JPH10194877A - Tungsten-carbon composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tungsten-carbon composite material not causing the peeling of its surface layer part because thermal stress is relieved even when thermal shock is applied to the top of the surface layer part, excellent in thermal shock resistance and also having high wear resistance by forming a functionally gradient tungsten-carbon layer in the surface layer part of a carbon substrate. SOLUTION: A tungsten layer 3 is formed on the top of the surface layer part 2 of a carbon substrate 1 made preferably of a carbon fiber reinforced carbon composite material and a functionally gradient tungsten-carbon layer 4 is formed in the part 2 under the tungsten layer 3. The carbon and tungsten particle contents of the layer 4 are in nearly inverse proportion to each other from the carbon substrate having 100% carbon content under the surface layer part 2 toward the tungsten layer 3 having 100% tungsten content. The tungsten particles in the surface layer part 2 form tungsten carbide films on the surfaces by reaction with carbon and the films act as a binder to tightly bond the tungsten and carbon particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, in particular, thermal shock resistance,
The present invention relates to a carbon-metal composite material having excellent wear resistance and the like.

[0002]

2. Description of the Related Art Conventionally, as a material suitable for lining the walls of a fusion reactor, the heat resistance (infusibility at atmospheric pressure or lower), thermal stability, corrosion resistance, and high strength of a lightweight yet lightweight carbon material have. Attention has been paid to characteristics such as high toughness, a low atomic number of carbon, and a low reduction in plasma temperature. C /
C material ". ) Is used.

[0003] However, the reactor wall of the nuclear fusion reactor is required to have a higher purity, that is, a member from which impurities (gas) are not released, in order to ensure the stabilization of plasma. At the same time, it is required that wear by plasma particles is smaller than that of carbon materials. Therefore, in order to satisfy these conditions, an actual furnace wall lining material is a C / C material whose base material is coated with tungsten. The fabrication of this tungsten coated C / C material generally involves large-scale chemical vapor deposition (hereinafter "CVD").
Deposition) ”), or by using a plasma spraying method.

[0004]

However, in the case of the above-mentioned tungsten-coated C / C material (hereinafter referred to as "W-coated C / C material"), when a thermal shock is applied to the surface, Is easy to peel off, and once peeling occurs, there is a problem that the C / C material as a base material is exposed and the plasma becomes unstable under the influence of the gas released from the C / C material. . In addition, since large-scale CVD equipment and plasma spray equipment are used for the production of W coat C / C material,
Material costs were very high.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a conventional tungsten / carbon composite material which is a composite material that makes full use of the respective material characteristics of tungsten and carbon. An object of the present invention is to provide an inexpensive composite material having much higher thermal shock resistance and abrasion resistance than a composite material.

[0006]

Means for Solving the Problems First, the present inventors have conducted various investigations on the cause of the weakness of the conventional tungsten / carbon composite material in thermal shock resistance. As a result, the outermost W coat and the C / C material as the base material were obtained. Tungsten carbide (W
C), a relatively brittle carbide film having a relatively brittle property, is formed in a uniform and continuous state as a so-called boundary layer. It has been found that this is the cause, and further studies have been conducted to eliminate this cause. The invention has been completed.

That is, the tungsten / carbon composite material according to the first aspect of the present invention, which has achieved the above object, is characterized in that a tungsten / carbon gradient-functionalized tissue layer is formed on a surface layer of a carbon base material. It is characterized by being formed. The invention according to claim 2 is characterized in that the carbon substrate is a C / C material.

Thus, the carbon substrate (for example, C / C
Since the situation is the same even for materials, a carbon base material will be representatively described below. The structure in the surface layer of (1) is a state in which a film of tungsten carbide is formed on the surface of tungsten particles dispersed and existing in the carbon base material. Further, the outermost surface of the surface portion of the carbon substrate has a tungsten content of 100%, the lower side of the surface portion has a carbon content of 100%, and carbon particles from the lower surface portion to the outermost surface. , The content of the tungsten particles is in inverse proportion to each other, that is, the content of the carbon particles decreases as the content of the tungsten particles increases.

Therefore, the existence state of the tungsten carbide film (spherical film) on the surface layer of the carbon base material is as follows.
Compared to the case of the conventional tungsten / carbon composite material (layered film), it is divided in the horizontal direction, and the divided independent film is spherical, and its density is changed linearly in the vertical direction. However, it is in a state of being present with a predetermined thickness. Further, each tungsten particle is in a state of being strongly bonded to the surrounding carbon particles via the tungsten carbide.

As a result, even when a thermal shock is applied to the outermost surface of the surface portion of the carbon base material, the thermal stress is alleviated in the surface layer portion composed of the tissue layer having a gradient function of tungsten / carbon. The phenomenon that the surface layer of the carbon base material is peeled off as described above is eliminated. Also, when forming a tissue layer with a gradient function of tungsten / carbon on the surface layer of a carbon base material, a general carbon member can be used without using a large-scale CVD device or the like as when coating tungsten. Since the method can be realized by directly using a manufacturing method, for example, a pressure sintering process, the manufacturing cost of the tungsten / carbon composite material can be reduced.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional explanatory view of a main part of a tungsten / carbon composite material of the present invention. FIG.
The surface layer portion 2 of the carbon substrate 1 is composed of a tungsten layer 3 on the outermost surface and a tissue layer 4 with a gradient function of tungsten / carbon below the tungsten layer 3. That is, the tungsten content of the tungsten layer 3 is 100
%. The lower side of the surface layer 2 is the carbon substrate 1 having a carbon content of 100%. The contents of the carbon particles and the tungsten particles from the lower portion of the surface layer portion 2 to the tungsten layer 3 on the outermost surface are almost in inverse proportion to each other, that is, the content of the carbon particles decreases as the content of the tungsten particles increases. It is in a state to do.

When the tungsten particles in the surface layer 2 are observed microscopically, a reaction with carbon forms a tungsten carbide film on the surface, and the tungsten carbide film becomes a kind of binder. The structure is such that the tungsten particles and the carbon particles are tightly linked.

In particular, when attention is paid to the existence state of the tungsten carbide film (spherical film), the horizontal direction is smaller than that of the conventional tungsten / carbon composite material of tungsten carbide (layered continuous film). And the separated independent membrane is spherical,
In addition, the density is present at a predetermined thickness while changing the density linearly in the vertical direction. In other words, the lower part of the tungsten layer 3 is the largest, and decreases linearly toward the lower part of the surface layer part 2.

As a result, even when a thermal shock is applied to the outermost surface of the surface layer portion 2 of the carbon substrate 1, the thermal stress is sufficiently reduced in the surface layer portion 2. The phenomenon that the surface layer portion is peeled off disappears.

Next, an example of the method for producing the tungsten / carbon composite material of the present invention will be described with reference to the drawings. FIG.
FIG. 2 is a schematic explanatory view of the manufacturing method. After blending the carbon powder 5 and the tungsten powder 6 as raw material powders and the necessary binder 7 such as synthetic resin and pitch, a mixer 8
And the tungsten / carbon ratio is varied stepwise according to a predetermined composition distribution.
The carbon mixed powders 12a, 12b, 12c,... (See FIG. 3B) are prepared in advance.

After the powder 11 of 100% tungsten is loaded into the lower mold 10 of the mold 9, the tungsten / carbon mixed powders 12a, 12b, 12c,... Is stacked and filled in the lower mold 10. Finally, after loading the carbon powder 13 of 100% carbon, which is to be the base material of the composite material, the upper mold 14 is pressed down to carry out mold molding to obtain the compacted body 15 of the tungsten / carbon mixed powder. The thickness of the layers of the tungsten / carbon mixed powders 12a, 12b, 12c,... Can be arbitrarily determined.

The obtained compact 15 is put into a normal pressure sintering furnace or a pressure sintering furnace 16 and an appropriate sintering temperature (for example, about 1000 to 2800 ° C.) in consideration of the sintering behavior of the component powders.
Then, sintering is performed by heating slowly so as not to generate thermal stress. As shown in FIG. 1, the obtained sintered body 17 is a tungsten / carbon composite material in which a tissue layer 4 having a tungsten / carbon gradient function is formed on a surface layer portion 2 of a carbon base material 1.

As described above, the tungsten / carbon composite material of the present invention can be realized by directly using a method for obtaining a general carbon sintered body, for example, a normal pressure or pressure sintering process. Since it is not necessary to use a large-scale CVD apparatus or the like as in the case of the conventional case, the manufacturing cost of the tungsten / carbon composite material can be significantly reduced.

In the above embodiment, the carbon material is representatively described as the base material of the composite material. However, even if the carbon material is a C / C material as described above, it is of course effective, It is applicable to the carbon material in the form.

[0020]

[Experimental example]

(Experimental Example 1) The following powder materials (1) to (5) were stacked and filled in a hydraulic press die (φ50 mm) in this order. Tungsten powder (purity 99.99%, average particle size about 5
μm). To 400 parts by weight of the tungsten powder, 100 parts by weight of graphite powder and 50 parts by weight of novolak phenol resin were added and kneaded at 50 to 150 ° C. for about 10 minutes. This kneaded material is pulverized so that the average particle size becomes several tens of μm. A pulverized product obtained by the same process as described above, but particularly having a composition distribution of 200 parts by weight of tungsten powder, 100 parts by weight of graphite powder, and 50 parts by weight of novolak phenol resin. It is a pulverized product obtained by the same process as described above, but excluding tungsten as a composition distribution.
Novolak phenol resin 50 parts by weight with respect to parts by weight.

After completion of the above-mentioned laminating filling, at room temperature, 1
Die molding was performed by applying a pressure of ton / cm ² .
The molded body thus obtained was further fired at about 2000 ° C. to obtain a sintered body. FIG. 3A shows a scanning electron micrograph (SEM photograph) of the surface portion of this sintered body. FIG. 3B shows a tungsten distribution diagram obtained as a result of analyzing the same site with an X-ray microanalyzer.
FIG. 3 shows that the concentration of tungsten changes from the outermost surface to the inside.

A test was conducted to compare the thermal shock resistance and wear resistance of the sintered body obtained above with those of the conventional product. As a conventional product, a product obtained by coating tungsten to a thickness of 100 μm on an isotropic graphite substrate by a CVD method was used. (A) Thermal shock resistance test Each of the above sintered body and the conventional product was irradiated with an electron beam at 5 MW / m ² for 1 second, and what kind of change occurred in the surface layer portion by this irradiation was examined. As a result, in the conventional product, cracks were observed just near the boundary between the graphite substrate and the tungsten coating layer. On the other hand, in the sintered body according to the present invention, no peeling of tungsten or the like was observed at all. (B) Abrasion resistance test A stainless steel ring (φ90 mm) plated with chrome was used to apply a surface pressure of 5 kg to the surface of the sintered body and the conventional product (the surface processed to 5 mm × 20 mm). /
By rotating (peripheral speed: 8.4 m / s) while energizing with a pressure of cm ² , it was examined what kind of change occurred on the sliding surface. As a result, in the conventional product, the coefficient of friction was increased and burning occurred, whereas in the sintered body according to the present invention,
No such baking was observed, and it was confirmed that good sliding performance was obtained.

(Experimental Example 2) A molded carbon fiber felt having a bulk density of 1.3 g / cm ³ (hereinafter referred to as “Felt C /
It is referred to as "C molded body". ) Was used as a substrate, and the so-called impregnation firing method was repeated to form a surface layer portion of the substrate into a texture layer in which the tungsten / carbon ratio was varied stepwise. That is, first, 300 parts by weight of tungsten dispersed in 100 parts by weight of a resole-based phenol resin were impregnated into the felt C / C molded body. The impregnation was carried out by immersing the felt C / C compact in a tungsten-dispersed resin into an autoclave, and pressurizing the inside of the autoclave to 10 kg / cm ² with nitrogen gas. The impregnating material was fired at 2000 ° C.

Next, the primary fired material was further impregnated with a dispersion of 500 parts by weight of tungsten in 100 parts by weight of a resole-based phenol resin, and was similarly fired at 2000 ° C. At the time of impregnation, the tungsten hardly enters the inside of the felt C / C molded body, so that a structure in which the surface portion of the molded body has a higher tungsten concentration is formed. Then, in order to further increase the concentration of tungsten in the final stage, a material obtained by dispersing tungsten in methyl alcohol was applied to the surface and dried, and then fired at 2000 ° C. to obtain a sintered body.

A test was conducted to compare the thermal shock resistance and wear resistance of the sintered body obtained above with those of the conventional product (Experimental Example 1).
I went in the same way. As a conventional product, a felt C / C formed body coated with tungsten to a thickness of 100 μm by a CVD method was used.
As a result of the thermal shock resistance test, in the conventional product, the tungsten coating layer was partially peeled. On the other hand, in the sintered body according to the present invention, no peeling of tungsten or the like was observed at all. In addition, as a result of the wear resistance test, in the conventional product, the coefficient of friction was increased and seizure occurred. On the other hand, in the sintered body according to the present invention, such seizure was not recognized at all and good sliding was observed. It was confirmed that performance was obtained.

As is clear from the results of the above-mentioned (Experimental Example 1) and (Experimental Example 2), the presence of tungsten in the surface layer of the sintered body so that its concentration is inclined,
It can be understood that the thermal shock resistance and the wear resistance were improved. It is considered that the improvement of the wear resistance is due to the so-called self-lubricating property exhibited by the presence of carbon even in the vicinity of the surface of the sintered body. Therefore, when emphasis is placed on the improvement of wear resistance, it is desirable that the outermost layer of pure tungsten in the surface layer is not too thick.

[0027]

According to the present invention, the tungsten / carbon composite material according to the first aspect of the present invention has a structure layer in which a gradient function of tungsten / carbon is formed on the surface of a carbon substrate. Therefore, even when a thermal shock is applied to the outermost surface of the surface portion of the carbon base material, the thermal stress is relieved in the surface portion composed of the tungsten / carbon gradient functionalized tissue layer, and the carbon The phenomenon that the surface layer of the base material is peeled off is eliminated. As a result,
Despite being a composite material that takes full advantage of the properties of each of tungsten and carbon, it offers much lower thermal shock and wear resistance than conventional tungsten-coated / carbon composite materials, and provides a less expensive composite material. be able to. Therefore, it is suitable as a high heat flux member such as a furnace wall lining material of a fusion reactor. Moreover, it is suitable especially when a slurry exists as a mechanical component (sliding component).

In the case of forming a tissue layer having a tungsten / carbon gradient function on the surface layer of a carbon base material, a large-scale CVD apparatus or the like is not used as in the conventional case of coating tungsten. Both can be realized by directly using a method of manufacturing a general carbon member, for example, a normal pressure or pressure sintering process, so that the manufacturing cost of the tungsten / carbon composite material can be significantly reduced.

According to the tungsten / C / C composite material of the second aspect of the present invention, in addition to the effects of the first aspect of the present invention, in particular, the tungsten / C / C composite material has a high performance as a furnace wall lining material for a fusion reactor. Products that are satisfactory in terms of price can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional explanatory view of a main part of a tungsten / carbon composite material of the present invention.

FIG. 2 is a view showing an example of a method for producing a tungsten / carbon composite material of the present invention, wherein (a) is a process explanatory view,
(B) is the figure which expanded the A section of (a).

FIGS. 3A and 3B are diagrams showing a structure of a surface layer portion of a sintered body according to the present invention obtained in Experimental Example 1, in which FIG. 3A is a diagram showing an SEM photograph, and FIG. It is a distribution map of tungsten.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Carbon base material 2 Surface layer 3 Tungsten layer 4 Functionally graded functional layer 5 Carbon powder 6 Tungsten powder 7 Binder 8 Mixer 9 Mold 10 Lower mold 11 Powder of 100% tungsten 12a, 12b, 12c Tungsten / carbon mixed powder 13 Powder of 100% Carbon 14 Upper Die 15 Compacted Body 16 Normal Pressure Sintering Furnace 17 Sintered Functionally Graded Material

Claims (2)

[Claims] 1. The method according to claim 1, wherein the surface portion of the carbon substrate has tungsten /
A tungsten / carbon composite material, wherein a tissue layer functionalized with carbon is formed. 2. The tungsten / carbon composite material according to claim 1, wherein said carbon substrate is a carbon fiber reinforced carbon composite material.