DE69130237T2 - Process for the production of composite material - Google Patents

Description

The present invention relates to a method for producing a composite material for combining two materials with different melting points that do not mix with each other in solid solution, such as W (tungsten) and Cu (copper). The composite material should be suitable for heat conduction.

In an apparatus having an ultra-hot area containing a molten metal, such as a radioactive metal crucible and a heat-absorbing plate, it is often essential to use a material that can withstand a high temperature and high energy density electron beam or plasma, i.e. the beam target material.

Since the beam target material is used under harsh conditions, it must have the following two properties:

(1) sufficient heat resistance directly under the heat source with increasing temperature,

(2) excellent thermal conductivity and excellent cooling properties.

The second point is necessary because the opposite side of the heat source is generally cooled by a device.

However, in a single material, heat resistance and thermal conductivity cannot be considered separately and when specifying one of these two, the others are automatically naturally fixed within a limited range. Therefore, in order to enhance both properties together, composite materials have been tried. One such attempt is to make a composite material with both excellent heat resistance and thermal conductivity by combining W, which has a high melting point among metals, and Cu, which has excellent thermal conductivity.

However, when combining W and Cu, since they do not mix with each other in solid solution, the joining method is limited and simple bonding or soldering or other mechanical joining methods are mainly used.

When such a compound of W and Cu is used in the high temperature field, the difference in thermal expansion between the two is very large. In particular, W has a thermal expansion factor of 4.5 x 10-6/K, while Cu has a thermal expansion factor of 17.1 x 10-6/K. The thermal stress generated by this is extremely large. Therefore, if W and Cu are only soldered and alloyed, W, which has the smaller thermal expansion factor, is likely to crack due to the tensile stress during heating, and to delaminate due to the thermal stress formed in the interface of W and Cu. This cracking and delamination lowers the overall thermal conductivity, which may lead to the temperature increase of the materials or, in the worst case, to the accident of melting together.

Therefore, attempts have recently been made to produce gradient materials with a controlled structure (hereinafter referred to as "gradient material"), whereby two Powders were mixed, these were laminated by varying the mixing ratio and the laminates were sintered.

This process makes it possible to obtain gradient materials if the melting points of the two powders to be mixed are similar. However, if they are very different, only one material will melt while the other will not, and it will be difficult to produce a gradient material with a controlled structure.

DE-A-24 50 361 describes the sintering of a framework of metal particles of different sizes in order to obtain the desired porosity gradient within the framework of the first metal. A second metal with a lower melting point than the first metal is converted into a liquid state and infiltrated into the pores of the skeleton.

A primary object of the invention is to provide a manufacturing process for a composite material with excellent thermal conductivity and bonding strength at the interface of the two starting materials to be joined together.

According to the invention there is provided a method for producing a composite material as specified in claim 1. Optional features of the invention are contained in the appended claims.

According to the invention, due to the continuous change of the composition in the gradient composition region (the interface) of the high-melting material and the low-melting material, ie the gradient of the composition, the bonding strength (adhesion) of the interface The surface of the two materials and the thermal conductivity are of high quality.

In addition, if the location where a large thermal stress is generated is made of a high-strength material, it can withstand harsher conditions, such as the high thermal stress condition in the case of a beam target.

Furthermore, since the sintering process is varied by using thermal spraying, a gradient composition having a three-dimensional surface, for example, a cylinder, is produced.

The continuously changing composition eliminates grain boundary fragility. The bond formed between the high-melting and low-melting material can withstand both stationary and non-stationary thermal loads. The composite material is therefore suitable for use as a heat-conducting material.

This invention can be better understood from the following detailed description taken in conjunction with the accompanying drawings. In the drawings:

Fig. 1 shows a schematic flow diagram of a first embodiment of the manufacturing process for a composite material according to the invention;

Fig. 2A and 2B show a schematic diagram of a composition gradient at the interface of W and Cu for a metallic composite of Fig. 1;

Fig. 3 is a schematic diagram of the stress generated at the interface of W and Cu of Fig. 1;

Fig. 4 is a graph showing the thermal conductivity in the mixed layer of W and Cu in the composition gradient part of Fig. 1;

Fig. 5A and 5B show a crucible of a radioactive metal in cross section and a schematic diagram showing the fine texture of part A of the material obtained in the embodiment in Fig. 1, respectively;

Fig. 6 shows a schematic flow diagram of a second embodiment of the manufacturing process for a composite material according to the invention;

Fig. 7 is a diagram for explaining the effect of the particle size of the W powder or the molding pressure on the relative density of the sintered body in the second embodiment;

Fig. 8 shows a schematic flow chart of the third and fourth embodiments of the manufacturing process for a composite material according to the invention;

Fig. 9 is a diagram for explaining the mechanical strength of the material obtained in the third embodiment;

Fig. 10 is a diagram showing possible examples of dispersion reinforcing materials of the third embodiment and their main properties;

Fig. 11A is a perspective view showing an electron beam target comprising the material obtained in the third embodiment;

Fig. 11B shows the electron beam target in cross section along a line A-A;

Fig. 12 is a diagram for explaining the infiltration process of Cu in the preparation of the electron beam target material of Fig. 11;

Figs. 13A to 13D show the results of analysis of the temperature distribution and the mechanical stress distribution, respectively, when an electron beam is emitted onto the electron beam target in Fig. 11;

Fig. 14 is a graph showing the relationship between the input heat density of the electron beam, the maximum main load (thermal load) and the maximum temperature reached when an electron beam is emitted onto the electron beam target in Fig. 11;

Fig. 15 shows a schematic flow diagram of a fifth embodiment of the manufacturing process for a composite material according to the invention;

Fig. 16 is an approximate cross-section of the material obtained in the fifth embodiment;

Fig. 17 shows a schematic flow diagram of a sixth embodiment of the manufacturing process for a composite material according to the invention;

Fig. 18 shows a schematic flow chart of a seventh embodiment of the manufacturing process for a composite material according to the invention;

Fig. 19 shows a schematic flow diagram of an eighth embodiment of the manufacturing process for a composite material according to the invention and

Fig. 20 is an approximate cross-sectional view of the material obtained in the eighth embodiment.

Referring to the drawings, some of the preferred embodiments of the present invention will be described in detail below. Fig. 1 is a schematic flow chart for explaining a first embodiment of the manufacturing process of a composite material according to the invention. In step 1, W powder is filled into a mold (not indicated) for molding into a specific shape. In step 2, the W powder obtained in step 1 is molded. In step 3, the mold obtained in step 2 is sintered to form pores, and a W sintered body whose porosity increases toward the infiltration side (the side where the infiltrated material becomes 100% as a result of infiltration) is obtained. In step 4, Cu is melted in a container (not indicated) and infiltrated into the pores of the W sintered body obtained in step 3. In stage 5, the material obtained in stage 4 is mechanically processed to obtain the final desired product shape.

The metallic composite material obtained in this way has the following effects.

1) The composition at the interface of W and Cu varies almost continuously, that is, the composition has a gradient. Fig. 2 is a schematic diagram of the alloy metal material prepared as described above, in which Fig. 2A is a composition distribution diagram and Fig. 2B is a distribution characteristic diagram. in terms of the weight ratio of W and Cu. From this diagram, it is apparent that the composite metal material of the invention has an increased contact area of W and Cu due to the gradient of composition in the gradient composition range of W and Cu, as compared with the conventional composite metal material using mechanical bonding such as bonding and thermal spraying of simple materials, since a microscopic network structure is formed between W and Cu so that the contact is significantly enhanced.

2) In the embodiment, the coefficient of thermal expansion stress in the mixed layer of W and Cu changes almost proportionally to the mixing ratio. The thermal stress of the layer (i.e., a combination of compressive stress and tensile stress) is relatively small and changes little as shown by the solid line in Fig. 3. In contrast, the thermal stress of the composite layer made by the conventional mechanical bonding method is large and changes greatly as shown by the dot-dash line in Fig. 3.

3) The material of the embodiment can close the gap between the materials in simple bonding (prior art) because the contact area of W and Cu increases. Accordingly, the thermal resistance at the interface of the gradient composition of W and Cu decreases and excellent thermal conductivity is obtained as with W alone or Cu alone. Fig. 4 is a characteristic diagram of thermal conductivity explaining this. From this diagram, it can be seen that an excellent thermal conductivity exceeding that of W alone can be obtained overall by utilizing the property that the thermal conductivity of the composition gradient region depends strongly on Cu, which has a higher conductivity.

Referring to Fig. 5, an example of applying the composite material obtained in the first embodiment to a crucible for melting radioactive metal or a heat-receiving plate will be explained below. Fig. 5A shows in cross section the main body 11 and the water-cooled frame 13 of a crucible for melting radioactive metal, and Fig. 5B is a schematic diagram of the fine texture of part A of Fig. 5A. The side of the crucible main body 11 is exposed to high temperature and therefore is made of refractory metal W. The water-cooled frame 13 is made of Cu having excellent thermal conductivity, and the gradient composition region 14 of W and Cu is a so-called gradient composition in which the composition varies continuously. Numeral 12 indicates a water cooling hole.

The method for producing such a structure is shown in Fig. 6. Here, in the first step 21, a fine W powder is prepared and laminated in the shape of the crucible main body 11 in Fig. 5. In the second step 22, the laminate obtained in the first step 21 is molded by, for example, CIP (cold isostatic pressing) to form a W shape. In the third step 23, the W shape obtained in the second step 22 is kept in H₂ or other reducing atmosphere at high temperature for several hours to produce a W sintered product. In the fourth step 24, the sintered W body obtained in the third step 23 is mechanically processed to finally obtain a crucible shape. In this case, the mechanical processing is carried out including the gradient region of the interface.

In the first to fourth stages 21 to 24, the density on the inside of the crucible main body 11 increases to 95% or more. In addition, the manufacturing conditions such as material powder, molding pressure, sintering temperature and others are controlled so that the density can continuously change up to about 50% on the outside of the crucible main body 11.

In the fifth step 25, Cu is melted by a device and the sintered W obtained in the third process 23 is infiltrated into this molten bath of W (presumably Cu) and cooled after holding until the molten Cu sufficiently penetrates into the pores of the sintered W. The fifth process step 25 is carried out in a high-temperature reducing atmosphere of H₂ or the like. In the sixth step 26, after sufficiently cooling, it is taken out to the atmosphere and machined to the specified dimensions of the crucible main body 11 and water-cooled frame 13.

The crucible made of such a composite metal material (Fig. 5) produced by such a manufacturing process has a wide contact area of the gradient composition region 14 with W and Cu, and thereby has excellent adhesion and thermal conductivity. Since the composition of the gradient composition region 14 has a gradient, the peak value of the thermal stress that occurs due to the difference in the thermal expansion coefficient between W and Cu during heating can be reduced.

On the other hand, the crucible of the embodiment is characterized in that a sintered W crucible is produced, the porosity of which on the outside of the crucible main body 11 continuously varied. Regarding the effect of the powdery raw material on the density of the sintered body, as shown in Fig. 7, by varying the size of the powder particles in a range of 1 µm to 10 µm, a W sintered body having the relative density of 60% to 95% can be produced. Using this property, by continuously varying the particle size of the W powder used in the lamination of the W powder, the sintered W crucible having a continuously varying density of 95% to 60% can be produced. Meanwhile, although the effect is not as great as when the size of the powder particles is changed, one method of changing the density of the sintered body is to vary the molding pressure and the sintering temperature. By combining these, the sintered W crucible main body 11 can be manufactured more effectively. In addition, when the sintered W crucible main body 11 is impregnated with molten Cu, the molten Cu penetrates into the closed pores in the sintered W body because it is likely to wet solid W. Since the demarcation of the closed pores and open pores of the sintered W body is about 90%, most of it is infiltrated into the low density region on the outside of the sintered W crucible main body 11. As a result, a crucible of a gradient composition of W and Cu is manufactured in this way because of the continuous change in density on the outside of the sintered W crucible main body 11.

According to a second embodiment described so far, the interface composition of W and Cu has a gradient and the contact area of W and Cu has an increased value, so that the following effects are achieved.

a) The adhesion in the gradient composition region 14 is increased and the thermal load in the gradient composition composition region 14 when used at high temperatures is reduced and cracks and peeling in the gradient composition region 14 are thereby reduced, so that the service life is increased.

b) The thermal resistance in the gradient composition region 14 is reduced and the total thermal conductivity is increased, so that the water cooling effect of the water-cooled frame 13 can be sufficiently utilized. As a result, the temperature gradient of the molten metal in the crucible main body 11 increases and the inner wall temperature of the crucible main body 11 can be reduced, which also contributes to the extension of the service life.

The second embodiment relates to a crucible of a radioactive metal or a heat-absorbing plate, but it can also be applied to other high-temperature devices requiring the combination of W and Cu. In the embodiment, the combination of W and Cu is specified as the raw materials for mixing. However, it is not limited to this and it can be applied to any two other raw materials as long as they are different in melting point and are not mutually miscible in solid solution. In any case, it must include the step of sintering the high-melting raw material and the step of impregnating the sintered body with the low-melting molten raw material. After these steps, a gradient material is obtained at the interface of the composite metal material.

The third and fourth embodiments of the manufacturing method of the composite material according to the invention are explained below with reference to Fig. 8 to 10. In the first embodiment mentioned, due to the reduction In the first embodiment, however, the mechanical strength is not fully satisfactory because it requires a step of preparing a W sintered body having a porosity distribution in the direction of the thickness of the plate and a step of sintering and infiltrating molten Cu into the pores of the W sintered body. That is, the grain boundary is particularly weak in the recrystallized grains because of the step of sintering W which is responsible for the mechanical strength. In addition, since this W sintered body is required to have a porosity distribution in the direction of the thickness of the plate, hot forging cannot be used as a post-treatment for increasing the mechanical strength. Therefore, even if the thermal stress is reduced by composition gradient formation at the interface of W and Cu, cracks may be formed in W because of the low mechanical strength.

Accordingly, in order to increase the mechanical strength of the first embodiment, in a combination of two raw materials of a single composition, e.g., a W/Cu gradient material, the solid solution composition in the third embodiment is given a gradient by adding a second solid solution-miscible element, e.g., powder of Re (rhenium), Ta (tantalum), Nb (niobium), or Hf (hafnium), so that only the mechanical strength is enhanced while maintaining the same functions.

Advantageously, according to the schematic flow diagram in Fig. 8, in the first stage 31, Re powder is fed to the W powder with different particle sizes. In the second stage 32, powders are successively fed from the smaller part In the third step 33, the laminate laminated in the second step 32 is shaped by die stamping or the CIP molding method. In the fourth step 34, the shape obtained in the third step 33 is sintered and the solid solution element is alloyed with W, thereby obtaining a W alloy sintered body having a porosity distribution in the direction of the plate thickness (W-HIP material in Fig. 9). In the fifth step 35, the W alloy sintered body obtained in the fourth step 34 is impregnated with molten Cu, whereby Cu penetrates into the pores, and allowed to cool. In the sixth step 36, the infiltrated material obtained in the fifth step 35 is mechanically processed and finished into a desired product shape.

The fourth embodiment is, similar to the third embodiment, a manufacturing method for a composite material in which only the mechanical strength is increased while maintaining the functions, wherein, in order to increase the mechanical strength of the first embodiment, when two starting materials are combined from a single composition, e.g., a W/Cu gradient material, a second element or compound that is not miscible in solid solution, e.g., ThO₂ (thorium dioxide) powder, is added and the dispersion is intensified to form a gradient of the composition.

More specifically, the fourth embodiment is the same as the third embodiment, except that ThO2 powder is added to the W powder having different particle sizes in the first stage 31 as shown in the schematic flow diagram in Fig. 8.

The materials obtained by the third and fourth embodiments have the following characteristics:

1) For W, which is responsible for the mechanical strength of the material, the bending strength increases significantly as shown in Fig. 9 by alloy formation.

2) Since the interface of W alloy and Cu has a compositional gradient, there is no abrupt change in the thermal expansion coefficient and the thermal stress is reduced compared to the connection by the conventional soldering method or other method.

3) Since the thermal conductivity of the W alloy mainly depends on W, which has the higher thermal conductivity, the overall thermal conductivity hardly decreases, even though the thermal conductivity of ThO2 is low, 10 W/m K.

5) As can be seen from the process for the material obtained in the fourth embodiment, the overall thermal conductivity is very good because the Cu with excellent thermal conductivity is in a network structure.

In the fourth embodiment, ThO₂ is used as the dispersion-enhancing agent, but basically any other material can be used as long as it is chemically stable and has a high melting point. Any of the dispersion-enhancing agents shown in Fig. 10, i.e., TaB₂, TiB₂, HfB₂, Y₂O₃, ZrO₂, can be used.

Therefore, according to the third and fourth embodiments, peeling at the interface of W and Cu and cracks in the material can be eliminated and finally a material can be produced which is affected by the increase in thermal stress due to peeling or The increase in temperature of the material resulting from cracking and a melt-through accident can be eliminated.

An example of the application of the material obtained in the third embodiment to the electron beam target will be explained below with reference to Figs. 11 to 14. Figs. 11A and 11B relate to an example of the application of the composite material obtained in the third embodiment to the beam target for a crucible for radioactive metal or the like, in which Fig. 11A is a schematic diagram of an electron beam (EB) target and Fig. 11B is a cross section in the direction of the arrow along the line A-A in Fig. 11A. Since the C side of the beam target 121 is exposed to the EB 116 and has a high temperature, it is made of the W alloy having a high melting point and high strength.

On the other hand, the D side on the opposite side of the beam target 121 is made of Cu with excellent thermal conductivity and mechanical workability and is cooled with water using the water cooling pipe 117. Between the C side and D side, the composition ratio of the W alloy and Cu changes continuously, i.e., the so-called gradient composition is produced.

The composite material used in Fig. 11A and Fig. 11B is manufactured by the following method. First, the W alloy sintered body 119 is prepared as shown in Fig. 8 from the first to the fourth stage. When infiltrating Cu 119 into the pores of the W alloy sintered body 118 shown in Fig. 12 in a slightly large graphite crucible 120, the side with low porosity is placed on the upper side and the build-up part of Cu is placed on the opposite side. In this state, after the completion of the infiltration of Cu machining and finishing to a desired size are performed, and a hole is drilled for the water cooling tube 117. Finally, the water cooling tube 117 is soldered using Ag-Cu solder or the like, thereby completing the beam target 121.

In the beam target 121 thus manufactured, the W alloy and Cu are in gradient composition and the Cu with excellent thermal conductivity is in a network structure. This can lower the temperature reached during use and reduce the thermal stress.

Fig. 13 shows the result of an analysis of the temperature distribution and the thermal stress distribution (main stress) when the electron beam target shown in Fig. 11 is exposed to an electron beam. Fig. 13A and Fig. 13C specifically show a comparison of the result of the temperature distribution analysis by the finite element method between the W alloy/Cu gradient material and the W alloy/Cu brazed material when each was heated by a linear EB of 5 kW/cm2. Fig. 13B and Fig. 13D show a comparison of the heat load distribution by the same finite element method between the W alloy/Cu gradient material and the W alloy/Cu brazed material when each was heated by a linear EB of 5 kW/cm2. From the result, it is clear that the maximum temperature reached can be lowered by about 80 K by creating the gradient material. It also shows that immediately below the EB, where the temperature gradient is greatest, the maximum thermal load is reduced to about 1/3.

Incidentally, since the strength of the beam target 121 is increased by alloying W, the EB performance can be increased to the point of collapse. Fig. 14 shows the EB input heat density, the maximum thermal stress induced, and the maximum temperature reached after analysis by the finite element method. According to Fig. 13, the maximum thermal stress is generated in the W alloy layer immediately under the heat source, and since the amount of strength reduction of the individual parts due to the compounding with Cu does not seem to be so large, the collapse of the beam target 121 is presumably induced when the stress generated in the alloy layer becomes larger than its strength.

The dashed lines indicated in Fig. 13A to 13D are the center lines of the distribution diagrams. Therefore, only the right half of each distribution diagram is indicated, since the left half is symmetrical to the right half.

Here, based on the result of measuring the strength of W or a W alloy at ordinary temperature, it is estimated how much the input heat can be increased by alloying. In the case of pure W, the strength is 0.4 GPa and the maximum applicable input heat density is about 4 kW/cm2 at most, but in the case of a W-5Re alloy with the addition of 5% Re, the strength is increased twice as much as 0.8 GPa, so that an EB power of about 8 kW/cm2 is possible. Furthermore, if the input heat density is 9 kW/cm2, the maximum temperature achieved is above the melting point of the W alloy and increasing the Re content to increase the strength is meaningless, which is the application limit for the beam target 121.

In the third and fourth embodiments described so far, the beam target 121 is mentioned, in particular heating with a linear EB, but they can also be used for all other high-temperature plant components that require heat resistance and thermal conductivity. The beam shape is not limited to EB, but can be used for all heat sources.

A fifth embodiment will be described below with reference to Figs. 15 and 16. The manufacturing process of the fifth embodiment includes the first step 41 with the fourth step 44. In the first step 41, a high-strength substrate 45 is manufactured by rolling, forging or other plastic working. In the second step 42, the high-strength substrate 45 manufactured in the first step 41 is sprayed with a known vacuum plasma spraying device mentioned below on the heating surface in the case of a beam target irradiated with an EB or a material on which a large stress is generated locally, and the spray film with a porosity gradient of two materials is manufactured. In the third stage 43, the material obtained in the second stage 42 is subjected to a capsule-free HIP (hot isostatic pressing) device in order to remove the closed pores (defects) that can cause collapse. In the fourth stage 44, a composite material with a layer 46 of a gradient composition as shown in Fig. 16 is completed by infiltrating the second material into the open pores present in the material obtained in the third stage 43.

The vacuum plasma spray (VPS) apparatus is briefly described below. A high pressure vessel is filled with inert gas reduced to about a few tens to a few hundred Torr and the work to be sprayed is placed in this atmosphere The powder from the powder feeding system is sprayed into this container together with the plasma from the plasma control unit.

Capsule-free HIP (open HIP) is a process of performing hot isostatic pressing on material not contained in a capsule. It differs from conventional HIP, in which no pressure is applied to the inner part of the material contained in a capsule that collapses at high temperatures.

In this way, by using the substrate 45 with high strength and by manufacturing it by plastic working, a composite material could be obtained and the mechanical strength could be enhanced. In addition, since the porosity by a spraying process depends largely on the particle size of the powder to be used, in other words, a spray film with gradient porosity is formed only by varying the particle size of the powder to be used. In addition, since the vacuum plasma spraying process sprays in a reduced inert atmosphere of about several tens to several hundred Torr, a film with a small oxide layer, strong bonding force between particles and firm contact with the substrate of high strength can be formed. Furthermore, by a capsule-free HIP, causes of an increase in thermal resistance or closed pores when the stress is concentrated can be eliminated. In this case, by carrying out infiltration at ordinary pressure or high pressure with inert gas or in a reducing atmosphere, the open pores can be filled with the second material.

As a result, according to the fifth embodiment, cracks and other defects can be removed when heated with an electron beam. can be reduced while the input heat density can be increased.

A sixth embodiment of the invention is explained with reference to Fig. 17, 10. According to the schematic flow diagram in Fig. 17, this method comprises the first stage 51 with the fifth stage 55. In the first stage 51, the substrate surface is cleaned as a first stage. In the second stage 52, the substrate cleaned in the first stage 51 is sprayed with the corresponding material, for example by vacuum plasma spraying, with the composition falling off continuously. In the third stage 53, the closed pores (not connected to the outside) are destroyed by the open HIP, in which the open pores formed in the second stage 52 (connected to the outside) are retained. In the fourth stage 54, a low-melting metal, for example Cu, is infiltrated into the pores obtained in the third stage 53. The fifth stage 55 consists of mechanical processing.

The sixth embodiment achieves the following effects. Since the vacuum plasma spraying in the second stage 52 consists of spraying in an atmosphere of an inert gas at several tens of Torr, the material is not oxidized. When using powdery material of large particle size for spraying, the inner unmelted particles migrate and deposit, and a film of relatively large porosity can be formed.

Furthermore, the closed pores can be eliminated in the open HIP treatment in the third stage 53, while the open pores formed by vacuum plasma spraying in the second stage 52 remain. By infiltrating the low-melting material Cu into the material W, the only open pores and a pore gradient obtained in this way, can be sprayed over a relatively wide area and a material with a large and continuous gradient can be produced.

Accordingly, a gradient structure can be formed even on the three-dimensional curved surface which was difficult to obtain in the first embodiment. This gradient is continuous, while it was step-like in the first embodiment, so that the thermal stress can be further reduced. Consequently, the reduction of the thermal stress at the interface of different materials such as a coating and a joint can be effectively performed, so that the thermal cycle properties and the heat resistance can be improved.

In the sixth embodiment, one of the compounds W, Mo, Ta, Nb, Re, V, ZrO2, MgO, Al2O3, Y2O3, SiC, Si3N4, BN, AlN can be used as the substrate and the low-melting starting material can be selected from Cu, Ag, Fe, Ni, Co or their alloys.

The vacuum plasma spraying in the sixth embodiment is not intended to be limitative. As long as the material has excellent oxidation resistance, any spraying method using an atmosphere, such as plasma spraying, gas spraying and arc spraying, can be used and the same effects can be obtained.

A seventh embodiment is explained with reference to the schematic flow diagram in Fig. 18. This embodiment is characterized by the high pressure HIP infiltration during the infiltration of the second material into the pores of the first material in the fourth stage of the first embodiment. This means that after the formation of the sintered body in the third stage 63, infiltration by open HIP is carried out in the fourth stage 64 and then HIP infiltration is carried out in the fifth stage 65.

For example, in order for a liquid with a surface tension δ to penetrate into a circular pore with radius r assuming a contact angle θ, the pressure P must satisfy the following equation:

P ≥ (2δcosθ) ÷ r

Therefore, once the material system is determined, θ and δ are automatically fixed and if the liquid is to penetrate into tiny holes, the pressure P must be increased. In other words, if more pressure P is applied, liquid can penetrate into smaller holes.

Therefore, by infiltrating using a HIP device that can generate high temperature and a high pressure region, the second material can be safely infiltrated into open pores. Meanwhile, regarding the type of gas, if an inert gas such as Ar and He is used, the problem of oxidation of the material can be eliminated.

On the other hand, as the temperature increases, the contact angle θ generally decreases. Consequently, cos θ becomes smaller and, therefore, assuming a constant pressure P, the radius r can be reduced. However, the problem of material reaction arises.

Accordingly, no open pores remain in the high pressure range during HIP infiltration and a gradient material with little reaction between the materials can be produced. By eliminating the pores, the mechanical strength is increased and the thermal conductivity is improved.

In the seventh embodiment, in order to reduce the contact angle θ, an active element may be added to the liquid to promote infiltration into the fine pores.

Referring to Figs. 19 and 20, the manufacturing process of the heat-conductive material according to the invention and the heat-conductive material obtained by this process (hereinafter referred to as the eighth embodiment) will be explained. Fig. 19 is a schematic flow chart for explaining the manufacturing process. In the first step 71, the doped rolled material for forming the heat-receiving side is prepared with single crystals of W, Mo. In the step 72, the surface of the rolled material obtained in the first step 71 is roughened by blowing or the like and laminated with W powder in a gradient form. In the third stage 73, while sintering and bonding the rolled W material and the W powder obtained in the second stage 72, the materials are sent to the fourth stage 74, in which, simultaneously with the third stage 73, using secondary recrystallization, the minimally surface-doped rolled W, MO materials are grown from W, Mo into macrocrystal grains, thereby producing a framework of W or Mo. In this case, the heat-absorbing side is the single crystal. Later, in the fifth stage 75, Cu is infiltrated into the pores created in the fourth stage 74 with a concentration gradient, and the whole is machined and finished in the sixth stage 76.

The heat-absorbing material 77 produced by such a method is shown in Fig. 20. In this case, the non-stationary large thermal stress is borne by the single crystal W or Mo having excellent ductility on the heat-absorbing surface 78, while the stationary thermal stress is reduced by the composition having a W/Cu gradient thereunder. By eliminating the grain boundary of W and Mo, where grain boundary brittleness is likely to occur, a heat-absorbing material in which W, Mo having extremely excellent ductility are located on the heating side is obtained. In addition to high-quality heating properties, thermal shock resistance is improved when heated rapidly.

This embodiment for producing the heat-absorbing material also avoids the following points. In the manufacture of a sintered body of W, Mo and the growth of macrocrystal grains, the sintering of W, Mo powder is sometimes promoted too much, and a region having a porosity gradient cannot be sufficiently formed. Accordingly, in this embodiment, by using particles of about 10 µm, this problem is avoided. In addition, a gradient region 80 of W, Mo can be formed on the back of the single crystal plate by vacuum plasma spraying. Moreover, by carrying out the macrocrystal growth in the first place, the powder can be laminated in a gradient form on the surface of the single crystal material and then Cu can be infiltrated into the sintered body, so that a similar heat-absorbing plate can be manufactured.

In the eighth embodiment for producing the heat-absorbing material 77, the heat-absorbing side 78 is made of W or Mo. However, this heat-absorbing side may also be made of Re or V or an alloy comprising mainly W, Mo, Re or V. Furthermore, on the side 79 opposite the heat-absorbing side 78 in Fig. 20 (for example the water-cooled surface), a highly thermally conductive material such as Cu, Ag, Fe or their alloys can be formed. The composition can have a gradient from the heat-absorbing side 78 to the opposite side.

In the embodiments given, a sintering process or a vacuum plasma spraying process may be used in forming pores in the high-melting material or the low-melting material. However, other processes, including a chemical and physical deposition process, may also be used.

Claims (11)

1. Method for producing a composite material from a first material and a second material, which do not mix with each other in solid solution and have a relatively high or relatively low melting point, by forming pores in the first material in a first stage to obtain a substrate material with a porosity distribution, the porosity decreasing gradually from a surface area defined in the first material towards a second area, using one or more methods selected from the group of thermal spraying method, chemical deposition method and physical deposition method, and infiltrating the second material in a molten state into the pores of the first material obtained in the first stage with the porosity distribution, in which the porosity decreases gradually, in a second stage to obtain a material with composition gradients of a gradient distribution of the composite ratio of the first material and the second material. 2. Manufacturing method according to claim 1, wherein the first stage for obtaining the substrate material having the porosity distribution with gradually decreasing porosity comprises the following sub-stages: (a) forming a mixture of the first material and an element miscible with the first material ment in the state of a solid solution during molding to form a molding and (b) sintering the molding obtained in sub-step (a) to reinforce the solid solution to obtain the substrate material having a porosity distribution in which the porosity gradually decreases. 3. Manufacturing method according to claim 1, wherein the first stage for obtaining the substrate material having the porosity distribution with gradually decreasing porosity comprises the following sub-stages: (c) molding a mixture of the first material and a material selected from the group consisting of a plurality of types of compound materials having the property of being dispersed without chemically reacting with the first material during molding, to obtain a molded article and (d) sintering the molding obtained in the sub-step (c) to strengthen the dispersion to obtain the substrate material with a porosity distribution in which the porosity decreases gradually. 4. A manufacturing process according to claim 1, wherein the first step comprises: (e) producing a reinforced part by strengthening the first material by a method selected from the group consisting of rolling, forging and alloying, and (f) spraying a common material onto the obtained reinforced part by vacuum plasma spraying means to obtain a substrate material with porosity distribution. 5. A manufacturing method according to claim 4, wherein the first stage of pore formation can be carried out by spraying a material similar to the reinforced part by spraying means. 6. Manufacturing process according to claim 4, wherein the first stage comprises the following sub-stages: (g) treating the reinforced part obtained in the first stage by spraying a material similar to the reinforced part by means of spraying measures to produce the porous substrate material and (h) treating the substrate material obtained in sub-step (g) by hot isostatic pressing. 7. A manufacturing method according to claim 6, wherein the hot isostatic pressing treatment is carried out according to a capsule-free process in which the substrate is treated without being placed in a capsule. 8. Manufacturing process according to claim 1, wherein the first stage comprises the following steps: forming a laminate of a substrate material, selected from the group consisting of doped, press-rolled material and wrought material as a low thermal conductivity material, and a powder of the same type as the substrate material, the powder being accumulated on one side of the selected substrate material, and Producing a sintered material with porosity distribution by sintering the laminate. 9. Manufacturing method according to claim 8, wherein one side of the selected substrate material is covered with the powder by vacuum plasma spraying. 10. Manufacturing process according to claim 1, wherein the first stage comprises the following sub-stages: Preparing a plurality of mixtures of different grain sizes by mixing a powdered first material of different grain sizes with a second powdered element which is soluble in solid solution with the first powdered material, forming a laminate part in which the mixtures formed in the first sub-stage are stacked on top of one another in such a way that the grain size of the mixtures increases from the bottom of the laminate part to the top thereof, forming a solid solution reinforced part by treating the laminate part obtained in the second sub-stage, and Producing a sintered part by sintering the laminate part formed in the third sub-step such that the sintered part has a porous distribution. 11. Manufacturing process according to claim 1, wherein the first stage comprises the following sub-stages: Preparing a plurality of mixtures of different grain sizes by mixing a powdered first material of different grain sizes with a second powdered element which is soluble in solid solution with the first powdered material, forming a laminate part in which the mixtures formed in the first sub-stage are stacked on top of one another in such a way that the grain size of the mixtures increases from the bottom of the laminate part to its top, Forming a dispersed and reinforced part by treating the laminate part formed in the second sub-stage and Producing a sintered porous part by sintering the laminate part formed in the third sub-step such that the sintered part has a porosity distribution.