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Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-849-
PAPER REF: 5762
THE EFFECT OF LA ON PROPERTIES OF AL2O3/CU COMPOSITES
Gui-min Liu(*)
, Tao Yan, Zhong-xu Yang, Bin Li
National Key Libratory of Remanufacture Engineering, Beijing 100072,China (*)Email: [email protected]
ABSTRACT
Dispersion strengthened copper matrix composites were fabricated by mechanical alloying
and spark-plasma sintering techniques. The effect of the content of rare earth, La, on the
microstructure and properties of sintered materials were studied. The results showed that
adding a trace of La to the Al2O3/Cu composite powder, accelerated the mechanical alloying
process, which can be revealed by the fine grain refinement and sufficient alumina particle
dispersion. And as a result, both the micro-hardness and tensile strength of the composites are
improved. The conductivity of the composite firstly increases and then decreases with the
increasing of the content of La, and the conductivity of the composite is increased 11.3%
IACS when the content of La is 0.1%.
Keywords: Al2O3/Cu, La, mechanical alloying.
INTRODUCTION
Electromagnetic rail launcher (EML) is one of the main launcher technologies and a current
research hot spot. However, poor performance of the rail material has impeded the
development of EML. In order to achieve higher performance of rail material, a lot of
composites based on Cu, such as Al2O3/Cu, SiO2/Cu, TiB2/Cu, etc. have been researched and
developed. Adding Rare earth element to the Cu-based composite can purify and refine the
organization, change the inclusion distribution, and then improve the properties of it.
In the present study, the composite, Cu-Al2O3-La, was fabricated by mechanical alloying and
spark-plasma sintering techniques. The effect of the content of rare earth, La, on the
microstructure and properties of the sintered materials were studied. The results showed that
adding a trace of La to the Al2O3/Cu composite powder can accelerate the mechanical
alloying process, which has been proved by the fine grain refinement and sufficient alumina
particle dispersion. As a result, both the micro-hardness and tensile strength of the composites
are improved. The conductivity of the composite firstly increases and then decreases with the
increasing of the content of La, and the conductivity of the composite is increased 11.3%
IACS when the content of La is 0.1%.
PREPARATION AND TESTS
The original powders include electrolytic Cu powders, nano-Al2O3 powders and CuLa alloy
powders. The size of electrolytic Cu and CuLa alloy powders was 300目,nano-Al2O3 powders
was 20nm. All the powders were mixed together according to their massfraction. For
example, Al2O3/Cu means Al2O3 content is 1%, the rest is Cu; Al2O3/Cu0.05La means Al2O3
content is 1%, La content is 0.05%, the rest is Cu.
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Nanotechnologies and Nanomaterials
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The preparetion process of the composite powders included making-up of charge, mixing,
mechanical alloying, being reduced in hydrogen and sintering by spark-plasma sintering
(SPS). The powders were mixed by vibrating ball mill with rotating speed of 1400r/min, ratio
of grinding media to material 10:1, milling time 80min. The reducing in hydrogen were under
the parameters of temperature 300F, holding 1h. The composite powders were sintered by
SPS-1050 with sintering temperature 850Fholding 6min, pressure 30MPa.
XRD ANALYSIS OF COMPOSITE POWDERS
The XRD7000 was used to analyze the phase and grain size of the composite powders. Fig 1
shows the XRD results of composite powders milled after 80min. Because of the little content
of La, there is only Cu diffraction peak in Fig 1(b), which La content is 0.05%. At the same
time, Cu was not oxidized because of the reducing of hydrogen. But there is also a little
difference between Fig1(a) and Fig1(b). That is the full width half maximum in Fig1(b) is
wider than Fig1(a). Distortions of Cu lattice and grain refinement lead to the results. By
means of Scherrer formula, grain size can be calculated which powders were got by different
milling time (Fig 2). At the former 20min of milling, Cu grain refinement was more obvious.
But then grain refinement speed was slower with time. As La (0.05%) adding to the Al2O3/Cu
composite powders, Cu grain refinement was promoted. After milling 80min, the grain size of
Al2O3/Cu0.05La was 95% than Al2O3/Cu.
Fig. 1 - XRD pattern of composite powder: (a) Al2O3/Cu; (b) Al2O3/Cu0.05La
Fig. 2 - Effect of crystallite size on milling time and rare La
MICROSTRUCTURE OF COMPOSITE POWDER AFTER SPS
Quanta-200 Scanning electron microscope (SEM) was used to get the microstructure of
composite powder after SPS. The results were shown in Fig 3. The white dots in the picture
were nano-Al2O3 powders, the gray area was the base Cu and the black area was void. From
Fig3(a) to (d), all these four kinds of composite materials Al2O3/Cu, Al2O3/Cu-0.05wt.%La,
Al2O3/Cu-0.1wt.%La, Al2O3/Cu-0.2wt.%La have little void. When La is 0, nano-Al2O3 powders were dispersed homogeneously, and there was little reunion phenomenon. But this
b a
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/
reunion phenomenon could be
test tell us the best La content
would be more serious. So, a conclusion
decrease the reunion phenomenon
Fig.3 SEM
(a) Al2O3/Cu; (b) Al2O3/Cu
RESULTS
Sigma2008A1 eddy electric conductivity meter
of the composite materials under
used with the load 100g and the holding
used to test the tensile strength.
electrical conductivity and h
materials obtained with various La contents. One can see that, comparing with the material of
Cu-Al2O3, the relative density of
the same time, electrical conductivity
(0.05% La content), the tested values of the relative density, e
and tensile strength, are simultaneo
Table 1 - Physics and mechanics
Relative
density[%]
Al2O3/Cu 94.7
Al2O3/Cu0.05La 95.1
Al2O3/Cu0.1La 94.4
Al2O3/Cu0.2La 93.6
From Fig.3, it can be seen that the
particle is sufficient. And this kind of microstructure has been concluded to
to the improvement of micro
a
c
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-851-
could be relieved by means of adding to proper quantities
test tell us the best La content is 0.05%. When La content is more, the reunion
o, a conclusion can be got: proper La content in Al
phenomenon of nano-Al2O3 powders.
Fig.3 SEM microstructures of composite powder after SPS
/Cu-0.05wt.%La; (c) Al2O3/Cu-0.1wt.%La; (d) Al2O3/Cu
electric conductivity meter was used to check the electrical conductivity
of the composite materials under room temperature. HVS-1000 micro hardness tester
used with the load 100g and the holding-time 15s. CMT4304 universal testing machine
used to test the tensile strength. Table 1 shows the testing values of the
and hardness, as well as tensile strength, of various composite
obtained with various La contents. One can see that, comparing with the material of
the relative density of Al2O3/Cu0.2La (0.2% La content) decrease 1.1%
lectrical conductivity decrease 1.5%. For the composite,
0.05% La content), the tested values of the relative density, electrical conductivity
simultaneously higher than Cu-Al2O3.
Physics and mechanics property of copper matrix composites
Electrical
conductivity[%IACS]
Hardness[HV]
55.6 155
64.7 160
66.9 146
54.1 130
From Fig.3, it can be seen that the grain refinement is fine and the dispersion
nd this kind of microstructure has been concluded to
micro-hardness and tensile strength of composites.
d
b
proper quantities of La. This
reunion phenomenon
Al2O3/Cu could
/Cu-0.2wt.%La
lectrical conductivity
hardness tester was
universal testing machine was
testing values of the relative density,
, of various composite
obtained with various La contents. One can see that, comparing with the material of
decrease 1.1%, while at
decrease 1.5%. For the composite, Al2O3/Cu0.05La
lectrical conductivity, hardness
of copper matrix composites
Tensile
strength[MPa]
395
409
375
334
dispersion of the alumina
nd this kind of microstructure has been concluded to contribute much
composites. And then a
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Nanotechnologies and Nanomaterials
-852-
conclusion, adding a trace of rare earth La to the Al2O3/Cu composite powders, can accelerate
the mechanical alloying process and improve the micro-hardness and tensile strength of
composites, has been obtained.
CONCLUSION
This study shows that La and Al2O3 content in the Cu-Al2O3-La composite can change the
conductivity and mechanical performance. Further tests will be carried out in order to reveal
the abrasion resistance performance under high carrier current and high velocity.
ACKNOWLEDGMENTS
The present work has been Supported by Beijing Natural Science Foundation (2152031), P.
R. China.
REFERENCES
[1]-Akhtar F, Askari S J, Shah K A, et al. Microstructure, mechanical properties, electrical
conductivity and wear behavior of high volume TiC reinforced Cu-matrix composites [J].
Materials Characterization, 2009, 60: 327-336.
[2]-Suryanarayana C, Nasser A A. Mechanically alloyed nanocomposites [J]. Progress in
Materials Science, 2013, 58: 383-502.