FAQ

 

What is Brazing?

• Brazing is known as the ‘joining of two pieces of metal by fusing layer of brass or spelter between the adjoining surfaces.’ The process basically involves a braze melting and flowing between the two pieces of material. This is commonly referred to as ‘wetting’ and is absolutely critical - particularly when brazing ceramics. Today there are many materials that can be fused to produce joints between materials - those that melt above ~450°C are classed, brazes, materials melting below ~450°C are called solders.

 

What is Wetting?

• If a braze alloy is melted between two ceramics, a poor joint is likely to result, because of poor wetting. Wetting is measured in terms of the contact angle between the braze and substrate after melting. For good wetting, the contact angle (?) is less than 90°; for poor wetting, the angle is greater than 90°.
  

 

What are Methods to Increase Wettability?

• In addition to a controlled atmosphere utilizing Nitrogen or Argon and vacuum environment, two methods are generally used to increase wetting. The first method is to apply something to the surface of the ceramic in order for the braze to wet; common surface treatments are metallization, metal coating, metal hydride treatment. The second method is to apply something to the braze to induce wetting.

 

What are Brazing Alloys?

• Brazing alloys are the alloys utilized for brazing. Currently, high temperature (appox. 1200°C) brazing of SiC and low temperature (420°C) active brazes, capable of joining ceramics in air versus a controlled atmosphere, are the most prospective alloys in the market.

 

What is High Temperature Active Metal Brazing?

• High-Temperature Active Metal Brazing process involves coating the ceramic with reactive or refractory metal (W, Ta, Cr, Mo) then brazing using high temperature braze alloys, such as palladium or platinium based systems. Although, high temperature alloys are not readily available commercially and the majority of active brazes are developed for moderate temperature use, high temperature braze alloys have the potential for higher strength, oxidation resistance, and ductility at a larger range of temperatures.

 

What is Reactive Air Brazing (RAB)?

• RAB is a novel brazing process that reactively modifies one or both ceramic surfaces with an oxide compound dissolved in a molten noble metal alloy such that the newly formed surface is readily wetted by the remaining liquid filler material. This technique forms a predominatly metallic joint directly in air without need of vacuum chamber/ inert cover gas or the use of surface reactive fluxes.