Copper Brazing Alloy Foils Containing Germanium

Germanium is a temperature depressant and forms low melting eutectics in the Cu-Ge system. In the Cu-Ge system the germanium content is currently restricted to about 10 atomic percent because of the difficulty in fabricating foil, containing 10 or more atomic percent of germanium.

The disadvantage of the present techniques is the restriction on the germanium content in the Cu-Ge systems imposed by the inability to fabricate foils of alloys of high germanium content by conventional techniques. The present invention provides thin ductile foils of a higher germanium content in Cu-Ge system than heretofore attainable and enables brazing at temperatures lower than that afforded by foil of a lesser Ge content made by conventional techniques.

U.S. Pat. No. 3,856,513 discloses a wire product where alloys are represented by the formula TiXj wherein T is a transition metal and X is Al, Sb, Be, B Ge, C, In, P, Si or Sn. The transition metals include metals from Groups IB, IIIB, IVB, VB, VIB, VIIB and VIIIB of the periodic table. The patent also teaches that the alloys are partially crystalline but contain at least 50 percent of an amorphous phase. As is apparent from that description, about 280 binary alloys are disclosed and an infinite number of ternary, quaternary, etc. alloys. Specific examples are given to a Pd.sub.77.5 Cu.sub.6 Si.sub.16.5 alloy and a Ni.sub.40 Pd.sub.40 P.sub.20 alloy. The patent also discloses ternary alloys of the formula M.sub.a Y.sub.b Z.sub.c in sheet, ribbon and powder form wherein M is Fe, Ni, Cr, Co or V, Y is P, C or B and Z is Al, Si, Sn, Sb, Ge, In or Be. These alloys also contain at least 50 percent of an amorphous phase and preferably are completely amorphous.

In accordance with one aspect of this invention there is provided alloys in the form of a thin foil having a thickness of from about 0.0005 to about 0.005 inches and a composition represented by the formula Cu.sub.x Ge.sub.y wherein x is from about 60 to about 95 atomic percent and y is from about 5 to about 40 atomic percent. The composition contains a sufficient amount of an amorphous phase and a microstalline, metastable solid solution single phase to render the foil ductile.

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above description of some of the aspects of the invention.

The Cu-Ge binary system is described in Hansen M. Constitution of Binary Alloys. Germanium is reported to have a substantial solid solubility in the Cu-Ge system.

In this invention, Cu.sub.x Ge.sub.y type alloys wherein x is from about 60 to about 95 atomic percent and y is from about 5 to about 40 atomic percent are made in the form of ductile foil by the presence of sufficient amounts of an amorphous phase and a metastable, micro-crystalline, solid solution single phase by rapid cooling at a rate of about 10.sup.5 .degree. C./sec. to 10.sup.6 .degree. C./sec. Such a cooling rate can be obtained by available techniques such as melt extraction, melt spin, vapor deposition and sputtering. Some techniques of producing rapidly quenched foil have been described in U.S. Pat. Nos. 3,896,203; 3,863,700; 3,881,540 and 3,881,541. Depending on the cooling rate during the rapid quenching, the resulting structure would consist of a combination of an amorphous phase, new phases not available under equilibrium conditions and solid solutions with solubility limits extended beyond their equilibrium values, as described by Pol Duwez and R. H. Willens in Transactions of the Metallurgical Society of AIME, Vol. 227, p. 362, April 1963. The amorphous phase is intrinsically ductile because the glassy structure allows for slip in all possible directions. Additional ductility results from the presence of a metastable micro-crystalline, single phase, solid solution which has a large grain-boundary area. The thin ductile foil so obtained is especially suited for fabricating into preforms for brazing applications.

As previously mentioned the materials of this invention are in the form of a thin metal foil having a thickness of from about 0.0005 to about 0.005 inches. A preferred technique for producing such foils is by using a stream of molten metal to impinge upon the external surface of a rotating drum having a coolant inside the drum. The molten metal flows across the surface of the drum in the form of a sheet or strip that solidifies. The sheet or strip is removed from the surface of the drum as a continuous piece of alloy. Preferred thicknesses range from about 0.0015 to about 0.004.

Preferred alloy composition contain from about 15 to 35 atomic percent germanium and balance copper.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.