Machinable Glass Ceramic - Process of Brazing Macor Machinable Glass Ceramic to Titanium (Ti)

Precision Ceramics, a division of McGeoch Technology, is a company dedicated to the engineering of technical ceramics. From procurement and supply through to technical design and specialist machining, we offer a complete service.

Our reputation for quality and service is truly international with specialist ceramic components engineered by Precision Ceramics finding their way into an ever-widening array of worldwide applications in industries as diverse as aerospace, opto-electronics and nuclear power.

Precision Ceramics is a Macor Distributor. Precision Ceramics is a Macor Expert. In fact, there is no other Macor Supplier who knows more about this unique machinable glass ceramic than Precision Ceramics. We're also experts in Macor Metallization and publishers of the Macor Technical Bulletin.

Macor Machinable Glass Ceramic

Macor is an outstanding engineering material and is machinable with ordinary metalworking tools. Macor is also a problem solving material combining the performance of a technical ceramic with the versatility of a high performance plastic.

Macor has a high use temperature (800°C continuous to 1,000°C peak). It has a low thermal conductivity and is a useful high temperature insulator as well as an excellent electrical insulator. Macor has no porosity and when properly baked out, will not outgas. It is strong and rigid and, unlike high temperature plastics, will not creep or deform. Macor is also radiation resistant.

Macor is pure white and can be highly polished. It can be thick or thin film metallised, brazed and epoxy bonded. Another major advantage of this unique material is that, even in small quantities, components are economical to manufacture.

Brazing Macor Machinable Glass Ceramic to Titanium

Macor machinable glass ceramic - to - titanium seals have been achieved with joint shear strength of 8000 psi and are leak tight to 10-10 (cc (STP) -mm .(S-cm2-cm Hg). This brazing procedure is outlined below.

The process was first developed in response to fusion energy project needs. A sealed ceramic-to-metal part is necessary for construction of the neutral ion beam injection source. Macor was selected as the optimal ceramic due to its low outgassing, excellent dielectric properties and ease of machining. Titanium was the selected metal due to its close thermal expansion match to Macor.

Procedure for Brazing Machinable Glass Ceramic to Titanium

Size and configuration of the parts play a major role in the success of the brazing operation. Applicability to a specific size or configuration can be confirmed by contacting Corning Incorporated or an authorised Macor distributor.

Materials Required for Brazing Macor to Titanium

The materials required for brazing Macor machinable glass ceramic to titanium is as follows:

  • Macor - code 9658
  • Brazing alloys - Cu-Sil, Ni-Cu-Sil no.3, Ni-Cu-sil no.8, Gapasil no.9 (available from GTE-WESGO, Belmont, CA
  • Ethylene glycol
  • Titanium hydride powder (325 mesh)
  • Acetone-trichlorethylene degreasing solution
  • 2% HF or 5% HNO3/2% HF etching solution
  • Titanium or titanium alloy

Surface Preparations for Brazing Macor Machinable Glass Ceramic

The surface preparation required for the Macor machinable glass ceramic and the titanium sample is outlined in the following.

Macor Glass Ceramic

  • Grind surface to better than 30 microinch AA and lap to 5 microinch AA for maximised braze strength.
  • Degrease in acetone - trichlorethylene solution in an ultrasonic bath.
  • Wash ultrasonically for 5 minutes in boiling distilled water.
  • Dry for 2 hours at 100ºC.
  • Handle with care to insure the cleanliness of the part.
  • Use as soon as possible.

Titanium

  • Degrease in acetone-trichlorethylene solution in an ultrasonic bath.
  • Etch at room temperature for approximately 30 seconds in etching solution
  • Rinse thoroughly in distilled water.
  • Dry thoroughly at 100ºC.
  • Handle with care to insure the cleanliness of the part.
  • Use as soon as possible.

Fixturing Macor Glass Ceramic to Titanium

The procedure for fixturing the Macor machinable glass ceramic to titanium is as follows.

  • Prepare a slurry of 2cc ethylene glycol with 1g titanium hydride powder - keep constantly agitated.
  • Apply a thin layer of the slurry on the surface of the Macor, making sure to completely cover the area to be brazed.
  • Allow the titanium hydride layer to air dry.
  • Place 0.001” to 0.003” brazing alloy over the hydride layer.
  • Place titanium metal part over the alloy.
  • Fixture to maintain alignment during firing.
  • Apply force of 5 psi on the parts to facilitate brazing alloy flow out.

Firing Procedure

The firing process involved for brazing Macor machinable glass ceramic to titanium is as follows.

  • Apply a vacuum of 10-5 Torr (or better) on the system and maintain throughout the firing cycle. At 350ºC the titanium hydride decomposes and a pressure increase may be detected. Be sure to maintain at least a 10-5 Torr vacuum at this temperature.
  • Heat at a rate of 50 - 200ºC/hr. Maintain equalised heating of both the Macor and metal parts.
  • Hold for 1 minute at 20 - 30ºC over the liquids temperature of the brazing alloy.

The liquidus temeprature is as follows:

  • Cu-Sil 790ºC
  • Ni-Cu-Sil no.3 & no.8 790ºC Gapasil no.9 880ºC

How to Optimise Brazing Macor Machinable Glass Ceramic

The furnace should be oxygen-free. Oxygen will react with the titanium hydride after it decomposes. Titanium metal ‘getters’ can be placed around the part being brazed.

When fixturing parts, use a ‘soft’ material (e.g. boron nitride). This facilitates removal of the finished part if the alloy flows onto the supports. Also, a ‘brazing stop’ material may be applied to the parts where the alloy is not wanted (available from GTE-WESGO, Belmont, Ca).

The titanium hydride slurry should be made fresh before each brazing operation. The shelf life of this system is relatively short.

The brazing alloys can be purchased in preformed shapes. Use of these preforms offers a more uniform seal and is advised when possible.

This information has been sourced, reviewed and adapted from materials provided by Precision Ceramics.

For more information on this source, please visit Precision Ceramics.

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