Method for producing a composite material

In production of a composite material such as an elongated Ti-base composite material advantageously used for eyeglass frames, a crude composite material formed by application of at least one surface layer of a component material to a base block by means of spraying processing is subsequently subjected to pressure application preferably with heat. A multi-layer construction can be easily obtained even starting from a base block of an intricate surface configuration thanks to employment of the spraying process, and the final pressure application assures strong diffusion bonding between the core block and the surface layers. The base block may be given in the form of a mold to be ultimately removed from the product.

BACKGROUND OF THE INVENTION 
The present invention relates to method for producing a composite material, 
and more particularly relates to an improvement in production of a 
composite material such as a Ti-base composite material generally used for 
eyeglass frames. 
Clad materials are typical example of a composite material made up of two 
or more different component materials bonded together in a superimposed 
disposition. For production of such a clad material, the component 
materials are conventionally bonded together by means of casting, welding, 
plasma spraying, blazing, dispersion, pressing, extrusion or detonation 
bonding. 
In production of a composite material, there are lots of process and 
quality demands in the field of the art. In the first place, the process 
is required to assure multi-layer construction of the product with 
sufficient inter-layer bonding strength. Next, low cost production is 
strongly required even in the case of an intricate configuration of the 
product. 
None of the above-described conventional processes could not well suffice 
these demands all together. That is to say, each of the processes was good 
for neither one demand nor the other. 
SUMMARY OF THE INVENTION 
It is the basic object of the present invention to produce a composite 
material at low production cost, with high inter-layer bonding strength 
and with possibility of forming a multi-layer construction even on an 
intricate configuration of the base material. 
In accordance with the basic aspect of the present invention, one or more 
surface layers of different component materials are formed on a base block 
by means of spraying process to obtain a crude composite material, and 
pressure is applied to the crude composite material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The first embodiment of the method in accordance with the present invention 
is shown in FIGS. 1 through 5, in which three surface layers of different 
component materials are sequentially formed on a base block to obtain a 
crude composite material and the crude composite material is then 
subjected to hot hydrostatic pressing to obtain a composite material. 
To begin with, a base block 1 such as shown in FIG. 1 is subjected to 
preliminary blasting for surface cleaning. Although the illustrated base 
block 1 takes the form of a plate with a corrugated surface, it may take 
the form of various rods, cylinders, blocks and plates. Preferably, the 
material for the base block exhibits thermal expansion close to that or 
those of the component material or materials for a surface layer or layers 
to formed on the base material. Sands or fine metal particles are 
preferably used for blasting. In addition to the surface cleaning, the 
blasting brings about adjusted surface roughness for better deposition of 
the sprayed component material or materials. 
Next, the first surface layer 2 is formed on the base block 1 by spraying 
molten metal or ceramic powder as shown in FIG. 2. Plasma spraying process 
is here preferably employed in which molten component material is sprayed 
by a plasma spray gun 3. Powder of the component material is introduced, 
being entrained on carrier gas, into high frequency plasma generated by 
high frequency induction or into DC plasma generated by heat exchange 
between DC arc and plasma gas. After melting in the plasma, the component 
material is sprayed onto the base material 1 for formation of the first 
surface layer 2. Although inert gas such as argon is most preferably used 
for the carrier gas, nitrogen can be used also. For the purpose of 
preventing oxidization of the first surface layer, spraying is preferably 
carried out in an inert environment of these gases or in a reductive 
environment of low pressure hydrogen. 
Further, as shown in FIG. 3, the second surface layer 4 is formed on the 
first surface layer 2 by spraying a composite material different from that 
for the first surface layer 2. Then the third surface layer 5 is formed on 
the second surface layer 4 from a composite material different from that 
for the second surface layer 4. In this way, at least two surface layers 
of different composite materials can be formed in superimposition even on 
a base material 1 having a intricate surface configuration. 
A crude composite material so obtained is then subjected to hot hydrostatic 
pressing as shown in FIG. 4 to form a composite material 6 of the present 
invention. To this end, the crude composite material is placed in a high 
pressure and high temperature furnace (not shown) with use of an inert gas 
such as argon and helium for the pressure medium filled in the furnace. 
Preferably, the pressing is carried out at a temperature from 0.5 to 0.7 
mp .degree.C., mp being the melting point of a material which has the 
lowest melting point among the base and component material used for 
formation of the crude composite material under a pressure from 50 to 180 
MPa, for a period of 0.5 to 4 hr. As concerns the temperature, "mp" 
indicates the melting point of a material which has the lowest melting 
point among the base and component materials used for formation of the 
crude composite material. 
Application of the hot hydrostatic pressing produces dispersion bonding 
between the base and component materials which is by far higher in bonding 
strength than the conventional mechanical bonding. 
The second embodiment of the present invention is different from the first 
embodiment in that the base block is finally removed from the product. 
More specifically, the base material takes the form of a model 7 having a 
surface configuration to be carried over to the product. As shown in FIGS. 
2 to 4, the first to third surface layers 2, 3 and 4 are formed on the 
model 7 by means of spraying process and, after the hot hydrostatic 
pressing, the model 7 is removed to obtain a composite material 8 such as 
shown in FIG. 5. 
Preferably, the material for the model 7 should exhibit thermal expansion 
by far greater than that of the material for the first surface layer 2 for 
easy removal of the model 7 after hot hydrostatic pressing by means of 
abrupt cooling. By properly selecting the material for the model 7, no 
preliminary coating of the model 7 with mold releasing agent is 
necessitated. More specifically, alumina or ceramics is preferably used 
for the model. When ceramic is used for the model 7, an alkali solution 
can be used for its removal. Since the surface layers 2, 4 and 5 are 
finally removed from the model 7, no initial surface flasting is required. 
In practical application, the method in accordance with the present 
invention is most advantageously used for a Ti-base composite material for 
eyeglass frames. 
Ti-base materials have recently experienced increased use in the field of 
high class eyeglass frames because of their high corrosion resistance, 
high mechanical strength and light weight. Despite these excellent 
properties, the Ti-base materials are in general quite unsuited for 
blazing and plating which are both indispensable in production of eyeglass 
frames. In an attempt to cover such demerits, it is conventionally 
proposed to combine a Ti-base material core with a Cu-base alloy or 
Ni-base alloy sheath by means of cladding since these alloys are well 
suited for blazing and plating. It is also widely employed to plate a 
Ti-base material core with precious metals. 
In a typical process of cladding, on elongated Ti-base material core is 
inserted into an alloy cylinder and, after vacuum sealing, the combination 
is subjected to hot hydrostatic pressing for clad bonding of the core with 
the sheath. After the pressing, the combination is formed into a thin wire 
by means of hydrostatic extrusion. 
For smooth insertion of the core into the sheath, a small gap must be left 
between the facing surfaces of the two components. At the hot hydrostatic 
pressing, however, presence of such a gap allows development of many, fine 
wrinkles on the outer surface of the sheath, i.e. the alloy cylinder. 
Since the configuration of the core is changed following the inner surface 
of the sheath, removal by cutting of the wrinkles on the outer surface of 
the sheath would partially expose the core outside the sheath. The 
wrinkles developed during the hot hydrostatic pressing may be more or less 
removed or diversed during the wiring process, such a process design is 
much complicated in particular when directly connected to the cladding 
process. In addition, the core is manually inserted into the sheath and 
presence of such a manual operation tends to contaminate the outer surface 
of the core. Poor bonding between the core and sheath caused by 
contamination would induce accidental separation of the core and sheath 
during the wiring process. 
In accordance with the present invention, formation of one or more surface 
layers is introduced into production of a Ti-base composite material for 
eyeglass frames. 
In the first place, as shown in FIG. 6, an intermediate layer 12 is formed 
on an elongated core 11 by means of spraying process and a sheath 13 is 
combined therewith by means of cladding process. The core 11 is made of a 
Ti-base material whereas the sheath 13 is made of a Ni-base material which 
is well suited for blazing and plating. The intermediate layer 12 is used 
for bonding the core 11 to the sheath 13, and mode of a material which 
exhibits good solid diffusion with Ti contained in the core 11 and 
generates no inter-metallic compounds in reaction with Ti. Preferably, the 
intermediate layer 12 is made of Mo, Nb, Ta and alloys of two of these 
metals. 
As shown in FIG. 7, two intermediate layers 12a and 12b may be made on the 
core 11. In this case, the second intermediate layer 12b is preferably 
made of a Cu-base material for stronger bonding between the core and the 
sheath. Three or more intermediate layers may be formed depending on 
quality demand for the product. 
The intermediate layer 12 so formed is very porous in construction and, as 
a consequence, pores in the intermediate layer 12 are filled with fine 
metal particles during the hot extrusion, thereby preventing development 
of wrinkles on the surface of the sheath 13. 
In the hot extrusion, the crude composite material is preferably subjected 
first to preliminary heating at a temperature of about 600.degree. C. for 
a period from 1 to 2 hr. and to hot extrusion at a temperature from 
800.degree. to 900.degree. C. Cladding of the core 11 with the sheath 13 
and wiring of the crude composite material are carried out concurrently 
during the hot extrusion, thereby simplifying the entire process greatly. 
In the other embodiment of the present invention applied to production of a 
Ti-base composite material for eyeglass frames, a surface layer is formed 
on a core made of a Ti-base material by means of spraying process, the 
combination of the core with the surface layer is encased in a capsule, 
the gap around the combination within the capsule is filled with metallic 
powder, the capsule is subjected to cold hydrostatic pressing after vacuum 
sealing, the metallic powder within the capsule is sintered, the capsule 
is subjected to hot extrusion for wiring and the capsule is removed. 
The capsule is preferably given in the form of a pipe made of soft steel. 
Preferably, a Ni-base materials is used for the metallic powder to be 
filled in the capsule because of its good fitness to blazing and plating. 
Sintering is carried out at a temperature from 800.degree. to 900.degree. 
C. for a period of 1 to 2 hr. 
EXAMPLES 
EXAMPLE 1 
A Ti base block 21 such as shown in FIG. 8 was prepared. This base block 21 
was 50 mm in outer diameter and 500 mm in length. The surface of the base 
block was blasted with sand. 
First, Mo particles of 30 to 70 .mu.m diameter were applied to the base 
block 21 by means of plasma spraying process to form the first surface 
layer 22 of 0.5 mm thickness. Spraying was carried out at a vacuum degree 
of 20 to 60 Torr. and with a spraying distance of 100 to 150 mm. Next, Cu 
particles of 45 to 90 .mu.m diameter were applied by means of vacuum 
plasma spraying process to form the second surface layer 23 of 0.5 mm 
thickness, and Ni particles of 10 to 45 .mu.m diameter were similarly 
applied to form the third surface layer 24 of 1.5 mm thickness, both under 
same conditions as in the case of the first surface layer 22. 
A crude composite material thus obtained was subjected to hot hydrostatic 
pressing in an argon environment at a temperature of about 1000.degree. 
C., under a pressure of about 180 MPa for a period of 2 hr. 
By a test after production, presence of high bonding strength between the 
base block and the surface layers in a composite material 25 was 
confirmed. 
EXAMPLE 2 
A stainless steel model 31 such as shown in FIG. 9 was prepared. This model 
31 was 40 mm in outer diameter and 200 mm in length. 
First, alumina gas atomized particles were applied to the model 31 by means 
of vacuum plasma spraying process to form the first surface layer 32 of 
1.0 mm thickness. Spraying was carried out under conditions same as in 
Example 1. Next, Cu particles of 45 to 90 .mu.m diameter were applied by 
means of vacuum plasma spraying process to form the second surface layer 
33 of 0.5 mm thickness and Ni particles of 10 to 45 .mu.m diameter were 
similarly applied to form the third surface layer 34 of 1.5 mm thickness. 
A crude composite material thus obtained was subjected to hot hydrostatic 
pressing in an argon environment at a temperature of about 1000.degree. 
C., under a pressure of about 180 MPa for a period of 2 hr. The model 31 
was removed utilizing difference in degree of thermal expansion between 
the model 31 and the first surface layer 32 which was also removed by 
means of cutting to obtain a cylindrical composite material 35 such as 
shown in FIG. 10. 
By a test after production, presence of high bonding strength between the 
surface layers was confirmed. 
EXAMPLE 3 
A Ti billet was used for the core 11 having a diameter of 92 mm and a 
length of 1000 mm. After application of blasting, Mo gas atomize particles 
of 30 to 75 .mu.m diameter ware applied to the Ti core 11 by means of cold 
plasma spraying process to form a Mo intermediate layer 12a of 0.5 mm 
thickness. Next, Cu gas atomize particles of 45 to 90 .mu.m diameter ware 
applied onto the Mo intermediate layer 12a by mean of cold plasma spraying 
process to form a Cu intermediate layer 12b of 0.5 mm thickness. A 
combination of the Ti core with the Mo and Cu intermediate layers was 
inserted into a sheath 13 made of a Ni-Cr alloy. The sheath was 97 mm in 
inner diameter and 3 mm in wall thickness. After vacuum sealing and 
preliminary heating at 600.degree. C. for 1 hr., the crude composite 
material was subjected to hot extrusion at 900.degree. C. to obtain a Ti 
composite material of 60 mm diameter. No surface wrinkles were observed on 
the product. 
Five samples were prepared as shown in FIGS. 11 and 12. In preparation of 
each sample, a Ti composite material produced was cut into a rod of 20 mm. 
Next, the intermediate layers and the sheath were partly removed so as to 
leave a local test projection of 3 mm length. The diameter of the core 11 
was 5 mm. A shearing force F was applied to the test projection for 
measurement of the shearing strength and the result is shown in Table 1. 
For comparison, a Ti billet of 92 mm diameter and 1000 mm length was 
inserted sequentially into a Mo pipe of 92 mm inner diameter and 0.5 mm 
wall thickness, a Cu pipe of 92.5 mm inner diameter and 0.5 mm wall 
thickness, and a Ni-Cr alloy pipe of 93 mm inner diameter and 3 mm wall 
thickness. A combination thus obtained was subjected to hot hydrostatic 
pressing at a temperature of 1000.degree. C., under a pressure of 180 MPa 
for a period of 2 hr. for cladding. Next, hydrostatic extrusion was 
carried out under a pressure of 900 MPa to obtain a Ti composite material 
of 60 mm diameter. Shearing strength tests were carried out in a manner 
same as in the case of the samples of the present invention. The results 
are also shown in Table 1. 
TABLE 1 
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shearing strength 
(GPa) 
sample inventional comparative 
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1 0.243 0.231 
2 0.285 0.214 
3 0.301 0.193 
4 0.274 0.222 
5 0.254 0.245 
average 0.271 0.221 
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*Shearing strength = (Load in kg. when the test projection was taken off 
the core)/(Surface area in mm.sup.2 of the test projection) 
It is clear from the data that the bonding strength between the core and 
the sheath was much raised by employment of the method in accordance with 
the present invention. Further, no substantial presence of wrinkles on the 
product was confirmed. 
EXAMPLE 4 
A Ti billet was used for the core 11 having a diameter of 92 mm. and a 
length of 1000 mm. After application of blasting, Mo gas atomize particles 
of 30 to 75 .mu.m were applied to the Ti core 11 by means of cold plasma 
spraying process to form a Mo intermediate layer 12a of 0.5 mm. thickness. 
Next, Cu gas atomize particles of 45 to 90 .mu.m diameter were applied 
onto the Mo intermediate layer 12a by means of cold plasma spraying 
process to form a Cu intermediate layer 12b of 0.5 mm thickness. A 
combination of the Ti core with the Mo and Cu intermediate layers was 
placed on the center axis in a soft steel capsule which was 97 mm in inner 
diameter and 3 mm in wall thickness. A gap between the combination and the 
capsule was filled with Ni-Cr alloy powder. After vacuum sealing, the 
capsule was heated at a temperature from 800.degree. to 900.degree. C. for 
1 hr. for sintering purposes. After subsequent preliminary heating, the 
capsule was subjected to hot extrusion at 900.degree. C. to obtain a wire 
of 60 mm diameter. Then the capsule was removed to obtain a Ti composite 
material. No surface wrinkles were observed on the product. 
Five samples were prepared and subjected to a shearing test just as in the 
preceding Example. Comparative samples were prepared also just as in the 
preceding Example. The results are shown in Table 2. 
TABLE 2 
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1 0.313 0.231 
2 0.272 0.214 
3 0.293 0.193 
4 0.285 0.222 
5 0.296 0.245 
average 0.292 0.221 
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It is again clear from the data that the bonding strength between the core 
and the sheath was significantly raised by employment of the method in 
accordance with the present invention. Further, no substantial presence of 
wrinkles on the product was confirmed.