Silver-copper-titanium brazing alloy containing crust inhibiting element

Abstract: A silver-copper-titanium brazing alloy contains a small amount of tin, indium, silicon, aluminum or manganese as a crust inhibiting element.

Description: This invention concerns copper-silver brazing alloys containing titanium as an active metal for brazing, for example, to ceramics. Such brazing alloys are disclosed in U.S. patents 4,766,041, 4,735,866, 4,698,271, 4,684,579, 4,643,875, 4,623,513, 4,591,535, 4,448,853, 3,455,663; in U.K. patent 2,167,989, 1,270,477, 932,729; in Canada patent 559,434; in European patent 0 038 584; in German Auslegeschrift 1 030 756; in France patent 1 174 330. When these brazing alloys are melted on a ceramic surface and cooled to room temperature, the alloy surface is a bright metallic color. However, when melted on metals such as stainless steel, Kovar (Westinghouse trademark for an Fe-Ni-Co alloy), cupronickel or 42Ni-58Fe alloy and cooled to room temperature, the surface is dull and a crusty oxidized layer is found on the surface. Such a crusty layer can compromise the quality of the brazed joint when a ceramic is brazed to a metal. Japanese 61-82995 discloses use of Ag-Cu-Ti brazing alloys with additions of 15% In or 9% Sn. The stated purpose of these alloys is to reduce energy loss during brazing. Japanese 62-81290 discloses Ag-Cu-Ti alloys again containing 15% In or 9% Sn. The stated purpose in this document is to improve wettability and fluidity of the brazing material. The inventor has found that the addition of a small amount of tin, indium, silicon, aluminium or manganese to the silver-copper-titanium brazing alloys can eliminate the surface crust formation. The present invention provides brazing alloy consisting of (in wt%): 0.5 to 5% titanium 55 to 73% silver 0.1 to less than 2% of a crust inhibiting element selected from one or more of tin, indium, silicon, aluminium, manganese, inhibiting crust formation of the brazing alloy when the brazing alloy is melted and cooled. the balance being copper (and incidental impurities). The invention also provides a process for inhibiting crust formation on melting and cooling of copper/silver/titanium brazing alloys, the process comprising the addition to the alloy of a crust inhibiting element selected from one or more of tin, indium, silicon, aluminium or manganese and in which the composition of the alloy comprises (in wt%): 0.5 to 5% titanium 55 to 73% silver 0.1 to <2% the crust inhibiting element the balance being copper and incidental impurities. The invention further comprises a process for brazing a ceramic article to a metal article comprising the use of such brazing alloys. In the following examples, all compositions are in weight percent. EXAMPLE 1 An Alloy B with a composition of 71% silver, 1.5% titanium, 0.5% tin, 27% copper was melted on a water cooled copper skull melter using tungsten electrode under argon atmosphere. The button was rolled down to 2 mil (0.051mm) thickness foil. An assembly consisting of 3/8" (9.5mm) diameter by 1/4" (6.3mm) long alumina cylinder was placed on 1"x1"x10 mil (25.4 x 25.4 x 0.25mm) thickness Kovar sheet with above foil between. The assembly was brazed at 820°C under 10⁻⁵ torr vacuum. The brazed assembly showed fillet around the ceramic base and the surface of the metal had a bright metallic finish. The seal was hermetic to helium mass spectrograph. EXAMPLE 2 As a control, an Alloy O with a composition 71% silver, 1.5% titanium, 27.5% copper was prepared and tested as in Example 1. The result of the braze test showed limited fillet and crusty looking finish. The seal was tested with He mass spectrograph and showed an unacceptable leak rate of 10⁻⁷cc. per sec. (acceptable is 10⁻⁹cc, per sec). This alloy did not contain a crust eliminating element. EXAMPLE 3 An Alloy F with a composition of 63% silver, 1.5% titanium, 0.5% tin, 35% copper was prepared and tested as in Example 1. The result showed that this alloy was crust free over Kovar, and formed a full smooth fillet between the alumina cylinder and Kovar substrate. EXAMPLE 4 An Alloy K with a composition of 63% silver, 1.5% Ti, 1% In, 34.5% Cu was prepared and tested as in Example 1. The result of the braze test was similar to Example 3. EXAMPLE 5 An Alloy M with a composition of 65% Ag, 1.5% Ti, 1% Si, 32.5% Cu was prepared and brazed as in Example 1 and resulted in a smooth metallic braze alloy with excellent fillet between ceramic cylinder and Kovar substrate. EXAMPLE 6 A powder consisting of Composition F, 63% Ag, 1.5% Ti, 0-5% Sn, 35% Cu was made into a screenable paste with a screening oil. Using 105 mesh screen, an alumina substrate was screened, dried and heated to 820°C under 10⁻⁵ torr vacuum. An excellent bond resulted. EXAMPLE 7 A button with a Composition K, 63% Ag, 1.5% Ti, 1% In, 34.5% Cu was drawn down to 40 mil (1.02mm) diameter wire. The wire was made into a circular shape preform and placed at a base of 1/4" (6.3mm) diameter by 1/4" (6.3mm) long type 410 stainless steel and placed on alumina substrate. The assembly was brazed at 820°C for 10 minutes under 10⁻⁵ torr vacuum. An excellent joint resulted. EXAMPLE 8 A button with Composition P, 63% silver, 1.5% titanium, 0.5% aluminium, 35% copper was prepared and brazed as in Example 1 and resulted in smooth metallic finish with fillet between ceramic cylinder and Kovar substrate. EXAMPLE 9 A button with Composition Q, 63% silver, 1.5% titanium, 0-5% manganese, 35% copper was prepared and brazed as in Example 1 and resulted in smooth metallic finish with fillet between ceramic cylinder and Kovar substrate. The following table shows compositions, liquidus, and solidus temperatures for examples within this invention (except for Samples L, N and O). Samples L, N and O did not contain crust eliminating elements as per this invention and did not yield crust free results. Sample Composition Liq.°C. Sol.°C A 71 Ag 0.75 Ti 0.5 Sn 27.75 Cu 807 778 B 71 Ag 1.5 Ti 0.5 Sn 27.0 Cu 813 776 C 67 Ag 1.5 Ti 0.5 Sn 31.75 Cu 788 774 D 67 Ag 1.5 Ti 0.5 Sn 31.0 Cu 795 772 E 63 Ag 0.75 Ti 0.5 Sn 35.75 Cu 813 770 F 63 Ag 1.5 Ti 0.5 Sn 35.0 Cu 811 770 G 63 Ag 1.5 Ti 0.25Sn 35.25 Cu 813 774 H 63 Ag 1.5 Ti 1.0 Sn 34.5 Cu 806 770 I 59 Ag 0.75 Ti 0.5 Sn 39.75 Cu 840 774 J 59 Ag 1.5 Ti 0.5 Sn 39.0 Cu 826 773 K 63 Ag 1.5 Ti 1 In 34.5 Cu 809 765 L 63 Ag 1.5 Ti 1 Ge 34.5 Cu 796 780 M 65 Ag 1.5 Ti 1 Si 32.5 Cu 805 786 N 63 Ag 1.5 Ti 35.5 Cu 815 780 O 71 Ag 1.5 Ti 27.5 Cu 810 780 P 63 Ag 1.5 Ti 0.5 Al 35 Cu 823 779 Q 63 Ag 1.5 Ti 0.5 Mn 35 Cu 816 779 Composition N, in a 2 mil (0.051mm) thick foil, was used to braze a Kovar cap to an alumina cylinder. An oxide layer impeded fillet flow and the joint had an unacceptable leak rate. However, Composition F, in a 2 mil (0.051mm) thick foil in the same braze test, produced a full fillet and an acceptable leak rate. Composition F was substantially identical to composition N, but with 0.5% Sn added.

Claims: A brazing alloy consisting of (in wt%) 0.5 to 5% titanium 55 to 73% silver 0.1 to less than 2% of a crust inhibiting element selected from one or more of tin, indium, silicon, aluminium, manganese, inhibiting crust formation of the brazing alloy when the brasing alloy is melted and cooled. the balance being copper (and incidental impurities). The brazing alloy of claim 1 having a composition of, in weight percent, 71 Ag, 1.5 Ti, 0.5 Sn, 27 Cu. The brazing alloy of claim 1 having a composition of, in weight percent, 63 Ag, 1.5 Ti, 0.5 Sn, 35 Cu. The brazing alloy of claim 1 having a composition of, in weight percent, 63 Ag, 1.5 Ti, 1.0 In, 34.5 Cu. The brazing alloy of claim 1 having a composition of, in weight percent, 65 Ag, 1.5 Ti, 1 Si, 32.5 Cu. The brazing alloy of claim 1 having a composition of, in weight percent, 63 Ag, 1.5 Ti, 0.5 Al, 35 Cu. The brazing alloy of claim 1 having a composition of, in weight percent, 63 Ag, 1.5 Ti, 0.5 Mn, 35 Cu. A process of brazing a ceramic article to a metal article comprising the use of an alloy as claimed in any of claims 1-7. A process for inhibiting crust formation on melting and cooling of copper/silver/titanium brazing alloys, the process comprising the addition to the alloy of a crust inhibiting element selected from one or more of tin, indium, silicon, aluminium or manganese and in which the composition of the alloy comprises (in wt %) 0.5 to 5% titanium 55 to 73% silver 0.1 to <2% the crust inhibiting element the balance being copper and incidental impurities.

Inventors: MIZUHARA HOWARD, MIZUHARA, HOWARD
Applicants: MORGAN CRUCIBLE CO, THE MORGAN CRUCIBLE COMPANY PLC
Application year: 1989
Main classification: B23K35
IPC codes: B23K35, C22C5