Active Metal Brazing is when a metal like titanium is added to the braze alloy, which chemically reacts with the surface of the parent ceramic, allowing the braze alloy to wet directly onto the surface in a vacuum. It eliminates process steps when brazing ceramics to metal, allowing one to braze directly to raw ceramics without having to metalize/plate the surface prior to brazing; the result is time and costs savings.
Vacuum brazing is used because it deoxidizes the metals being brazed, but more importantly, eliminates undesirable reactions that would have occurred in hydrogen brazing and helps to vaporize or remove high vapor pressure materials that are seen as contaminants.
Here at Altair Technologies we routinely perform active metal brazing in a vacuum, achieving strong hermetic bonds between ceramic and various metals. Active-Metal braze alloys helps us to simplify and condense the process by allowing us to braze directly to raw ceramics (with prior clean firing) and without metalizing the ceramic material prior to brazing.
Active metal alloys typically include titanium or aluminum, which when correctly heated, form bonds with virtually any ceramic-like material. These alloys contain an “active” element (typically titanium) which chemically reacts with the surface of the parent ceramic, allowing the braze alloy to wet directly onto the surface. The titanium’s ability to react chemically with oxides, forming a reaction layer of metal-oxides, in effect creates a metalized layer that is wettable by the other constituents of the active-metal alloy. Hence, active metal brazing is a common method to braze ceramic to metal.