21.4 Welding Reactive Metals
David Colameco, M.Ed.
Reactive metals are metals that, when heated to elevated temperatures, react with the oxygen and nitrogen. The heat of welding raises the temperature of the weld and adjacent base material above the reaction temperature. Reactive metals are zirconium, titanium, and beryllium.
As a welder starting to learn the trade you will not be welding on these metals, however it is important to know that they exist because these metals are used and welded on in Washington State. Due to the increased cost of the base materials and their use in critical applications, most welding will be performed with automatic processes. Does your program offer classes on robots? Welding processes are automated with robotics in many industries. If you are interested in robotics, look into your school’s course offerings to see if an introductory class to robotics you might like is offered in a mechatronics program.
Development of welding reactive metals
Reactive metals are just that, metals that react when welding. These metals react with the gasses in the atmosphere at elevated temperatures in a negative way leading to contamination of your weld and/or heavy oxidation of the nearby base materials. To avoid this contamination, special care is needed in applying protective shielding gasses.
If welding reactive metals requires more preparation and more care when welding, why weld them? The material properties of these metals are needed for the applications of aerospace, nuclear, and other demanding in-service environments where the extra cost of fabrication is required.
Basics of welding reactive metals
All three reactive metals are welded. Beryllium is a dangerous metal if inhaled and should not be used in fabrications unless adequate safety precautions are taken.
Due to the reactive nature of these metals, cleanliness and the application of inert shielding gasses are even more important than stainless steel welding. If you have welded on low carbon steel and then switched to stainless steel, then you know the importance of cleanliness and shielding gas when welding. Reactive metals are another step above stainless steel in terms of both cleanliness and shielding gasses.
GTAW is used to weld zirconium and titanium. GMAW can be used to weld titanium. Other processes that are beyond the scope of this text are also used, such as laser beam welding (LBW). When GTAW and GMAW are used to weld titanium, argon is normally used. Helium and mixtures of argon and helium can be used but the price of helium has increased significantly in the 2020s resulting in its decreased use. As with all welding, but especially more expensive metals, welders are encouraged to test their machine settings on a scrap piece of material prior to production welding. This is especially important with reactive metals to help ensure quality welds.
Due to the low thermal conductivity of titanium, you will notice that the weld pool will be larger than with metals that more easily move heat into the base material. Larger gas nozzles with higher flows are used to compensate for these larger weld pools. Chill bars may also be used to help with heat dissipation.
For GTAW of titanium it is important for the welder to keep the filler metal covered in shielding gas while it is hot, otherwise the filler metal will become contaminated by the atmosphere. For production welding out of position or of more complex shaped fabrications, it is important to protect the weld pool from air drafts with additional pieces of material to block air flows such as using baffles.
In some cases a welding box or chamber may need to be used when welding reactive metals. Less so for titanium, but it may become a must for complex shapes that would be difficult to ensure shielding gas coverage. Common welding defects for titanium include porosity and cracks which, of the many causes, can be attributed to bad shielding gas coverage. This chamber essentially submerges the weldment in shielding gas.
Uses of reactive metals in industry today
Titanium is used in the aerospace industry for its strength to weight ratio and corrosion resistance. The X-3 Stiletto aircraft was the first aircraft with major titanium airframe components and was built in 1953. The plane was intended for Mach 2 speeds but had underpowered engines which limited it to Mach 1 speeds.
The X-3 represents the first major use of titanium for airplanes but it was not the last. The SR-71 Blackbird “airframes were built almost entirely of titanium and other exotic alloys to withstand the heat generated by sustained high-speed flight” (NASA, 2017). The plane was capable of Mach 3 speeds for an hour. Many planes since then have titanium components due to their desirable mechanical properties. Boeing’s 787 uses titanium for its lighter weight to improve fuel efficiency.
Titanium also has desirable anti-ballistic properties. Due to the limited availability of certain grades of titanium, these specialty alloys are mostly used for high performance aircraft. However, it is also used for ballistic armor plating. The two ballistic test plates below show the test results and holes in an effort to develop armor plating for ground vehicles.
Titanium is also used in high end bicycle frames. Figure 21.12 shows a cracked bicycle frame on a model bicycle that was recalled for safety reasons. Cracks on any weldment that is subjected to cyclical motion such as vibration from riding on worn road surfaces can speed up crack propagation.
The failure in the titanium bicycle frame in Figure 21.12 goes through the weld and its HAZ. It is highly likely that the crack started in the HAZ and spread from there. Welds on bicycle frames are typically performed using GTAW.
Zirconium is used for nuclear fuel cladding. Cladding is the metal tubing that contains ceramic uranium fuel pellets (not shown). These tubes are about 12 feet long and are arranged into fuel bundles such as the one shown in Figure 21.13 below. These fuel rods are built by sliding the ceramic pellets into the zirconium rods, and then welding the end caps.
GTAW is used, however it is an automated process due to the large number of high quality welds required. Each commercial reactor core in the United States contains approximately 52,000 of these fuel rods, each of which has circumferential welds at the top and bottom of the rod. About one-third of these rods are replaced every 18 to 24 months in what is called a fuel outage. This means each refueling campaign consists of about 35,000 circumferential welds on the fuel rods alone.
Beryllium is used for its superior mechanical properties for special applications. The James Webb Telescope, which has been returning amazing pictures of deep space not seen before, was fabricated with Beryllium due to its stiffness at low temperatures. When operating in space, the telescope experiences temperatures of about -415 °F.
Beryllium is used in many common applications due to it being “stronger than steel and lighter than aluminum” (OSHA, n.d.). It also has a high melting point, and excellent thermal conductivity and thermal stability. The department of labor lists the following uses for beryllium:
|
Industry |
Industry Uses |
|---|---|
|
Aerospace |
Aircraft braking systems, engines, satellites, space telescopes |
|
Automotive |
Anti-lock brake systems, ignition |
|
Ceramic Manufacturing |
Rocket covers, semiconductor chips |
|
Defense |
Components for nuclear weapons, missile parts, guidance systems, optical systems |
|
Dental Labs |
Alloys in crowns, bridges, and dental plates |
|
Electronics |
X-rays, computer parts, telecommunication parts, automotive parts |
|
Medicine |
Laser devices, electro-medical devices, X-ray windows |
|
Nuclear Energy |
Heat shields, reactors |
|
Sporting Goods |
Golf clubs, bicycles |
|
Telecommunications |
Optical systems, wireless base stations |
Note. Common Beryllium Uses by Industry from Beryllium – Overview by OSHA (n.d.), U.S. Department of Labor.
Beryllium is a health hazard as mentioned towards the beginning of this chapter. Any fabrication activities need to follow all applicable safety precautions to help prevent severe damage to your health.
Attributions
- Figure 21.10: X-3: First Use of Titanium in Major Airframe Components by National Aeronautics and Space Administration in the Public Domain; United States government work
- Figure 21.11: SR-71 Takeoff with Afterburner Showing Shock Diamonds in Exhaust by National Aeronautics and Space Administration in the Public Domain; United States government work
- Figure 21.12: Ballistic Tests of P/M Ti © Oak Ridge National Laboratory, U.S. Dept. of Energy Used with permission. Courtesy of Oak Ridge National Laboratory, U.S. Dept. of Energy. ORNL Security & Privacy Notice
- Figure 21.13: CPSC, CF Roark Welding & Engineering Announce Recall of Bicycle Frames by U.S. Consumer Product Safety Commision in the Public Domain; United States government work
- Figure 21.14: Fuel rods in a nuclear reactor are mainly made of zirconium alloys. These long metal tubes contain pellets of fissionable material, typically uranium oxide pellets. © International Atomic Energy Agency Used with permission. Courtesy of the International Atomic Energy Agency. IAEA Terms of Use
- Figure 21.15: Into the Looking Glass For Webb Telescope Tests by The National Aeronautics and Space Administration in the Public Domain; United States government work
These metals react with the gasses in the atmosphere at elevated temperatures in a negative way leading to contamination of your weld and/or heavy oxidation of the nearby base materials.
The measure of strength of a material as compared to how heavy it is.