| 1. |
Brazing
is accomplished using active alloy braze techniques. The active alloys
generally contain titanium. |
| 2. |
Brazing
can be accomplished with titanium doped braze preforms available from
Wesgo and Degussa. These are typical silver bearing braze alloys
containing a few percent titanium. The other alternative is to paint
the ceramic surface with an active metal hydride film followed by
brazing using a standard commercially available braze alloy. |
 |
|
| Surface Preparation |
| Macor |
| 1. |
Grind
surface to .8 micron (30 microinch) average roughness then lap to .1
micron (5 microinch) average roughness for best braze strength. |
| 2. |
Degrease
surface with organic degreasing agent. Isopropanol and acetone are
acceptable. |
| 3. |
Wash
ultrasonically a minimum of 5 minutes in deionized water heated to at
least 65° C (150° F) |
| 4. |
Dry 2
hours at 100° C (212° F) |
| 5. |
Handle
with gloves to ensure cleanliness |
| 6. |
Use as
soon as possible to prevent contamination of cleaned surfaces. |
| Metal |
| 1. |
Degrease
using isopropanol and acetone. |
| 2. |
Lightly
etch the metal surface using standard etching solutions. The objective
is to remove any contamination from the surface, lightly roughen the
surface and provide a virgin metal surface for braze alloy flow. |
| 3. |
Rinse
in deionized water. (See MACOR preparation above) |
| 4. |
Dry at
100° C. (See MACOR preparation above) |
| 5. |
Handle
with gloves. |
| 6. |
Use as
soon as possible. |
|
|
| Fixturing |
| Active
Alloy Preforms |
| 1. |
Place a
14 to 75 micron (.001" to .003") thick preform on the area to be brazed. |
| 2. |
Place
the metal part over the preform. |
| 3. |
Fixture
to maintain alignment during firing. |
| 4. |
Apply
approximately 34 kPa (5psi) load on the assembly to facilitate braze
alloy flow-out. |
| Hydride
Process |
| 1. |
Prepare
a slurry of 2 cc ethylene glycol with 1 gram titanium hydride powder.
Keep the mixture agitated. |
| 2. |
Apply
a thin layer of the slurry to the surface of the MACOR to be brazed.
The hydride must completely cover the area to be brazed. Thickness
should be less than 15 microns (.0007"). |
| 3. |
Allow
the hydride layer to air dry. |
| 4. |
Place a
14 to 75 micron (.001" to .003") thick braze preform over the hydride
layer. |
| 5. |
Place
the metal part over the preform. |
| 6. |
Fixture
to maintain alignment during firing. |
| 7. |
Apply
approximately 34 kPa (5psi) load on the assembly to facilitate braze
alloy flow-out. |
|
|
| Firing |
| 1. |
Apply a
minimum vacuum of 10–5
Torr or lower in the furnace and be sure to maintaim throughout the
firing cycle. If using the hydride process, a pressure increase near
350° C (660° F) can be expected as the hydride
decomposes. It
is important to maintain the minimum vacuum level even during the
pressure rise. |
| 2. |
Heat
at 50° to 200° C (90° to 360° F) per
hour. Maintain
equalized heating of both Macor and metal components. |
| 3. |
Hold
for 1 minute 20° to 30° C (65° to 85°
F) over the braze
alloy liquidus temperature. |
| 4. |
Cool
at a rate of 50° to 200° C (90° to 360°
F) per hour.
Maintain equalized temperatures on both the Macor and metal components. |
|
|
| Hints |
| 1. |
Maintain
an oxygen free environment in the vicinity of the components being
brazed. If necessary, titanium getters can be placed in close proximity
to the braze joint. |
| 2. |
Use
a soft fixturing material such as boron nitride or graphite. It will
help facilitate removal of the brazed assembly should the alloy flow
onto the fixture supports. A brazing stop-off of liquid boron nitride
can be applied to help keep braze alloy from flowing onto critical
surfaces. |
| 3. |
If
using the hydride process, a fresh slurry should be prepared before
each brazing operation due to the short shelf life of the hydride
slurry. |
| 4. |
Braze
alloy preforms are recommended for consistent and uniform joint
thicknesses. |
| |
|
