Rapid solidification and advanced manufacturing of Cu-based shape memory alloys with complex geometries
Synthesis and Properties of Functional Materials
Mechanical Properties of Metallic Materials and their Microstructural Origins
Final Report Abstract
The following bullet lines summarize the most important scientific and non-scientific aspects of the collaboration with our Brazilian partners: • Cu-11.85Al-3.2Ni-3Mn and Cu-11.35Al-3.2Ni-3Mn-0.5Zr shape memory alloys were successfully prepared by selective laser melting (SLM). The samples are fully martensitic. • High-quality bulk samples and samples with complex shapes can be prepared in a relatively large processing window. • Precipitation of Cu2ZrAl in Cu-11.35Al-3.2Ni-3Mn-0.5Zr hampers and even suppresses the martensitic transformation based on its size and distribution. This behaviour can be used to switch on and off the shape memory effect in this alloy. A patent has been filed. • Zr does not act as grain refiner at relatively high quenching rates. On annealing, however, it pins the movement of the grain boundaries and suppresses grain growth. • The processing parameters (thermal history) determine the grain size and the ordering. The transformation temperatures can be adjusted within a window of about 30 °C. • The substrate plate temperature should not exceed 280 °C or pronounced gradients in the transformation temperatures arise along the building direction. Moreover, the eutectoid decomposition into the equilibrium phases commences. • Selective laser remelting (SLRM) with high energy inputs leads to higher transformation temperatures. Simultaneously, the pseudoelastic strain can be increased to about 4%, which is unusually high and unmatched for polycrystalline Cu-based shape memory alloys. • Additively manufactured Cu-11.85Al-3.2Ni-3Mn and Cu-11.35Al-3.2Ni-3Mn-0.5Zr exhibit both a one-way and two-way shape memory effect and their performance is comparable to conventionally processed specimens. This renders time- and cost-intensive thermos-mechanical post-treatments unnecessary. • All samples have a fine-grained microstructure and do not fail in a brittle manner. Despite the residual porosity of the SLM samples, they even exhibit a larger ductility than their cast or sprayformed counterparts. • Oligocrystalline microstructures could be prepared by annealing Ti-35Nb-5T-7Zr (TNTZ) tubes, which were prepared by SLM. The formation of this unique microstructure seems to be related to a bimodal grain size distribution, which is obtained by SLM. Oligocrystalline microstructures cannot be obtained by annealing as-cast microstructures. • The oligocrystalline microstructure of Ti-35Nb-5T-7Zr exhibits an improved pseudoelastic behaviour. • The experiments conducted within this project raised additional problems and questions, which should be tackled in the future. Moreover, it would be interesting to extend our approach to other shape memory alloy systems. We are convinced that 4D printing bears great potential and, consequently, will gain in importance and significance in the near future. This project has contributed to a better understanding of the underlying processing-microstructure-properties relationships in additively manufactured Cu-based shape memory alloys.
Publications
- Influence of processing parameters on the fabrication of a Cu-Al-Ni-Mn shape-memory alloy by selective laser melting. Addit. Manuf. 11, 23 (2016)
T. Gustmann, U. Kühn, A. Neves, P. Gargarella, C.S. Kiminami, C. Bolfarini, J. Eckert and S. Pauly
(See online at https://doi.org/10.1016/j.addma.2016.04.003) - Properties of Cu-based shape-memory alloys prepared by selective laser melting. Shape Memory Superelast. 3, 24 (2017)
T. Gustmann, J.M. dos Santos, P. Gargarella, U. Kühn, J. Van Humbeeck and S. Pauly
(See online at https://doi.org/10.1007/s40830-016-0088-6) - Microstructural characterization of a laser remelted Cu-based shape memory alloy. Mater. Res. (Ibero-American Journal of Materials) 21, e20171044 (2018)
M. Romero da Silva, P. Gargarella, W. Wolf, T. Gustmann, C.S. Kiminami, S. Pauly, J. Eckert and C. Bolfarini
(See online at https://doi.org/10.1590/1980-5373-MR-2017-1044) - Selective laser remelting of an additively manufactured Cu-Al-Ni-Mn shape-memory alloy. Mater. Design 153, 129 (2018)
T. Gustmann, H. Schwab, U. Kühn and S. Pauly
(See online at https://doi.org/10.1016/j.matdes.2018.05.010)
