The subject of this study was to examine and compare the impact of intense hydrostatic extrusion on grain refinement in three different alloys: duplex stainless steel, commercially used aluminum alloy (6060) and Ag-Cu12 alloy. As a result of the process grain sizes from 370 nm to 90 nm were obtained in aluminum and duplex steel. To analyze the of hydrostatic on mechanical properties tensile tests were also carried out. The highest grain refinement (70 nm) and yield strength increase (over 300%) was observed in duplex steel af-ter hydrostatic extrusion.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3560

Adamczyk-Cieslak, B.

Maj, P.

Mizera, J.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 3, 03AET08(4pp) (2013) 
 
 
2304-1862/2013/2(3)03AET08(4) 03AET08-1  2013 Sumy State University 
Comparison of Grain Refinement in Selected Materials Subjected to Hydrostatic Extrusion 
 
J. Mizera*, P. Maj, B. Adamczyk-Cieslak 
 
Warsaw University of Technology, Warsaw Woloska 141 02-507, Poland 
 
(Received 08 June 2013; published online 02 September 2013) 
 
The subject of this study was to examine and compare the impact of intense hydrostatic extrusion on grain 
refinement in three different alloys: duplex stainless steel, commercially used aluminum alloy (6060) and 
Ag-Cu12 alloy. As a result of the process grain sizes from 370 nm to 90 nm were obtained in aluminum and 
duplex steel. To analyze the of hydrostatic on mechanical properties tensile tests were also carried out. The 
highest grain refinement (70 nm) and yield strength increase (over 300%) was observed in duplex steel af-
ter hydrostatic extrusion. 
 
Keywords: Hydrostatic Extrusion, Severe Plastic Deformation, Nanomaterials, Duplex Steel, Aluminium 
Alloy, Silver Alloy. 
 
 PACS number(s): 81.07.Bc 
 
 
                                                          
* jmizera@inmat.pw.edu.pl 
1. INTRODUCTION 
 
Nanomaterialsare defined as substances where at 
least one dimension is less than approximately 100 
nanometers. This has a significant impact on the ob-
served properties comparing to the commonly used ma-
terials [1,2]. The scale effect causes increased ratio of 
surface area to volume and excess energy in the mate-
rial. There are two main strategies to achieve this. In 
the first one where the material is formed atom by at-
om is called bottom-up approach. The second group 
involves the transformation of the initial structure to 
nanoscale material and is referred a stop–down. So far 
this is the most effective way to obtain bulk nano-
materials. 
Severe plastic deformation (SPD) belongs to the top-
down approach and is a generic term describing a 
group of methods used to produce ultrafine-grained and 
nano-materials [3]. The concept of this method is to 
induce large strains during forming. To achieve this 
special tool geometries are used to prevent the free flow 
of material. Due to large deformation the microstruc-
ture undergoes a series of transformation. During the 
process high densities of crystal lattice defects are pro-
duced, particularly dislocations, this results in a signif-
icant refining of the grains. The most common methods 
in this group are equal channel pressing (ECAP)[4,5], 
high-pressure torsion (HPT) [6,7] and hydrostatic ex-
trusion (HE) [8,9]. After the process the material exhib-
its increase in strength and reduced elongation caused 
by decrease in dislocation mobility. Various materials 
can react differently to large deformations. In particu-
lar, the grain refinement process is still not fully un-
derstood by the researchers [10]. 
Hydrostatic extrusion is a process in which the ma-
terial is pushed through a die of the desired cross-
section. The process is carried out in a sealed cylinder 
in a hydrostatic medium in which the piston movement 
produces pressure to extrude the rod. The schematic of 
the process is shown in the Fig. 1. During the process 
large grain refinement and high strains are achieved 
under subsequent extrusion processes[11]. What is 
noteworthy the material is continuously cooled which 
greatlyreducesgrain growth that may occurdurin de-
formation. Recent developments in hydrostatic extru-
sion lead to significant grain refinement, down to na-
nometric scale for different materials like aluminum 
[12], titanium [13], and austenitic steel[14]. 
 
 
 
Fig. 1 - Schematic representation of the hydrostatic 
extrusion process 
 
2. EXPERIMENTAL PROCEDURE 
 
The materials used in the investigations were a 
commercial 1.4462 duplex stainless steel, Al-Mg-Si 
(6060) aluminum alloy and Ag-12Cu alloy. The three 
materials after hydrostatic extrusion were deformed to 
approximately ε=3.5. The processes was performed at 
the Institute of High Pressure Physics "UNIPRESS" 
(Poland). 
Transmission Electron Microscopy (TEM) was used 
to study the microstructural evolution. Observations 
were carried out on section perpendicular to the extru-
 J. MIZERA, P. MAJ, B. ADAMCZYK-CIESLAK PROC. NAP 2, 03AET08 (2013) 
 
 
03AET08-2 
sion direction. The mean grain size (deq defined asthe 
diameter of a circle which has the surface area equal to 
the surface area of a given grain) was determined by a 
computer equipped with an image analyzer. The deq 
value was determined for more than 200randomly se-
lected grains. The microscopic observations were car-
ried out using a JEOL JEM 1200 EX II with an accel-
erating voltage of 120 kV. 
The tensile tests were conducted on MTS Q/Test 10 
machine with a uniaxial quasistatic strain rate of 10-3 
s-1. 
The aim of this research was to compare micro-
structure and mechanical properties of three different 
face-centred cubic (FCC) metals. 
 
3. RESULTS 
 
Fig. 2. shows the microstructure of Ag-12Cu alloy 
subjected to hydrostatic extrusion. HE process resulted 
in fragmentation of the microstructure, and conse-
quently the average output grain size equal to 90 nm 
was obtained. It should be noted that the deformation 
led to the apparent fragmentation of original grains 
and their elongation. There were also regions with high 
dislocation density in the vicinity of grains free of dislo-
cations. Electron microscopy observations revealed the 
appearance of plastic deformation bands which contain 
grains with the smallest size. The selected area diffrac-
tion (SAD) patterns indicate that the microstructure 
contains grains separated by high angle grain bounda-
ries. 
In contrast the structure of duplex stainless steel 
after hydrostatic extrusion is more diverse (Fig. 3). 
Ferrite forms ultrafine equiaxed grains with diameter 
of approximately 0.37 µm. There are still some disloca-
tion walls and clusters that didn’t yet evolve to sub-
grains. The austenite regions are much more fragment-
ed. Nanosized blocks of diameter about 70 nm circum-
navigate along elongated bands through the material. 
The SAD-patterns are blurred and stretched (especially 
for austenite) compared to other materials. This indi-
cates a high disorder in the crystallographic structure 
and very small grain size with large misorientation. 
Completely different from the previously described 
material is the microstructure of aluminum alloy (Fig. 
4). Hydrostatic extrusion to the value of ε  3.5 leads to 
the refinement on microstructure and obtain the aver-
age grain size deq  0.35μm. The SAD pattern from this 
section consists of diffuse rings characteristic of poly-
crystalline materials. These spots form nearly continu-
ous diffraction rings, which suggest a large number of 
high angle grain boundaries. The observation indicates 
that most of the grains are free of dislocations or sepa-
rated into cells. This suggests that the microstructure 
of investigated alloy is related to dynamic recovery un-
der large strain. Dynamic recovery occurs easily during 
aluminum deformation at room temperature due to the 
high value of stack fault energy. (SFE) The severe 
strain induced in the material provides enough energy 
for the dislocations to move from the interior of the 
grains to the vicinity of the grain boundaries. However, 
ome areas with high density of dislocations are visible. 
 
 
 
Fig. 2 - Bright field TEM images of Ag-12Cu alloy processed 
by HE (insets are the corresponding selected-area diffraction 
patterns). 
 
 
 
Fig. 3 - Bright field TEM images of the duplex stainless steel 
processed by HE (insets are the corresponding selected-area 
diffraction patterns). 
 
 
 
0.5 m
 
  
 
Fig. 4 - Bright field TEM images of the aluminum alloy pro-
cessed by HE (insets are the corresponding selected-area dif-
fraction patterns). 
 
For mechanical properties tensile tests were con-
ducted for each material before and after hydrostatic 
extrusion. The results are summarized in Table 1. Ac-
cording to assumptions strength of the materials rose 
and maximum elongation decreased after hydrostatic 
extrusion in all materials.  
The largest force was needed to deform duplex 
stainless steel although the maximum elongation was 
deformation bands 
 COMPARISON OF GRAIN REFINEMENT IN SELECTED MATERIALS... PROC. NAP 2, 03AET08 (2013) 
 
 
03AET08-3 
the lowest. What is worth noting the percent change of 
strength -yield stress (YS) 309%, ultimate tensile 
strength (UTS) 250% and maximum elongation (10%) 
after hydrostatic extrusion were the most significant 
from all tested materials. In case of the aluminum the 
mechanical properties altered only slightly compared to 
the initial state. Yield stress increased about 170 % and 
ultimate tensile stress rose to 131% a decrease in the 
maximum elongation was insignificant compared to 
initial state. What is worth noting the total strain for 
aluminum is merely ε=3.5 whereas some researchers 
achieved ε=60 using cyclic extrusion-compression[15]. 
The change of properties for Ag-12Cu alloy was moder-
ate compared to previously described materials. The 
highest increase of strength was accompanied by the 
largest decrease in grain size which is in accordance 
with the Hall-Petch equation. 
 
 
4. DISCUSION 
 
The aim of this study was to evaluate microstruc-
ture and mechanical properties changes for different 
material subjected to hydrostatic extrusion. To achieve 
this three different metals with FCC crystallographic 
structure were extruded to a total strain of 3.5. TEM 
was carried out to compare the microstructure changes 
which have taken place under the influence of plastic 
deformation. Additional tensile tests were conducted in 
order to compare the mechanical properties of tested 
materials. 
The largest grain refinement was observed for du-
plex stainless steel along with it the highest strength 
needed to deform the material. This is directly related 
to the increase of dislocations density and grain re-
finement. The dominating mechanism of grain refine-
ment all materials was subdivision by dislocation 
walls. During deformation density of dislocations in-
creases rapidly. Cellular structures with incidental 
dislocation boundaries are formed within the grains 
and cell blocks separated by geometrically necessary 
boundaries. With further increase of strain misorienta-
tion grows and subgrains are created [4].The process is 
continuously repeated leading to structure fragmenta-
tion although there is a certain asymptotic limit that 
the grain size tends resulting from thermodynamic 
conditions. Additional mechanisms that facilitate dis-
location accommodation increase grain refinement [16]. 
An example of such behavior was observed in austenite 
of duplex stainless steel where twinning occurred. The 
structure was most fragmented from all tested materi-
als.  
The two primary methods of deformation in metals 
are slip and twinning. Slip occurs by dislocation glide 
of either screw or edge dislocations within a slip plane. 
Slip is by far the most common mechanism. Twinning 
is less common but readily occurs under some circum-
stances [17]. Twinning proceeds when there are not 
enough slip systems to accommodate deformation 
and/or when the material has a very low SFE. Twins 
are abundant in many low SFE metals like copper[18], 
nickel [19]and silver [20].The microstructure observa-
tions in deformed, low SFE FCC materials (duplex 
steel and silver alloy) are often difficult to characterize 
because of the complexity of the deformation micro-
structures; the latter usually result from a combination 
of dislocation glide and fine mechanical twinning and 
then, at higher strains, shear banding at different 
scales. 
It has been proved that SFE is an important mate-
rial parameter that affects the deformation mecha-
nisms and the mechanical behavior of metals and al-
loys[21].In the case of aluminum alloy which is a mate-
rial with high SFE (~ 160mJ/m2)plastic deformation 
process is realized by slip. Additionally during defor-
mation occurs dynamic recovery. The severe strain 
induced in the material provides enough energy for the 
dislocations to move from the interior of the grains to 
the vicinity of the grain boundaries. In the case of du-
plex steel and Ag-Cu alloy the deformation and grain 
refinement were facilitated. The structures of low SFE 
material tend to twin and create partial rather than 
screw dislocation. Due to this five or more slip systems 
must be active for large deformations. When shear de-
formation and twinning occurs at the same time grains 
align towards a more preferred orientation such as 
<111> and <100>. This leads to formation of bands 
both seen in duplex stainless steel and Ag-Cu alloy[22]. 
The observed forces needed for deformation were 
higher than in the initial state for all materials after 
hydrostatic extrusion. This is due to the increase of 
defects concentration and grain refinement in the ma-
terial. However the increase of strength is at the ex-
pense of elongation. This is particularly notice able for 
the duplex steel where the most significant changes 
were observed. The SAD patterns were most irregular 
and blurred for austenite of the studied materials. For 
the rest of the metals the changes of microstructure 
weren’t so noticeable and thus the mechanical proper-
ties differed not so much from the initial state. 
Table 1 - Average grain size and mechanical properties of tested materials 
 
Material 
Yield stress [MPa] 
 
Ultimate tensile 
strength [MPa] 
εMAX[%] 
 
deq[µm] 
 
Before 
HE 
After 
HE 
Change 
ratio 
[%] 
Before 
HE 
After 
HE 
Change 
ratio 
[%] 
Before 
HE 
After 
HE 
Change 
ratio 
[%] 
Before 
HE 
After 
HE 
Duplex 
steel 
572 1770 309% 748 1872 250% 23.4 2.4 10% 
Ferrite 
4.3 
Austenite 
3.7 
Ferrite 
0.37 
Austenite 
0.07 
Ag-12Cu 378 630 167% 382 800 209% 13.5 5.6 41% 0.46 0.09 
Aluminum 
6060 
170 290 171% 261 341 131% 16.2 13.4 83% 1.24 0.35 
 J. MIZERA, P. MAJ, B. ADAMCZYK-CIESLAK PROC. NAP 2, 03AET08 (2013) 
 
 
03AET08-4 
5. CONCLUSIONS 
 
From all tested materials subjected to hydrostatic 
extrusion (strain ε=3.5)only two with the lowest SFE 
exhibited nanocrystalline structure – duplex steel and 
Ag-12Cu alloy. In each case the main mechanism was 
shear deformation and twinning.  
The largest increase in strength of the material was 
observed for duplex stainless (increase over 300% in 
UTS) steel and the smallest for aluminum 6060 (130% 
increase in UTS). This is directly correlated to the de-
formation mechanisms in both materials. Additional 
twinning and large grain refinement in the austenite 
phase resulted in more effective blockade of dislocation 
movement. 
 
 
REFERENCES 
 
1. L. Zhang, T.J Webster, Nano Today. 4, 66. (2009). 
2. M. Lines, Journal of Alloys and Compounds 449, 242 
(2008). 
3. A. Azushima, R. Kopp, A. Korhonen, D.Y. Yang, F. Micari, 
G. D. Lahoti, P. Groche, J Yanagimoto, N Tsuji, 
A Rosochowski, A. Yanagida, CIRP Annals - 
Manufacturing Technology 57, 716 (2008). 
4. Y.T. Zhu, T.C. Lowe. Materials Science and Engineering 
A. 291, 46 (2000). 
5. Y.H. Zhao, X.Z. Liao, Z. Jin, R.Z. Valiev, Y.T. Zhu, Acta 
Materialia 52, 4589 (2004). 
6. A. Vorhauer, R. Pippan, Scripta Materialia. 51, 921 
(2004).  
7. G. Sakai, K. Nakamura, Z. Horita, T.G. Langdon. 
Materials Science and Engineering A. 406, 268 (2005) 
8. B. Adamczyk-Cieślak, J. Mizera, K.J. Kurzydłowski, 
Materials Characterization 62, 327 (2011). 
9. J. Bohlen, S.B. Yi, J. Swiostek, D. Letzig, H.G. Brokmeier, 
K.U. Kainer. Scripta Materialia 53, 259 (2005).  
10. Y. Estrin, A. Vinogradov. Acta Materialia 61, 782 (2013). 
11. J-C. Hung, C. Hung, Journal of Materials Processing 
Technology 104, 226 (2000). 
12. M. Lewandowska, H. Garbacz, W. Pachla, A. Mazur, 
K.J. Kurzydlowski. Materials Science- Poland 23, 279 
(2005). 
13. W. Pachla, M. Kulczyk, M. Sus-Ryszkowska, A. Mazur, 
K.J. Kurzydlowski. Journal of Materials Processing 
Technology 205, 173 (2008). 
14. P. Czarkowski, A.T. Krawczynska, R. Slesinski, T. Brynk, 
J. Budniak, M. Lewandowska, K.J. Kurzydlowski, Fusion 
Engineering and Design. 86, 2517 (2011). 
15. M. Richert, Q. Liu, N. Hansen, Materials Science and 
Engineering A 260, 275 (1999). 
16. A.S.B. Davenport, R.L. Higginson, C.M. Sellars, 
P.J. Withers, P.V. Houtte, 357 (2013). 
17. J.W. Christian, S. Mahajan, Progress in Materials Science 
39,1 (1995). 
18. P. Gerber, T. Baudin, R. Chiron, B. Bacroix Materials 
Science Forum 495, 1303 (2005). 
19. D. Horton, C.B. Thomson, V. Randle, Materials Science 
and Engineering A 203, 408 (1995). 
20. I.J. Beyerlein, N.A. Mara, D. Bhattacharyya, 
D.J. Alexander, C.T. Necker, International Journal of 
Plasticity 27, 121 (2011). 
21. C.X. Huang, W. Hu, G. Yang, Z.F. Zhang, S.D. Wu, 
Q.Y. Wang, G. Gottstein, Materials Science and 
Engineering: A 556, 638 (2012). 
22. I. Dillamore, E. Butler, D. Green Metal Science Journal 2, 
161 (1968). 
 
 
 


English

Comparison of Grain Refinement in Selected Materials Subjected to Hydrostatic Extrusion

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 3, 03AET08(4pp) (2013)   2304-1862/2013/2(3)03AET08(4) 03AET08-1  2013 Sumy State University Comparison of Grain Refinement in Selected Materials Subjected to Hydrostatic Extrusion  J. Mizera*, P. Maj, B. Adamczyk-Cieslak  Warsaw University of Technology, Warsaw Woloska 141 02-507, Poland  (Received 08 June 2013; published online 02 September 2013)  The subject of this study was to examine and compare the impact of intense hydrostatic extrusion on grain refinement in three different alloys: duplex stainless steel, commercially used aluminum alloy (6060) and Ag-Cu12 alloy. As a result of the process grain sizes from 370 nm to 90 nm were obtained in aluminum and duplex steel. To analyze the of hydrostatic on mechanical properties tensile tests were also carried out. The highest grain refinement (70 nm) and yield strength increase (over 300%) was observed in duplex steel af-ter hydrostatic extrusion.  Keywords: Hydrostatic Extrusion, Severe Plastic Deformation, Nanomaterials, Duplex Steel, Aluminium Alloy, Silver Alloy.   PACS number(s): 81.07.Bc                                                             * jmizera@inmat.pw.edu.pl 1. INTRODUCTION  Nanomaterialsare defined as substances where at least one dimension is less than approximately 100 nanometers. This has a significant impact on the ob-served properties comparing to the commonly used ma-terials [1,2]. The scale effect causes increased ratio of surface area to volume and excess energy in the mate-rial. There are two main strategies to achieve this. In the first one where the material is formed atom by at-om is called bottom-up approach. The second group involves the transformation of the initial structure to nanoscale material and is referred a stop–down. So far this is the most effective way to obtain bulk nano-materials. Severe plastic deformation (SPD) belongs to the top-down approach and is a generic term describing a group of methods used to produce ultrafine-grained and nano-materials [3]. The concept of this method is to induce large strains during forming. To achieve this special tool geometries are used to prevent the free flow of material. Due to large deformation the microstruc-ture undergoes a series of transformation. During the process high densities of crystal lattice defects are pro-duced, particularly dislocations, this results in a signif-icant refining of the grains. The most common methods in this group are equal channel pressing (ECAP)[4,5], high-pressure torsion (HPT) [6,7] and hydrostatic ex-trusion (HE) [8,9]. After the process the material exhib-its increase in strength and reduced elongation caused by decrease in dislocation mobility. Various materials can react differently to large deformations. In particu-lar, the grain refinement process is still not fully un-derstood by the researchers [10]. Hydrostatic extrusion is a process in which the ma-terial is pushed through a die of the desired cross-section. The process is carried out in a sealed cylinder in a hydrostatic medium in which the piston movement produces pressure to extrude the rod. The schematic of the process is shown in the Fig. 1. During the process large grain refinement and high strains are achieved under subsequent extrusion processes[11]. What is noteworthy the material is continuously cooled which greatlyreducesgrain growth that may occurdurin de-formation. Recent developments in hydrostatic extru-sion lead to significant grain refinement, down to na-nometric scale for different materials like aluminum [12], titanium [13], and austenitic steel[14].    Fig. 1 - Schematic representation of the hydrostatic extrusion process  2. EXPERIMENTAL PROCEDURE  The materials used in the investigations were a commercial 1.4462 duplex stainless steel, Al-Mg-Si (6060) aluminum alloy and Ag-12Cu alloy. The three materials after hydrostatic extrusion were deformed to approximately ε=3.5. The processes was performed at the Institute of High Pressure Physics "UNIPRESS" (Poland). Transmission Electron Microscopy (TEM) was used to study the microstructural evolution. Observations were carried out on section perpendicular to the extru- J. MIZERA, P. MAJ, B. ADAMCZYK-CIESLAK PROC. NAP 2, 03AET08 (2013)   03AET08-2 sion direction. The mean grain size (deq deﬁned asthe diameter of a circle which has the surface area equal to the surface area of a given grain) was determined by a computer equipped with an image analyzer. The deq value was determined for more than 200randomly se-lected grains. The microscopic observations were car-ried out using a JEOL JEM 1200 EX II with an accel-erating voltage of 120 kV. The tensile tests were conducted on MTS Q/Test 10 machine with a uniaxial quasistatic strain rate of 10-3 s-1. The aim of this research was to compare micro-structure and mechanical properties of three different face-centred cubic (FCC) metals.  3. RESULTS  Fig. 2. shows the microstructure of Ag-12Cu alloy subjected to hydrostatic extrusion. HE process resulted in fragmentation of the microstructure, and conse-quently the average output grain size equal to 90 nm was obtained. It should be noted that the deformation led to the apparent fragmentation of original grains and their elongation. There were also regions with high dislocation density in the vicinity of grains free of dislo-cations. Electron microscopy observations revealed the appearance of plastic deformation bands which contain grains with the smallest size. The selected area diffrac-tion (SAD) patterns indicate that the microstructure contains grains separated by high angle grain bounda-ries. In contrast the structure of duplex stainless steel after hydrostatic extrusion is more diverse (Fig. 3). Ferrite forms ultrafine equiaxed grains with diameter of approximately 0.37 µm. There are still some disloca-tion walls and clusters that didn’t yet evolve to sub-grains. The austenite regions are much more fragment-ed. Nanosized blocks of diameter about 70 nm circum-navigate along elongated bands through the material. The SAD-patterns are blurred and stretched (especially for austenite) compared to other materials. This indi-cates a high disorder in the crystallographic structure and very small grain size with large misorientation. Completely different from the previously described material is the microstructure of aluminum alloy (Fig. 4). Hydrostatic extrusion to the value of ε  3.5 leads to the refinement on microstructure and obtain the aver-age grain size deq  0.35μm. The SAD pattern from this section consists of diffuse rings characteristic of poly-crystalline materials. These spots form nearly continu-ous diffraction rings, which suggest a large number of high angle grain boundaries. The observation indicates that most of the grains are free of dislocations or sepa-rated into cells. This suggests that the microstructure of investigated alloy is related to dynamic recovery un-der large strain. Dynamic recovery occurs easily during aluminum deformation at room temperature due to the high value of stack fault energy. (SFE) The severe strain induced in the material provides enough energy for the dislocations to move from the interior of the grains to the vicinity of the grain boundaries. However, ome areas with high density of dislocations are visible.    Fig. 2 - Bright ﬁeld TEM images of Ag-12Cu alloy processed by HE (insets are the corresponding selected-area diffraction patterns).    Fig. 3 - Bright ﬁeld TEM images of the duplex stainless steel processed by HE (insets are the corresponding selected-area diffraction patterns).    0.5 m    Fig. 4 - Bright ﬁeld TEM images of the aluminum alloy pro-cessed by HE (insets are the corresponding selected-area dif-fraction patterns).  For mechanical properties tensile tests were con-ducted for each material before and after hydrostatic extrusion. The results are summarized in Table 1. Ac-cording to assumptions strength of the materials rose and maximum elongation decreased after hydrostatic extrusion in all materials.  The largest force was needed to deform duplex stainless steel although the maximum elongation was deformation bands  COMPARISON OF GRAIN REFINEMENT IN SELECTED MATERIALS... PROC. NAP 2, 03AET08 (2013)   03AET08-3 the lowest. What is worth noting the percent change of strength -yield stress (YS) 309%, ultimate tensile strength (UTS) 250% and maximum elongation (10%) after hydrostatic extrusion were the most significant from all tested materials. In case of the aluminum the mechanical properties altered only slightly compared to the initial state. Yield stress increased about 170 % and ultimate tensile stress rose to 131% a decrease in the maximum elongation was insignificant compared to initial state. What is worth noting the total strain for aluminum is merely ε=3.5 whereas some researchers achieved ε=60 using cyclic extrusion-compression[15]. The change of properties for Ag-12Cu alloy was moder-ate compared to previously described materials. The highest increase of strength was accompanied by the largest decrease in grain size which is in accordance with the Hall-Petch equation.   4. DISCUSION  The aim of this study was to evaluate microstruc-ture and mechanical properties changes for different material subjected to hydrostatic extrusion. To achieve this three different metals with FCC crystallographic structure were extruded to a total strain of 3.5. TEM was carried out to compare the microstructure changes which have taken place under the influence of plastic deformation. Additional tensile tests were conducted in order to compare the mechanical properties of tested materials. The largest grain refinement was observed for du-plex stainless steel along with it the highest strength needed to deform the material. This is directly related to the increase of dislocations density and grain re-finement. The dominating mechanism of grain refine-ment all materials was subdivision by dislocation walls. During deformation density of dislocations in-creases rapidly. Cellular structures with incidental dislocation boundaries are formed within the grains and cell blocks separated by geometrically necessary boundaries. With further increase of strain misorienta-tion grows and subgrains are created [4].The process is continuously repeated leading to structure fragmenta-tion although there is a certain asymptotic limit that the grain size tends resulting from thermodynamic conditions. Additional mechanisms that facilitate dis-location accommodation increase grain refinement [16]. An example of such behavior was observed in austenite of duplex stainless steel where twinning occurred. The structure was most fragmented from all tested materi-als.  The two primary methods of deformation in metals are slip and twinning. Slip occurs by dislocation glide of either screw or edge dislocations within a slip plane. Slip is by far the most common mechanism. Twinning is less common but readily occurs under some circum-stances [17]. Twinning proceeds when there are not enough slip systems to accommodate deformation and/or when the material has a very low SFE. Twins are abundant in many low SFE metals like copper[18], nickel [19]and silver [20].The microstructure observa-tions in deformed, low SFE FCC materials (duplex steel and silver alloy) are often difficult to characterize because of the complexity of the deformation micro-structures; the latter usually result from a combination of dislocation glide and fine mechanical twinning and then, at higher strains, shear banding at different scales. It has been proved that SFE is an important mate-rial parameter that affects the deformation mecha-nisms and the mechanical behavior of metals and al-loys[21].In the case of aluminum alloy which is a mate-rial with high SFE (~ 160mJ/m2)plastic deformation process is realized by slip. Additionally during defor-mation occurs dynamic recovery. The severe strain induced in the material provides enough energy for the dislocations to move from the interior of the grains to the vicinity of the grain boundaries. In the case of du-plex steel and Ag-Cu alloy the deformation and grain refinement were facilitated. The structures of low SFE material tend to twin and create partial rather than screw dislocation. Due to this five or more slip systems must be active for large deformations. When shear de-formation and twinning occurs at the same time grains align towards a more preferred orientation such as <111> and <100>. This leads to formation of bands both seen in duplex stainless steel and Ag-Cu alloy[22]. The observed forces needed for deformation were higher than in the initial state for all materials after hydrostatic extrusion. This is due to the increase of defects concentration and grain refinement in the ma-terial. However the increase of strength is at the ex-pense of elongation. This is particularly notice able for the duplex steel where the most significant changes were observed. The SAD patterns were most irregular and blurred for austenite of the studied materials. For the rest of the metals the changes of microstructure weren’t so noticeable and thus the mechanical proper-ties differed not so much from the initial state. Table 1 - Average grain size and mechanical properties of tested materials  Material Yield stress [MPa]  Ultimate tensile strength [MPa] εMAX[%]  deq[µm]  Before HE After HE Change ratio [%] Before HE After HE Change ratio [%] Before HE After HE Change ratio [%] Before HE After HE Duplex steel 572 1770 309% 748 1872 250% 23.4 2.4 10% Ferrite 4.3 Austenite 3.7 Ferrite 0.37 Austenite 0.07 Ag-12Cu 378 630 167% 382 800 209% 13.5 5.6 41% 0.46 0.09 Aluminum 6060 170 290 171% 261 341 131% 16.2 13.4 83% 1.24 0.35  J. MIZERA, P. MAJ, B. ADAMCZYK-CIESLAK PROC. NAP 2, 03AET08 (2013)   03AET08-4 5. CONCLUSIONS  From all tested materials subjected to hydrostatic extrusion (strain ε=3.5)only two with the lowest SFE exhibited nanocrystalline structure – duplex steel and Ag-12Cu alloy. In each case the main mechanism was shear deformation and twinning.  The largest increase in strength of the material was observed for duplex stainless (increase over 300% in UTS) steel and the smallest for aluminum 6060 (130% increase in UTS). This is directly correlated to the de-formation mechanisms in both materials. Additional twinning and large grain refinement in the austenite phase resulted in more effective blockade of dislocation movement.   REFERENCES  1. L. Zhang, T.J Webster, Nano Today. 4, 66. (2009). 2. M. Lines, Journal of Alloys and Compounds 449, 242 (2008). 3. A. Azushima, R. Kopp, A. Korhonen, D.Y. Yang, F. Micari, G. D. Lahoti, P. Groche, J Yanagimoto, N Tsuji, A Rosochowski, A. Yanagida, CIRP Annals - Manufacturing Technology 57, 716 (2008). 4. Y.T. Zhu, T.C. Lowe. Materials Science and Engineering A. 291, 46 (2000). 5. Y.H. Zhao, X.Z. Liao, Z. Jin, R.Z. Valiev, Y.T. Zhu, Acta Materialia 52, 4589 (2004). 6. A. Vorhauer, R. Pippan, Scripta Materialia. 51, 921 (2004).  7. G. Sakai, K. Nakamura, Z. Horita, T.G. Langdon. Materials Science and Engineering A. 406, 268 (2005) 8. B. Adamczyk-Cieślak, J. Mizera, K.J. Kurzydłowski, Materials Characterization 62, 327 (2011). 9. J. Bohlen, S.B. Yi, J. Swiostek, D. Letzig, H.G. Brokmeier, K.U. Kainer. Scripta Materialia 53, 259 (2005).  10. Y. Estrin, A. Vinogradov. Acta Materialia 61, 782 (2013). 11. J-C. Hung, C. Hung, Journal of Materials Processing Technology 104, 226 (2000). 12. M. Lewandowska, H. Garbacz, W. Pachla, A. Mazur, K.J. Kurzydlowski. Materials Science- Poland 23, 279 (2005). 13. W. Pachla, M. Kulczyk, M. Sus-Ryszkowska, A. Mazur, K.J. Kurzydlowski. Journal of Materials Processing Technology 205, 173 (2008). 14. P. Czarkowski, A.T. Krawczynska, R. Slesinski, T. Brynk, J. Budniak, M. Lewandowska, K.J. Kurzydlowski, Fusion Engineering and Design. 86, 2517 (2011). 15. M. Richert, Q. Liu, N. Hansen, Materials Science and Engineering A 260, 275 (1999). 16. A.S.B. Davenport, R.L. Higginson, C.M. Sellars, P.J. Withers, P.V. Houtte, 357 (2013). 17. J.W. Christian, S. Mahajan, Progress in Materials Science 39,1 (1995). 18. P. Gerber, T. Baudin, R. Chiron, B. Bacroix Materials Science Forum 495, 1303 (2005). 19. D. Horton, C.B. Thomson, V. Randle, Materials Science and Engineering A 203, 408 (1995). 20. I.J. Beyerlein, N.A. Mara, D. Bhattacharyya, D.J. Alexander, C.T. Necker, International Journal of Plasticity 27, 121 (2011). 21. C.X. Huang, W. Hu, G. Yang, Z.F. Zhang, S.D. Wu, Q.Y. Wang, G. Gottstein, Materials Science and Engineering: A 556, 638 (2012). 22. I. Dillamore, E. Butler, D. Green Metal Science Journal 2, 161 (1968).    

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Comparison of Grain Refinement in Selected Materials Subjected to Hydrostatic Extrusion

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