Stock material or miscellaneous articles – All metal or with adjacent metals – Having composition – density – or hardness gradient
Reexamination Certificate
2001-10-04
2004-11-30
La Villa, Michael (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having composition, density, or hardness gradient
C428S650000, C428S658000, C428S649000, C428S660000, C428S674000, C428S663000, C428S675000, C428S333000, C428S334000, C428S336000
Reexamination Certificate
active
06824888
ABSTRACT:
BACKGROUND ART
1. Technical Field
The present invention relates to a bonded body of a beryllium member and a copper or copper alloy member, and a method of producing the same. More particularly, it relates to the bonded body and method capable of increasing the bonding strength and further improving the bonding reliability against thermal load.
2. Prior Art
In recent years, as an armor material used for a first wall of a nuclear fusion reactor, beryllium, which has a small atomic number and a relatively high melting point and is effective as a getter for oxygen etc., has attracted interest. Since this first wall is subjected to a high thermal load applied by plasma generated in the nuclear fusion reactor, there have been proposed various structures for effectively cooling an armor material (beryllium etc.) by bonding a member formed of the armor material, located on the outermost surface of the first wall, to a member formed of copper or copper alloy having a cooling structure.
As a method for bonding a beryllium member to a copper or copper alloy member to produce these structures, a brazing process, diffusion bonding process, thermal spraying process, hot isostatically pressing (HIP) process, and the like processes have been proposed. Among these bonding processes, the HIP process is anticipated as a method of bonding the beryllium member to the copper or copper alloy member because the bonded surfaces are brought into close contact with and bonded to each other even when the bonded surface has a three-dimensional shape.
Conventionally, in order to HIP-bond the beryllium member to the copper or copper alloy member, it has been necessary to raise the heating temperature to a high temperature not lower than 700° C. The reason for this is that since an oxide film usually exists on the surface of the beryllium member, the bonding due to mutual diffusion of beryllium and copper cannot be effected unless the beryllium member is heated to a temperature not lower than 700° C. In this method, however, a brittle intermetallic compound (for example, Be
2
Cu or BeCu) is easily formed at the interface between beryllium and copper alloy, so that separation sometimes occurs at the interface due to thermal cycle. Also, there remains a problem in that the treatment at a high temperature not lower than 700° C. is remarkably disadvantageous in terms of energy and cost.
In this respect, if a film of pure copper is formed on the purified surface by ion plating etc. after oxides on the surface of beryllium member are removed under vacuum, since no oxides exist at the interface between pure copper and beryllium, the beryllium member can be bonded strongly to the copper alloy member even at a low temperature in the range of 400 to 550° C. when the beryllium member is HIP-bonded to the copper alloy member. In this case, an intermetallic compound is not formed excessively at the interface between beryllium and pure copper. However, even if the bonding is performed as described above, when the temperature at the time when the bonded body is used becomes 400° C. or higher, a brittle intermetallic compound of beryllium and copper is yielded excessively at the interface at which an intermetallic compound scarcely existed at the time of bonding, and thus there is a fear that a fracture occurs at the interface.
As a solution to the above problem, it may be possible to provide a soft metal that does not form an intermetallic compound with beryllium, for example, an aluminum layer adjacently to the beryllium member. On the other hand, however, when an aluminum layer is bonded adjacently to the copper alloy, a brittle compound of aluminum and copper is formed at the interface between the beryllium member and the copper alloy member, so that satisfactory bonding cannot be performed. In this case, therefore, it is important to provide an Al—Cu diffusion inhibition layer formed of titanium etc. at the interface between the aluminum layer and the copper alloy member. Specifically it is necessary that an intermediate layer of aluminum be provided in advance on the beryllium member side, and an intermediate layer of titanium be provided in advance on the copper alloy member side.
However, even if an intermediate layer of aluminum, titanium, etc. is provided in advance on each of the beryllium member and the copper alloy member, it is difficult to obtain a strongly bonded state because aluminum and titanium have high activity and the surface thereof is easily oxidized. In particular, since metallic foil has conventionally been used as means for forming the intermediate layer, it cannot practically be desired to obtain a strongly bonded state because of an oxide film on the surface thereof. Also, in the method in which metallic foil of aluminum etc. is used as an insert material, dislocation of the beryllium member and the copper alloy member occurs when the method is applied to a member having an intricate construction. Further, when this method is used in combination with titanium foil, copper foil, etc., dislocation or wrinkle occurs. Therefore, reliable bonding cannot be performed likewise.
In this respect, as a solution to the above problems, the inventors have proposed a method of producing a HIP-bonded body of beryllium and copper alloy in U.S. Pat. No. 6,164,524. In this method, basically, when a beryllium member and a copper alloy member are bonded to each other, a thin layer of titanium, chromium, molybdenum or silicon is formed as a diffusion inhibition layer for beryllium and copper by the PVD or thermal spraying process, and successively a pure copper layer or a pure nickel layer is formed as a bonding promotion layer on the surface of the diffusion inhibition layer. Subsequently, the beryllium member and the copper alloy member are HIP-bonded with the intermediate layer formation side being the bonding surface.
The art disclosed in the aforementioned U.S. Pat. No. 6,164,524 is based on the following knowledge.
(a) From the viewpoint of stress relaxation at the interface, it has conventionally been thought that the diffusion inhibition layer for beryllium and copper must be a soft metal such as aluminum. However, even a hard metal such as chromium and molybdenum sufficiently functions as a Be—Cu diffusion inhibition layer if the film thickness thereof is small.
(b) Nevertheless, in the case where a hard thin film of chromium etc. is formed on the beryllium member, if an oxide film exists on the surface of beryllium, a sufficient bonding strength cannot be obtained. Therefore, when a hard metal film is formed, it is necessary to remove the oxide film from the surface of beryllium.
(c) By the above-described configuration, a bonded body having high bonding strength and thermal cycle resistance property can be obtained. However, when an excessive thermal load is applied repeatedly, such a configuration cannot be said to be sufficient. To withstand such a thermal load, the thickness of the aluminum layer serving as a stress relaxation layer must be increased.
By the above-described art, a bonded body having high bonding strength and thermal cycle resistance property can be obtained. Recently, however, to further increase the reliability, it is demanded to further increase the bonding strength and thermal cycle resistance property.
SUMMARY OF THE INVENTION
The present invention advantageously meets the above-described demands, and an object thereof is to provide a bonded body of a beryllium member and a copper or copper alloy member, which has further improved bonding strength and thermal cycle resistance property as compared with the art disclosed in U.S. Pat. No. 6,164,524, and an advantageous method of producing the same.
The inventors carried out studies earnestly to achieve the above object; and obtained the following knowledge.
(a) In the art disclosed in U.S. Pat. No. 6,164,524, a pure copper layer is used as the final bonding surface on the beryllium member side. However, it is advantageous to provide a thin layer of aluminum or zinc, which is an element that forms a solid solution with copper, on th
Hatano Toshihisa
Iwadachi Takaharu
Uda Minoru
Burr & Brown
La Villa Michael
NGK Insulators Ltd.
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