US 3137545 A
Description (OCR text may contain errors)
Ju 1964 J. SCHULTZ, JR
ALLOY FOR BONDING METALS TO CERAMICS Filed March 22, 1962 F'IGJ F'IG.2
H \s ATTORNEY United States Patent 3,137,545 ALLOY FOR BGNDING METALS T CERANICS John Schultz, Jra, Louisville, Ky., assignor to General Electric Company, a corporation of New York Filed Mar. 22, 19:32, Ser. No. 181,539 4 Claims. (Cl. 259-495) The present invention relates to an improved brazing alloy and is more particularly concerned with a fusible alloy material for directly sealing a metal member to acaramic member.
Various alloys have been used or proposed for making a direct joint between a metal member and a ceramic member. In recent years preferred alloys for forming such seals have included small amounts of titanium as such or in the form the hydride as this metal has been found to provide an extremely intimate bond with ceramic surfaces. For example, Patent 3,00l,269.Moore et al., describes metal-to-cer amic joint structures in which the bonding material is a fusible alloy consisting essentially offrom about 2m 10% by Weight of titanium or zirconium, about 10 to 85% lead and the remainder a metal selected from the group consisting of copper, silver and nickel or combinations thereof. While zinc, bismuth, cadmium, indium and tin are described as being possible substitutes for all or part of the lead component of the alloy, the alloys commercially employed for metal to ceramic bonding purposes have generally consisted of lead, copper and titanium with or without small amounts of silver. In these alloys, the lead component has been employed as being the most effective ductile metal for lowering the melting point and increasing the iiow of the alloy and its wetting effect.
The present invention is based on the discovery that certain alloys containing both lead and tin in addition to copper and titanium, introduced in the form of titanium hydride, unexpectedly provide joints which are substantially strong than those obtained by means of similar copper, lead, titanium alloys free of tin. More specifically, it has been found that marked improvements in bond strengths are obtained with fusible alloys consisting of from 45 to 70 parts by weight of copper, 25 to 40 parts by weight of lead, 1 to 5 parts by weight of titanium hydride and 2.5 to parts by weight of tin. A preferred alloy contains about 58.5 parts copper, 31.5 parts lead, 2.5
parts titanium hydride and 7.5 parts tin. Titanium. may be substituted for all or part of the titanium hydride.
Features of the invention which are believed novel are set forth in the appended claims. The invention itself together with the various advantages thereof may be better understood from the following description taken in connection with the accompanying drawing in which: 7
FIGURE 1 is a sectional view of a metal-ceramic structure with the essential components thereof shown in their positions prior to formation of a joint between the metal and ceramic bodies; and
FIGURE 2 is a sectional view of the same component joined by the alloy of the present invention.
With reference to the accompanying drawing there is shown a ceramic bushing or insulator in the form of a disc 1 having an opening 2 therein for receiving an elec-. trically conducting metal pin 3.
For the purpose of making a strong hermetic joint bepresence of a non-oxidizing atmosphere such as hydrogen Patented June 16, 1964 "Ice 0 opening 2. After cooling, there is obtained by means of the alloy of the present invention a joint between the ceramic member 1 and the pin 3 possessing an unusually high bonding strength. V
Preferably the brazing ring 4 is made by compounding finely divided lead, copper, tin, and titanium hydride with or without small amountsof binders or lubricants such as parafiin or stearic acid which facilitate molding of the mixture. The mixed powders are then compressedin dies to form rings of the desired size and shape. Following the above procedure, a number of metalceramic seals were producedemploying ceramic members composed of: discs lot 96% alumina having a thickness of inch and holes of 2 or A; inch diameter. The terminal pins 3 were made from wire of 42% nickel-iron alloy orother suitable alloy cold-headed to form the shoulder 5. After cleaning these pins with hydrochloric acid solution, they were inserted into the holes 2 and with the brazing rings 4 in place were fired at a temperature of 1800 F. in atmospheres of either hydrogen or diassociated ammonia for 10 to 12 minutes. The compositions of the tested alloys including both those known prior to the present invention and those produced in accordance Table I.Braze Compositions Constituents, Percent by Weight Braze No.
Cu Pb Tl Ag TlHz Sn Bronze 1 Oil-10% Sn.
tion was measured. A steady increased load was applied at a slow rate using a tensile machine.
From the results of these tests as set forth in the above table, it-will be seen that the joints formed with alloys containing no tin were in general broken by the application of loads ranging from 450 to 850' pounds to the pin.
However as shown for example by, a comparisonof alloy' 20 containing no tin with the alloys 23 to 28 inclusive con- I taining tin, the substitution of bronze for the copper thereby introducing tin into the alloy or the substitution of tin for a portion of the copper content of the previously known alloys, resulted in substantial increases in the strength of the joints. cluded in the alloy, a force in excess of 1000 pounds was required to produce failure. However as the application f of these additional loads, cause the pins to yield and upset to the extent that they could not be pushed out, the
, results were tabulated as merely being greater than 1000 Inall cases where tin was in- 3 pounds. In these tests'in which the load exceeded 1000 pounds, the ceramic members broke at loads ranging from 1050 upwards to 2000 pounds.
The exact reasons for the improvements obtained by the presence of tin is not known. It is possible that the alloying of the tin with the copper contents of the alloy may account for at least some of the improvement obtained by the addition of tin. For example, braze #23 containing 31.5% lead, 66% bronze in the form of a 90% copper-% tin alloy, and 2.5% titanium hydride appeared to produce the most homogeneous joint. Photomicrographs of this joint disclosed a bronze matrix surrounding islands of lead and a thin layer of titanium at the ceramic surface. At the pin surface, there was an irregular layer resulting from the reaction between the alloy and the pin material. Sincetin is more expensive than lead or copper, it is desirable to limit the tin content to a maximum of about 10%. In fact there appears to be no advantage in a tin content in excess of 10%.
While there has been shown and described particular embodiments of the present invention, it will be obvious to those skilled in the art that changes and modifications may be made therein without departing from the invention and it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. A brazing material for bonding a metal member to a ceramic member consisting essentially of from 1 to 5 parts by weight of titanium hydride, to parts copper, 2540 parts lead and 2.5 to 10 parts tin.
2. A brazing material for bonding a metal member to a ceramic member consisting of about 2.5 parts by weight of titanium hydride, 58.5 parts copper, 31.5 parts lead and about 7.5 parts tin.
3. A joint structure comprising a ceramic member and a metal member joined by a bonding material formed by fusing l-5 parts by Weight of titanium hydride, 45 to 70 parts copper, 25-40 parts lead and 2.5 to 10 parts tin.
4. A joint structure comprising a ceramic member and a metal member joined by an alloy formed by fusing 1-3 parts by weight of titanium hydride, 45 to 70 parts copper, 2540 parts lead and 2.5 to 10 parts tin fused in an inert atmosphere.
References Cited in the'file of this patent v UNITED STATES. PATENTS 2,351,798 Alexander June 30, 1944 2,570,248 Kelley Oct. 9, 1951 3,001,269 Moore Sept. 26, 1961