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Welding-titaniumand titanium alloys:SOLUTIONS with Effective, Powerful Advice
Welding-titanium is still considered a quite uncommon process because titanium applications cover only specialized niches, due mostly to high metal cost. But its unique properties make it the preferred selection when considering the lifetime cost of the structure. Welding titanium is feasible and rewarding and should be welcomed as a winnable challenge. It requires however proper understanding of requirements and some adaptation of equipment and techniques. If you are not yet familiar with Welding-titanium and its alloys, maybe that, by reading on here, you can get some confidence. Then consider if it would make sense to specialize in this particular but affordable new field: less competition, more profitable results... Welding-titanium and titanium alloys must be performed with special precautions because these materials are very reactive to contamination from atmosphere gases. But Welding-titanium is possible if these alloys are shielded from air in a very effective way either in vacuum or in an enclosure containing an inert gas.
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Some basic properties which make titanium alloys the natural choice for a specific range of applications are low density (about 60% relative to steel) with appreciable strength at intermediate temperatures. This characteristic, called specific strength at certain temperatures, makes titanium the preferred selection for low pressure compressor stages of gas turbines. Titanium alloys are also favored for their corrosion resistance in the marine environment and in chemical processing operations. Therefore commercial applications are numerous due to their intrinsic corrosion resistance to a variety of agents present in chemical plants and to seawater for marine applications. Find here a short overview of Welding-titanium alloys.
What types?... Besides unalloyed or commercial titanium, different classes of titanium alloys are described. Reference is made to metallurgical types called alpha, alpha-beta and beta. These indicate the main phases present in the microstructure, as seen under an optical metallographic microscope on the surface of suitably prepared, ground, polished and etched specimens. Titanium alpha alloys can be strengthened only by cold work (called also strain hardening) (not by heat treatment), are weldable in annealed condition and retain their strength at high temperature. Titanium alpha-beta alloys can be welded in certain conditions but with limited weld ductility or heat affected zone ductility, however they can be strengthened by heat treatment. Welding-titanium of beta alloys is performed in the annealed condition, and then, if necessary, they can be cold worked and heat treated to preserve ductility in the weld. How do we know which type?... Different alloys have different compositions and are given different names. They are then grouped according to their prevailing microstructure. But before Welding-titanium one must also check the condition, meaning the mechanical properties, produced by cold work or by the last heat treatment that was performed before welding. An Article on "Titanium Microstructure" was published in Practical Welding Letter issue No. 22 for June 2005. An Article on Titanium Clad Steel was published (11) in the Issue 23 of Practical Welding Letter for July 2005. Click on PWL#023 to read it. An Article on Welding Titanium to Stainless Steel was published (3) in the Issue 33 of Practical Welding Letter for May 2006. To read it click on PWL#033. An Article on Filler Metal for Brazing Titanium Alloys was published (4) in Issue 46 of Practical Welding Letter for June 2007. An Article on Surface Treatments for Titanium was published (7) in Issue 81 of Practical Welding Letter for May 2010. An Article on Aerospace Materials Competition was published (2) in Issue 123 of Practical Welding Letter for November 2013. An Article on Brazing Titanium was published (3) in Issue 151 of Practical Welding Letter for March 2016. An Article on Minimizing Alpha Case was published (11) in Issue 152 of Practical Welding Letter for April 2016. An Article on Large Scale Additive Manufacturing was published (2) in Issue 153 of Practical Welding Letter for May 2016.
To receive each month at no cost our publication Practical Welding Letter please subscribe. Welding-titanium and titanium alloys can be performed by FRICTION WELDING to themselves and to other materials, with notable success in that most or all of the contaminated metal is expelled in the flash material ring subsequently removed. RESISTANCE WELDING is used for Welding-titanium and titanium alloys, in sheet metal or extruded thin sections, much as it is for other materials. The fact that the material has high electrical resistivity and low thermal conductivity helps in obtaining good welds while limiting the electric current to relatively normal values. Resistance Welding-titanium needs schedules developed taking into account these particular characteristics. Magnetic Pulse Welding, a cold welding process, can be used without special problems to join elements of suitable geometry. Tip!: Although titanium is a highly reactive material, which should be protected from air contamination when hot, there is no need to employ inert gas for cold welding or when spot or seam welding, but the metal should always be clean and the electrodes must be thoroughly water cooled. Which Fusion welding?... Oxyacetylene welding is NOT applicable to Welding-titanium or titanium alloys. Fusion Welding with Arc Welding Processes, is used for Welding-titanium Alloys, considered one of the easiest materials to weld. Most used are GTAW (Gas Tungsten Arc Welding)(Tig), Direct Current Straight Polarity, Electrode Negative, and PAW (Plasma Arc Welding), with argon or mixtures of argon and helium. Power supply should have high frequency facility for arc initiation without contact to avoid contaminating the weld with tungsten bits. GMAW (Gas Metal Arc Welding)(Mig) of titanium, although being performed successfully, requires special attentions, like Direct Current Reverse Polarity, Electrode Positive, and is considered for joints at least 13 mm (0.5 in) thick. Tip!:Fabricators wishing to specialize in Welding-titanium should set up a training and familiarization period to understand the requirements of gas shielding and the risks of contamination and porosity in the weld. Titanium alloys usually welded are considered having good weldability, except that due to their extreme reactivity, unusual precautions must be taken to shield the molten pool and the hot metal from contact with air. This is done best in a special enclosure (glove box) filled with inert gas, but is also possible with special equipment that covers the hot metal with a continuous flow of inert gas. Always clean the metal with utmost care, and chemically pickle or at least stainless steel wire brush. Tip!: Always remember that Chlorinated Fluoro Carbon (CFC) solvents are forbidden for cleaning titanium and titanium alloys because they produce embrittlement. Use instead only Acetone or Methyl Ethyl Ketone (MEK).
Only chamber welding?... Tip!: In the past it was considered that Tig Welding-titanium could be performed only in chambers, equipped with glove ports and viewing ports, filled with argon. However with accumulating experience and especially for welding of large structures, it was concluded that this is not an absolute need, provided sufficient trailing inert gas is continuously provided by suitable equipment. An Article on Trailing Shields for Welding Titanium was published (11) in Issue 130 of Practical Welding Letter for June 2014.
For Titanium welding the conventional thoriated Tungsten electrodes known as EWTh-1 and EWTh-2 are used (with 1 or 2% Thorium respectively), ground to a point. PAW (Plasma Arc Welding) with keyhole technique permits high productivity welding of thick plates at higher depths and at higher speeds (although slower than those used in high energy processes), with less porosity problems when compared to GTAW. A version, called micro-plasma, employing lower currents, is used for welding light gauges. Filler materials used for Welding-titanium alloys are described in
ANSI/AWS A5.16/A5.16M:2007 See also:
ANSI/AWS D17.1/D17.1M:2010-AMD1
ANSI/AWS G2.4/G2.4M:2007
A section on Titanium is found in: An Article on Selection of Titanium Alloy Filler Metals has been published in our Practical Welding Letter No. 07, issue of March 2004. You can read it by clicking on PWL#007.
An Article titled Update: Titanium Specification Revised on the changes recently introduced in AWS specification A5.16 is quoted in Section 5 (Online Press) in the June 2004 Issue No. 10 of Practical Welding Letter. Click on PWL#010 to see the Reference. An Article on joining Niobium to Titanium was published in the November 2004 of Practical Welding Letter Issue No. 15, in Section 4 - Filler Metal. To read the Article click on PWL#015. An Article on Gas Metal Arc Welding of Titanium was published (3) in Issue 58 of Practical Welding Letter for June 2008. An Article on Superplasticity was published (2) in Issue 82 of Practical Welding Letter for June 2010. Click on PWL#082 to read it. An Invitation to a Titanium Welding Workshop was published (11) in Issue 105 of Practical Welding Letter for May 2012. Although the workshop is due on June 26, 2012, readers may enjoy other benefits even past this date. Click on our new page on Welding Nitinol. To receive free of charge all the issues of Practical Welding Letter as they are published, please subscribe. Welding-titanium should be followed by stress relieving in order to prevent cracks, and also to avoid stress corrosion cracking in service. A Table showing Stress-relieving times and temperatures for selected Titanium alloys can be found at page 786 of the ASM Handbook Volume 6 (1993). ASM Handbook : Welding, Brazing & Soldering
[Note: The new Volume 6A of the ASM Handbook, deals with Fundamentals of processes. It does not include a Chapter on Welding Titanium] Arc Welding-titanium using fluxes have been attempted variously in experimental settings, but with limited success and at present they are not considered an interesting industrial application. High Energy Welding High Energy Welding-titanium Processes are widely used. Laser Beam Welding needs proper means of inert gas protection for the molten pool and the hot joint. In Electron Beam Welding, the contamination problems are taken care of in a vacuum chamber. Tip!: A thin titanium foil is sometimes interposed between surfaces of materials difficult to weld by Electron Beam, like alloy steels, where it may provide a helpful contribution to weld ductility. NEW RESOURCES
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