FORMING OF FULLERENE-DISPERSED ALUMINUM COMPOSITE
BY THE COMPRESSION SHEARING METHOD
Noboru NAKAYAMA
Akita Prefectural University,
84-4 Tsuchiya-Ebinokuti, Yurihonjyo, Akita/ 015-0055, JAPAN
[email protected]
Hiroyuku TAKEISHI
Chiba Institute of Technology
2-17-1 Tsudanuma, Narashino, Chiba/ 275-8588, JAPAN
[email protected]
ABSTRACT
In this paper, fullerene-dispersed aluminum composites were fabricated by the compression shearing method. The mechanical
properties, friction coefficient and microstructures of the compacted powder were investigated. The addition of 1 vol.%
fullerene to Al-Si-Cu-Mg improved the friction coefficient. The average friction coefficients of Al-Si-Cu-Mg (the 0 vol.% fullerene
sample), the 1 vol.% fullerene sample, and the 15 vol.% fullerene sample were found to be 1.00, 0.94 and 0.33, respectively.
Compared with the Al-Si-Cu-Mg results, the values for the samples with fullerene account for a reduction of 6% and 67%,
respectively. This result suggests that the Al-Si-Cu-Mg/fullerene composite has excellent solid-lubricating properties.
Introduction
Fullerenes (C60 or C70, etc.) or cluster diamonds (CD or GCD) exhibit lubrication characteristics that cannot be matched by
conventional materials. Therefore, it is likely that fullerene or the cluster diamond will be utilized as solid lubricants in a variety
of applications. In recent years, composite materials containing cluster diamond (CD or GCD) uniformly dispersed in a metal
matrix have been examined as ultra-high-performance solid lubricating materials with superior lubricating properties [1]-[12].
However, since the composite materials were fabricated by a powder metallurgy method (hot press or dynamic compaction
method), the materials contained many pores and exhibited poor mechanical properties [9]-[12]. As a result, the composite
material is not capable of producing enhanced lubricating properties.
A new solidification method concept has been developed that employs compression shearing [13]. Using this method, the
grain size of the fabricated material is on a nanometer scale, and the strength of the specimen is improved. When the
compression shearing process is applied to powdered aluminum under room temperature and atmospheric air conditions, a
thin plate specimen consisting of ultra-fine crystal grains with preferred orientation can be obtained. Conventional methods are
not capable of obtaining such a specimen at room temperature.
In this paper, aluminum composites were fabricated by the compression shearing method. First, pure aluminum powder was
created by the compression shearing method. The mechanical properties, friction coefficient and microstructures of the
compacted powder were investigated. Second, fullerene-dispersed aluminum composites were fabricated by the compression
shearing method. The Vickers hardness and friction coefficient of the fullerene-dispersed aluminum composites were
investigated.
Compression shearing method of forming under room temperature and atmospheric air conditions.
Figure 1 shows a schematic drawing of the setup for the compression shearing method. The lower plate is filled with the
powder, and the upper plate is loaded on the lower plate with the powder between the two surfaces. The plates are then
placed inside the test equipment. Shear stress is applied to the powder by moving the lower steel plate in the direction of an
axial compression presser. The compressive load P is generated by rotating an upside screw using a lever rod. The
compressive load P given to the sample was determined from the value of the strain gauges.
This forming procedure can be carried out under room temperature and atmospheric air without heating.
Torque
Square thread
Strain gauge
Shaft
Axial force
Upper plate
Al Powder
Lower plate
Load
Figure 1 Schematic diagram of compression sharing device
Mechanical properties of pure aluminum formed by the compression shearing method
Experiment
First, pure aluminum powder was created by the compression shearing method. In this research, the powder was 99.9% pure
aluminum powder of 9 µm average particle diameter produced by the gas atomizer method. On the surface of each grain, a
hard and stable oxide layer of 5 µm thickness was naturally generated.
The shear stress applied to the compacted powder was calculated to be 500 MPa for the compacted powder with a compacted
2
area of 400 mm . The moving distances L of the lower steel plate ranged from 0 to 10 mm. The moving speed of the lower
plate was maintained at around 0.1 mm/s. This forming procedure was carried out under room temperature and air.
Results
Figure 2 shows the typical microstructure observed in the pure Al by TEM (L=2 mm). The average crystal grain size measured
by the micrograph was about 200 nm. Since the powder compacted by the compression shearing method has small crystal
grains (nano-size crystal grains), the mechanical properties are higher than those produced by the hot press and dynamic
compaction methods.
1 µm
200 nm
Figure 2 TEM micrograph of compression-sheared cross-section (L=2 mm)
Figure 3 shows the relationship between the moving distance L of the lower steel plate and the relative density. The relative
density ρ is obtained by the following equation:
ρ=ρg/ρ0
where ρg is the density of the compacted powder and ρ0 is the density of pure aluminum (2.69 g/cm3). Regardless of the
moving distance L of the lower steel plate in the compression shearing method, the relative density was high.
Relativedensity ρ
1.00
0.95
0.90
0.85
0
1
2
3
4
5
6
7
8
9
10
Moving distance (mm)
Figure 3 Relationship between the moving distance L of the lower steel plate and relative density (for pure aluminum)
Figure 4 shows the test piece used for the tensile test. The test pieces were based on a piece of JIS Z 2201 No. 7. The tensile
test speed was 1 mm/min. The strain of the test piece was measured by a strain gauge with a 2-mm gauge length attached to
the parallel portion.
Moving direction
5
R1
8
4
strain gauge
7.2
40
Unit of measurement: mm
Fig. 4 Tensile test piece.
Figure 5 shows the stress-strain curve of the powder compacted by the compression shearing method. The maximum tensile
strength and the elongation after fracture for the L=5 mm sample are 2 times and 13 times higher, respectively, than those for
the L=2 mm sample. However, the tensile strength and elongation after fracture decreases for samples L=7 and L=10 mm.
Figure 6 shows the fracture surfaces of the pure Al compacted powder. The L=2 mm sample is not long enough to obtain a
large plastic deformation. However, by increasing L, the oxidation layer on the surface of the pure aluminum powder is
destroyed by the shear deformation between the powder particles during compression shearing. Therefore, in the cases of L=5,
7, and 10 mm, the shape of the Al powder was not retained because the oxidation layer on the surface was broken.
Furthermore, the prior particle boundaries joined together. This characteristic increased the tensile strength.
From the above result, the optimum forming condition of aluminum composites by the compression shearing method was
found to be L=5 mm.
Stress (MPa)
300
200
100
L=10mm
L=5mm
L=2mm
0
1
L=7mm
2
3
4
Strain (%)
Figure 5 Stress-Strain curve of the compacted powder (pure aluminum)
(a) L=2 mm
(b) L=5 mm
10 µm
(c) L=7 mm
(d) L=10 mm
Figure 6 SEM micrographs of the fracture surface of compression-sheared pure aluminum
Friction properties of fullerene-dispersed aluminum composite formed by the compression shearing method
Experiment
The shear stress applied to the compacted powder was calculated to be 500 MPa for the compacted powder with a compacted
2
area of 400 mm (20 mm × 20 mm). The moving distance L of the lower steel plate was 5 mm. The moving speed of the lower
plate was maintained at around 0.1 mm/s. This forming procedure can be carried out under room temperature and in the air
without heating.
The matrix consisted of a rapid-solidified Al-Si-Cu-Mg alloy powder with an average particle size of 41.4 µm. The chemical
composition of the Al-Si-Cu-Mg powder is shown in Table 1. On the surface of each grain, a hard and stable oxide layer of 5µm thickness was naturally generated. The amounts of fullerene were a 0 - 30% volume fraction. The entire procedure was
carried out in an Ar atmosphere using a glove box. The enclosed powders were mechanically mixed at 500 rpm for four hours
by the ball-milling method.
Table 1
Chemical compositions of Al-Si-Cu-Mg (mass%)
The relation between the friction characteristics and the mechanical properties (Vickers hardness, etc.) has not yet been
solved completely. However, it is clear that the friction characteristics are affected by the mechanical properties. In order to
investigate the influences on friction by the mechanical properties of fullerene-dispersed aluminum composites, the Vickers
hardness test was performed. The load of the Vickers hardness test was 3 N and load time was 15 s.
To examine the friction properties, friction measurements were carried out by the pin–on–disk method in air. For these
measurements, the pin was made of stainless steel (SUS304) and had a spherical head surface of 4 mm in diameter. Friction
tests were conducted using a test load of 0.2 N at a sliding speed of 1.7 mm/s. The friction test was conducted in air.
Results
Figure 7 shows the relationship between the Vickers hardness and volume fraction of fullerene. The Vickers hardness of Al-SiCu-Mg is 150 Hv. The Vickers hardness improves as the volume fraction of fullerene increases due to the effect of the
hardness of fullerene, and the hardness number is enhanced as the volume fraction of fullerene increases up to 10%.
However, the number decreases suddenly at the volume fraction of 15% and greater. Since fullerene and pores exist at the
powder boundary and it is not possible to suppress the plastic deformation of the powder and destroy the oxide film of the
powder surface, the binding power of the Al matrix powder decreases with the increase in fullerene.
Figure 8 shows TEM (Transmission Electron Microscope) images of the (a) 0 vol.% fullerene sample and (b) 30 vol.% fullerene
sample. The pores cannot be observed in the 0 vol.% fullerene sample. However, the pores can be visibly observed in the
microstructure of the 30 vol.% fullerene sample. The Vickers hardness decreases due to the existence of these pores.
Vickers hardness (Hv)
250
200
150
100
50
0
0
5
10
15
20
Volume fractions of fullerene
25
30
(vol.%)
Figure 7 Relationship between volume fraction and Vickers hardness of Al-Si-Cu-Mg/ fullerene
(a) 0 vol.% fullerene sample
(b) 30 vol.% fullerene sample
Figure 8 TEM images of the (a) 0 vol.% fullerene sample and (b) 30 vol.% fullerene sample
Figure 9 (a)-(i) shows the relationship between the friction coefficients of Al-Si-Cu-Mg/fullerene solidified by the compression
shearing method and the sliding distance. In the initial frictional stages of the 0 vol.% fullerene sample, the friction coefficient is
about 0.5-0.6. However, the friction coefficient of the 0 vol.% fullerene sample increases with the sliding distance, and repeats
the increase and decrease. The friction coefficients of the 1.0-12.5 vol.% fullerene sample also increase with the sliding
distance, repeating the increase and decrease. However, the friction coefficients of the samples with distributed fullerene 15
vol.% or more decrease suddenly. These results suggest that fullerene has excellent solid-lubricating properties.
Figure 10 shows the friction coefficients of Al-Si-Cu-Mg composites containing various volume fractions of fullerene. The
addition of 1 vol.% fullerene to Al-Si-Cu-Mg improves the friction coefficient. The average friction coefficient of the 0 vol.%
fullerene sample, the 1 vol.% fullerene sample, and the 15 vol.% fullerene sample were found to be 1.00, 0.94 and 0.33,
respectively. Compared with the 0 vol.% fullerene sample results, these values account for a reduction of 6% and 67%,
respectively.
These results suggest that the Al-Si-Cu-Mg/fullerene composite has excellent solid-lubricating properties.
1.2
1.0
1.0
0.8
0.6
0.4
0.2
0
0
Friction coefficient
1.2
1.0
Friction coefficient
Friction coefficient
1.2
0.8
0.6
0.4
0.2
0.4
0
0
10000
20000
30000
Sliding distance (mm)
(b) 1.0 vol.% fullerene sample
1.2
1.0
1.0
1.0
0.6
0.4
0.2
0
0
Friction coefficient
1.2
0.8
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
0
0
10000
20000
30000
Sliding distance (mm)
(d) 10.0 vol.% fullerene sample
0
0
10000
20000
30000
Sliding distance (mm)
(e) 12.5 vol.% fullerene sample
1.0
0.4
0.2
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
0
0
10000
20000
30000
Sliding distance (mm)
(g) 20.0 vol.% fullerene sample
0
0
10000
20000
30000
Sliding distance (mm)
(h) 25.0 vol.% fullerene sample
10000
20000
30000
Sliding distance (mm)
(i) 30.0 vol.% fullerene sample
Figure 9 Relationship between the friction coefficients of Al-Si-Cu-Mg / fullerene and the sliding distance
1.5
Friction coefficient
0
0
Friction coefficient
1.2
1.0
Friction coefficient
1.2
1.0
0.6
10000
20000
30000
Sliding distance (mm)
(f) 15.0 vol.% fullerene sample
1.2
0.8
10000
20000
30000
Sliding distance (mm)
(c) 5.0 vol.% fullerene sample
1.2
Friction coefficient
Friction coefficient
(a) 0 vol.% fullerene sample
Friction coefficient
0.6
0.2
0
0
10000
20000
30000
Sliding distance (mm)
0.8
1.0
0.5
0
0
5
10
15
20
25
30
Volume fractions of fullerene(%)
Figure 10 Effect of volume fraction of fullerene on friction properties
Conclusions
Pure aluminum powder and fullerene-dispersed aluminum composites were created by the compression shearing method. The
microstructures and friction coefficients of the compacted powders were investigated. The following conclusions were obtained.
1)
The mechanical properties of the sample fabricated by the compression shearing method improved.
2)
The friction coefficients of the samples that distributed fullerene 15% or more decreased suddenly. This
result suggests that fullerene has excellent solid-lubricating properties.
3)
Compared with the Al-Si-Cu-Mg results, the friction coefficient of 15% fullerene sample decreased 67%.
Acknowledgments
This research was sponsored by TOYO GAGE CO., LTD. The authors are grateful to encouragement and cooperation at
TOYO GAGE CO., LTD
References
1.
H. Makita: Refinement and characterization of fine-diamond particles, New Diamond 1996. 12 (3), 8-13.
2. T. Sano, Y. Murakoshi, et al.: Characterization of diamond dispersed Cu-matrix composite, Mater. Trans. JIM, 1996. 37 (5),
1132-1137.
3.
T. Xu, J. Zhao, et al.: Study on the tribological properties of ultradispersed diamond containing soot as an oil additive,
Tribol. Trans., 1997. 40 (1), 178-182.
4.
T. Sasada, M. Jinbo: Role of fine diamond particles in three body wear, Rep. Chiba Institute Technol., 1999. 46, 57-65.
5.
Q. Ouyang, K. Okada: Friction properties of aluminum-based composites containing cluster diamond, J. Vacuum Sci.
Technol., 1994. A 12 (4), 2577-2580.
6. Q. Ouyang, K. Okada: Fundamental studies on the rolling friction of ultra-fine particles of cluster diamond, Trans. Jpn. Soc.
Mech. Engineers, 1995. 61 (585), 2051-2056.
7.
Q. Ouyang, B. Wang, K. Okada: Atomic force microscopy investigations on the surface topographies of aluminum-based
composite containing nanocluster diamond, J. Vac. Sci. Technol., 1997. B 15 (4), 1449-1451.
8.
Q. Ouyang, K. Okada: Nano-ball bearing effect of ultra-fine particles of cluster diamond, Appl. Surf. Sci., 1994. 78, 309313.
9.
N. Nakayama, K. Hanada, T. Sano, S. Horikoshi, H. Takeishi: Thin Film Forming of Pure Aluminum Powders by Dynamic
Compaction, Adv. Technol. Plasticity, 1999. 1321-1326.
10. N. Nakayama, M. Mayuzumi, K. Hanada, T. Sano, R. Tominaga, H. Takeishi: Thin-film forming of cluster diamonddispersed aluminum composite by dynamic compaction, Key Eng. Mater., 2000. 177-180, 787-792.
11. K. Hanada, N. Nakayama, M. Mayuzumi, T. Sano, H. Takeishi: Tribological properties of Al-Si-Cu-Mg alloy-based
composite dispersing diamond nanocluster, Diamond and Related Materials, 2002. 11, 749-752.
12. K. Hanada, K. Umeda, N. Nakayama, M. Mayuzumi, H. Shikata and T. Sano: Characterization of Diamond Nanoclusters
and Applications to Self-Lubricating Composites, New Diamond and Frontier Carbon Technology, 2003. 13 (3), 133-142.
13. T. Saito, H. Takeishi and N. Nakayama: New method for the production of bulk amorphous materials of Nb-Fe-B alloys, J.
Mater. Res., 2005. 20 (3), 563-566.