Plasma Arc Welding of Titanium alloys

요약:

Welding of titanium can be relatively complex since at high temperatures the material can be very reactive and depending on the inclusion of impurities, they can also have a negative effect on overall weld integrity.
Key advantages of PAW compared to TIG include, lower heat inputs, high welding speeds and high metallurgical quality levels.

For successful welding of titanium, some factors need to be considered. Titanium is extremely reactive in temperatures exceeding 500-650°C. It reacts with elements in impurities or air such as C, O, N, and H. These elements strengthen titanium but small amounts also impair ductility and toughness of titanium joints. The effects of the heating and cooling cycles involved in welding processes on the mechanical properties of the alloys and the specific alloy composition also need to be considered.

Titanium alloys are readily joined with several common fusion welding processes such as tungsten inert gas welding (TIG), plasma arc welding (PAW), electron beam welding (EBW), and laser beam welding (EBW). Fusion welding processes can be characterized generally by the heat-source intensity.

The most common welding techniques to joint titanium and its alloys are Gas Metal Arc Welding (GMAW), such as Metal Inert Gas (MIG); Plasma Arc Welding (PAW); Laser Beam Welding (LBW); and Electron Beam Welding (EBW). The first three methods fall in the arc welding category with high heat input and low power density of heat source, while the last two techniques belong to the high-energy beam group.

Plasma arc welding (PAW) is an arc welding process which uses a constricted arc between a non-consumable electrode and the workpiece (transferred arc mode) or between the electrode and the nozzle (non-transferred arc mode). Two separate gas flows are used in PAW; plasma gas which flows through the orifice and becomes ionized and shielding gas which flows through the outer nozzle. Usually these gases are the same. Helium, argon and their mixtures are used as shielding gases. Hydrogen and nitrogen may also be added in the mixture. PAW is essentially an extension of the TIG welding process and the differences between the processes are illustrated in Figure 1. TIG uses an open arc while in PAW, the electrode and arc are surrounded by a gas chamber. The plasma gas in the orifice gets heated and ionized which creates a narrow, constricted arc that provides excellent directional control and produces a very favorable depth-to width weld profile.



Figure 1: The plasma arc is confined in PAW which makes it straighter and more concentrated

PAW can be used in two distinct operating modes, the melt-in mode and the keyhole mode. At lower arc currents, the process resembles TIG and produces a similar weld pool. This melt-in mode is used for material thicknesses below 3 mm. At higher arc currents and plasma gas flow rate, the plasma column can displace the molten metal and form a keyhole. Keyhole mode welding is used for single pass butt welds on material thicknesses from 2.4 mm to 8 mm. Compared to laser welding and electron beam welding, keyhole PAW is more cost effective and more tolerant of joint preparation, though its energy is less dense and its keyhole is wider.

The advantages of PAW compared to TIG include:
• High welding speed: up to 5 times higher than conventional TIG
• Reliable arc ignition and concentrated stable arc with little sensitivity to arc length variation
• Lower heat input leading to smaller heat affected zone and little distortion
• Ability to perform keyhole welding and melt-in-mode welding with the same equipment
• Possibility to weld very thin materials (0.1 mm) and thick materials (8 mm) with a single pass without filler material
• High metallurgical quality in comparison to conventional TIG.

PAW can be used to weld the same materials as TIG. Keyhole plasma welding is extensively used to weld stainless steel pipes and tanks. In aerospace industry, PAW is used for airframe components, fuel vessels and gas turbine components. The greater capital cost and complexity of PAW equipment are why PAW has not become more common.


References

1. S. Tolvanen: Microstructure and mechanical properties of Ti-6Al-4V welds produced with different processes, ISSN 1652-8891 Technical report no 109/2016 Department of Materials and Manufacturing Technology Chalmers University of Technology SE-412 96 Gothenburg Sweden, Accessed AUG 2019;

2. J. M. Sánchez-Amaya, T. Pasang, M. R. Amaya-Vazquez, J. De Dios Lopez-Castro, C. Churiaque, Y. Tao, F. J. Botana Pedemonte: Microstructure and Mechanical Properties of Ti5553 Butt Welds Performed by LBW under Conduction Regime, Metals 2017, 7, 269; doi:10.3390/met7070269

3. T. Pasang, Y. Tao, O. Kamiya, Y. Miyano, G. Kudo: Research on Various Welding Methods on Aerospace Titanium Alloys, Collaboration between Akita University and AUT University, Accessed AUG 2019.

기술 자료 검색

검색할 어구를 입력하십시오:

검색 범위

본문
키워드

머릿글
요약

Total Materia는 용접용으로 적합한 다양한 국가와 규격 내 수천개의 재질에 대한 정보를 포함하고 있습니다.

재질의 화학적 조성, 기계적 특성, 물리적 특성, 탄소 등가 데이터와 용접용으로 재질 이용 시 필요한 정보 등의 전체적인 특성 정보들을 어디서든 검토하실 수 있습니다.

고급 검색을 이용하여, 검색 조건의 재질 리스트에서 '용접 필러 재료'를 선택합니다. 검색 범위 좀 더 줄이기를 원하신다면 국가/규격과 같은 다른 조건을 지정할 수 있습니다.

검색 버튼을 클릭합니다.


선택된 정보에 부합하는 일련의 재질이 검색됩니다.


결과 리스트에서 재질을 선택하시면, 일련의 규격 사양 소그룹이 나타납니다.

여기에서 선택한 재질의 특정 특성 데이터를 검토하실 수도 있고, 강력한 상호 참조 표를 이용하여 유사 재질이나 등가 재질을 검토하는 것 또한 가능합니다.


자세한 특성 데이터를 보시려면 특성 데이터 링크를 클릭하세요.


Total Materia 데이터베이스를 사용해 보실 수 있는 기회가 있습니다. 저희는 Total Materia 무료 체험을 통해 150,000명 이상의 사용자가 이용하고 있는 커뮤니티로 귀하를 초대합니다.