Rapid solidification and advanced manufacturing of Cu-based shape memory alloys with complex geometries

• Applicant: Professor Dr.-Ing. Jürgen Eckert
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Metal-Cutting and Abrasive Manufacturing Engineering
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 223525886

• Final Report Year: 2016

Final Report Abstract

In the following we merely list the most important findings resulting from our project. Almost all of the objectives and aims of the project proposal were accomplished: The shape memory alloys Cu-11.85Al-3.2Ni-3Mn and Cu-11.35Al-3.2Ni-3Mn-0.5Zr were successfully prepared by selective laser melting. • A process map was created for the single-track experiments to identify the optimum SLM parameters. • Single-track experiments do not necessarily provide reliable information regarding the optimum processing parameters for bulk samples. • Compact samples with relative densities near 99% could be obtained. • We could reveal a clear link between the distribution of porosity and the scanning strategy. • Next to simple geometries like cubes we could prepare complex structures. These comprise lattices with an isotropic Young’s modulus or auxetic structures. • The grain size depends on the processing route and the alloy. Zr has a refining effect only up to a critical cooling rate. Above this cooling rate there is no difference in the grain size between Cu-11.85Al-3.2Ni-3Mn and Cu-11.35Al-3.2Ni-3Mn-0.5Zr. • Annealing treatments were performed to modify the microstructure and monitored how the martensitic transformation changes. • The various samples were thermally cycled and the reversibility of the martensitic transformation was analysed. • The presence of Zr results in the formation of the Y-phase. The microstructures resulting from suction casting or SLM are metastable and are altered during thermal cycling or an isothermal anneal. • The applied cooling rate determines whether Zr is either dissolved or forms second phase precipitates. • The presence of the Y-phase most likely causes a discontinuous martensitic transformation. • The martensitic transformation is shifted significantly by such small amounts of Zr like 0.5 wt.%. • There appears to be a grain-size effect on the martensitic transformation for the present alloys. It is difficult to be precisely revealed because the microstructures do not have uniform grain size distributions. • Despite the residual porosity, the SLM samples exhibit promising mechanical properties. Even in tension the plasticity exceeds 6% and the intrinsic brittleness of coarse-grained Cu-based shape memory alloys can be effectively overcome. • The mechanical properties of the lattices have been measured. • A vibrant scientific exchange with partner from Brazil could be established. • The work raised additional problems and questions, which have formed the motivation for submitting a renewal proposal. Since the DFG has agreed on providing the required funds, the work on Cu-based shape memory alloys is going to continue.

Publications

• Atomization and selective laser melting of a Cu-Al-Ni-Mn shape memory alloy. Mater. Sci. Forum 802, 343 (2015)
  E. Mazzer, C.S. Kiminami, P. Gargarella, R.D. Cava, L.A. Basilio, C. Bolfarini. W.J. Botta, J. Eckert, T. Gustmann and S. Pauly
  
• Phase formation, thermal stability and mechanical properties of a Cu-Al-Ni-Mn shape memory alloy prepared by selective laser melting. Mater. Res. 18, 35 (2015).
  P. Gargarella, C.S. Kiminami, E.M. Mazzer, R.D. Cava, L.A. Basilio, C. Bolfarini, W. Botta, J. Eckert, T. Gustmann and S. Pauly
  
• Fabrication of Cu-Al-Ni-Mn shape-memory parts by selective laser melting. Proceedings of the Fraunhofer Direct Digital Manufacturing Conference (DDMC) conference 2016, Berlin (ISBN 978-3-8396-1001-5)
  T. Gustmann, A. Neves, U. Kühn, P. Gargarella, C.S. Kiminami, C. Bolfarini, J. Eckert and S. Pauly
  
• Influence of processing parameters on the fabrication of a Cu-Al-Ni-Mn shape-memory alloy by selective laser melting. Add. Manufact. 11, 23 (2016)
  T. Gustmann, A. Neves, U. Kühn, P. Gargarella, C.S. Kiminami, C. Bolfarini, J. Eckert and S. Pauly
  
• Laser surface remelting of a Cu-Al-Ni-Mn shape memory alloy. Mater. Sci. Eng. A 661, 61 (2016)
  M.R. da Silva, P. Gargarella, T. Gustmann, W.J. Botta, C.S. Kiminami, J. Eckert, S. Pauly and C. Bolfarini