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: liuguimin1971@sina.com

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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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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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.