Wear resistant film

Disclosed is a wear-resistant film deposited on an aluminum alloy substrate with high adhesiveness by a physical vapor deposition process. On the surface of the aluminum alloy substrate, an aluminum oxide film is formed through the medium of a silicon oxide film. The deposition of the silicon oxide film and the aluminum oxide film on the surface of the aluminum alloy substrate is carried out by a physical vapor deposition process such as the sputtering process and the ion plating process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a wear-resistant film and more particularly to a 
wear-resistant film having an aluminum oxide film formed on a surface of a 
substrate made of aluminum or an aluminum alloy (hereinafter referred to 
as "aluminum alloy substrate") through the medium of a silicon oxide film. 
2. Description of the Prior Art 
It is known that an aluminum oxide film manufactured by a sputtering 
process has a low friction coefficient and relatively large durability to 
resist friction as compared with films of such other ceramic substances as 
TiC, TiN, BN, and SiO.sub.2. Thus, the adoption of the aluminum oxide film 
as a surface protecting film (wear-resisting film) for aluminum alloy 
building materials, personal ornaments made of aluminum alloy (such as 
watches), machine parts, and the like has been contemplated. 
Such surface protecting films as wear-resistant films are generally 
required to excel in adhesiveness to substrates. 
The formation of a wear-resistant film on an aluminum alloy substrate is 
generally carried out by directly superposing an aluminum oxide film on 
the aluminum alloy substrate. The aluminum oxide film formed by this 
method, however, does not exhibit satisfactory adhesiveness to the 
aluminum alloy substrate and entails the possibility of being peeled off 
the substrate under high load and cannot be expected to manifest excellent 
wear resistance. 
In the circumstances, a technique which is capable of forming an aluminum 
oxide film exhibiting high adhesiveness to an aluminum alloy substrate has 
long been desired. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide a wear-resistant 
film which is produced by forming an aluminum oxide film with high 
adhesiveness on an aluminum alloy substrate by a physical vapor deposition 
process and consequently enabled to withstand friction under high load. 
Another object of the present invention is to provide an article made of 
aluminum or an aluminum alloy and coated with a wear-resistant film which 
exhibits high resistance to scratching and to wear under high load. 
To accomplish the objects mentioned above, in accordance with the present 
invention, there is provided a wear-resistant film formed on an aluminum 
alloy substrate, which comprises a silicon oxide film deposited on the 
surface of the substrate and an aluminum oxide film deposited on the 
silicon oxide film. 
The formation of the silicon oxide film and the aluminum oxide film on the 
surface of the aluminum alloy substrate is carried out by the physical 
vapor deposition process such as, for example, a sputtering process and an 
ion plating process. Among other physical vapor deposition processes 
available for the formation, the sputtering process proves particularly 
desirable.

DETAILED DESCRIPTION OF THE INVENTION 
The present inventors have found that a silicon oxide (SiO.sub.2) film 
exhibits high adhesiveness to both an aluminum alloy substrate and an 
aluminum oxide (Al.sub.2 O.sub.3) film. On the basis of this knowledge, 
the wear-resistant film of the present invention is formed by precoating 
an aluminum alloy substrate with the silicon oxide film exhibiting high 
adhesiveness to both the aluminum alloy substrate and the aluminum oxide 
film, as an intermediate layer, by such a physical vapor deposition 
process as the sputtering process and then forming the aluminum oxide film 
on the intermediate layer by a physical vapor deposition process such as 
the sputtering process. 
By causing the silicon oxide film excelling in adhesiveness to both the 
aluminum alloy substrate and the aluminum oxide film to be interposed as 
the intermediate layer therebetween as described above, there is obtained 
a wear-resistant film which manifests a large critical load (the load 
existing at the moment of film peeling) in a scratch test, enjoys improved 
adhesiveness, exhibits enhanced resistance to scratching and to wear under 
high load, and fully functions as a surface-protecting film of the 
aluminum alloy substrate. 
The thickness of the precoat layer of silicon oxide mentioned above is 
desired to be not less than 0.005 .mu.m, preferably to fall in the range 
of from 0.01 to 20 .mu.m. If the thickness of the silicon oxide film as an 
intermediate layer is less than 0.005 .mu.m, the silicon oxide film will 
be at a disadvantage in incurring difficulty in acquiring a fully 
satisfactory function as a layer for enhancing adhesiveness of the 
aluminum oxide film to the aluminum alloy substrate and consequently 
suffering a decrease in the effect of improving the adhesiveness of the 
films. Conversely, if the thickness of the silicon oxide film exceeds 20 
.mu.m, the silicon oxide film will be at a disadvantage in diminishing the 
improvement to be attained in the durability to resist friction. 
Then, the thickness of the aluminum oxide film of the surface layer is 
desired to be in the range of from 0.1 to 20 .mu.m. If the thickness of 
the aluminum oxide film is less than 0.1 .mu.m, the produced film will 
suffer a deterioration in the characteristics such as low friction and 
durability to resist friction. Conversely, if this thickness exceeds 20 
.mu.m, the excess will bring about no proportional addition to the 
improvement of durability to resist friction and will attain no economy. 
Now, the present invention will be described more specifically below with 
reference to working examples and a comparative example. 
FIG. 1 schematically shows the construction of a sputter device used in the 
following working examples and a comparative example. The sputter device 1 
has a substrate holder 3 disposed in a film-forming chamber or deposition 
chamber 2 and has a silicon oxide target (source of evaporation) 6, a 
titanium target 7, and an aluminum target 8 each opposed to the substrate 
holder 3. The silicon oxide target 6 and the aluminum target 8 are 
connected respectively to high frequency (RF) power sources 10 and 12 and 
the titanium target 7 is connected to a direct current (DC) power source 
11. The substrate holder 3 which supports a substrate 5 in place is 
capable of rotating round a rotating shaft 4 as the center and moving the 
substrate 5 to the position A opposed to the silicon oxide target 6, the 
position B opposed to the titanium target 7, and the position C opposed to 
the aluminum target 8. A shutter 9 is movably interposed between the 
substrate holder 3 and the targets 6, 7, and 8 so as to shield the targets 
during the pre-sputtering process. 
EXAMPLE 1 
Manufacture of aluminum oxide film on an aluminum alloy substrate precoated 
with silicon oxide film: 
An aluminum alloy A6063 sheet destined to form a substrate was subjected to 
mirror polishing, set in the substrate holder of the sputter device shown 
in FIG. 1, and left standing in an evacuated interior of the deposition 
chamber. After the evacuation, Ar gas was introduced into the deposition 
chamber to adjust the internal pressure thereof to 1.0 to 2.0 Pa. Then, 
the aluminum alloy sheet was subjected to sputter etching. The internal 
pressure of the deposition chamber was adjusted to 1.0 to 0.3 Pa and the 
silicon oxide target was energized with RF power to induce sputter 
discharge. Consequently, a silicon oxide film was deposited in a 
prescribed thickness on the substrate. 
After the deposition of the precoat layer of silicon oxide on the 
substrate, the substrate was moved onto the aluminum target. Subsequently, 
a mixed gas of Ar and O.sub.2 was introduced into the deposition chamber 
and the internal pressure of the deposition chamber was adjusted to 1.0 to 
0.3 Pa. At this time, the partial pressure of O.sub.2 was in the range of 
from 0.2 to 0.02 Pa. Then, the aluminum target was energized with RF power 
to induce sputter discharge and deposit an aluminum oxide film in a 
prescribed thickness on the silicon oxide film of the substrate. 
Evaluation of adhesiveness: 
The adhesiveness of a film was evaluated by the use of a scanning scratch 
tester. This tester is adapted to press a diamond ball 100 .mu.m in 
diameter attached to a spring onto the film at a prescribed rate of fall 
and inflict a scratch on the film. At this time, a vibration 100 .mu.m in 
amplitude is exerted on the diamond ball perpendicularly to the direction 
of scratching. In this test, the load under which the film peels is 
referred to as "critical load, Lc". The magnitude of Lc is used for rating 
the adhesiveness of the film under test. 
The construction of the wear-resistant film manufactured in Example 1 
mentioned above and the critical load, Lc, of the film are shown in Table 
1. For comparison, a sample was produced by following the procedure of 
Example 1 while omitting the step of precoating the substrate with a 
silicon oxide film and tested. The results are also shown in Table 1. 
TABLE 1 
______________________________________ 
Thickness of 
Thickness of 
Critical 
silicon oxide 
aluminum oxide 
load, Lc 
Substrate film (.mu.m) 
film (.mu.m) 
(gf) 
______________________________________ 
Aluminum None 0.5 14.6 
alloy 
A6063 
Same as 0.01 0.5 18.2 
above 
______________________________________ 
It is clearly remarked from the results shown in Table 1 that the 
precoating of the substrate with the silicon oxide film increased the 
critical load by 25% and improved the adhesiveness of the wear-resistant 
film to the substrate. 
COMATIVE EXAMPLE 1: 
Manufacture of aluminum oxide film on an aluminum alloy substrate precoated 
with titanium oxide film (comparative piece): 
In the same manner as in the manufacture of the precoat of silicon oxide in 
Example 1 cited above, the setting of a substrate (using aluminum alloy 
A1100 and A6063, in this case) and the evacuation of the deposition 
chamber were carried out, and then a mixed gas of Ar and O.sub.2 was 
introduced into the deposition chamber. Thereafter, the internal pressure 
of the deposition chamber was adjusted to 1.0 to 2.0 Pa. At this time, the 
partial pressure of O.sub.2 was 0.2 to 0.02 Pa. Subsequently, the titanium 
target was energized with a DC voltage to induce sputter discharge and 
deposit a titanium oxide film in a prescribed thickness on the substrate. 
After the deposition of the precoat layer of titanium oxide, the substrate 
was moved onto the aluminum target. Then, a mixed gas of Ar and O.sub.2 
was introduced to adjust the internal pressure of the deposition chamber 
to 1.0 to 0.3 Pa. At this time, the partial pressure of O.sub.2 was 0.2 to 
0.02 Pa. Subsequently, the aluminum target was energized with RF power to 
induce sputter discharge and deposit an aluminum oxide film in a 
prescribed thickness on the titanium oxide film of the substrate. 
The produced film was subjected to the scanning scratch test in the same 
manner as in Example 1. The construction of the film and the critical 
load, Lc, found in the test are shown in Table 2. For comparison, samples 
were obtained by following the procedure described above while omitting 
the step of precoating with a titanium oxide film. The results obtained of 
these samples are also shown in Table 2. 
TABLE 2 
______________________________________ 
Thickness of 
Thickness of 
titanium aluminum Critical 
oxide film oxide film load, Lc 
Substrate (.mu.m) (.mu.m) (gf) 
______________________________________ 
Aluminum None 0.5 6.9 
alloy A1100 
Same as above 
0.01 0.5 6.7 
Aluminum None 0.5 15.1 
alloy A6063 
Same as above 
0.01 0.5 14.5 
______________________________________ 
It is clearly noted from the results shown in Table 2 that the precoating 
with titanium oxide did not attain the effect aimed at by the present 
invention and rather tended to lower the critical load Lc as compared with 
a sample not precoated with titanium oxide. 
EXAMPLE 2 
By the same method as described in Example 1, a silicon oxide film and an 
aluminum oxide film were formed in varying thicknesses so as to obtain the 
total thicknesses, 0.1 .mu.m, 0.5 .mu.m, 1.0 .mu.m, and 5.0 .mu.m, 
respectively, on aluminum alloy Al100 substrates. The produced films were 
evaluated for adhesiveness by the same scanning scratch test as in Example 
1. 
The relation between the thickness and the critical load, Lc, of the film 
having a silicon oxide film and an aluminum oxide film formed in a total 
thickness of 0.1 .mu.m on the substrate is shown in FIG. 2, the relation 
of the film of a total thickness of 0.5 .mu.m in FIG. 3, the relation of 
the film of a total thickness of 1.0 .mu.m in FIG. 4, and the relation of 
the film of a total thickness of 5.0 .mu.m in FIG. 5 respectively. 
It is clearly noted from the results shown in FIGS. 2 through 5 that the 
precoating with a silicon oxide film improved the critical load, Lc, to a 
discernible extent and augmented the adhesiveness. It is further noted 
that the precoating of silicon oxide film was effective when the thickness 
thereof was not less than 5 nm, that the increase of the critical load, 
Lc, practically reached a state of saturation when the thickness exceeded 
10 nm, and that the critical load, Lc, increased in proportion as the 
total thickness of a silicon oxide film and an aluminum oxide film 
increased. In the films having large total thicknesses, a change in the 
thickness of the silicon oxide film produced no marked change in the 
critical load, Lc (see FIG. 5). This is because the aforementioned method 
used for the evaluation of the adhesiveness is adapted for thin films not 
exceeding 1 .mu.m. 
EXAMPLE 3 
By following the procedure of Example 1 while changing the material for the 
substrate to a rapidly solidified aluminum alloy material, a film was 
obtained by depositing a silicon oxide film and an aluminum oxide film on 
the substrate mentioned above by the sputtering process and was evaluated 
for adhesiveness by the same scanning scratch test as described in Example 
1. 
The construction of the film thus obtained and the critical load, Lc, found 
in the test are shown in Table 3. For comparison, a sample was produced by 
following the procedure described above while omitting the steps of 
precoating with a silicon oxide film and similarly evaluated. The results 
are also shown in Table 3. 
TABLE 3 
______________________________________ 
Thickness of 
Thickness of 
Critical 
silicon oxide 
aluminum oxide 
load, Lc 
Substrate film (.mu.m) 
film (.mu.m) 
(gf) 
______________________________________ 
Rapidly None 0.5 81.3 
solidified 
aluminum 
alloy 
Same as 0.01 0.5 96.7 
above 
______________________________________ 
EXAMPLE 4 
By following the procedure of Example 1 while changing the material for the 
substrate to an extruded material of a rapidly solidified powder 
(crystalline texture; fine crystals) having a composition of Al.sub.88.5 
Ni.sub.8.0 Mm.sub.3.5 (in atomic %), a film was obtained by depositing a 
silicon oxide film and an aluminum oxide film on the substrate mentioned 
above by the sputtering process and was evaluated for adhesiveness by the 
same scanning scratch test as described in Example 1. The scratch test in 
this case used a diamond pressure ball 15 .mu.m in diameter. 
The construction of the film thus obtained and the critical load, Lc, found 
in the test are shown in Table 4. For comparison, a sample was produced by 
following the procedure described above while omitting the steps of 
precoating with a silicon oxide film and similarly evaluated. The results 
are also shown in Table 4. 
TABLE 4 
______________________________________ 
Thickness of 
Thickness of 
Critical 
silicon oxide 
aluminum oxide 
load, Lc 
Substrate film (.mu.m) 
film (.mu.m) 
(gf) 
______________________________________ 
Extruded material 
None 0.5 4.3 
of Al-Ni-Mm rapidly 
solidified powder 
Same as above 
0.01 0.5 5.9 
______________________________________ 
It is clearly noted from Tables 3 and 4 that the effect of the precoating 
with a silicon oxide film manifested in improving the adhesiveness was 
obtained likewise when a rapidly solidified aluminum alloy and an extruded 
material of rapidly solidified powder were used as the material for the 
substrate. 
Since the wear-resistant film of the present invention is produced by 
precoating an aluminum alloy substrate with a silicon oxide film and then 
forming an aluminum oxide film further thereon as described above, it 
exhibits improved adhesiveness, shows a large critical load in the scratch 
test, and consequently enjoys high resistance to scratching and to wear 
under high load as compared with a film not precoated with a silicon oxide 
film. 
The wear-resistant film of the present invention, therefore, finds 
extensive utility as wear-resistant films for various sliding members and, 
because of transparency, further finds utility as surface-protecting films 
for aluminum alloy building materials and articles of fine art and design. 
While certain specific working examples have been disclosed herein, the 
invention may be embodied in other specific forms without departing from 
the spirit or essential characteristics thereof. The described examples 
are therefore to be considered in all respects as illustrative and not 
restrictive, the scope of the invention being indicated by the appended 
claims rather than by foregoing description and all changes which come 
within the meaning and range of equivalency of the claims are, therefore, 
intended to be embraced therein.