J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
849–853
EFFECT OF SEVERE PLASTIC AND HEAVY COLD
DEFORMATION ON THE STRUCTURAL AND MECHANICAL
PROPERTIES OF COMMERCIALLY PURE TITANIUM
U^INEK PLASTI^NOSTI IN DEFORMACIJE PRI
PODHLAJEVANJU NA STRUKTURNE IN MEHANSKE LASTNOSTI
^ISTEGA KOMERCIALNEGA TITANA
Jan Palán1, Pavol [utta2, Tomá{ Kubina1, Mária Dománková3
1COMTES FHT, Prumyslova 995, 334 41 Dobrany, Czech Republic
2New Technologies – Research Centre Westbohemian Region, University of West Bohemia, 306 14 Plzen, Czech Republic
3Institute of Materials Science, Faculty of Materials Science and Technology Trnava, STU Bratislava, Bottova 25, 917 24 Trnava, Slovakia
jpalan@comtesfht.cz
Prejem rokopisa – received: 2016-10-25; sprejem za objavo – accepted for publication: 2017-01-23
doi:10.17222/mit.2016.307
SPD (severe plastic deformation) processing of materials provides a great potential associated with the enhancement of their
properties by refining the initial grain structure. The present experiments involved mechanical working of commercial-purity
titanium (Ti Grade 2) with the CONFORM SPD technique, which is one of the SPD methods, and with rotary swaging. The
objective was to process the material at as low temperatures as possible in order to avoid softening processes and, therefore, to
achieve the maximum strengthening through a microstructure refinement. Three passes through a CONFORM SPD machine
were completed and the resulting ultimate strength was 673 MPa. The average grain size was 330 nm. The greatest improvement
of the mechanical properties was achieved in the first pass. In the subsequent passes, the contributions were minor. The pro-
cessing in the CONFORM SPD machine did not impair the ductility of the material. Subsequently, the wires were rotary
swaged. The ultimate strength achieved was 1070 MPa. The response of the properties to this forming method was markedly
different. The reason is that rotary swaging does not belong to SPD techniques. It causes rapid work hardening and reduces the
ductility of the material. The workpiece was subsequently investigated with the aid of several techniques. Light and trans-
mission electron microscopy and X-ray diffraction were employed for evaluating the grain size, distribution and orientation.
Keywords: equal-channel angular pressing, CONFORM SPD technique, rotary swaging, titanium, extrusion
Velika plasti~na deformacija (angl. SPD) pri obdelavi materialov omogo~a veliko mo`nosti, povezane z izbolj{anjem njihovih
lastnosti z izbolj{avo izvorne strukture zrn. Pri~ujo~i preizkus je vklju~eval mehansko obdelavo komercialno dostopnega ~istega
titana (Ti Grade 2) s CONFORM SPD-tehniko, ki je ena od SPD-metod, in s kovanjem. Namen je bil, da bi se material obdelalo
pri ~im ni`jih temperaturah, kot je mogo~e, da bi se izognili procesom meh~anja in, da bi dosegli maksimalno krepitev s pre-
~i{~enjem strukture. Narejeni so bili trije nizi v CONFORM SPD-stroju in kon~na mo~ je dosegla 673 MPa. Povpre~na velikost
zrn je bila 330 nm. Najve~je izbolj{ave mehanskih lastnosti so bile dose`ene v prvem nizu. V slede~ih nizih so bile le-te manj{e.
Obdelava v CONFORM SPD-stroju ni {kodovala duktilnosti materiala. Posledi~no so bile `ice zvite. Kon~na mo~ je bila 1070
MPa. Odziv lastnosti na to metodo oblikovanja je bil izrazito druga~en. Razlog je v tem, da rotacijsko zvijanje ne sodi v tehnike
SPD. Rotacijsko zvijanje povzro~i hitro utrjevanje in zmanj{uje duktilnost materiala. Vzorec je bil nato raziskan s pomo~jo ve~
tehnik. Za ovrednotenje velikosti, razporeditve in orientacije zrn, sta bili uporabljeni transmisijska elektronska mikroskopija in
rentgenska difrakcija.
Klju~ne besede: enakomerno kotno stiskanje, CONFORM SPD-tehnika, rotacijsko zvijanje, titan, iztiskanje
1 INTRODUCTION
Severe plastic deformation (SPD) is a generic term
for a group of methods which cause grain refinement in a
material and produce equiaxed grains.1 The occurrence
of an ultrafine structure or nanostructure is conditional
on high hydrostatic pressure (P >1 GPa) and large shear
deformation applied at relatively low temperatures. The
temperatures of SPD processes should meet the
condition of T(SPD) < 0.4 T(melting).1 Another aspect is
the strain magnitude, defined as e(true strain) > 6–8.
When the above conditions are met, the forming process
leads to a high density of lattice defects, predominantly
dislocations, and to the formation of subgrains, which
reduces the stored energy.2 The relationship between the
mechanical properties and the grain size is described
with the Hall-Petch equation3,4. In the present study,
commercially pure (CP) titanium Grade 2 was worked by
means of the CONFORM SPD (CONSPD) method. This
method uses continuous angular pressing through a die
chamber of a modified design to produce ultrafine
structures and nanostructures of the materials.5–7 The
design modification reflects the principles of the ECAP
method (equal-channel angular pressing), as described in
studies.5–7 Continuous operation is the key advantage of
this forming method. The processing of CP titanium
Grade 2 with the CONFORM SDP machine was des-
cribed in multiple papers.5,7 The main outcomes were the
improved mechanical properties (ultimate tensile
strength (UTS) = 698 MPa, 0.2 % offset yield stress
(0.2 OYS) = 637 MPa), no significant decrease in the
Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853 849
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 67.017:620.1:536.421.48 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(5)849(2017)
elongation, and an equiaxed ultrafine-grained (UFG)
microstructure.7
The present study proposes a process route which
involves CONFORM SPD forming and rotary swaging
(RS) in order to enhance the mechanical properties of a
workpiece.8–10 The effects of severe plastic deformation
and work hardening are thus combined. The proposed
technology allows the mechanical properties of pure
titanium to be improved dramatically. The ultrafine-
grained CP Ti Grade 2 has a great potential because its
mechanical properties are comparable to the Ti6Al4V
alloy, which is mostly used in medicine. Recently, it was
suggested that Al and V might be toxic for the human
body.11,12
2 EXPERIMENTAL PART
The material under investigation was CP titanium
Grade 2 with the chemical composition given in Table 1.
The composition was measured by means of the Bruker
Q4 Tasman optical emission spectrometer and the Bruker
G8 Galileo gas analyser. The diameter of Ti rods was
10 mm.
Table 1: Chemical composition of feedstock in weight percent
Fe O C H N Ti
0.046 0.12 0.023 0.0026 0.0076 99.822
The processing was carried out in a CONFORM SPD
machine, type 315i with a modified die chamber (Figure
1), and in a HMP R4-4 rotary-swaging machine. During
the CONFORM SPD process, the temperature was
220 °C, the wheel speed was 0.5 min–1, and the angle of
the die chamber was 90°. Three passes through the
CONFORM SPD machine were completed. The pro-
duct’s cross-section was identical to that of the feed-
stock. Rotary swaging, the subsequent process, was
carried out at ambient temperature. In this operation, the
cross-section area was reduced by 20 % in each pass.
The total area reduction was 90 %.
For the purpose of observation with a transmission
electron microscope (TEM), thin foils were prepared
with the final electrolytic thinning in a Tenupol 5 device,
using a solution of 300 mL CH3OH + 175 mL 2-butanol
+ 30 mL HClO4 at –10 °C and a voltage of 40 V. The
TEM analysis was performed with a JEOL 200CX
instrument with an acceleration voltage of 200 kV. Selec-
tive electron diffraction was used for the determination
of the phases. The grain size was measured using the
linear intercept method.
The preferred orientation of crystallites (texture) was
analysed with an automatic powder diffractometer
X’Pert-Pro equipped with an ultra-fast semiconductor
position-sensitive detector Pixcel. Cu-K1 radiation
( = 0.154056 nm) was used. The texture was characte-
rized from the radial X-ray diffraction patterns using the
Harris (1952) texture index, Equation (1):
T
n I /R
I /R
i
i i
j j
j
n=
⋅
=
∑
1
(1)
where n is the number of the reflections investigated, Ii
is the observed intensity and Ri is the corresponding
intensity for the sample with randomly oriented
crystallites. The Ri values were obtained from the ICDD
PDF standard diffraction data file (reference code
00-005-0682). The texture was analysed in the direction
of the material flow, both after CONFORM SPD
(longitudinal direction), and after CONFORM SPD +
rotary swaging.
3 MICROSTRUCTURE
The mean grain size in the initial condition of the
feedstock was 5390 nm. After the first pass, the mean
grain size was daverage ~ 320±35 nm in the transverse
direction. After the first pass, the microstructure was
equiaxed with a non-uniform dislocation density (Figure
2a). Some locations exhibited a preferential orientation
(Figure 2b). After the second pass (Figure 2c), the mean
grain size was daverage ~ 250±25 nm in transverse
direction. The dislocation density was still non-uniform
after the second pass. After the third pass, the mean grain
size was daverage ~ 330±30 nm (Figure 3d): the grain was
larger than after the second pass. This increase can be
attributed, in part, to the non-uniform deformation and to
the high surface activity of the UFG microstructure.
High surface activity and dislocation density (strain mag-
nitude) lower the temperatures of softening processes. A
certain grain growth can be expected to occur during the
forming due to deformation heat and the heat retained in
the die chamber (220 °C). The grain growth upon multi-
ple passes through the CONFORM SPD machine was
already reported in 9.
Figure 3a is a micrograph of the structure in the
transverse direction after three passes through the CON-
FORM SPD machine and after a 35 % area reduction
J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
850 Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: Schematic illustration of the CONFORM SPD process
with rotary swaging (RS). The mean grain size in the
transverse direction is daverage ~ 300±150 nm. The large
standard deviation is due to a large variation in the grain
size. Figure 3b is a micrograph taken in the longitudinal
direction after CONFORM SPD and RS. The grains are
elongated and aligned in the direction of forming due to
the nature of the deformation introduced by rotary
swaging. Unlike in CONFORM SPD, the grains become
elongated instead of being refined or converted into new
polyhedral grains. After the additional reduction due to
rotary swaging (3 passes through CONFORM SPD + the
total area reduction of 50 % by RS), it became im-
possible to determine the grain size due to the high
dislocation density, as seen in Figure 3c. The summary
of the average grain sizes is given in Table 2.
Table 2: Average grain size in the transverse and longitudinal sections
obtained from TEM images
Condition
Grain size (nm)
Transverse Longitudinal
as received 5390±20
CON SPD – 1 pass 320±35 340±30
CONSPD – 2 passes 250±25 310±30
CONSPD – 3 passes 330±30 420±30
CON SPD – 3 passes +
RS (35 %) 300±150 220±50
CONSPD – 3 passes +
RS (50 %)
Not possible to evaluate due to high
dislocation density
J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853 851
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 3: TEM images: a) CON SPD – 3 passes + RS (area reduction
by 35 %) in the transverse direction, b) CON SPD – 3 passes + RS
(35 %) in the longitudinal direction, c) CON SPD – 3 passes + RS
(50 %) in the transverse direction
Figure 2: TEM images: a) CON SPD – 1 pass (transverse), b) CON
SPD – 1 pass (longitudinal), c) CON SPD – 2 passes (transverse),
d) CON SPD – 3 passes (transverse)
elongation, and an equiaxed ultrafine-grained (UFG)
microstructure.7
The present study proposes a process route which
involves CONFORM SPD forming and rotary swaging
(RS) in order to enhance the mechanical properties of a
workpiece.8–10 The effects of severe plastic deformation
and work hardening are thus combined. The proposed
technology allows the mechanical properties of pure
titanium to be improved dramatically. The ultrafine-
grained CP Ti Grade 2 has a great potential because its
mechanical properties are comparable to the Ti6Al4V
alloy, which is mostly used in medicine. Recently, it was
suggested that Al and V might be toxic for the human
body.11,12
2 EXPERIMENTAL PART
The material under investigation was CP titanium
Grade 2 with the chemical composition given in Table 1.
The composition was measured by means of the Bruker
Q4 Tasman optical emission spectrometer and the Bruker
G8 Galileo gas analyser. The diameter of Ti rods was
10 mm.
Table 1: Chemical composition of feedstock in weight percent
Fe O C H N Ti
0.046 0.12 0.023 0.0026 0.0076 99.822
The processing was carried out in a CONFORM SPD
machine, type 315i with a modified die chamber (Figure
1), and in a HMP R4-4 rotary-swaging machine. During
the CONFORM SPD process, the temperature was
220 °C, the wheel speed was 0.5 min–1, and the angle of
the die chamber was 90°. Three passes through the
CONFORM SPD machine were completed. The pro-
duct’s cross-section was identical to that of the feed-
stock. Rotary swaging, the subsequent process, was
carried out at ambient temperature. In this operation, the
cross-section area was reduced by 20 % in each pass.
The total area reduction was 90 %.
For the purpose of observation with a transmission
electron microscope (TEM), thin foils were prepared
with the final electrolytic thinning in a Tenupol 5 device,
using a solution of 300 mL CH3OH + 175 mL 2-butanol
+ 30 mL HClO4 at –10 °C and a voltage of 40 V. The
TEM analysis was performed with a JEOL 200CX
instrument with an acceleration voltage of 200 kV. Selec-
tive electron diffraction was used for the determination
of the phases. The grain size was measured using the
linear intercept method.
The preferred orientation of crystallites (texture) was
analysed with an automatic powder diffractometer
X’Pert-Pro equipped with an ultra-fast semiconductor
position-sensitive detector Pixcel. Cu-K1 radiation
( = 0.154056 nm) was used. The texture was characte-
rized from the radial X-ray diffraction patterns using the
Harris (1952) texture index, Equation (1):
T
n I /R
I /R
i
i i
j j
j
n=
⋅
=
∑
1
(1)
where n is the number of the reflections investigated, Ii
is the observed intensity and Ri is the corresponding
intensity for the sample with randomly oriented
crystallites. The Ri values were obtained from the ICDD
PDF standard diffraction data file (reference code
00-005-0682). The texture was analysed in the direction
of the material flow, both after CONFORM SPD
(longitudinal direction), and after CONFORM SPD +
rotary swaging.
3 MICROSTRUCTURE
The mean grain size in the initial condition of the
feedstock was 5390 nm. After the first pass, the mean
grain size was daverage ~ 320±35 nm in the transverse
direction. After the first pass, the microstructure was
equiaxed with a non-uniform dislocation density (Figure
2a). Some locations exhibited a preferential orientation
(Figure 2b). After the second pass (Figure 2c), the mean
grain size was daverage ~ 250±25 nm in transverse
direction. The dislocation density was still non-uniform
after the second pass. After the third pass, the mean grain
size was daverage ~ 330±30 nm (Figure 3d): the grain was
larger than after the second pass. This increase can be
attributed, in part, to the non-uniform deformation and to
the high surface activity of the UFG microstructure.
High surface activity and dislocation density (strain mag-
nitude) lower the temperatures of softening processes. A
certain grain growth can be expected to occur during the
forming due to deformation heat and the heat retained in
the die chamber (220 °C). The grain growth upon multi-
ple passes through the CONFORM SPD machine was
already reported in 9.
Figure 3a is a micrograph of the structure in the
transverse direction after three passes through the CON-
FORM SPD machine and after a 35 % area reduction
J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
850 Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: Schematic illustration of the CONFORM SPD process
with rotary swaging (RS). The mean grain size in the
transverse direction is daverage ~ 300±150 nm. The large
standard deviation is due to a large variation in the grain
size. Figure 3b is a micrograph taken in the longitudinal
direction after CONFORM SPD and RS. The grains are
elongated and aligned in the direction of forming due to
the nature of the deformation introduced by rotary
swaging. Unlike in CONFORM SPD, the grains become
elongated instead of being refined or converted into new
polyhedral grains. After the additional reduction due to
rotary swaging (3 passes through CONFORM SPD + the
total area reduction of 50 % by RS), it became im-
possible to determine the grain size due to the high
dislocation density, as seen in Figure 3c. The summary
of the average grain sizes is given in Table 2.
Table 2: Average grain size in the transverse and longitudinal sections
obtained from TEM images
Condition
Grain size (nm)
Transverse Longitudinal
as received 5390±20
CON SPD – 1 pass 320±35 340±30
CONSPD – 2 passes 250±25 310±30
CONSPD – 3 passes 330±30 420±30
CON SPD – 3 passes +
RS (35 %) 300±150 220±50
CONSPD – 3 passes +
RS (50 %)
Not possible to evaluate due to high
dislocation density
J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853 851
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 3: TEM images: a) CON SPD – 3 passes + RS (area reduction
by 35 %) in the transverse direction, b) CON SPD – 3 passes + RS
(35 %) in the longitudinal direction, c) CON SPD – 3 passes + RS
(50 %) in the transverse direction
Figure 2: TEM images: a) CON SPD – 1 pass (transverse), b) CON
SPD – 1 pass (longitudinal), c) CON SPD – 2 passes (transverse),
d) CON SPD – 3 passes (transverse)
4 TEXTURE EVALUATION
The preferred orientation of crystallites expressed
with the texture index Ti (Equation 1, Table 3) is, in all
the cases, in the [001] direction perpendicular to the
sample surface analysed. The highest value was found
for CONSPD – 3 passes + RS (75 %) titanium sample,
i.e., the sample that was processed using the CONFORM
SPD device and rotary swaging (basal texture, Figure 5).
An increased value of the texture index can be seen in
the initial state, due to the previous wire-drawing process
(Figure 4). The texture index is lower for the samples
that were processed with the CONFORM SPD device.
Texture indices for the [101] direction are listed for the
sake of comparison. Nevertheless, all their values are
lower than 1. It means that no preferred orientation of
crystallites in the [101] direction is present, as opposed
to the sample surface.
Table 3: Texture evaluation using X-ray diffraction
Plane (h k l)
Texture index
as received CONSPD – 1pass
CONSPD – 2
passes
Ti (002) 3.13 2.49 2.67
Ti (101) 0.66 0.69 0.86
CONSPD – 3
passes
CONSPD – 3
passes + RS
(75 %)
Standard
Ti (002) 2.37 3.48 1
Ti (101) 0.97 0.24 1
4 MECHANICAL PROPERTIES
Table 4 indicates that the largest increase in the
mechanical properties was obtained during the first pass
through CONFORM SPD. The subsequent passes led to
smaller increments. It is important to note that the
increase in the ultimate strength and yield stress upon
CONFORM SPD is not offset by a decrease in the
ductility. The improvement in the mechanical properties
is mainly due to the grain refinement and the increased
dislocation density, which impede the dislocation move-
ment. A further increase in the mechanical properties
was obtained with rotary swaging applied after the three
passes through the CONFORM SPD machine. In compa-
rison with the CONFORM SPD process, rotary swaging
leads to a decrease in the ductility as a result of work
hardening.
Table 4: Mechanical properties in the as-received condition, after
CONFORM SPD processing and after RS
Condition
0.2
OYS UTS A5 RA
MPa MPa % %
as received 370 480 25 52
CONSPD – 1 pass 540 580 23 62
CONSPD – 2 passes 560 600 23 62
CONSPD – 3 passes 570 623 20 64
CONSPD – 3 passes + RS
(50 %) 830 885 13 54
CONSPD – 3 passes + RS
(75 %) 930 1000 12 57
CONSPD – 3 passes + RS
(85%) 950 1070 12 58
RS only (85 %) 780 850 12 50
5 DISCUSSION
The CONFORM SPD processing led to higher ulti-
mate strengths and yield stresses without a reduced
ductility. This is characteristic of the process of the for-
mation of a UFG equiaxed structure shown in Figure 2.
The grain size and distortion are non-uniform due to
non-uniform deformation during the forming process.
The preferred orientation of crystallites in the [001]
direction perpendicular to the surfaces of the investigated
samples is not too significant, except for the sample
which was processed with CONFORM SPD and the
rotary swaging machine where the highest value of the
texture index was observed (the basal texture).
Major increases in the ultimate strength and yield
stress were found after the first pass through the CON-
J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
852 Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 5: Diffraction radial profile of the specimen with the strongest
texture: CONSPD – 3 passes + rotary swaging (75 %)
Figure 4: Diffraction radial profile of the as-received specimen
FORM SPD machine, whereas the increments from the
subsequent passes were small. This is closely related to
the grain size, which did not decrease during the sub-
sequent passes. It is possible to say that the additional
deformation causes the subgrains to rotate into high-
angle grain boundaries, typically with an equiaxed shape
of the grains.5,7,9 The subsequent rotary swaging led to a
further increase in the mechanical properties, but the
strengthening mechanism was different this time. Instead
of the formation of equiaxed grains, the grains became
elongated in the direction of forming, with a much
higher dislocation density (Figure 3).10,11 When com-
pared to the CONFORM SPD route, rotary swaging led
to a reduced ductility as a consequence of work harden-
ing.
6 CONCLUSION
This study involved the processing of Ti Grade 2
using CONFORM SPD and rotary swaging with the goal
of improving its mechanical properties. The results and
findings are described below:
• The CONFORM SPD processing substantially
refined the grain from its initial size of 5390 nm to
350 nm. The subsequent rotary swaging did not
provide for a further grain refinement but led to a
grain elongation and to a higher dislocation density.
• The processing led to the basal texture. The most
significant form of texture was found in the specimen
processed with CONFORM SPD and rotary swaging.
• Three passes through the CONFORM SPD machine
led to a strength of 623 MPa and a yield stress of
570 MPa without any notable decrease in the elon-
gation.
• After CONFORM SPD, the specimens were rotary
swaged, which brought their strength to 1070 MPa
and the yield stress to 950 MPa. In the initial con-
dition, the ultimate strength was 480 MPa and the
yield stress was 370 MPa.
Acknowledgment
These results were obtained under the project entitled
"Development of West-Bohemian Centre of Materials
and Metallurgy" No. lo1412, financed by the Ministry of
Education of the Czech Republic.
7 REFERENCES
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4 A. Mishra, B. Kad, F. Gregori, M. Meyers, Microstructural evolution
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5 M. Duchek, T. Kubina, J. Hodek, J. Dlouhy, Development of the pro-
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7 T. Kubina, J. Dlouhý, M. Kover, Preparation and thermal stability of
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CONFORM equipment, Mater. Tehnol., 49 (2015), 2, doi:10.17222/
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8 L. Ostrovska, L. Vistejnova, J. Dzugan, P. Slama, T. Kubina, E.
Ukraintsev, D. Kubies, M. Kralickova, M. Kalbacova, Biological
evaluation of ultra-fine titanium with improved mechanical strength
for dental implant engineering, J. Mater. Sci., 23 (2015),
doi:10.1007/s10853-015-9619-3
9 M. Zemko, T. Kubina, J. Dlouhý, J. Hodek, Technological aspects of
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machine, IOP Conference Series: Materials Science and Engineering,
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10 D. V. Gunderov, A. V. Polyakov, I. P. Semenova, Evolution of
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drawing, Materials Science and Engineering, 562 (2013), 128–136,
doi:10.1016/j.msea.2012.11.007
11 I. P. Semenova, R. Z. Valiev, E. B. Yakushima, G. H. Salimgareeva,
T. C. Lowe, Strength and fatigue properties enhancement in ultra-
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J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853 853
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
4 TEXTURE EVALUATION
The preferred orientation of crystallites expressed
with the texture index Ti (Equation 1, Table 3) is, in all
the cases, in the [001] direction perpendicular to the
sample surface analysed. The highest value was found
for CONSPD – 3 passes + RS (75 %) titanium sample,
i.e., the sample that was processed using the CONFORM
SPD device and rotary swaging (basal texture, Figure 5).
An increased value of the texture index can be seen in
the initial state, due to the previous wire-drawing process
(Figure 4). The texture index is lower for the samples
that were processed with the CONFORM SPD device.
Texture indices for the [101] direction are listed for the
sake of comparison. Nevertheless, all their values are
lower than 1. It means that no preferred orientation of
crystallites in the [101] direction is present, as opposed
to the sample surface.
Table 3: Texture evaluation using X-ray diffraction
Plane (h k l)
Texture index
as received CONSPD – 1pass
CONSPD – 2
passes
Ti (002) 3.13 2.49 2.67
Ti (101) 0.66 0.69 0.86
CONSPD – 3
passes
CONSPD – 3
passes + RS
(75 %)
Standard
Ti (002) 2.37 3.48 1
Ti (101) 0.97 0.24 1
4 MECHANICAL PROPERTIES
Table 4 indicates that the largest increase in the
mechanical properties was obtained during the first pass
through CONFORM SPD. The subsequent passes led to
smaller increments. It is important to note that the
increase in the ultimate strength and yield stress upon
CONFORM SPD is not offset by a decrease in the
ductility. The improvement in the mechanical properties
is mainly due to the grain refinement and the increased
dislocation density, which impede the dislocation move-
ment. A further increase in the mechanical properties
was obtained with rotary swaging applied after the three
passes through the CONFORM SPD machine. In compa-
rison with the CONFORM SPD process, rotary swaging
leads to a decrease in the ductility as a result of work
hardening.
Table 4: Mechanical properties in the as-received condition, after
CONFORM SPD processing and after RS
Condition
0.2
OYS UTS A5 RA
MPa MPa % %
as received 370 480 25 52
CONSPD – 1 pass 540 580 23 62
CONSPD – 2 passes 560 600 23 62
CONSPD – 3 passes 570 623 20 64
CONSPD – 3 passes + RS
(50 %) 830 885 13 54
CONSPD – 3 passes + RS
(75 %) 930 1000 12 57
CONSPD – 3 passes + RS
(85%) 950 1070 12 58
RS only (85 %) 780 850 12 50
5 DISCUSSION
The CONFORM SPD processing led to higher ulti-
mate strengths and yield stresses without a reduced
ductility. This is characteristic of the process of the for-
mation of a UFG equiaxed structure shown in Figure 2.
The grain size and distortion are non-uniform due to
non-uniform deformation during the forming process.
The preferred orientation of crystallites in the [001]
direction perpendicular to the surfaces of the investigated
samples is not too significant, except for the sample
which was processed with CONFORM SPD and the
rotary swaging machine where the highest value of the
texture index was observed (the basal texture).
Major increases in the ultimate strength and yield
stress were found after the first pass through the CON-
J. PALÁN et al.: EFFECT OF SEVERE PLASTIC AND HEAVY COLD DEFORMATION ...
852 Materiali in tehnologije / Materials and technology 51 (2017) 5, 849–853
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 5: Diffraction radial profile of the specimen with the strongest
texture: CONSPD – 3 passes + rotary swaging (75 %)
Figure 4: Diffraction radial profile of the as-received specimen
FORM SPD machine, whereas the increments from the
subsequent passes were small. This is closely related to
the grain size, which did not decrease during the sub-
sequent passes. It is possible to say that the additional
deformation causes the subgrains to rotate into high-
angle grain boundaries, typically with an equiaxed shape
of the grains.5,7,9 The subsequent rotary swaging led to a
further increase in the mechanical properties, but the
strengthening mechanism was different this time. Instead
of the formation of equiaxed grains, the grains became
elongated in the direction of forming, with a much
higher dislocation density (Figure 3).10,11 When com-
pared to the CONFORM SPD route, rotary swaging led
to a reduced ductility as a consequence of work harden-
ing.
6 CONCLUSION
This study involved the processing of Ti Grade 2
using CONFORM SPD and rotary swaging with the goal
of improving its mechanical properties. The results and
findings are described below:
• The CONFORM SPD processing substantially
refined the grain from its initial size of 5390 nm to
350 nm. The subsequent rotary swaging did not
provide for a further grain refinement but led to a
grain elongation and to a higher dislocation density.
• The processing led to the basal texture. The most
significant form of texture was found in the specimen
processed with CONFORM SPD and rotary swaging.
• Three passes through the CONFORM SPD machine
led to a strength of 623 MPa and a yield stress of
570 MPa without any notable decrease in the elon-
gation.
• After CONFORM SPD, the specimens were rotary
swaged, which brought their strength to 1070 MPa
and the yield stress to 950 MPa. In the initial con-
dition, the ultimate strength was 480 MPa and the
yield stress was 370 MPa.
Acknowledgment
These results were obtained under the project entitled
"Development of West-Bohemian Centre of Materials
and Metallurgy" No. lo1412, financed by the Ministry of
Education of the Czech Republic.
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MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS