Development of semifinished products with optimized damping properties based on pseudoelastic iron-based shape memory alloys

• Applicants: Dr.-Ing. Thomas Hassel; Professor Dr.-Ing. Hans Jürgen Maier; Professor Dr.-Ing. Thomas Niendorf
• Subject Area: Production Automation and Assembly Technology ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 401738767

• Final Report Year: 2023

Final Report Abstract

For the development of semi-finished products with good damping properties from iron-based shape memory alloys, the influence of industrial process routes and welding procedures on abnormal grain growth was investigated. In order to characterize the weldability of the FeMn34Al15Ni7.5 (at.%) alloy, experiments were carried out using MIG, TIG, electron beam and laser beam welding. It was found that the higher heat input and the associated higher γ-fraction resulted in crack-free joints for all parameters of TIG and MIG welding, while a narrower process window was determined for electron beam and laser beam welding. The experiment with different heat-treatments showed that even after solution annealing, grain growth is significantly influenced by the industrial process, resulting in single abnormally grown grains. The quenching behaviour and the associated formation of the low-temperature γ-phase were strongly affected by the sample size. While an oligocrystalline microstructure showing pseudoelasticity was obtained for miniature samples after cyclic heat-treatment, an increase in specimen size and the associated lower cooling rate led to increased γ-precipitation in the grain interior. This resulted in a loss of pseudoelasticity. The influence of welding on abnormal grain growth depends on the actual process used. For MIG and laser welding, the fusion line presents an impenetrable obstacle for grain growth, whereas for TIG and electron beam welded specimens, grain growth occurred across the fusion zone. Additionally, dissimilar welds of S355 and FeMn34Al15Ni7.5 (at.%) were performed. As a 50:50 mixture of the materials used is susceptible to both hardening and warm cracking, dissimilar filler metals were used to join square butt joints. The use of high chromium filler metals (1.4015, 1.4551) resulted in defectfree joints.

Publications

• Microstructural Investigation of a FeMnAlNi Shape Memory Alloy Processed by Tungsten Inert Gas Wire and Arc Additive Manufacturing. Metals, 12(10), 1731.
  Viebranz, Vincent Fabian; Hassel, Thomas & Maier, Hans Jürgen
  
• Welding characteristics and microstructure of an industrially processed Fe-Mn-Al-Ni shape memory alloy joined by tungsten inert gas welding. Welding in the World, 66(11), 2207-2216.
  Viebranz, Vincent Fabian; Hassel, Thomas; Niendorf, Thomas & Maier, Hans Jürgen
  
• Electron Beam Welding of Hot-Rolled Fe–Mn–Al–Ni Shape Memory Alloy Sheets. Shape Memory and Superelasticity, 9(2), 364-376.
  Bauer, A.; Wiegand, M.; Wicke, P.; Sommer, N.; Vollmer, M.; Böhm, S. & Niendorf, T.
  
• Structural and superelastic properties of Fe–Mn–Al–Ni shape memory alloy sheets produced on industrial process routes by hot rolling. Journal of Materials Research and Technology, 24, 6982-6991.
  Bauer, André; Vollmer, Malte; Viebranz, Vincent Fabian; Maier, Hans Jürgen & Niendorf, Thomas