushed in o powde , an in e ma ensi ic ans o ma ion occu s, leading
o a non-modula ed L1
0
s uc u e [20]. When uniaxial p essu e is
applied on he ibbons, a pa ially in e ma ensi ic ans o ma ion be-
ween he 14M modula ed o a non-modula ed phase occu s [20]. On he
o he hand, he mal ea men s can induce he p ecipi a ion o he γ
phase [21]. Con e sely, he a c-mel ing me hod ails o yield a
single-phase sample, esul ing in he simul aneous p esence o a
non-modula ed ma ensi e s uc u e and γ phase a RT. In he bulk
sample, he modula ed phase eme ges ollowing an ex ended hea
ea men (1073 K o 24 h) and subsequen apid wa e quenching, wi h
a small inc ease o γ phase a e his ea men . The cha ac e is ic
Table 1
Cha ac e is ic empe a u es associa ed wi h he MT measu ed by DSC scans a
20 K min
−1
and he s uc u e o he analyzed samples a RT. ND: Non-de ec ed;
AS: As-spun; AP: As-p epa ed; TT: The mally- ea ed; PT: P essu ed- ea ed. In
he case o he PT sample, he p esen ed da a co espond o he MT o he 14M
s uc u e.
Sample S uc u e Ms (K) M (K) As (K) A (K)
Ribbon AS 14M 370.3 346.9 379.5 399.5
TT 14M+γ360.6 338.5 371.2 388.0
PT 14M +L1
0
370.3 346.9 379.5 399.5
Powde L1
0
ND ND ND ND
Bulk AP L1
0
+γ321.1 288.4 322.9 353.0
TT 14M+γ300.3 283.3 311.9 324.8
Fig. 2. SEM mic og aphs using backsca e ed elec ons a di e en magni ica ions: a) and b) as-spun ibbon, c) and d) he mally ea ed ibbon, and e) and ) powde
ob ained om manually g inding he as-spun ibbon. Figu es b) and d) shows highe magni ica ions o selec ed a eas o panels a) and c), espec i ely.
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
3
empe a u es o he MT a e lowe in he bulk sample compa ed o he
ibbon, in luenced by he al e a ion o he e/a pa ame e due o he
p esence o he γ phase wi h a lowe con en in Ga [21].
The mic os uc u e o he samples was analyzed using SEM. Fig. 2
shows ep esen a i e backsca e ed elec on (BSE) images o he AS-R
(panels a and b), TT-R (panels c and d), and he powde de i ed om
he ibbons (panels e and ). Simila ly, Fig. 3 shows BSE images o he
AP-B (panels a and b) and he TT-B samples (panels c and d).
The hickness o he ibbons a ied sligh ly, anging om 30 o 40
μ
m (Fig. 2a), and p edominan ly ea u ed a single-phase ma ensi ic
mic os uc u e. This mic os uc u e consis ed o se e al a ian s o
ma ensi e pla es wi h coa se g ains measu ing se e al mic ons in size.
The ma ensi e lamellas, exhibi ing a pla e-like shape, we e clea ly
isible, along wi h small black po es (indica ed wi h a ows) o med
du ing he quenching p ocess om he mel . No signi ican di e ences
we e obse ed be ween he ee and wheel side o he ibbons. The
mic os uc u e shows ew g ain bounda ies, in which g ain g ow h was
inhibi ed by he ini e hickness o he ibbons [28]. Wi hin he
ma ensi e pla es, conjuga ion bounda ies, CB, we e isible, sepa a ing
egions wi h di e en ly o ien ed nano wins [29]. These CBs we e
commonly ound in he sel -accommoda ed s a e o ma ensi e mic o-
s uc u e, pa icula ly nea g ain bounda ies whe e b anching occu s
[30]. B anching is ealized by a shi in nano win o ien a ion o i s
conjuga ed coun e pa wi hin a single ma ensi e pla e, o ming CBs
[31].
In he TT-R, he hickness o he ma ensi e pla es inc eased, e en
occupying he en i e c oss-sec ion o he ibbon. In e es ingly, despi e
he ela i ely low ea men empe a u e and he sho annealing ime,
his p ocess appea ed o igge he p ecipi a ion o an addi ional phase
dispe sed wi hin he ma ix (indica ed by dashed a ows in Fig. 2d). The
p ecipi a ed phase was disce nible by i s da k g ey con as and s ong
alignmen oughly pe pendicula o he su ace o he ibbon. Fig. 2e and
displays SEM-BSE images o powde s p oduced by manually milling he
mel -spun ibbons. The pa icle sizes is no homogeneous and anged
om 50 o 150
μ
m, p edominan ly exhibi ing a polygonal shape, which
esul ed om he b i leness o ibbons due o he absence o gamma
p ecipi a es.
Fig. 3 con i ms he signi ican a ia ion in mic os uc u e depending
on he p epa a ion me hod. Speci ically, while he AS-R samples dis-
played a single-phase mic os uc u e, he samples p oduced using he
a c-mel ing echnique e ealed he p esence o a clea ly dis inguishable
second phase. The mo phology o his second phase changed wi h
he mal ea men , leading o an inc ease in he size o he p ecipi a es.
The p ecipi a ion o he gamma phase, which is en iched in Fe and
impo e ished in Ga, educed he Fe con en in he ma ensi e ma ix.
This is quali a i ely shown in Re . [25] by EDS measu emen s. Al hough
he quan i a i e changes a e oo small, quali a i e beha io is clea and
may lead o an inc ease in e/a ac o , he eby lowe ing he ma ensi ic
ans o ma ion empe a u es. I is also wo h no ing ha he dis ibu ion
o p ecipi a es in Fig. 2d ollows he same pa e ns as hose obse ed in
Fig. 3a.
Unlike ibbon samples, po osi y is no obse ed in bulks. Mo eo e ,
he low empe a u e a which he ibbons ha e been ea ed a e no
expec ed o p oduce any e olu ion in he po ous densi y. The e o e,
al hough his di e ence may also in luence he a ying beha io
obse ed be ween ibbon and bulk samples, i is unlikely o accoun o
he di e ences obse ed speci ically among ibbon samples.
3.1. Tempe a u e memo y e ec in Ni
55
Fe
19
Ga
26
as-mel spun ibbons
Fig. 4 shows (dashed lines) he di ec and e e se ans o ma ion in
he AS-R samples a e con en ional hea ing ( e e se MT) and cooling
uns (di ec MT). I is impo an o emphasize ha he dashed line,
ep esen ing he en i e he mal cycle o a elaxed sample, is consis en ly
ea u ed in he DSC plo s o compa a i e pu poses.
We choose β= ± 20 K min
−1
o op imize he signal- o-noise a io in
DSC measu emen s [18]. No ably, he ibbon specimens unde wen wo
p e- he mal cycles om RT o 473 K ( elaxed sample) o emo e po-
en ial inhomogenei ies among di e en ibbon pieces, in luenced by
p e ious he mo-mechanical his o ies [21]. The ac ual p ocedu e o
es ing he TME in ol ed: i) Hea ing om RT o Ts op (AS <TS op <A ); ii)
Kine ic s op a Ts op o 10 min; iii) Cooling down o 323 K; and i )
Hea ing om 323 K o 473 K. S eps i) and ii) could be epea ed mul iple
imes wi h a ying Ts op in each incomple e e e se MT.
Fig. 3. SEM mic og aphs using backsca e ed elec ons: a) and b) as-p epa ed bulk, and c) and d) he mally ea ed bulk a di e en magni ica ions.
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
4
Fig. 4a–b displays he cha ac e is ic cu es ob ained om a TME es
wi h a single s op, whe e he Ts op was se a 381 K and 383 K, espec-
i ely. No ably, kine ic s ops a e clea ly disce nible on he hea low
cu es du ing he second hea ing. In addi ion o he single-s op expe i-
men s, a double-s op es was execu ed. Fig. 2c displays DSC scans a e
pe o ming wo consecu i e incomple e cycles du ing he hea ing phase
a empe a u es o 383 K and 381 K in dec easing o de . In such case,
wo kine ic s ops show up in he subsequen comple e e e se MT. These
indings a e consis en wi h p e ious esul s, ha associa e he numbe
o he mal a es s a anged in dec easing Ts op wi h he numbe o in-
e up ions in he subsequen hea ing un. In con as , when Ts op is a -
anged in an inc easing o de , hen one kine ic s op a he highes
empe a u e Ts op is only obse ed [4,32,33].
Incomple e di ec MT we e also es ed on cooling expe imen s,
inco po a ing di e en Ts op (be ween M and Ms) and du a ions. He e,
only a ac ion o he aus eni e unde goes ans o ma ion in o he
ma ensi e phase, lea ing he es o he aus eni e una ec ed. A e his
in e up ed di ec MT, he ans o med ma ensi e has he po en ial o
e e o aus eni e upon u he empe a u e ele a ion beyond A .
Howe e , he ou comes e eal ha he subsequen cooling scans egis-
e ing di ec MT does no display any indica ions o kine ic in e up ion.
These esul s a e in line wi h hose p e iously epo ed [4,16].
3.2. Tempe a u e memo y e ec in Ni
55
Fe
19
Ga
26
he mally ea ed
ibbons
P e ious s udies show ha hea ea men s conduc ed abo e he MT
led o an i e e sible downwa d shi in MT due o s uc u al modi i-
ca ions. In he case o he mal ea men s pe o med below 573 K, s ess
elaxa ion accumula ed du ing ibbon ab ica ion occu ed. Annealing
ea men s below 873 K cause sligh changes in he la ice pa ame e s,
al e ing he b/a and des abilizing he 14M modula ed s uc u e. A
empe a u es abo e 873 K, he monophasic na u e o he ibbon is los ,
and he ma ens ic modula ed s uc u e ans o ms in o wo dis inc
phases: aus eni e and he γ-phase [21]. In o de o analyze he di e -
ences in TME due o hese mic os uc u al changes, TT-R samples we e
ob ained a e hea ing AS-R samples up o 623 K.
Fig. 5 illus a es he DSC scans o he Ni
55
Fe
19
Ga
26
ibbon a e
being hea ed up o 623 K. M and Ms ha e dec eased wi h he he mal
ea men in compa ison wi h he AS-R. The sample was hea ed un il he
MT e e se ans o ma ion was hal ed a 373 K o 10 min. Then, he
Fig. 4. DSC scans egis e ed using he p o ocol o Fig. 1 (con inuous black
lines) along wi h comple e DSC scans (dashed blue lines) ep esen ing he
ansi ion om e e se and di ec MT in Ni
55
Fe
19
Ga
26
ibbons. These scans
we e pe o med ollowing ei he a singula a es a Ts op1 =381 K (shown in
panel a), a singula a es a Ts op2 =383 K (illus a ed in panel b), and a
combina ion o a es a Ts op2 and Ts op1, each las ing 10 min a hei espec i e
empe a u es (depic ed in panel c). (Fo in e p e a ion o he e e ences o
colou in his igu e legend, he eade is e e ed o he Web e sion o
his a icle.)
Fig. 5. DSC scan egis e ed using he p o ocol o Fig. 1 using a Ts op =373 K
and a dwell ime o 10 min (con inuous black line) along wi h comple e DSC
scan (dashed blue line) cap u ing he ansi ion om ma ensi e o aus eni e in
he Ni
55
Fe
19
Ga
26
ibbon a e hea ed up o 623 K (TT-R sample). (Fo in e -
p e a ion o he e e ences o colou in his igu e legend, he eade is e e ed
o he Web e sion o his a icle.)
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
5

sample was cooled down o 323 K and he subsequen hea ing un
showed a smoo he kine ic in e up ion. This e idence sugges s ha he
des abiliza ion o he modula ed s uc u e (b/a<7) was smea ing he
TME. Inc easing iso he mal dwell ime up o 60 min does no enhance
he TME.
The phase ac ion o he 14M s uc u e in he TT-R sample can be
in e ed om he en halpy change obse ed in he TT-R Sample and he
AS-R sample. Assuming ha he AS-R is 100 % in 14M (ΔH =5.46 J
g
−1
), hen we in e ∼90 % o TT-R is 14M phase (ΔH =5.06 J g
−1
).
3.3. Tempe a u e memo y e ec in Ni
55
Fe
19
Ga
26
mechanically ea ed
ibbons
The applica ion o a uniaxial p essu e on he AS-R sample induces a
g adual ans o ma ion om he 14M modula ed phase o he non-
modula ed L1
0
s uc u e [20]. Speci ically, a load o 2 ons was
applied o a 0.785 cm
2
su ace (~250 MPa) o 5 min a RT o p oduce
PT-R sample.
DSC scans o PT-R sample a e depic ed in Fig. 6. The dis inc peaks
a ibu ed o he MT obse ed in he AS-R exhibi a no iceable dec ease.
This sugges s ha he 14M, he ans o mable phase, becomes des abi-
lized unde p essu e. F om ΔH =2.64 J g
−1
, we in e ha ∼50 % o he
PT-R sample is 14M, he emaining hal belongs o he non-modula ed
L1
0
phase, as he γ−phase is no induced by p essu e [20]. Addi ion-
ally, he in e up ed e e se MT conduc ed a he same Ts op han hose
employed in Fig. 1 e eals some TME.
Fig. 6c depic s he DSC plo s o he Ni
55
Fe
19
Ga
26
powde s de i ed
om as-p epa ed ibbons, exhibi ing a L1
0
monophasic ma ensi e
s uc u e (see Re . [20]). Unde he es ed condi ions, no MT is obse ed,
indica ing he elimina ion o he modula ed phase h ough mechanical
ea men . These indings align wi h p io esea ch on Ni-Mn-Sn milled
alloys, whe e he peak associa ed wi h MT diminishes no ably wi h
p olonged milling ime, e en ually disappea ing a e 45 min [34].
3.4. Tempe a u e memo y e ec in Ni
55
Fe
19
Ga
26
as-p epa ed bulk
Fig. 7 displays he DSC scans o he Ni
55
Fe
19
Ga
26
AP-B sample,
ea u ing a biphasic s uc u e (L1
0
+γ p ecipi a es [21]), ollowing an
in e up ed e e se MT a a Ts op =323 K, be ween As and A du ing
hea ing. In all es ed condi ions, he e is no indica ion o a kine ic
in e up ion o he subsequen comple e ans o ma ion. This appa en
Fig. 6. DSC scans egis e ed using he p o ocol o Fig. 1 (con inuous black line)
wi h Ts op se a a) 381 K and b) 383 K, along wi h comple e DSC scan (dashed
blue line) cap u ing he ma ensi ic ans o ma ion in he Ni
55
Fe
19
Ga
26
PT-R
samples. Panel c) co esponds o DSC hea ing and cooling cu es o he
Ni
55
Fe
19
Ga
26
powde s de i ed om as-p epa ed ibbons. (Fo in e p e a ion o
he e e ences o colou in his igu e legend, he eade is e e ed o he Web
e sion o his a icle.)
Fig. 7. DSC scans egis e ed using he p o ocol o Fig. 1 (con inuous black line)
wi h Ts op =323 K and dwell ime se a 10 min, along wi h comple e DSC scan
(dashed blue line) cap u ing he ansi ion om ma ensi e o aus eni e in he
Ni
55
Fe
19
Ga
26
as-p epa ed bulk. (Fo in e p e a ion o he e e ences o colou in
his igu e legend, he eade is e e ed o he Web e sion o his a icle.)
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
6
absence o TME aligns wi h hose documen ed in Re . [17], whe e bulk
NiFeGa samples did no exhibi dis inc dips linked o TME a e an
incomple e e e se phase ansi ion.
3.5. Tempe a u e memo y e ec in he mally- ea ed bulk
The NiFeGa TT-B sample exhibi s a biphasic s uc u e wi h 14M
ma ensi e phase and γ−phase p ecipi a es. Fig. 8 shows he DSC e-
sul s. Wi h a ΔH =3.30 J g
−1
and om he p e ious ΔH o he AS-R
sample we in e a ∼60 % 14M and ∼40 % γ−phase mix u e.
The TT-B sample was also placed in a home-made conduc ion calo-
ime e ha ope a es as a high-sensi i e DTA ace . The sample sus-
ained wo ul aslow hea ing uns. As a e e ence, i was hea ed a a a e
o 40 mK h
−1
and he e e se ans o ma ion was eco ded. Resul s om
his expe imen we e shown p e iously in Re . [25]. Then, he sample
was cooled om he aus eni e phase and hea ed again a a a e o 40 mK
h
−1
. The empe a u e was hal ed o i e days a 315.7 K. The sample
was hen cooled down a a a e o 40 mK h
−1
un il 309 K was eached. I
was hen quenched down o 280 K, hea ed back o 306 K when he
s anda d hea ing p o ile was esumed, and he sample comple ed he
e e se MT. The hea ing DTA aces in he empe a u e egion close o
he MT a e shown in Fig. 9. A kine ic s op is clea ly disce nible on he
hea low cu es du ing he hea ing a e a smoo h baseline was
sub ac ed.
4. Discussion
MT empe a u es can a y wi hin a ce ain empe a u e ange,
depending on β [19,35]. The e o e, calo ime ic measu emen s a e
he mal a es we e conduc ed wi h β anging om 5 o 40 K min
−1
o
iden i y he dependence o he MT empe a u e in e al a e kine ic
a es . Ini ially, hea ing o Ts op ollowed by subsequen cooling o 323 K
was conduc ed a 20 K min
−1
. Subsequen ly, a hea ing scan up o 473 K
was pe o med a di e en β anging om 5 o 40 K min
−1
.
The esul ing DSC scans a e illus a ed in Fig. 10 (le panels). Panels
a and b depic he cha ac e is ic cu es ob ained om a single Ts op o
381 K and 383 K, espec i ely. Addi ionally, a double es was con-
duc ed, as shown in panel c. A sligh shi owa ds highe empe a u es is
obse ed o A as β inc eases, while β has no disce nible in luence on As.
Consequen ly, he ans o ma ion empe a u e in e al ΔT=A −As
inc eases wi h β. These esul s a e consis en wi h hose epo ed by
Wang e al. [36], sugges ing ha β leads o a la ge a ia ion in A
compa ed o As.
Righ panels o Fig. 10 show he co esponding ans o med ac ions
which we e app oxima ed by he no malized ans o med en halpy, X=
ΔH(T)/ΔH o al, whe e ΔH(T) ep esen s he en halpy de eloped up o
empe a u e T, and ΔH o al deno es he o al en halpy o he MT. All
cu es collapse in o a common line below Ts op, wi hin he s anda d
unce ain y associa ed o baseline de e mina ion in he DSC [37].
Howe e , de ia ions can be obse ed abo e Ts op in ag eemen wi h he β
e ec desc ibed abo e. When compa ing he ob ained cu es wi h hose
o a comple e ans o ma ion wi hou any in e up ion, a kine ic delay
e idenced by a shi o he MT o highe empe a u es (∼5K) om Ts op is
obse ed. This delay seems o be accumula i e as obse ed in he
expe imen wi h wo Ts op in Fig. 10 , wi h a delay >10 K.
The impac o he TME on he e olu ion o he ans o med ac ion
in he o he s udied samples has also been analyzed and depic ed in
Fig. 11. As an icipa ed, he shi o X in he case o he TT-R (Fig. 11a)
and PT-R (Fig. 11b) samples is signi ican ly educed compa ed o he AS-
R, wi h a shi o highe empe a u es o app oxima ely 1 K. Howe e , in
he case o he bulk samples, his shi is wi hin he esolu ion o he
equipmen , ega dless o he ma ensi e phase s uc u e (see panels c
and d o he AP-B and TT-B samples, espec i ely).
Fig. 12 shows he esul s o he high- esolu ion DTA expe imen
co esponding o he TT-B sample. In ul aslow DTA expe imen , he
ans o med ac ion was app oxima ed by he no malized ans o med
en halpy om 310 K (whe e he aus eni e ac ion is ze o) and assuming
ha , a 323 K, he aus eni e phase ac ion is 1. The educ ion in he
wid h o e e se MT is in ag eemen wi h he hea ing a e e ec
desc ibed abo e. When compa ing he ans o med ac ion wi h hose
o he comple e e e se MT wi hou in e up ion (dashed-line in
Fig. 12), a sligh shi o highe empe a u es can be obse ed. The e o e,
i s beha io is simila o ha shown by ibbon samples a e analyzing
TME (see Fig. 10), bu no in he case o he bulk. The highe esolu ion
o he DTA scans a e y low hea ing a e, along wi h he e y long
iso he m dwell, enables us o assess ha TME also occu s in he TT-B
sample.
The TME obse ed in ul aslow DTA o TT-B sample is highe han
ha p esumed o DSC expe imen s. This di e ence could be due o he
e y long iso he m and he e ec o educed β, which could be mo e
Fig. 8. DSC scans egis e ed using he p o ocol o Fig. 1 (con inuous black line)
wi h Ts op =310 K and dwell ime se a 10 min, along wi h comple e DSC scan
(dashed blue line) cap u ing he ansi ion om ma ensi e o aus eni e in he
Ni
55
Fe
19
Ga
26
he mally ea ed bulk. (Fo in e p e a ion o he e e ences o
colou in his igu e legend, he eade is e e ed o he Web e sion o
his a icle.)
Fig. 9. DTA aces o TT-B sample wi hou he mal a es ( e e ence in blue)
and a e he mal a es a 315.7 K (black) in he empe a u e anges a ound
e e se ma ensi ic ans o ma ion. (Fo in e p e a ion o he e e ences o
colou in his igu e legend, he eade is e e ed o he Web e sion o
his a icle.)
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
7
e icien in eleasing s ain in he un ans o med ma ensi e phase. As i
will be discussed below, his could be a sui able mechanism o TME.
In TME expe imen s, du ing he pa ial e e se MT, he ansi ion
om ma ensi e o aus eni e hal s a a speci ic empe a u e be ween AS
and A . In ha si ua ion, only a po ion o he ma ensi e e e s o he
aus eni e phase, while he es o he ma ensi e pe sis s. This esidual
ma ensi e is commonly e e ed as M1. Upon subsequen cooling down
o M , he aus eni e phase unde goes e- ans o ma ion in o ma ensi e,
esul ing in he o ma ion o a new ma ensi e phase, deno ed as M2.
Du ing he nex hea ing scan, M2 and M1 sequen ially ansi o he
aus eni e phase, leading o a kine ic delay be ween bo h ans-
o ma ions.
Se e al s udies ha e ied o explain he TME by a ibu ing i o he
elease o elas ic s ain ene gy du ing he i s in e up ed ans-
o ma ion in he emnan M1. This s o ed elas ic s ain would ac as
ins abili ies o launch nuclea ion p ocess in he e e se ans o ma ion
[2]. The e o e, M1 is s abilized in a second e e se ansi ion as he
elas ic s ain is lowe ed. Howe e , he p oposed mechanisms
Fig. 10. DSC scans egis e ed (a,b,c) and co esponding ans o med ac ions (d,e, ) using he p o ocol o Fig. 1 (con inuous lines) along wi h DSC signal o un-
ea ed sample (dashed blue lines) ep esen ing he ansi ion om e e se and di ec MT in Ni
55
Fe
19
Ga
26
ibbons a he indica ed hea ing a es. These scans we e
pe o med ollowing ei he a singula a es a Ts op1 =381 K (a,d), a singula a es a Ts op2 =383 K (b,e), and a combina ion o a es a Ts op2 and Ts op1, each las ing
10 min a hei espec i e empe a u es (c, ). (Fo in e p e a ion o he e e ences o colou in his igu e legend, he eade is e e ed o he Web e sion o
his a icle.)
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
8
conside ably a y and a e subjec o deba e. Madangopal e al. [8]
sugges ed ha M2 migh accumula e mo e elas ic s ain ene gy han M1,
he eby po en ially p e-posi ioning he e e se ans o ma ion o M2.
Howe e , we do obse e a common As alue independen ly o he
p esence o TME (o e en a delay when e y long iso he ms occu a
Ts op) bu a delay ha ini ia e app oxima ely a he empe a u e whe e
he hal ha e occu ed (in he absence o e y long iso he m a Ts op).
Con e sely, i has been p oposed ha he TME a ises om he educ ion
o elas ic s ain ene gy in M1, equi ing a highe empe a u e o ini ia e
he ans o ma ion o M1 once he ans o ma ion o M2 is comple e [9].
Ou esul s a e in ag eemen wi h his second in e p e a ion.
Upon cooling, he a omic a angemen adop s a winning s uc u e
wi h pe iodic s acking o de , po en ially esul ing in 24 a ian s o
ma ensi e [13]. The MT s o es some elas ic s ain ene gy wi hin he
he moelas ic ma ensi e a ian s. The e o e, while he elease o elas ic
s ain ene gy om ma ensi e a ian s is o en associa ed wi h he TME,
i is impo an o no e ha he cohe en ene gy o adjacen phases also
in luences he TME [38]. This e ec is clea ly obse ed in ou esul s. On
he one hand, he p esence o he non-modula ed phase and he des a-
biliza ion o he 14M phase es ic s he occu ence o TME (see Figs. 5
and 6). Con e sely, in bulk samples, he p esence o a ound 40 % γ
p ecipi a es inhibi s TME o equi e high p ecision echniques o e i-
dence i .
5. Conclusions
The s udy o he he mal memo y e ec , TME, in ol ed six samples
sha ing he Ni
55
Fe
19
Ga
26
composi ion bu di e ing in mic o and
mac os uc u e. The esul s show ha he TME, igge ed by a pa ial
e e se ans o ma ion om ma ensi e o aus eni e phase, is no a
common phenomenon in he s udied shape memo y alloys. Ins ead, i
appea s o be con ingen upon he speci ic mic os uc u e o he sample.
Fig. 11. T ans o med ac ion as a unc ion o empe a u e o he e e se MT a e kine ic a es in he case o he a) TT-R and b) PT-R samples; and c) AP-B and d)
TT-B samples. Inse s show he enla ged 0.4<X <0.6 egion.
Fig. 12. T ans o med ac ion as a unc ion o empe a u e o he e e se MT
a e kine ic a es in he TTB sample in he ul aslow calo ime e along as o
he o iginal ans o med ac ion (dashed line) o o iginal scans.
A. Vidal-C espo e al.
In e me allics 180 (2025) 108695
9