Method of brazing parts of Ti-Al-Nb alloy

Abstract

A brazing alloy-filler metal for brazing parts made of TiAlNb alloys has a brazing temperature of about 1020.degree. to 1250.degree. C. and a composition of, in weight percent, 37-75 titanium, 5-43 niobium, 20-58 nickel.

Description

This invention discloses a brazing alloy - filler metal useful in joining, for example, titanium-aluminum-niobium (TiAlNb) alloys. Such TiAlNb alloYs are useful in the aircraft industry because they are lightweight and can withstand elevated temperatures.

A brazing alloy-filler metal in accordance with this invention comprises 37-75% titanium, 5-43% niobium, 20-58% nickel, all percentages by weight, having a brazing temperature between about 1020.degree. to 1250.degree. Centigrade. Because the solution heat treatment temperature of the TiAlNb alloy is about 1200.degree. C., brazing and solution heat treating can be advantageously carried out simultaneously when the brazing alloy of this invention is used.

U.S. Pat. No. 3,662,455 discloses a nickel-titanium-niobium alloy for metal-to-ceramic and ceramic-to-ceramic braze bonds especially useful in the manufacture of alkali metal vapor arc lamps. The alloy constituents lie within the following percentage weight ranges: 22.8-36.4% Ti; 26.9-42.9% Ni; 20.7-50.3% Nb.

A brazing alloy-filler metal as per the instant invention is outside the disclosure of U.S. Pat. No. 3,662,455 in titanium content. The density of the brazing alloy as per this invention is a closer match to the low density of a TiAlNb alloy than is the nickel-titanium-niobium alloy disclosed in U.S. Pat. No. 3,662,455.

Several TiNbNi alloys, as per this invention, in the form of small skull melted buttons were placed at the ends of T joints made from 65% Ti, 14% Al, 21% Nb alloy and brazed with the following results

Brazing alloy number 5 (50 Ti, 15 Nb, 35 Ni) was brazed at 1040.degree. C. for 10 minutes with an excellent full filleted joint.

Brazing alloy number 2 (60 Ti, 15 Nb, 25 Ni) was brazed at 1100.degree. C. for 10 minutes with excellent results.

Brazing alloy number E (45 Ti, 20 Nb, 35 Ni) was brazed at 1100.degree. C. for 10 minutes with excellent results.

Brazing number M (40 Ti, 20 Nb, 40 Ni) was brazed at 1200.degree. C. under 10.sup.-5 Torr vacuum for 10 minutes with excellent results.

Brazing alloy number 6 (40 Ti, 25 Nb, 35 Ni) was brazed at 1200.degree. C. under 10.sup.-5 Torr vacuum for 10 minutes with excellent results. Photomicrographs of the joints showed excellent alloying with little sign of a seam. An additional 10 minutes hold time will eliminate the presence of the original filler metal. A homogeneous joint is considered ideal because a second phase can act as a stress riser and can lead to stress induced corrosion. Table I shows the composition in weight percent of TiNbNi alloys within this invention on which solidus and liquidus temperatures were determined.

TABLE 1______________________________________Sample Ti Nb Ni Sol. .degree.C. Liq. .degree.C.______________________________________1 70 5 25 938 10502 60 15 25 938 10763 50 25 25 933 10944 60 5 35 948 10505 50 15 35 934 10206 40 25 35 958 11457 50 5 45 933 12548 40 15 45 1108 128210 55 15 30 935 101011 45 15 40 946 1171D 55 10 35 937 1020E 45 20 35 938 1054J 60 10 30 933 1000K 50 10 40 928 1160L 50 20 30 937 1020M 40 20 40 1076 1172______________________________________

Claims

1. The method of joining metal parts made of a TiAlNb alloy having a solution heat treating temperature of about 1200.degree. C. comprising the steps of disposing a brazing alloy at the joint between the parts, the brazing alloy having a brazing temperature between about 1020.degree. C. to 1250.degree. C. and having a composition of, in weight percent, 37-75 titanium 5-43 niobium, 20-58 nickel and brazing the parts at a temperature of about 1020.degree. C. to 1250.degree. C. to form a uniform fillet at the joint.

2. The method of claim 1 wherein the brazing alloy has a composition of 45 Ti, 20 Nb, 35 Ni.

3. The method of claim 1 wherein the brazing alloy has a composition of 40 Ti, 25 Nb, 35 Ni.

4. The method of claim 1 wherein the brazing alloy has a composition of 40 Ti, 20 Nb, 40 Ni.

5. The method of claim 1 wherein the brazing alloy has a composition of 60 Ti, 15 Nb, 25 Ni.

6. The method of claim 1 wherein the brazing alloy has a composition of 50 Ti, 15 Nb, 35 Ni.