P. POKORNÝ et al.: Fe-Zn INTERMETALLIC PHASES PREPARED BY DIFFUSION ANNEALING ...
253–256
Fe-Zn INTERMETALLIC PHASES PREPARED BY DIFFUSION
ANNEALING AND SPARK-PLASMA SINTERING
Fe-Zn INTERMETALNE FAZE, PRIPRAVLJENE Z DIFUZIJSKIM
@ARJENJEM IN S SINTRANJEM V ISKRE^I PLAZMI
Petr Pokorný1, Jakub Cinert2,3, Zdenek Pala2
1Czech Technical University, Klokner Institute, Solinova 7, 166 08 Prague 6, Czech Republic
2Institute of Plasma Physics, ASCR v.v.i., Za Slovankou 1782/3, 182 00 Prague 8, Czech Republic
3University in Prague, Faculty of Electrical Engineering, Department of Electrotechnology, Prague 6, Czech Republic
cinert@ipp.cas.cz
Prejem rokopisa – received: 2014-12-22; sprejem za objavo – accepted for publication: 2015-03-10
doi:10.17222/mit.2014.309
The feasibility of iron-zinc intermetallic-phase preparation by spark-plasma sintering (SPS) was investigated. The samples were
prepared with a combination of powder metallurgy, where the powder was prepared in evacuated quartz tubes, and a sintering
process using SPS. Since the Fe-Zn intermetallic phases are mostly used for hot-dip galvanized steels, the knowledge of the
properties of individual intermetallic phases is vital for a better understanding and even further optimization of galvanization
processes. The main aim of the article is to compare the phase composition of the initial powder with the SPS samples using
X-ray diffraction. Furthermore, the hardness and microstructure were investigated as well.
Keywords: Fe-Zn intermetallics, spark-plasma sintering, diffusion annealing, phase composition, hardness
Preu~evana je bila izvedljivost priprave `elezo-cink intermetalnih faz s sintranjem v iskre~i plazmi (SPS). Vzorci so bili
pripravljeni s pomo~jo metalurgije prahov, kjer so bili prahovi zaprti v evakuirane kvar~ne cevi, ki mu je sledil postopek SPS.
Ker se Fe-Zn intermetalne faze ve~inoma uporablja pri vro~em cinkanju jekel, so lastnosti posamezne faze pomembne za bolj{e
razumevanje in celo za optimiranje procesa galvanizacije. Glavni namen ~lanka je primerjava sestave faz s pomo~jo rentgenske
difrakcije v za~etnih prahovih in SPS vzorcih. Preiskovani sta bili tudi trdota in mikrostruktura.
Klju~ne besede: Fe-Zn intermetalne zlitine, sintranje z iskre~o plazmo, difuzijsko `arjenje, sestava faz, trdota
1 INTRODUCTION
Hot-dip galvanized coating is one of the most
common protection surfaces of low-alloy steels as it
offers a good corrosion protection under normal atmo-
spheric conditions. During a hot-dip galvanizing process,
iron-zinc diffusion coating grows on the surface of gal-
vanized steel. This coating consists of a specific inter-
metallic formation, in which the iron content decreases1
towards the galvanized steel giving rise to a sequence2 of
Fe-Zn intermetallic phases. These new phases are joined
with the substrate and with each other by a system of
elementary intermetallic bonds.3 Individual phases are
different in composition, structure, morphology, thick-
ness and mechanical properties.4
Both the composition and the thickness of the coating
depend on impurity elements concentrations in the gal-
vanized steel, composition and temperature of the galva-
nized zinc bath, time of submersion, thickness of galva-
nized profiles, mechanical and thermal processing of the
galvanized steel and the cooling process after the coating
deposition.2 There is an unevenly thick layer of galva-
nized zinc, or the so-called  phase representing the
substitutional solid solution of iron in zinc, on the sur-
face. The -phase layer fosters the galvanizing process
by facilitating the formation of specific intermetallic gal-
vanized layers. These layers provide a good protection
against the corrosion and an increased resistance to wear
because the intermetallic phases are harder than the 
phase.2
With respect to the mechanical properties of interme-
tallic phases, the microhardness and compressive
strength5,6 have mostly been analysed. According to
single-crystal hardness studies,7 the highest hardness is
achieved by  and 1 phases. The results of the studies
clearly prove that the 1 phase is the hardest phase in the
hot-dip galvanized coating. It has also been shown6 that
the compression strength and hardness decrease with the
increasing hardness, hence, the  and 1 phases are rela-
tively fragile. Both  and 1 phases do not experience
plastic deformation after exceeding the yield stress;
instead a brittle fracture occurs.2 On the other hand, it is
possible to plastically deform the  phase up to the elon-
gation of 2.2 %.8 For the  phase, the elongation is only
0.5 %.9 The values of the microhardness and compressi-
ve strength for each Fe-Zn intermetallic phase are shown
in Table 1.
In our contribution, we have striven to analyse the
hardness of the  and  phases, i.e., one brittle and one
ductile phase, prepared by spark-plasma sintering.10 The
preparation of the powders for individual intermetallic
phases is relatively complicated. We took the path of
sealing the powder in an evacuated quartz ampoule
followed by a diffusion annealing process.11,12
Materiali in tehnologije / Materials and technology 50 (2016) 2, 253–256 253
UDK 621.762:669.017.12:621.762.5 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(2)253(2016)
Table 1: Mechanical properties of Fe-Zn intermetallic phases
Tabela 1: Mehanske lastnosti Fe-Zn intermetalnih faz
Phase Formula Hardness, HV Stress-strain condition
 Zn 52 –
 FeZn13 208 ductile (= 0.5 %)
 FeZn10 358 brittle
1 Fe5Zn21 505 brittle
 Fe3Zn10 326 ductile (= 2.2 %)
2 EXPERIMENTAL PART
The Fe-Zn intermetallics were prepared with the
powder-metallurgy technique. First of all, iron powder
(iron-powder, Sigma Aldrich, particles size < 150 μm,
purity of mass fractions of 100 % Fe) and zinc powder
(zinc powder, AlfaAesar, the median particle size of 6–9
μm, purity of mass fractions of 99 % Zn) were mixed
under appropriate conditions of the atomic ratio. These
mixtures ( and ) were compressed with 50 kN using a
Heckert FPZ 100/1DO universal loading machine, into
forms with a diameter of 10 mm. The obtained samples
were sealed into pre-evacuated quartz ampoules. The
sealed samples were diffusion annealed at 50 °C, below
their thermal stability, as shown on Figure 1. The
duration of diffusion annealing was 12 h and the heating
rate was 5 °C/min.
After the diffusion annealing, the powder was re-
moved from the quartz tubes and sintered with the rapid
SPS technique. Each sample was made from 9 g of the
specific phase powder. The temperature rate was 100
°C/min; 100 °C bellow the maximum sintering tempera-
ture, the temperature rate decreased to 50 °C/min. After
the maximum temperature of the sintering was achieved,
a force of 60 MPa was applied to the samples and the
holding time was 5 min. The values measured during the
sintering process are in Figure 2.
Powder X-ray diffraction (PXRD) was employed to
ascertain the phase compositions of the feedstock mate-
rials and sintered samples. The samples were mounted
onto the x, y, z positioning stage of a D8 Discover
diffractometer in the Bragg-Brentano geometry,
equipped with a 1D LynxEye detector (Bruker AXS,
Germany) and inspected with Cu-K radiation. After the
identification of crystalline phases, the CIFs (crystallo-
graphic information files) were taken from the ICSD (the
Inorganic Crystal Structure Database) and the COD (the
Crystallography Open Database) containing 13 and 2
files for the Fe-Zn systems, respectively. The obtained
PXRD patterns were subjected to the Rietveld analysis in
the TOPAS 4.2 software. Utmost care was taken to
follow the guidelines for measuring and data eva-
luation.13
The microstructures of the sintered samples were
observed with a scanning electron microscope, Carl
Zeiss SMT, EVO MA 15. Hardness measurements were
performed on polished surfaces using Innovatest Nexus
with a Vickers indenter with a force of 0.1 kg, i.e,
HV0.1, and a dwell time of 10 s according to EN ISO
6507-1. The hardness was tested twelve times in diffe-
rent places across the lengths of the polished surfaces.
3 RESULTS AND DISCUSSION
In Figure 3, both the  powder after the diffusion
annealing and its sintered sample contained only two
phases, i.e., zincite (ZnO) and the  phase. The  phase
is bcc with the  Cu5Zn8 brass type and I m43 space
group. Concerning the stoichiometry, Brandon et al.14
indicate that it is Fe3Zn10 (ICSD code 2094), Belins15
give Fe13Zn39 (ICSD code 150198) and Johansson et al.16
give Fe4Zn9 (ICSD code 103708). Employing the CIFs
for all these four stoichiometries, we obtained virtually
the same refined lattice parameter of a = 0.8972 nm, but
the correspondence between the structural model and the
measured data was the best for the Fe13Zn39 stoichio-
metry. The result of the Rietveld refinement of the 
feedstock powder is in Figure 4. When comparing the
254 Materiali in tehnologije / Materials and technology 50 (2016) 2, 253–256
P. POKORNÝ et al.: Fe-Zn INTERMETALLIC PHASES PREPARED BY DIFFUSION ANNEALING ...
Figure 2: Courses of the temperature (full lines) and changes in the
samples’ thickness (dotted lines) during SPS of both samples
Slika 2: Potek temperature (polni ~rti) in spremembe v debelini
vzorca (prekinjeni ~rti) med SPS obeh vzorcev
Figure 1: Detail of phase diagram Fe-Zn defining intermetallic phases
created by hot-dip galvanizing2
Slika 1: Detajl faznega diagrama Fe-Zn, ki dolo~a intermetalne faze,
nastale pri vro~em cinkanju2
diffraction patterns from the viewpoint of profile
analysis, the sintered sample exhibited markedly smaller
crystallite sizes whose average value was 30 nm, as
determined with the Rietveld refinement. This result is
mirrored by the broader diffraction profiles of the sin-
tered-sample PXRD pattern. The microstructure of the
metallographic specimen of the sintered sample is in
Figure 5.
For the  feedstock powder and the sintered sample,
the PXRD patterns contain a fairly large number of
reflections, which have the same 2 positions, but are
significantly broader for the sintered sample, as seen in
Figure 6. During the phase identification, the presence
of zincite and hexagonal phase of the Fe-Zn system was
established in both patterns. There are only two phases
with such a structure, one in the ICSD with code
15019915 and one in the COD with code 2105806.17 Of
these two, the former leads to a better fit; however, the fit
was not satisfactory for the lower 2 range where the
used CIFs indicated the presence of more reflections
than observed. Since both CIFs are relevant for the
so-called 1p phase, the results of the Rietveld refinement
thus indicate that the present phase is 1k. The micro-
structure of this sintered sample, which can be seen in
Figure 7, is notable by a higher intergranular porosity
when compared to the  phase of the SPS sample. More-
over, while there are clearly visible particles of zincite
(dark grey areas) in Figure 7, the oxide in the  phase of
the SPS sample is mostly seen around the Fe-Zn inter-
metallic grains.
The microhardness results are summarized in Figure
8 and they, indeed, show that the  phase is generally
about 10 % harder than the  phase, as indicated in
Table 1. The obtained hardness values of the  phase fall
P. POKORNÝ et al.: Fe-Zn INTERMETALLIC PHASES PREPARED BY DIFFUSION ANNEALING ...
Materiali in tehnologije / Materials and technology 50 (2016) 2, 253–256 255
Figure 3: PXRD patterns of  feedstock powder and sintered sample.
Vertical shift was introduced to make the features of both patterns
distinguishable.
Slika 3: Rentgenograma prahu  surovca in sintranega vzorca. Verti-
kalni zamik je izvr{en zaradi prikaza obeh diagramov.
Figure 6: PXRD patterns of the  feedstock powder and sintered
sample. Vertical shift was introduced to make the features of both
patterns distinguishable.
Slika 6: Rentgenograma prahu  surovca in sintranega vzorca. Verti-
kalni zamik krivulj je izvr{en zaradi bolj{e preglednosti krivulj.
Figure 4: Result of Rietveld refinement of the feedstock powder. Dots
are the measured data and the line is the fit. The grey curve at 0 inten-
sity is difference between measured data and fit; Rwp = 3.98. Informa-
tion about the quantitative presence of both phases in the top-right
corner is in mass fractions (w/%).
Slika 4: Rezultati Rietveld udrobnjenja prahu  surovca. Izmerjeni
podatki so to~ke, ~rta so prilegajo~i se podatki. Siva krivulja pri inten-
ziteti 0 je razlika med izmerjenimi in prilegajo~imi podatki; Rwp =
3,98. Podatki o kvantitativnem prikazu so v zgornjem desnem kotu v
masnih dele`ih, (w/%).
Figure 5: Microstructure of the  phase of the spark-plasma-sintered
sample
Slika 5: Mikrostruktura faze  v vzorcu, sintranem v iskre~i plazmi
Figure 7: Microstructure of the  phase of the spark-plasma-sintered
sample
Slika 7: Mikrostruktura  faze vzorca, sintranega v iskre~i plazmi
within a comparatively broad range from 330 HV to 460
HV, which is probably due to the porosity. However, the
values above 400 HV are substantially higher than so far
indicated for this phase.
The preparation of the pure Fe-Zn intermetallic
phases, from the phase-composition point of view, can
facilitate a better understanding of their properties. By
using diffusion annealing in the pre-evacuated quartz
ampoules and rapid sintering during the SPS process,
compact samples with around 10 % of mass fractions of
zincite were obtained, with the remaining material being
either the  or  phase. However, the zincite phase was
already in the material after the diffusion annealing and,
hence, the sintering process did not changed the phase
composition. Moreover, the diffraction-profile analysis
shows that a significant grain- or crystallite-size refine-
ment took place during the SPS process. Concerning the
presence of zincite and its effect on the hardness,
microhardness mapping of the sintered samples’ surfaces
will be performed in our next study.
4 CONCLUSIONS
By applying diffusion annealing and spark-plasma
sintering of Fe-Zn intermetallics, compact samples were
obtained. After 5 min of sintering at 500 °C and 600 °C
of the  or  Fe-Zn phases, respectively, no change in the
phase composition was observed and only the grain-
refinement phase took place. The level of zincite, or
ZnO, remained the same, at around 10 % of mass
fractions. Hence, spark-plasma sintering is a viable way
of obtaining a system, where only one Fe-Zn inter-
metallic is present.
The measured hardness of individual compact
samples verifies the fact that the brittle  phase is
generally about 10 % harder than the ductile  phase. As
for their microstructures, the brittle phase exhibits a
higher intergranular porosity.
Acknowledgments
This research has been supported by Czech Science
Foundation, Project GA ^R No P105/12/G059 and
Author Z. Author Z. Pala acknowledges the support of
the Czech Science Foundation through project number
14-36566 Gentitled Multidisciplinary research centre for
advanced materials.
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256 Materiali in tehnologije / Materials and technology 50 (2016) 2, 253–256
Figure 8: Microhardness results for the sintered-sample polished sur-
faces
Slika 8: Rezultati meritve mikrotrdote polirane povr{ine sintranih
vzorcev