Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Patent
1996-09-27
1997-11-04
Simmons, David A.
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
428679, 428680, 148403, 420451, 420448, 420588, 2282624, 22826241, 2282623, 228195, B23K 2000, C22C 1905, C22C 3000
Patent
active
056838220
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to liquid-phase diffusion bonding of metals, and more specifically to liquid-phase diffusion bonding materials suited for the liquid-phase diffusion bonding of heat-resisting steels and alloy steels or between heat-resisting alloy steels and carbon steels in oxidizing atmospheres that form joints having high bonding strength and good creep characteristics at high temperatures.
BACKGROUND OF THE INVENTION
Liquid-phase diffusion bonding is carried out by inserting between the materials to be joined an alloy having a melting point lower than that of the materials to be joined and an eutectic composition in the form of foil, powder or plated coating. Bonding is achieved by applying pressure and heating to a temperature just above the liquidus line of the inserted alloy (hereinafter called the inserted metal). This is a kind of solid-phase bonding in which the bond is completed by melting and isothermal solidification.
Liquid-phase diffusion bonding is used where residual stress and deformation must be avoided as far as possible and also for joining high-alloy and heat-resisting steels that are difficult to weld.
The metals to be bonded by liquid-phase diffusion bonding often contain 0.50 percent or more chromium. Chromium-bearing steels generally have high oxidation and corrosion resistance because of the coherent films of chromium oxide (mostly as Cr.sub.2 O.sub.3) formed on the surface. The heat applied for bonding forms oxide films on the surface of the bond which inhibit the wetting of the inserted metal and significantly prevent the diffusion of atoms required for the completion of the bond.
It has therefore been necessary to carry out liquid-phase diffusion bonding in a vacuum or in an inert or a reducing atmosphere, as disclosed in Japanese Provisional Patent Publications Nos. 81458 of 1978, 34685 of 1987 and 227595 of 1987. This requirement has greatly increased the bonding cost.
By making many studies, the inventors found that liquid-phase diffusion bonding can be carried out in oxidizing atmospheres if the inserted metal contains vanadium. Although vanadium raises the melting point of the inserted metal, it was also found that the vanadium-bearing inserted metal can have an excellent bondability when other elements (such as silicon that is controlled in this invention) are properly controlled.
Practically no vanadium-bearing alloy foils, which increased silicon contents, for liquid-phase diffusion bonding have been proposed. U.S. Pat. No. 3,856,513 discloses alloys having a composition MaYbZc. M is a metal selected from the group comprising iron, nickel, cobalt, vanadium and chromium, Y is an element selected from the group comprising phosphorus, boron and carbon, Z is an element selected from the group comprising aluminum, silicon, tin, germanium, indium, antimony and beryllium, a is in the range of approximately 60 to 90 atomic percent, b is in the range of approximately 10 to 30 atomic percent, and c is in the range of approximately 0.1 to 15 atomic percent. Alloys of this type have been manufactured on an industrial scale by rapidly cooling molten products with conventional technologies.
Being amorphous, with vanadium used as the base component, these alloys are not intended as alloy foils for bonding. Besides, it is extremely difficult to achieve liquid-phase diffusion bonding with this type of alloys whose silicon contents are low and melting points are considerably higher than the foils according to this invention. The boron content of this alloy is entirely different from that of the foils according to this invention. Because of the high boron content, coarse precipitates are formed in the molybdenum- or chromium-bearing metal near the bond. The resulting bond has a much lower strength than the bonds formed by the use of the foils according to this invention. Japanese Provisional Patent Publication No.81458 of 1978 discloses the foil of the alloy according to U.S. Pat. No. 3,856,513. Containing no vanadium at all, however, this foil does not permit l
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Hasegawa Yasushi
Naoi Hisashi
Satoh Yuuichi
Ukeba Hiroshi
Nippon Steel Corporation
Phipps Margery S.
Simmons David A.
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