Altair's Brazing, Welding & Engineering Blog

Recall the blistering or ruptures that can be experienced when you braze non-OFE Copper in Hydrogen (see Blog Post October 7, 2009).  As a follow-up post, we want to briefly discuss “stringers.”  Stringers are actual holes or leaks paths in the material that follow grain directions and are intrinsic to many grades of materials that are used in vacuum applications.  (more…)

Back in September 2009 we published a Post titled, “Wetting, Braze Flow and Filler Spreading,” and for those of you who were left hanging, here is our new Post on using phase diagrams to understand Spreading.

Why do we experience excessive spreading with some filler (braze alloys)/substrate interactions and poor spreading in others? Let’s examine phase diagrams to explain the following observations:

• Cusil on Cu blushes (excessive flow)
• Cu/Au on Cu flows well
• Cu on Ni flows poorly
• Cu on Fe flows very well (blush potential)

It is widely known by many in the brazing industry, that “Cusil” an Ag/Cu eutectic, flows like crazy on copper. In this interaction, molten Cusil dissolves copper (Cu) thereby increasing the melt volume, but the solidus temp doesn’t rise at all! (more…)

Metallization vs. Active Alloy Brazing

Applications for brazing ceramic to metal are most commonly found in microwave tube, semiconductor feedthru and laser devices, where high vacuum integrity and dielectrical properties are required.

More recently, medical and military devices have brought forward new demands for ceramic to metal seals, which require biocompatibility and high joint strength.

The difficulty in brazing ceramics to metals is largely due to the inability of most braze alloys to “wet” directly to ceramic materials and the accumulation of residual stress once the materials have been successfully “wetted”.  (more…)

Hydrogen Brazing
Here at Altair Technologies most of our products are for high vacuum applications and we therefore do most of our brazing in Hydrogen Gas or in a high vacuum atmosphere. During the braze run, while assemblies are being heated up to braze temperature, the furnace “bell” sees a steady flow of Hydrogen gas. This process continues until parts are below a certain temperature at which time the bell is backfilled with Nitrogen gas. Products or assemblies that are commonly hydrogen brazed include X-Ray Tubes, Traveling Wave Tubes, Linear Accelerators for medical, research and security applications and similar ion or electron beam devices. For reasons to be explained below, Hydrogen brazing is arguably the best process for bonding metals and ceramics regardless of the application. (more…)

Braze alloy penetrates full thickness of cavity wall

When fabricating complex geometries, whether it’s by die casting, e-beam welding, or 5- axis machining, there can be distinct advantages when brazing is used as a means of creating the final assembly.  Manufacturing of cavity structures utilizing standard brazing principles, for example, is becoming a current trend.
 
Structures with internal cavities are used in many applications including RF power, fuel cells, heat exchangers, cryogenic systems and chemical processing.  These arrangements are fabricated from many types of materials including copper, stainless steel, niobium, Inconel, titanium and alumina.

• Brazing vs. E-beam welding (EBW)

Orbital EBW is often used to bond two hemispheres together in order to produce a cavity; however, due to the limits in the amount of penetration possible with EBW, there are limits on possible wall thicknesses of the cavity (typically 2” in soft vacuum machines and 6” in hard vacuum machines).  With brazing, there is virtually no limit on wall thickness.  (more…)

The term “wetting” is commonly used to describe the flow of braze alloy or braze filler across a surface. However, before we get more into wetting, let’s recap the brazing process: First, two components are placed very close to or in contact with each other and a braze filler metal is placed in contact with BOTH parts. The filler and components are heated to just past the melting temperature of the filler braze alloy. The filler alloy “wets” the parts and capillary forces draw the braze alloy between the mating components, making up what is called the braze joint. The assembly is then cooled, solidifying the braze joint.

Good wetting occurs when the surface is clean & metallic and is (more…)

Laser Beam Welding (LBW) is a high energy welding process that continues to expand into modern industries and new applications because of its many advantages.  Some of the advantages of laser welding versus arc-welding are:

• High power density: deep weld penetration with minimal Heat Affected Zone (HAZ)
• Automation: easily automated using robotic machinery or CNC
• Accessibility: non-contact nature allows normally inaccessible areas to be welded along a “line of sight” or through thin parts as in the case of a cover plate (see Laser Welding page on our Website for more info)
• Versatility: capable of welding steels, aluminum, titanium, kovar, precious and refractory metals
• “Laser brazing”: high degree of accuracy allows melting of a filler metal placed within a joint without affecting the base material
• Laser welders can also be used for precision cutting and engraving

From a furnace brazing standpoint, laser welding is an important process used to reduce cost and increase productivity.  (more…)

Most of the brazing we do at Altair Technologies occurs between 800° C – 1270° C. Finding a suitable braze-alloy or “filler” to melt in this temperature range is not difficult. However finding a braze alloy, or even base materials, that will withstand operation over 1000° C can be tricky. One of the first questions to ask is what is the operating atmosphere or environment (high vacuum, air or?) and what are the base materials? At those elevated temperatures, many unwanted phenomena can occur. (more…)

Here at Altair Technologies we don’t maintain in-house plating capability and in general we try to avoid the use of plating(s) due to its additional costs and lead-times as well as yield issues associated with poor process controls. However, the plating of base material can benefit the operational performance and reliability of certain applications, benefit the brazing process and even assembly. (more…)