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ASM International®
Materials Park, Ohio 44073-0002

www.asminternational.org

Brazing
Second Edition

Mel M. Schwartz

© 2003 ASM International. All Rights Reserved.
Brazing (#06955G)

www.asminternational.org

Page 204

196 / Brazing, Second Edition

Table 5.9 Gold-base active brazing filler
metals

Content, wt% Melting range

Alloy Au Ni Mo V °C °F

Baseline 82.0 18.0 . . . . . . 955 1750
1 82.8 15.6 0.7 1.0 949–958 1740–1755
2 81.8 15.7 0.7 1.8 940–960 1725–1760
3 80.9 15.5 0.7 2.9 953–958 1747–1755

Source: Ref 61

metals, but produced significantly more joint
leaks. The 99.8% alumina specimens brazed
with the 2% V filler metal yielded the poorest
tensile properties. Only the 3% V composi-
tion yielded joint strengths approaching the
94% alumina values. The fracture paths in the
99.8% alumina specimens occurred across
the metal-ceramic interface.

• Differences in joint strength between the two
types of alumina can be attributed to the pres-
ence of a greater amount of glassy grain-
boundary binder phase present in the 94%
alumina ceramic.

New filler metals, based on the Au-Ni-Cr-Fe
system, were developed and tested at room tem-
perature and at 650 °C (1200 °F) for ceramic-
metal brazed joints in ceramic heat engines (Ref
62).

The two filler-metal systems developed were
approximately Au-33–35Ni-3–4.5Cr-1–2Fe-1–
2Mo (SK-1) and Au-34–36Ni-4–5.5Cr-2–3Fe
(SK-2) (wt%). These filler metals showed supe-
rior wetting and atomic bonding characteristics
as well as excellent ductility, compared to the
other compositions studied.

These two systems were able to satisfy the
requirements of high-temperature performance
at 650 °C (1200 °F) for ceramic-metal joints in
ceramic heat-engine applications. In the design
of new filler metals, the microstructural crite-
rion of both solid-solution and dual-phase
strengthening was employed for high-tempera-
ture filler metals. Also, an effort was made to
balance the property requirements of the filler
metals for the ease of manufacture and high-
temperature properties.

The new filler metals provided superior joint
performance at high temperature, as compared
to conventional solid-solution filler metals. The
SK-1 filler metal resulted in a significant gain in
the torsion strength at 650 °C (1200 °F) for
PY6-nickel-Incoloy 909 (Special Metals Corp.)
joints, with a moderate loss at room temperature

compared with baseline Au-Pd-Ni joints. The
average SK-1 joint strength was 35.8 N·m at
650 °C (1200 °F), whereas the strength at room
temperature was 43.1 N·m. The high-tempera-
ture torsion strength was far better than the Au-
5Pd-2Ni filler metal system (1.6 to 7.7 N·m).

The creep performance of these joints at 650
°C (1200 °F) was outstanding. The rupture life of
the SK-1 braze joint exceeded 160 h at the 20.9
N·m torque level. Most rupture failures occurred
at the interface between the braze and PY6.
Excellent performance was obtained when the
atomic bonded area exceeded 80%. In addition,
excellent room-temperature mechanical fatigue
properties, as well as thermal fatigue resistance,
were noted for the SK-1 joint at a fatigue ampli-
tude of 3.9 to 20.9 N·m. The significant improve-
ment in high-temperature torsion strength and
creep performance is ascribed to the dual-phase
microstructure of the SK-1 filler metal. The
microstructures of the joints made of the filler
metals show two discrete gold- and nickel-rich
phases, which have different melting points.

A patent (Ref 63) was issued for a gold-base
filler metal in paste form for use with high-per-
formance ceramics. The use of such ceramics,
with their favorable properties in respect to hard-
ness, wear and corrosion resistance, and electri-
cal resistivity in high-technology applications,
depends very much on the ability to reliably join:

• Simple shape components to form complex
assemblies

• Unit length of material to form large systems
• Ceramic components to metals

For such bonds, active-metal brazing has been
developed. With this technique, the wetting and
bonding of the braze material is improved by the
presence of small amounts of highly reactive
metals such as titanium or zirconium.

Preferred materials contained in the filler
metal are 85 to 90Au, 0.5 to 7Ni, 0.5 to 6V, 0.25
to 4Mo, and 0.3 to 5Cr (wt%). In addition, rela-
tively large amounts of vanadium can be added
to the basic gold-nickel filler metals, which nev-
ertheless maintain good ductility. Ductility can
be further enhanced by adding small amounts of
molybdenum. The corrosion and oxidation re-
sistance of the filler metals is improved by
minor amounts of chromium.

Nickel Filler Metals (Designated BNi)
Nickel filler metals are used for corrosion and

heat resistance (up to 980 °C, or 1800 °F, con-

Page 406

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Brazing #06955G


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