15. Tips for welding titanium metals

Welding Titanium Metals

Shielding Gas is Critical

The oxide layer must be removed prior to welding because it melts at a much higher temperature than the base metal and because the oxide could enter the molten weld pool, create discontinuities and reduce weld integrity.

When heated, titanium becomes highly reactive and readily combines with oxygen, nitrogen, hydrogen and carbon to form oxides (titanium’s famous colors actually come from varying thickness of the oxide layer). Interstitial absorption of these oxides embrittles the weldment and may render the part useless. For these reasons, all parts of the heat-affected zone (HAZ) must be shielded from the atmosphere until the temperature drops below 800°F (note: experts disagree on the exact temperature, with recommendations ranging from 500°F to 1000°F. Use 800°F as a reasonable median unless procedures, standards or codes indicate otherwise).

GR2 Titanium Stub End Long Pattern

Clean, Clean, Clean,

Contamination from oil on your fingers, lubricants, cutting fluid, paint, dirt and many other substances also causes embrittlement, and it is a leading cause of weld failure. When working with titanium, follow the three Cs of welding: clean, clean, clean! Keep a clean work area, one free from dust, debris and excess air movement that could interfere with the shielding gas. Clean the base metal and bag parts not immediately welded, clean the filler rod and wear nitrile gloves when handling the filler rod and parts.

On the most critical parts, using a small hot-air blower (hair dryer-style) to warm the part slightly ensures no moisture has condensed on the surface to be welded. Don't overlook the fact that rubber gloves may contain chlorine as part of a vulcanizing process. Plastic gloves are recommended.

Titanium Welded Components GR2

Pure Argon Applied Correctly

The argon must be 99.999 percent pure. Even if the argon is as pure as the 50 parts-per-million (PPM) range (99.995 percent), some yellow-straw discoloration can result.


Always buy your gas from a trusted supplier. The argon must be 99.999% pure to ensure the weld isn’t discolored from contamination. That’s 10 parts per million or less contamination. A perfect titanium weld looks like frozen mercury and has little or no coloration. Any blue tinting or mottling often means the argon was not pure enough.

Welding Titanium Fittings GR2

Finishing Up

The end of the weld is equally important. The titanium is hot, and the protective argon flow is still needed until the metal has cooled below about 500 degrees F. Color can be your best indicator of sufficient argon use. Some discoloration may occur beyond the HAZ and, depending on the criticalness of the weld, may be acceptable.

Titanium Welding Chlorite Fittings

Notice

• Once welding begins, the air itself becomes a contaminant to the molten titanium. 

• Oxygen contamination is an extremely common cause of substandard welds. Not only the weld itself but the HAZ and root side of the weld must be shielded from air when their temperature rises to over 800°F. Usually, pure argon is the preferred shield gas. Occasionally, you’ll see argon mixed with helium. For some high-performance applications, cryogenic (liquid) argon is used. 

 

• Joint surfaces must be smooth, clean, and completely free of contamination. Weld joints and wire must be free of mill scale, dirt, dust, grease, oil, moisture, and other contaminants. Any contaminants introduced to the titanium will degrade its performance and corrosion resistance. 

• Never use any chlorine-based cleaning solvent. 

• If you cannot weld immediately after cleaning, cover the weld joints with paper or plastic to avoid recontamination.

Welding Titanium Pumps GR2

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