Metal fusion bonding – Process – Using bond inhibiting separating material
Reexamination Certificate
2000-03-22
2001-09-11
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Using bond inhibiting separating material
C228S193000, C228S195000
Reexamination Certificate
active
06286750
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a method of producing hot isostatic press (HIP) bonded bodies. More specifically, but without restriction to the particular embodiment hereinafter described in accordance with the best mode of practice, this invention relates to HIP-bonded bodies comprised of a beryllium member and a copper alloy member as well as the method of manufacturing the beryllium-copper alloy HIP-bonded bodies.
2. Background of the Prior Art
Beryllium has recently attracted the attention of industry due to its remarkable neutron reflecting capabilities. Industrial applications involving neutron production and manipulation, such as material testing furnaces, electromagnetic energy reflectors and large scale neutron accelerators, take full advantage of this characteristic. Most of these applications, however, subject the beryllium to significant thermal loads. Although beryllium has excellent thermal conductivity properties, it is necessary to combine the beryllium with another compound to increase the beryllium's thermal conductivity. The most common compound used, alumina dispersion strengthened copper alloy (“DSCu”), is commonly bonded to the beryllium by hot isostatic pressing (“HIP”).
Conventional HIP bonding of beryllium and copper alloy requires processing temperatures in excess of 700° C. to prevent the formation of an undesirable oxidation film on the surface of the beryllium member which can occur at temperatures below 700° C. The oxide film arrests the interdiffusion of the beryllium substrate and the copper alloy at temperatures not less than 700° C. In addition, brittle intermetallic precipitates, such as Be
2
Cu or BeCu form at the beryllium substrate copper alloy interface and degrade the strength of the bond. Moreover, the high temperatures required for traditional HIP bonding of beryllium-copper alloy bodies drive up production costs due to the extreme energy consumption demand.
The undesirable oxide film on the beryllium member can be removed in a vacuum atmosphere by ion plating and the like. Usually, a layer of pure copper is deposited on the beryllium surface to promote interdiffusion of the beryllium and copper alloy members. This method has resulted in HIP-bonded beryllium copper alloy bodies being formed at temperatures ranging from 400° C. to 550° C. However, when the bonded body formed by the aforementioned process is used in an application subject to temperatures greater than 400° C., brittle intermetallic compounds form at the beryllium-copper interface resulting in the aforementioned problem. It has also been discovered that incomplete copper diffusion occurs at temperatures below 600° C. due to the effects of the oxide film.
In an attempt to overcome the above-discussed problems, the present inventor proposed a process for bonding a beryllium member to a copper alloy member as shown in FIG.
1
. This process is described in detail in U.S. patent application Ser. No. 09/243,664, now U.S. Pat. No. 6,164,524 the entirety of which is incorporated herein by reference. The process shown in
FIG. 1
employs an aluminum layer formed on the beryllium member to act as a stress relaxation layer which accounts for the difference in coefficient of thermal expansion between the beryllium and copper alloy members. A diffusion inhibition layer such as Ti is then formed on the aluminum layer to suppress diffusion of beryllium and copper from their respective members, and thus suppress formation of the brittle intermetallic compounds discussed above. A bonding promotion layer such as Cu is then formed on the diffusion inhibition layer to enable the copper alloy (DSCu) member to be bonded to the Ti layer. The Be—Al—Ti—Cu subassembly is then HIP-bonded to the copper alloy member.
Although the process shown in
FIG. 1
is a dramatic improvement over the prior art discussed above, it still produces a relatively low-strength joint between the beryllium and copper alloy members. Specifically, the HIP-bonding step needs to be performed at a temperature less than 600° C. in order to avoid melting the aluminum layer. The diffusivity of Cu at such a low temperature, however, is relatively low, and thus the joint between the Cu bonding promotion layer and the copper alloy member is relatively weak (albeit much stronger than the joints of the prior art discussed above).
It is therefore highly desirable to produce stronger beryllium-copper alloy HIP bonds by preventing the formation of oxide films and intermetallic brittle compounds that cause peeling during the HIP process while at the same time promoting complete copper diffusion of the copper alloy member.
SUMMARY OF THE INVENTION
The present invention serves to solve the above-mentioned problems with the prior art. It is therefore an object of the present invention to provide a novel HIP-bonded body comprised of a beryllium member and a copper alloy member, as well as a method for manufacturing the same, wherein the beryllium member and copper alloy member are subjected to HIP-bonding temperatures sufficient to allow for complete diffusion of the metals into the interface therebetween, thus resulting in bonds having improved strength over the prior art beryllium-copper alloy bonds. The present invention also prevents the formation of brittle intermetallic compounds during the bonding stage and during use, to thereby maintain a strong bond at the interface between the two members.
Based on the foregoing, one aspect of the present invention resides in a HIP-bonded body comprising a beryllium member, a copper alloy member and an aluminum-magnesium alloy or aluminum-silicon-magnesium alloy insert body juxtaposed between the beryllium member and the copper alloy member during HIP bonding. The copper alloy member includes on its interface surface a thin diffusion inhibiting layer composed of titanium, vanadium, niobium, chromium, molybdenum or silicon. Preferably, a bond promoting layer of aluminum or aluminum alloy is formed on the surface of the diffusion inhibiting layer.
More preferably, a copper or copper alloy layer is interposed between the copper alloy member and the diffusion inhibiting layer.
Most preferably, an aluminum or aluminum alloy bond promoting layer is formed on the interface surface of the beryllium member prior to HIP bonding. This layer also serves as a stress relaxation layer.
The alloy insert body can be used in bulk form, or presented as an aluminum or aluminum alloy core material having aluminum-magnesium or aluminum-silicon-magnesium alloy surface layers formed thereon.
Another aspect of the present invention resides in a method of producing a HIP-bonded body comprised of a beryllium member and a copper alloy member comprising the steps of: forming a diffusion inhibiting layer of titanium, vanadium, niobium, chromium, molybdenum or silicon on one side of a copper alloy member; juxtaposing an aluminum-magnesium or aluminum-silicon-magnesium alloy insert body between the beryllium member and the coated copper alloy member; subjecting the beryllium member—insert body—copper alloy member to HIP bonding to bond the beryllium member to the copper alloy member with the diffusion inhibiting layer and alloy insert body situated between the two members.
Preferably, the method of the present invention further comprises a step of forming an aluminum or aluminum alloy bond promoting layer on the outer surface of the diffusion inhibiting layer. It also preferred to form a copper or copper alloy bond promoting layer on the surface of the copper alloy member prior to depositing the diffusion inhibiting layer thereon.
Preferably an aluminum or aluminum alloy bond promoting layer is also formed on the beryllium member prior to HIP-bonding with the alloy insert body. This layer also serves as a stress relaxation layer.
The method of the present invention overcomes the drawbacks associated with the prior art by forming the necessary layers on the beryllium and copper alloy members before the HIP-bonding is performed. The layers formed on the copper allo
Burr & Brown
Dunn Tom
NGK Insulators Ltd.
Pittman Zidia
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