Hyperion's Versimax diamond composite may be attached to tungsten carbide, metal, or ceramic substrates using active brazing methods in vacuum or inert gas atmosphere furnaces. Commercially available active brazing alloys, available as foil, wire, preforms, or paste, can be used successfully to attach Versimax to WC. Shear strengths of the braze joints range from about 250 MPa to 350 MPa, depending on the substrate, brazing alloy, furnace conditions, and brazing temperature chosen.
The following recommendations for good brazing practices are based on brazing shear strength experiments and accumulated brazing experience. Please contact your Hyperion account representative to discuss your specific application and determine the best options for brazing your Versimax tools.
Furnace brazing with active brazing alloys is required for brazing with Versimax. Vacuum brazing is the preferred method, with vacuum levels below 5 x 10-5 Torr or better, but the use of furnaces with inert brazing atmospheres (Ar) is also possible. The selection of braze alloy should be made accounting for braze joint strength requirements, operating temperatures, and the development of residual stresses due to the coefficients of thermal expansion (CTE) mismatch between diamond and substrate materials.
|Brazing Temperature (°C)||Composition (wt %)||Alloy Designation|
|941 - 968||68.8||26.7||4.25||APA 4*|
|850 - 950||70.5||26.5||3.0||CB4‡|
|760 - 816||60.3||23.0||14.7||2.0||APA 8*|
|668 - 696||43.6||29.1||24.3||3.0||APA 9*|
* Prince-Izant, Cleveland, OH
† Morgan Advanced Materials, Hayward, CA
‡BrazeTec, Wolfgang, Germany
Because active braze alloys do not flow by capillary action on ceramic surfaces, it is necessary to place braze alloy at all braze joints. The use of foil, wire, or preforms assures complete coverage, proper placement, and correct amount of braze is used. Paste can be applied by screen printing, manually, or using automated dispensing systems. The braze assembly may be clamped or weighted with 0.5 to 1 g/mm2 in order to promote a thin and fully dense braze joint.
Due to the very low coefficient of thermal expansion of Versimax, (CTE = 1.6 x 10-6/°C), it is preferable to braze to WC substrates, which have CTEs lower than those of metals. Selecting the braze alloy with the lowest melting point suitable for planned operating conditions will further reduce thermal stresses. The use of Cu interlayers to reduce thermal stresses is recommended when brazing large parts, at high temperatures, or when brazing Versimax to metals when the CTE mismatch is very large. Cu interlayers are compatible with all Ag-Cu braze alloys, and a thickness of 125 microns (0.005 inch) is normally suitable. The use of braze foils greatly simplifies assembly of parts using Cu interlayers.
When brazing Versimax cylinders into cylindrical pockets, the pocket diameter should be 0.1 mm (0.004 inch) larger than the Versimax diameter, resulting in a joint thickness of 50 microns (0.002 inch) at room temperature. The bottom of the Versimax cylinder must be chamfered, or relief formed into the pocket, to prevent interference and provide a clean fit. To ensure a well filled and pressure tight braze joint, apply braze foil or paste in the bottom of the pocket and enough braze paste to fill the cylindrical gap, insert the Versimax, and press to seat it in the pocket. Finally, apply a bead of braze paste around the circumference of the Versimax cylinder where it exits the pocket, and braze with a weight of at least 1 g/mm2.
Your Hyperion sales person can offer their expertise in selecting the wire die product best suited to solve your needs.