INSERT FOR LIQUID PHASE DIFFUSION BONDING

Abstract: Insert l comprises thin substrate (2) made by cold-rolling, and two bonding alloy layers (3) formed by plating on the upper and lower surfaces of substrate (2), respectively. Both layers (3) are extremely thin, and are made of an alloy having a melting point lower than that of substrate (2). Insert(l)is used to achieve liquid phase diffusion bonding of first and second base metals (4, 5). Insert(l)is interposed between first base metal (4) and second base metal (5). Then, insert (l)and base metals (4, 5) are clamped together with a pressure of, for example, 50 bar, and are placed in an atmosphere of a low pressure of about l0⁻⁴ Torr and heated to the melting point of alloy layers (3) or to a temperature above this melting point but below the melting points of substrate and plates (4, 5).

Description: The invention relates to an insert to be interposed between first and second base metals, each made of a metal or an alloy, for joining the first and second base metals by liquid phase diffusion bonding, comprising a thin substrate made of a metal or an alloy, and one or two bonding alloy layers formed by plating on one or the two major surfaces on the substrate, respectively, and having a melting point lower than that of the first and second base metals. The invention further relates to a method of liquid phase diffusion bonding of first and second base metals using such an insert. In order to join base metals such as high-alloy materials which are difficult to apply fusion-weld techniques, or in order to join base metals which have large joining interfaces, the method called "diffusion bonding" is employed. This method consists in first holding two base metals to be bonded together by proper means and then heating them in vacuum or an inert-gas atmosphere, thereby diffusing metal atoms from one base metal into the other, or from an insert into one or both base metals, and thus bonding the base metals together without melting the base metals. Various methods of diffusion bondings are known, they are classified into three types, direct diffusion bonding, solid phase diffusion bonding, and liquid phase diffusion bonding. In direct diffusion bonding, two base metals are held in face-to-face contact. In solid phase diffusion bonding, an insert is interposed between two base metals and metal atoms diffuse from the insert into the base metals without melting the insert. In liquid phase diffusion bonding, an insert is interposed between two base metals and is melted, whereby metal atoms diffuse from the insert into the base metals. Liquid phase diffusion bonding is advantageous over the other two diffusion bonding methods in that a lower pressure is required to hold the base metals and/or the insert together. The insert used in the liquid phase diffusion bonding is made of a metal or an alloy having a melting point lower than that of the base metal. The assembly consisting of the base metals and the insert interposed between the base metals is heated in vacuum or an inert-gas atmosphere to the melting point of the insert or a higher temperature, thereby melting the insert. As the insert melts, the metal atoms diffuse from the insert into the base metals, whereby the base metals are bonded. (See US-A-3,678,570 to Paulonis et al.) It is desirable that the insert be thin enough, 5 to 200 µm, to allow the metal atoms to diffuse easily into the base metals. Two types of such thin inserts are available. The first type is a film made of powder of insert material or a foil of insert material. The second is an insert made of one or two layers of insert material formed on the joining surfaces of the base metals, respectively, either by plating or by spraying. When the insert used in the liquid phase diffusion bonding is a film made of powder of insert material or consists of one or two layers of insert material formed on the base metals by spraying, respectively, an oxide is likely to be formed on the joining surfaces of the base metals. Further, since it is difficult to make such an insert having a uniform thickness, some portions of the insert will remain on the joining surfaces of the base metals after the base metals have been heated. For these reasons, the bonding strength attained is insufficient. On the other hand, the insert, which consists of one or two layers of insert material plated on the base metals, can have a uniform thickness if the base metals have simple shapes If these base metals are large, or have complicated shapes, the insert can hardly have a uniform thickness. On the other hand, it is relatively easy to form a foil of insert material, having a uniform thickness. This foil can therefore provide an insert layer having a uniform thickness for large joining surfaces. The foil can be made either by rolling or by rapid solidification process. One of the alloys that can be rolled into a foil having 5 to 200 µm is Aℓ-13% Si alloy. This alloy is usually used in component of a so-called brazing sheet. The brazing sheet is made first by sandwiching a thin aluminum plate between two thin plates of Aℓ-13% Si alloy and then by rolling all these plates together. As is disclosed in Japanese Patent Disclosure No. 119683 (1981) KOKAI, the brazing sheet is interposed between a Ti plate and an Aℓ plate, or between two Aℓ plates, thus to join these plates by liquid phase diffusion bonding. To fasten two base metals of Ni-based alloy by liquid phase diffusion bonding, an insert made of a Ni-based alloy containing P, B or Si which lowers the melting point of the Ni-based alloy, is after used. This alloy and the other low melting-point alloys forming inserts for liquid phase diffusion bonding can hardly be rolled into foils having a thickness of 5 to 200 µm. This is because all these alloys has a small workability and the foils made by hot-rolling these metals are apt to have cracks. Indeed rapid solidification process can provide thin foils made of these alloys and having a thickness of 5 to 200 µm, but cannot provide thin foils having a size of 1 m (length) x 0,5 m (width) or a wider size. Most of the low melting-point alloys, generally used as the materials of inserts for liquid phase diffusion bonding, are brittle. A thin foil made of any of these alloys and interposed between two base metals will be apt to be torn when the base metals slide against each other. In some cases, the thin foil can be torn while it is inserted into the gap between the base metals. US-A-4 029 479 relates to a plated foil for liquid interface bonding of titanium wherein a honeycomb core for a honeycomb sandwich panel is provided with two facing sheets. For this purpose, further sheets of plated foil of titanium or a selected titanium alloy are interposed, respectively, between the facing sheets and the core. As explained in detail, the foil sheets have a foil thickness of the order of 0,001 inch corresponding to 25 µm wherein it is preferred that the thickness does not exceed 0,0006 inch corresponding to 15 µm. So, an insert according to the preamble of claims 1 and 7 is known from US-A-4 029 479, wherein the metal or the alloy of the thin substrate consists of Ti or a Ti-based alloy. FR-A-2 147 512 relates to a specific technical field, namely to a method of soldering base metals. In this document FR-A-2 147 512 it is intended to solder pieces having precise details wherein care is to be taken that the solder will not flow down from the respective surface during soldering. According to the specific purpose of the method in FR-A-2 147 512 a substrate of 3 µm is used which is provided with an outer alloy layer of 4 µm. The substrate is made of a material selected from the group consisting of an Fe-based alloy, an Ni-based alloy, a Cu-based alloy and an Mo-based alloy. Since this document is concerned with soldering, the aspect of bonding base metals by liquid phase diffusion bonding is not touched in this document. Accordingly, the object underlying the present invention is to provide an insert which is capable of providing a reliable liquid phase diffusion bonding having a high shearing strength between two base metals even if the respective base metals have a large contacting area or a contacting surface with a complex or complicated shape. A further object underlying the present invention is to provide a method of liquid phase diffusion bonding of two or first and second base metals using an insert, in order to provide a reliable liquid phase diffusion bonding having a high shearing strength between the two or the first and second base metals even if the respective base metals have a large contacting area or a contacting surface with a complex or complicated shape. According to one aspect of the present invention, the insert according to the preamble of claim 1 is characterized in that the thin substrate has a thickness in the range of 50 to 500 µm and is made of a material selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy and a Ti-based alloy; and in that the two bonding alloy layers have a thickness in the range of 5 to 20 µm. According to another aspect of the present invention, the insert according to the preamble of claim 7 is characterized in that the thin substrate has a thickness in the range of 50 to 500 µm and is made of the same material as the first base metal or a material containing an element which is the main component of the first base metal, the material being selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy and a Ti-based alloy; and in that the bonding alloy layer has a thickness in the range of 5 to 20 µm. According to specific embodiments of the inserts according to the invention, the substrate is made by rolling. According to further developments of the inserts according to the invention, the plating of the respective bonding alloy layer includes electroplating, vacuum plating, hot dipping, non-electrode plating, sputtering and ion plating. According to a further development of the inserts according to the present invention, the respecitve bonding alloy layers are made of a material selected from the group consisting of an Ni-based alloy, a Cu-based alloy and a Ti-based alloy. According to a further development of the inserts according to the present invention, the substrate has a melting point higher than that of the respective bonding alloy layers by 100 °C or more. According to a further development of the inserts according to the present invention, the respective bonding alloy layers have a melting point lower than that of the first and second base metals by 200 °C or more. According to a further aspect of the invention, the method of liquid phase diffusion bonding of two base metals using an insert comprises the following steps: forming bonding alloy layers having a melting point lower than that of the two base metals on both major surfaces of a thin substrate made of a material selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy, and a Ti-based alloy, by plating the bonding alloy layers on the substrate to produce the insert; inserting the insert between the base metals; and heating the two base metals and the insert to a temperature not lower than the melting point of the bonding alloy layers and lower than the melting point of the two base metals and the substrate to diffuse the atoms of the substrate and the two base metals, thereby joining the two base metals, wherein a substrate is used having a thickness in the range of 50 to 500 µm and being sufficiently thick in its material to remain after heating as a layer joining the two base metals, and wherein bonding alloy layers are used having a thickness in the range of 5 to 20 µm. According to a further aspect of the present invention, the method of liquid phase diffusion bonding of first and second base metals using an insert comprises the following steps: forming a bonding alloy layer of a material having a melting point lower than that of a substrate and the second base metal by plating the material of the bonding alloy layer on a major surface of a thin substrate made of the same material as the first base metal or a material containing an element which is the main component of the first base metal, the material of the substrate being selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy, and a Ti-based alloy, the substrate and the bonding alloy layer constituting the insert, the material of the bonding alloy layer being selected to contain atoms diffusible by heat into the substrate and into the second base metal; inserting the insert between the first and second base metals so that the bonding alloy layer faces toward the second base metal; and heating the base metals and the insert to a temperature not lower than the melting point of the bonding alloy layer and lower than the melting point of the base metals and the substrate to diffuse atoms of the bonding alloy layer into the substrate and into the second base metal, and to diffuse the atoms of the substrate into the first base metal, thereby joining the first and second base metals, wherein a substrate is used having a thickness in the range of 50 to 500 µm, and wherein a bonding alloy layer is used having a thickness in the range of 5 to 20 µm. According to the specific concept of the present invention, the bonding alloy layers can have a uniform thickness even if the bodies of the first and second base metals are large and/or have a complicated and uneven shape. It results that these bonding alloy layers can strongly and firmly join the base metals together. Since the substrate is made of a mechanically strong material, the insert is easy to manufacture and to handle. Further, since the bonding alloy layers are formed by plating, they can be extremely thin. Therefore, they can be heated to their melting point or a higher temperature in a short period of time. The invention will be explained in more detail in the following description in conjunction with the accompanying drawings, in which: Fig. 1 is a cross-sectional view of an insert according to the present invention; Fig. 2 is a cross-sectional view of two base metals joined by the insert of Fig. 1 interposed between the two base metals; Fig. 3 is a cross-sectional view of another insert according to the invention; and Fig. 4 is a cross-sectional view of two base metals joined by the insert of Fig. 3 interposed between the base metals. The embodiments of the present invention will now be described in detail, with reference to the accompanying drawings. Fig. 1 is a cross-sectional view of an insert 1 according to a first embodiment of the invention. Fig. 2 shows two base metals 4 and 5 joined by the insert 1 interposed between them. As is shown in Fig. 1, the insert 1 comprises a thin substrate 2 made by cold-rolling, and two bonding alloy layers 3 formed by plating on the upper and lower surfaces of the substrate 2, respectively. Both layers 3 are extremely thin, and are made of an alloy having a melting point lower than that of the substrate 2. The insert 1 is used to achieve liquid phase diffusion bonding of the first and second base metals 4 and 5. More precisely, the insert 1 is interposed between the first base metal 4 and second base metal 5. Then, the insert 1 and the base metals 4 and 5 are clamped together with a pressure of, for example, 50 bar, and are placed in a atmosphere of a low pressure of about 1,3 · 10⁻⁷ bar (10⁻⁴ Torr) and heated to the melting point of the alloy layers 3 or to a temperature above this melting point but below the melting points of the substrate 2 and the base metals 4 and 5. Hence, neither the substrate 2 nor the base metals 4 and 5 melt or be deformed. As the heating proceeds, the atoms of the alloy layers 3 diffuse into the base metals 4 and 5. When the layers 3 cease to exist at all, the base metals 4 and 5 are firmly bonded by the substrate 2. The base metals 4 and 5 can be made of a metal or an alloy. The substrate 2 is made of a material selected from the group consisting of Fe, Ni, Cu, Ti, a Fe-based alloy, a Ni-based alloy, a Cu-based alloy and a Ti-based alloy. Of these materials, the most workable, strongest after working, and most ductile is cold-rolled into a foil. Since the substrate 2 is made of such material, the bonding of the base metals 4 and 5 can be sufficiently strong even if the substrate 2 remains between the base metals 4 and 5. When the substrate 2 is as mechanically strong as, or mechanically stronger than, the base metals 4 and 5, the combined structure made up of the substrate 2 and the base metals 4 and 5 does not break at the substrate 2 when a tensile stress is applied on this structure. This also ensures a sufficiently firm bonding of the base metals. Further, when the substrate 2 is as strong as, or stronger than the base metals 4 and 5, the insert 1 can be strong enough to be interposed between the base metals 4 and 5 without being broken. There will arise no practical problem even if the bonding alloy layers 3 are not so strong mechanically. It is desirable that the substrate 2 be 50 to 500 µm thick, for some reasons. First, it is difficult to manufacture a foil having a thickness less than 5 µm. Secondly, such a thin foil, even if obtained, is hard to handle. Thirdly, if the substrate 2 has a thickness over 500 µm, the insert 2 will be too thick to successfully accomplish liquid phase diffusion bonding of base metals whose joining surfaces are uneven. It is more desirable that the substrate 2 be 50 to 300 µm. This is because the substrate 2, if having a thickness within this range, can be more easily manufactured and handled. As described above, the substrate 2 is made by cold rolling. Hence, it has smooth surfaces, and its surface regions are formed of small crystals. Therefore, the atoms of both metal layers 3 can easily diffuse into the substrate 2. When two base metals are bonded by using any conventional insert of the kind not comprising a substrate, atoms of one base metal, which may adversely affect the crystal structure of the other base metal, can diffuse into the other base metal. This undesirable phenomenon does not occur when the insert of this invention is used since the insert comprises the substrate 2 whose composition and thickness have been adjusted. The bonding alloy layers 3 are made of a Ni-P alloy, an Ni-B alloy, a Ni-Si alloy, a Ni-Si-B alloy, a Cu-Mn-Ni alloy, a Cu-Zn alloy, a Ag-Ti-Cu alloy or a Cu-Ti alloy. All these alloys have relatively low melting points, ranging from 800 to 1140°C, and can thus easily achieve liquid phase diffusion bonding. In other words, the atoms of these alloys can easily diffuse into the substrate 2 and the base metals 4 and 5. Since the bonding alloy layers 3 are formed on both major surfaces of the substrate 2 by plating, they can be extremely thin. Their thickness is preferably 5 to 20 µm. If their thickness is less than 5 µm, the layers 3 fail to fasten the base metals 4 and 5 at the entire joining surfaces thereof since the base metals 4 and 5 have a surface roughness of about 5 µm. Conversely, if the thickness of layers 3 is too high, it takes a long time for the atoms of the layers 3 to diffuse into the substrate 2 and the base metals 4 and 5, thereby reducing the efficiency of liquid phase diffusion bonding. The liquid phase diffusion bonding can be accomplished in a relatively short time if the bonding alloy layers 3 have a thickness falling within the above range. It is desirable that a difference between the melting point of the alloy layers 3 and that of the base metals 4 and 5 be at least 200°C. It is also preferable that a difference between the melting point of the substrate 2 and that of the layers 3 be at least 100°C. Otherwise the substrate 2 and the base metals 4 and 5 would be deformed in some cases when they are heated to a temperature higher than the melting point of the layers 3. When the base metals 4 and 5 are made of the same material (e.g., carbon steel), it would be advisable that both bonding alloy layers 3 be made of this material. In this case, both layers 3 can simultaneously be formed by electroplating on the both major surfaces of the substrate 2. If the base metals 4 and 5 are made of the same material, the insert 1 can serve to firmly join the base metals 4 and 5. On the other hand, when the base metals 4 and 5 are made of different materials, alloy layers 3 of different materials which can well be bonded to the materials of the base metals 4 and 5, respectively, are formed on the major surfaces of the substrate 2. In this case, too, the layers 3 can serve to strongly bond the base metals 4 and 5. Therefore, the insert of this invention can bond two base metals made of different materials, strongly unlike the conventional inserts for liquid phase diffusion bonding. Fig. 3 is a cross-sectional view of an insert 10 according to a second embodiment of the invention. Fig. 3 shows two base metals 8 and 9 joined by the insert 10 interposed between them. As is shown in Fig. 3, insert 10 comprises a thin substrate 2 made by cold-rolling, and one bonding alloy layer 3 formed by plating on one surface of the substrate 2. This insert 10 can be used when the base metals 8 and 9 are made of, for example, stainless steel and carbon steel, respectively. The substrate 2 is made of carbon steel. The layer 3 is formed on the lower surface of the substrate 2, so as to contact the base metal 8. Since the substrate 2 and the base metal 9 are made of the same material, they can be joined by direct diffusion bonding. The base metal 8 and the substrate 2, which are made of different materials, are readily bonded by means of liquid phase diffusion bonding, as the atoms of the alloy layer 3 diffuse into the substrate 2 and the base metal 8. Therefore, the substrate 2 can strongly bond the base metals 8 and 9 together. In either the first or the second embodiment, each bonding alloy layer 3 can be formed by various plating methods, such as electroplating, hot dipping, non-electrode plating, sputtering, vacuum plating and ion plating. Several examples of the invention will now be described. Example 1 An Ni foil having a thickness of 100 µm was made by rolling. Two layers of Ni-11wt%P alloy, having a thickness of 20 µm, were formed on the both surfaces of the Ni foil, respectively, by the known electroplating process. Thus was obtained an insert. This insert was interposed between two plates of Fe-18wt%Cr-18wt%Ni alloy. The two plate-like base metals and the insert were placed within a furnace filled with Ar gas. They were then heated at 1000°C for one hour, while a pressure of 100 bar was being applied on the insert by pressing both plates onto the insert. As a result, a combined structure was obtained. It was observed that the atoms of Ni-11wt% P alloy had diffused into the Ni foil and both base metals, uniformly over the entire joining interface of the foil and the base metals. The combined structure was put to a tensile strength test. It was broken, not at the joining interface of the foil and the base metals, but at a portion of one of the base metals. Example 2 An Ni foil having a thickness of 50 µm was made. Two layers of Ni-4,0wt%B alloy, having a thickness of 5 µm, were formed on the both surfaces of the Ni foil, respectively, by magnetron sputtering process, thus obtaining an insert. The magnetron sputtering process was performed in an Ar gas atmosphere of 1,3 · 10⁻⁸ bar (10⁻⁵ Torr), by supplying a DC current of 500 to 1000 V to the Ni foil for 30 minutes. This insert was interposed between two block-like base metals of Inconel 718 (an Ni-Cr-Fe alloy), each being 500 mm wide, 500 mm long, and 100 mm thick. The base metals and the insert were placed within a furnace in which a reduced pressure of 1,3 · 10⁻⁷ bar (10⁻⁴ Torr) was maintained. They were then heated at 1150°C for 30 minutes, while a pressure of 50 bar was being applied on the insert by pressing both base metals onto the insert. As a result, a combined structure was obtained. It was observed that both base metals were as firmly bonded as the plate-like base metals were in Example 1. The combined structure was put to a tensile strength test. It was broken, not at the joining interface of the foil and the base metals, but at a portion of one of the base metals. Example 3 An Inconel 713C foil having a thickness of 100 µm was made. Two layers of Ni-7,0wt%Si-2.0wt%B alloy, having a thickness of 5 µm, were formed on the surfaces of the Inconel 713C foil, respectively, by magnetron sputtering process, thereby obtaining an insert. The magnetron sputtering process was performed under the same conditions as in Example 2. This insert was interposed between two block-like base metals of Inconel 713C, each being 500 mm wide, 500 mm long, and 200 mm thick. The base metals and the insert were placed within a furnace in which a reduced pressure of 1,3 · 10⁻⁸ bar (10⁻⁵ Torr) was maintained. They were then heated at 1150°C for 6 hours, while a pressure of 50 bar was being applied on the insert by pressing both base metals onto the insert. As a result, a combined structure was obtained. It was observed that the joining interface of both blocks had the same crystal structure of any other portions of the base metals. Example 4 A Cu foil having a thickness of 50 µm was made by rolling. One layer of Cu-35wt%Mn-9,0wt%Ni alloy, having a thickness of 20 µm, were formed on one surface of the Cu foil by the known hot dipping process, thus obtaining an insert. The insert was interposed between two base metals which were a Cu plate and a carbon steel plate, respectively, with the layer of Cu-35wt%Mn-9,0wt%Ni alloy contacting the carbon steel plate. The base metals and the insert were placed within a furnace in which a reduced pressure of 1,3 · 10⁻⁸ bar (10⁻⁵ Torr) was maintained. They were then heated at 1000°C for 30 minutes, while a pressure of 50 bar was being applied on the insert by pressing both base metals onto the insert. As a result, a combined structure was obtained. It was observed that the base metals were as firmly bonded together as in Example 1. The combined structure was put to a tensile strength test. It was broken, not at the joining interface of the foil and the base metals, but at a portion of one of the base metals. Example 5 A Cu foil having a thickness of 50 µm was made by rolling. A layer of Cu-32,5wt%Zn alloy and another layer of Ni-11wt%P alloy, both having a thickness of 20 µm, were formed on two surfaces of the Cu foil, respectively, by the known electroplating process. Thus an insert was obtained. The insert was interposed between two base metals which were a Cu plate and a carbon steel plate, respectively with the Cu-32,5wt%Zn alloy layer contacting the Cu plate, and with the Ni-11wt%P alloy layer contacting the carbon steel plate. The base metals and the insert were placed within a furnace in which a reduced pressure of 1,3 · 10⁻⁸ bar (10⁻⁵ Torr) was maintained. They were then heated at 1000°C for 30 minutes, while a pressure of 50 bar was being applied on the insert by pressing both base metals onto the insert. As a result, a combined structure was obtained. It was observed that the base metals were as firmly bonded together as in Example 4. The combined structure was put to a tensile strength test. It was broken, not at the joining interface of the foil and base metals, but at a portion of the Cu base metal. Example 6 A Cu foil having a thickness of 300 µm was made by rolling. A layer of Ag-2wt%Ti-30wt%Cu alloy, having a thickness of 5 µm, was formed on one surface of the Cu foil by magnetron sputtering process under the same conditions as in Example 2. Further, another layer of Ni-11wt%P alloy, having a thickness of 10 µm, was formed on the other surface of the Cu foil, by the known non-electrode plating process. Thus was obtained an insert. The insert was interposed between two base metals which were a Ti plate and a carbon steel plate, respectively with the Ag-2wt%Ti-30wt%Cu alloy layer contacting the Ti plate, and with the Ni-11wt%P alloy layer contacting the carbon steel plate. The base metals and the insert were placed within a furnace in which a reduced pressure of 1,3 · 10⁻⁸ bar (10⁻⁵ Torr) was maintained. They were then heated at 950°C for 3 hours, while a pressure of 50 bar was being applied on the insert by pressing both base metals onto the insert. As a result, a combined structure was obtained. It was observed that the base metals were as firmly bonded together as in Example 1. The combined structure was put to a tensile strength test. It was broken, not at the joining interface of the foil and the base metals, but at a portion of the Ti base metal. Example 7 A Ni foil having a thickness of 50 µm was made by rolling. Two layers of 72wt%Cu-28wt%Ti alloy, having a thickness of 5 µm, were formed on the two major surfaces of the Ni foil, respectively, by magnetron sputtering process the same conditions as in Example 2, thus obtaining an insert. The insert was interposed between two base metals which are a Ti plate and a carbon steel plate. The base metals and the insert were placed within a furnace in which a reduced pressure of 1,3 · 10⁻⁸ bar (10⁻⁵ Torr) was maintained. They were then heated at 950°C for 3 hours, while a pressure of 50 bar was being applied on the insert by pressing both base metals onto the insert. As a result, a combined structure was obtained. It was observed that the base metals were as firmly bonded together as in Example 6. The combined structure was put to a tensile strength test. It was broken, not at the joining interface of the foil and the base metals, but at a portion of the Ti base metal.

Claims: An insert (1) to be interposed between first and second base metals (4, 5), each made of a metal or an alloy, for joining the first and second base metals (4, 5) by liquid phase diffusion bonding, the insert (1) comprising a thin substrate (2) made of a metal or an alloy, and two bonding alloy layers (3) formed by plating on the two major surfaces of the substrate (2), respectively, and having a melting point lower than that of the first and second base metals (4, 5), characterized in that the thin substrate (2) has a thickness in the range of 50 to 500 µm and is made of a material selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy and a Ti-based alloy; and in that the two bonding alloy layers (3) have a thickness in the range of 5 to 20 µm. The insert according to claim 1, wherein the substrate (2) is made by rolling. The insert according to claim 1 or 2, wherein the plating includes electroplating, vacuum plating, hot dipping, non-electrode plating, sputtering and ion plating. The insert according to any of claims 1 to 3, wherein the bonding alloy layers (3) are made of a material selected from the group consisting of an Ni-based alloy, a Cu-based alloy and a Ti-based alloy. The insert according to any of claims 1 to 4, wherein the substrate (2) has a melting point higher than that of the bonding alloy layers (3) by 100 °C or more. The insert according to any of claims 1 to 5, wherein the bonding alloy layers (3) have a melting point lower than that of the first and second base metals (4, 5) by 200 °C or more. An insert (10) to be interposed between first and second base metals (9, 8), each made of a metal or an alloy, for joining the first and second base metals (9, 8) by liquid phase diffusion bonding, the insert (10) comprising a thin substrate (2) made of a metal or an alloy, and a bonding alloy layer (3) formed by plating on a major surface of the substrate (2), and having a melting point lower than that of the first and second base metals (9, 8), characterized in that the thin substrate (2) has a thickness in the range of 50 to 500 µm and is made of the same material as the first base metal (9) or a material containing an element which is the main component of the first base metal (9), the material being selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy and a Ti-based alloy; and in that the bonding alloy layer (3) has a thickness in the range of 5 to 20 µm. The insert according to claim 7, wherein the substrate (2) is made by rolling. The insert according to claim 7 or 8, wherein the plating includes electroplating, vacuum plating, hot dipping, non-electrode plating, sputtering and ion plating. The insert according to any of claims 7 to 9, wherein the bonding alloy layer (3) is made of a material selected from the group consisting of an Ni-based alloy, a Cu-based alloy and a Ti-based alloy. The insert according to any of claims 7 to 10, wherein the substrate (2) has a melting point higher than that of the bonding alloy layer (3) by 100 °C or more. The insert according to any of claims 7 to 11, wherein the bonding alloy layer (3) has a melting point lower than that of the first and second base metals (9, 8) by 200 °C or more. A method of liquid phase diffusion bonding of two base metals (4, 5) using an insert (1), the method comprising the following steps: forming bonding alloy layers (3) having a melting point lower than that of the two base metals (4, 5) on both major surfaces of a thin substrate (2) made of a material selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy, and a Ti-based alloy, by plating the bonding alloy layers (3) on the substrate (2) to produce the insert (1); inserting the insert (1) between the base metals (4, 5); and heating the two base metals (4, 5) and the insert (1) to a temperature not lower than the melting point of the bonding alloy layers (3) and lower than the melting points of the two base metals (4, 5) and the substrate (2) to diffuse the atoms of the substrate (2) and the two base metals (4, 5), thereby joining the two base metals (4, 5), wherein a substrate (2) is used having a thickness in the range of 50 to 500 µm and being sufficiently thick in its material to remain after heating as a layer joining the two base metals (4, 5), and wherein bonding alloy layers (3) are used having a thickness in the range of 5 to 20 µm. A method of liquid phase diffusion bonding of first and second base metals (9, 8) using an insert (10), the method comprising the following steps: forming a bonding alloy layer (3) of a material having a melting point lower than that of a substrate (2) and the second base metal (8) by plating the material of the bonding alloy layer (3) on a major surface of a thin substrate (2) made of the same material as the first base metal (9) or a material containing an element which is the main component of the first base metal (9), the material of the substrate (2) being selected from the group consisting of Fe, Ni, Cu, Ti, an Fe-based alloy, an Ni-based alloy, a Cu-based alloy, and a Ti-based alloy, the substrate (2) and the bonding alloy layer (3) constituting the insert (10), the material of the bonding alloy layer (3) being selected to contain atoms diffusible by heat into the substrate (2) and into the second base metal (8); inserting the insert (10) between the first and second base metals (9, 8) so that the bonding alloy layer (3) faces toward the second base metal (8); and heating the base metals (9, 8) and the insert (10) to a temperature not lower than the melting point of the bonding alloy layer (3) and lower than the melting point of the base metals (9, 8) and the substrate (2) to diffuse atoms of the bonding alloy layer (3) into the substrate (2) and into the second base metal (8), and to diffuse the atoms of the substrate (2) into the first base metal (9), thereby joining the first and second base metals (9, 8), wherein a substrate (2) is used having a thickness in the range of 50 to 500 µm and wherein a bonding alloy layer (3) is used having a thickness in the range of 5 to 20 µm.

Inventors: KAGECHIKA, HIROSHI C/O PATENT DIVISION, KOJIMA, TOSHIFUMI C/O PATENT DIVISION, KOSUGE, SHIGEYOSHI C/O PATENT DIVISION, UENO, YASUHIRO C/O PATENT DIVISION, WATANABE, ITARU C/O PATENT DIVISION
Applicants: NIPPON KOKAN KABUSHIKI KAISHA
Application year: 1987
Main classification: B23K35
IPC codes: B23K35