Elec ical discha ge consolida ion o Al and Ti powde s
F. Te ne o1
*
, R.M. A anda2, P. U ban1, R. As acio1 and J.M. Mon es1
1Ad anced Ma e ials Enginee ing G oup, Escuela Técnica Supe io de Ingenie ía,
Uni e sidad de Se illa, 41092 Se illa, Spain
2Ad anced Ma e ials Enginee ing G oup, Escuela Técnica Supe io de Ingenie ía,
Uni e sidad de Huel a, 21071 Huel a, Spain
Abs ac
In his pape , elec ical-discha ge-consolida ion (EDC echnique) expe imen s we e ca ied ou wi h an equipmen
based on he echnology de eloped o he s ud welding echnology. The main ad an age o he EDC echnique is i s
high speed, on he o de o milliseconds o less, which makes i pa icula ly in e es ing when a high inal po osi y is
aimed, o when he inhe en nanos uc u e o he powde s needs o be p ese ed. Compac s o Ti and Al we e
consolida ed wi h his echnique, bo h di ec ly om loose powde s and om cold p essed g een compac s. Two
di e en con igu a ions (200 V – 66 mF and 800 V - 1.1 mF) we e es ed. Rela i e densi y, mic oha dness, elec ical
esis i i y and me allog aphic and SEM s udies we e ca ied ou o unde s and he changes in powde pa icles caused
by he elec ical discha ge. The use o a high capaci y in he capaci o s bank, despi e he use o a lowe ol age, esul s
in a be e consolida ion p ocess.
Keywo ds: Elec ical Discha ge Consolida ion; Capaci o s bank; Po osi y; Al powde ; Ti powde .
1. In oduc ion
The con en ional powde me allu gical p ocessing ou e essen ially consis s o cold compac ion o a mass o me al
powde o ob ain a g een compac , ollowed by u nace sin e ing o p o ide he inal o nea - inal pa . Al hough his
is he ou e mos equen ly used in he indus y, new al e na i es a e cons an ly being in es iga ed o imp o e, a leas
pa ially, he p oblems and sho comings o he cu en echnology. In his sense, he di ec use o elec ici y as a
means o consolida ing powde s (me allic and ce amic) has been sugges ed on nume ous occasions.
The g ea di e si y o p oposed me hods can be g ouped unde he gene ic name o Elec ic Cu en Assis ed
Sin e ing Techniques (ECAST) o by he e m FAST (Elec ic Field Assis ed Sin e ing Techniques). In ac , he speed
o he p ocesses is he mos ema kable ea u e and he common ac o o all hese echniques. In addi ion o he ime
sa ings, he high speed o elec ical consolida ion echniques ep esen s an impo an ad an age, as i o en makes he
use o acuum o ine a mosphe es unnecessa y.
These echniques, like he con en ional ou e, p o ide a pa whose shape is i ually he inal o m. Howe e , one
o he p oblems equen ly men ioned by esea che s who ha e expe imen ed wi h FAST echniques ela es o he
du abili y o he dies used, especially in cases whe e he die mus be elec ically insula ing. The p oblem o choosing
a ma e ial wi h accep able du abili y and cos -e ec i eness is o g ea in e es and equi es ho ough s udy. Only wi h
he sa is ac o y esolu ion o his p oblem will elec ical consolida ion echniques be able o ind sui able niches o
he indus ial scale. Howe e , on he labo a o y scale, i is easy o ind su icien ly accep able solu ions o wo k wi h.
In he so-called Elec ical Discha ge Consolida ion (EDC), he elec ic cu en passing h ough he powde is also
o high cu en in ensi y [11-18], howe e , compa ed o he ERS echnique, he ol age can each much highe alues.
This combina ion o high in ensi y and mode a e (o high) ol age can be achie ed by discha ging he ene gy s o ed
in a capaci o bank, a echnique also known in he elec ical ield o welding. Because he elec ic cu en p oduces
e y as mic o-welds a he in e pa icle con ac s, he equi ed consolida ion ime can be ex ao dina ily sho , as li le
as a ew milliseconds o e en mic oseconds. As Okazaki [11] concluded, he high speed o he EDC p ocesses allows
he nanos uc u e o amo phous cha ac e o he powde s o be p ese ed, which is one o he mos impo an
ad an ages o he echnique.
*
Co esponding au ho . Tel.: +34954487305
E-mail e ne [email p o ec ed]
Else ie . Licencia C ea i e Commons CC BY-NC-ND
In gene al, in he con en ional ou e, he cold compac ion s ep is su icien o ac u e and o pa ially emo e he
oxide (and/o hyd oxide) laye s su ounding he me al powde pa icles, al hough in cases whe e his p ocess is no
e icien , i may be use ul o apply an ex usion p ocess o he powde s. The emo al o oxide laye s in he EDC
p ocess is p obably one o i s g ea es s eng hs and a consequence o he applica ion o ela i ely high s esses. These
ol ages induce he dielec ic b eakdown o he laye s, making hem conduc i e and allowing he passage o a high
cu en in ensi y [11]. The hea gene a ed by his high elec ic cu en so ens (o e en mel s) he me al unde he oxide
laye , so ha i e en ually ac u es. Subsequen pa icle ea angemen p ocesses emo e he emaining oxides om
he con ac zones, a phenomenon ha is e ec i e e en when no p essu e is applied. The e o e, he EDC echnique
makes i possible o ob ain compac s wi h high po osi y. This p esen s an impo an di e ence be ween he EDC
p ocesses wi h espec o he ERS echnique, whe e he ini ial esis i i y o he powde s is e y high and hinde s
sin e ing, as he cu en in ensi y h ough he powde agg ega e is negligible due o he lowe ol age applied o he
powde column, and no su icien o b eak he oxide laye s.
The main ad an age o he EDC echnique is an ex ao dina y sho consolida ion ime (a ound milliseconds o
mic oseconds), which makes unnecessa y he use o acuum o p o ec i e a mosphe es. This as p ocess allows o
p ese e he inhe en s uc u e o he ma e ial and o ob ain high-po osi y compac s. This wo k desc ibes he EDC
expe imen s ca ied ou wi h di e en powde s (Al and Ti), and he ob ained compac s p ope ies a e discussed.
2. Expe imen al P ocedu e and equipmen s
2.1. Desc ip ion o he EDC Equipmen
Figu e 1 shows a diag am o he basic componen s o he expe imen al equipmen .
Figu e 1. Diag am o he basic componen s o he EDC equipmen : (1) he mally and elec ically insula o die, (2) powde , (3)
elec odes (uppe and lowe ), (4) elec ic insula o (uppe and lowe ), (5) connec ion wi es o he capaci o s bank, (6) ex e nal powe
supply (elec ical ne wo k, 220 V), (7) pneuma ic p ess.
Two di e en con igu a ions we e used: con igu a ion I uses a cha ging ol age o 200 V and a capaci o s bank
wi h a capaci ance o 66 mF, whe eas con igu a ion II uses a cha ging ol age o 800 V and a capaci ance o only 1.1
mF. Bo h capaci o s’ banks we e adap ed om s ud welding equipmen s.
2.2. Ma e ials and Expe imen al P ocedu e
Two di e en comme cial powde s we e s udied: Al AS61 (wi h 0.15% Fe as main impu i y) and Ti Sejong-325
(0.0038% Fe, 0.08% N, 0.035% Si, 0.003% Mn and 0.45% O).
These powde s we e analysed ega ding hei pa icle size by lase di ac ion (Mal e n Mas e size 2000), and
hei mo phology was s udied by scanning elec on mic oscopy (SEM, Philips XL-30 coupled wi h BSE and EDS
de ec o s). Thei comp essibili y cu es we e ob ained by a comp ession es pe o med wi h a uni e sal es ing
machine (Ins on 5505). The powde s absolu e densi y was de e mined using a helium pycnome e (Accupy II1340).
Figu e 2 shows he pa icle size dis ibu ion and comp essibili y cu es o he wo powde s. Size dis ibu ion cu es
show a na ow and symme ic shape o he Al AS61 and Ti Sejong-325 powde s. These mo phological cha ac e is ics
we e co obo a ed by SEM obse a ion o he powde s, as shown in Figu e 3.
a) b)
Figu e 2. (a) G anulome ic, and (b) comp essibili y cu es o Al and Ti powde s.
Figu e 3. SEM mic og aphs o s udied powde s: (a) Al AS61, (b) Ti Sejong-325.
EDC expe imen s we e ca ied ou bo h s a ing wi h loose powde s and s a ing wi h cold p essed g een compac s.
In his las case, a cylinde die o 8 mm diame e was used o p ess he compac s. Comp essibili y cu es show ha
di e en p essu es a e needed in he di e en powde s in o de o each a simila ini ial no malised po osi y (de ined
as he a io be ween he po osi y and he ap po osi y) in g een compac s. Ini ial ela i e po osi ies o 0.1 and 0.25
we e chosen o Al powde , and 0.25 and 0.40 o Ti powde . Thus, wo di e en p essu es we e applied o each
powde : 990 and 490 MPa o Al and 1076 and 553 MPa o Ti powde . The p essu e used o each ype o powde
depends on he p ope ies o each powde o allow he compac o ha e su icien consis ency o be handled.
The powde s (loose o p e-compac ed) we e subjec ed o elec ic discha ge ollowing h ee di e en ias: (1)
discha ging om con igu a ion I (200 V-66 mF), (2) discha ging wi h con igu a ion II (800 V-1.1 mF) and (3)
discha ging wi h con igu a ion II + I (one s age a e he o he ).
The ob ained compac s we e cha ac e ised ega ding hei ela i e densi y (by weigh and geome ic measu es), he
Vicke s mic oha dness HV (by S ue s Du amin-A300) and he elec ical esis i i y (by he ou p obes me hod,
Mic ohmme e CA 10 Chau in A noux). Mo eo e , diame ical sec ions o he compac s we e obse ed by op ical
mic oscopy and ac u e su aces o mechanically b oken compac s we e s udied by SEM.
3. Resul s and Discussion
3.1. Rela i e Densi y, Elec ical Resis i i y and Vicke s Mic oha dness
Figu e 4a, 4b and 4c espec i ely show ela i e densi y, mic oha dness and elec ical esis i i y o loose powde s
and highe -p essu e p e-compac ed compac s consolida ed wi h con igu a ion I (200 V-66 mF). Fo he p e-
0
2
4
6
8
10
12
0.01 0.1 1 10 100 1000
Volume, %
Pa icle size, mm
Al
Ti
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0200 400 600 800 1000 1200 1400
Rela i e Densi y
P essu e, MPa
Al
Ti
(a)
(b)
compac ed compac s, esul s a e also shown in Figu e 4d, 4e and 4 , bo h be o e he EDC (g een compac s) and a e
he di e en discha ge con igu a ions.
As expec ed, EDC compac s ob ained om loose powde s show a lowe ela i e densi y han he p e iously p essed
ones (Figu e 4a); his is due o he compac ion p essu e. The low densi y o he compac s p epa ed om loose powde s
is also accompanied by a low mic oha dness, as shown in Figu e 4b, wi h a educ ion o 20-40%. This is due o he
highe po osi y o hese compac s, which also inc eases hei esis i i y, as shown in Figu e 4c.
On he o he hand, ela i e densi y and mic oha dness o p e-p essed compac s consolida ed wi h con igu a ion II
(800 V-1.1 mF) esul simila o hese p ope ies ob ained in g een compac s (Figu e 4d and 4e). Bo h p ope ies a e
imp o ed when con igu a ion I (200 V-66 mF) is used. Finally, compac s ha we e subjec ed o he double discha ge
cycle (II + I) show a sligh ly highe ela i e densi y and mic oha dness han any o he s. I migh be caused by he
b eakdown o he oxide laye s o he powde pa icles aking place du ing he con igu a ion II s age, making easie
he la e elec ical cu en passing when con igu a ion I is applied.
Figu e 4. Compa ison o (a) ela i e densi y, (b) Vicke s mic oha dness and (c) elec ical esis i i y o high-p essu e p e-p essed
compac s and compac s consolida ed om loose powde s by EDC, bo h wi h con igu a ion I; and (d) ela i e densi y, (e) Vicke s
mic oha dness and ( ) elec ical esis i i y o p e-p essed compac s wi h he wo di e en p essu es, consolida ed wi h bo h
con igu a ions (II + I).
Finally, he elec ical esis i i y o he compac s consolida ed wi h con igu a ion I esul s e y simila o he one
ob ained a e consolida ing wi h con igu a ion II + I, whe eas ha o he compac s consolida ed wi h he con igu a ion
0
10
20
30
40
50
60
70
80
90
100
Al
Ni
Fe
Ti
Rela i e Densi y, %
Powde s + Con igu a ion I
Compac s + Con igu a ion I
0
10
20
30
40
50
60
70
80
90
100
Al
Ni
Fe
Ti
Rela i e Densi y, %
Powde s + Con igu a ion I
Compac s + Con igu a ion I
0
10
20
30
40
50
60
70
80
90
100
Al
Ni
Fe
Ti
Rela i e Densi y, %
Powde s + Con igu a ion I
Compac s + Con igu a ion I
(a)
(b)
(c)
(d)
(e)
( )
II is almos he same ha he one o he g een compac s (Figu e 4 ). The e o e, he EDC wi h con igu a ion II does
no ha e an impo an e ec on powde s consolida ion; howe e , i may a o he elec ical cu en passing in a
subsequen discha ge.
3.2. Mic os uc u al S udy
Fo he Al compac s, op ical mic og aphs we e ca ied ou on a diame ical sec ion o he compac , di e en ia ing
wo zones: ou e (pe iphe y) and cen e (Figu e 5).
Since he elec ic cu en akes p e e en ial pa hs in i s passage h ough he powde column, a li le homogeneous
po osi y dis ibu ion is o be expec ed. Howe e , he highe po osi y obse ed a he pe iphe y o he diame ical
sec ion is inc eased by he loss o ma e ial du ing he mechanical cu ing and me allog aphic p epa a ion p ocess. This
di e ence is mo e p onounced in he samples ob ained om loose powde , whe e consolida ion is poo e . Howe e ,
in he samples ha we e p e iously p essed, he di e ences a e smalle , due o he g ea e consis ency o hese
compac s.
Figu e 5. Op ical mic og aphs o he Al compac s: (a) and (b) pe iphe y and cen e, espec i ely, o he compac consolida ed om
loose powde s and discha ging wi h con igu a ion I; (c) and (d) pe iphe y and cen e, espec i ely, o he compac consolida ed om
a p e-p essed g een compac (990 MPa) and subsequen discha ge wi h con igu a ion II; (e) and ( ) pe iphe y and cen e, espec i ely,
o he compac consolida ed om a p e-p essed g een compac (990 MPa) and subsequen discha ge wi h con igu a ion II + I.
On he o he hand, Figu e 7 shows di e en mic og aphs aken on ac u e su aces o he di e en compac s
ob ained a di e en p essu es: (a) none (loose powde ), (b) 490 MPa and (c) 990 MPa. Con igu a ion I was used o
(a) (b)
(c) (d)
(e) ( )

pe o m he EDC o he compac ob ained om loose powde , and a combined con igu a ion (II + I) o he cold-
p essed compac s.
Figu e 7. SEM mic og aphs o Al AS61 compac s: (a) loose powde s and con igu a ion I, (b) g een compac p essed a 490 MPa and
subsequen discha ge wi h con igu a ion (II + I) and (c) g een compac p essed a 990 MPa and subsequen discha ge wi h con igu a ion
(II + I) and de ails o he possible join s (mic o-welds) be ween pa icles.
Figu e 7a shows he SEM mic og aphs o he ac u e su ace o he compac ob ained om loose powde and
discha ge o he I equipmen . I can be seen ha , as is ypical o compac s ob ained om loose powde s, he e ec o
he p e e en ial elec ic cu en pa hs is mo e clea ly mani es ed, wi h mo e po ous a eas (ci cled in igu e 7a). In e -
pa icle bonds can be seen, o example, in he squa es shown in Figu e 7a, al hough in gene al, he e a e no many
such bonds ac oss he su ace s udied.
I can be seen ha he compac s p essed a 990 MPa show sligh ly be e consolida ion (no signi ican po e size in
Figu e 5.11c) han he compac s p essed a 490 MPa (po es ci cled in Figu e 7b) and he compac s ha we e no
p e iously p essed (clea ly highe po osi y, ci cled in Figu e 7a). This co obo a es he esul s ob ained o he
p e iously measu ed p ope ies ( ela i e densi y, elec ical esis i i y and Vicke s mic oha dness) whe e i was s a ed
ha he compac s p essed a 990 MPa had he lowes ela i e densi y and he lowes elec ical esis i i y, which
a ou ed consolida ion. On he o he hand, he p e iously p essed compac s ha e de o med pa icles so ha no
possible join s be ween hem can be seen. Howe e , he compac s ha ha e no been p e iously p essed do allow
some join s be ween pa icles o be seen (join s be ween pa icles su ounded by a squa e in Figu e 7a, co esponding
o he compac ob ained om loose powde ). In addi ion, he di e en mo phology o he ac u e is clea ly seen,
being mo e homogeneous and less po ous a highe applied p essu e. This is due, as men ioned abo e, o he ac ha
he compac s p essed a highe p essu e inc ease he pa hs o he passage o he cu en , which imp o es hei
consolida ion.
As wi h Al and Ti compac s clea ly shows ha he cen al zone o he compac has ewe po es han he pe iphe y.
Figu e 8 shows, as expec ed, ha he compac s ob ained om loose powde s and discha ging wi h con igu a ion I
p esen highe po osi y han he compac s ha we e p e iously p essed.
Figu e 8: (a) cen e and (b) pe iphe y o Ti compac p e iously p essed a (553 MPa) and wi h a discha ge o combined con igu a ion
(II+I) .
Figu e 9 shows he mic og aphs o Ti compac s p e-p essed a 1073 and 553 MPa and subsequen discha ge wi h
combined con igu a ion (II + I), and compac ob ained s a ing om loose powde s and con igu a ion I discha ge. I
can be seen ha , as be o e, he mos po ous compac s a e he non-p ep essed compac s (ci cled in Figu e 9a), while
he p essed compac s show lowe po osi y. The homogenei y o he p essed compac s is e iden in Figu e 9b and
Figu e 9c. The di e ences in he compac s subjec ed o di e en p essu es and he same discha ge cycle (con igu a ion
II + I) a e no no iceable in hese mic og aphs. No join s be ween pa icles caused by he passage o he elec ic cu en
can be seen in any o he cases, bu i can be obse ed ha he pa icles o he p essed compac s a e de o med due o
he p essu e o which hey ha e been subjec ed.
Figu e 9 SEM mic og aphs o Ti compac s: (a) unp essed powde s and discha ge wi h con igu a ion I, (b) p e-p essed a 553 MPa
compac s and subsequen discha ge wi h a combined modali y (II + I) and (c) p e-p essed a 1076 MPa compac s and subsequen
combined discha ge (II + I).
4. Conclusions
Comme cial powde s o Al and Ti ha e been consolida ed by passing h ough hem an elec ical cu en om a
capaci o s bank, achie ing a low ela i e densi y (high po osi y).
P e-compac ed powde s each a e he EDC p ocess a highe ela i e densi y (lowe po osi y) and highe ha dness
(a)
(c)
(b)
han he ob ained in compac s p epa ed s a ing om loose powde .
The di e en discha ge con igu a ions applied show ha con igu a ion II (800 V - 1.1 mF) a o s he b eaking o
he oxide laye co e ing powde pa icles, howe e i has no signi ican e ec on he mic oha dness and elec ical
esis i i y. On he o he hand, con igu a ion I (200 V – 66 mF) has a c i ical con ibu ion on hese p ope ies. The
highe mic oha dness is ob ained applying a discha ge wi h a combined con igu a ion (II+I) .
Acknowledgemen s
This esea ch was unded by Minis e io de Economía y Compe i i idad (Spain) and Fede (EU) h ough he esea ch
p ojec s DPI2015-69550-C2-1-P and DPI2015-69550-C2-2-P.
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