Shape memory alloys based on Cu are cost-effective candidates for high-temperature applications. Generally, they are produced by conventional metallurgical routes and subjected to a thermo-mechanical treatment to adjust the microstructure and the resulting martensitic transformation. The latter is primarily governed by microstructural characteristics like ordering of the austenite/martensite, lattice defects, presence of additional phases and grain size.
In this work, we process two shape memory alloys, viz. Cu-11.85Al-3.2Ni-3Mn and Cu-11.35Al-3.2Ni-3Mn-0.5Zr, by selective laser melting (SLM) and investigate the microstructure, phase formation and transformation behaviour. After optimization of the SLM parameters, samples with a high relative density can be obtained by this additive manufacturing technique. The resulting, fully martensitic samples (β’) are then compared with specimens prepared by melt quenching such as suction casting and spray forming. Especially the role of Zr and the cooling rate in refining the grain size and stimulating the formation of second phases is addressed. The dissolution of Zr in the martensite/austenite and the morphology of the second phase is a function of the cooling rate. Hence, the microstructure critically depends on the thermal history of the alloys and annealing/ageing treatments significantly alter the grain size and distribution of the second phase. The mechanical properties of all specimens were determined in tension as well as compression and were found to exhibit a pronounced dependence on the microstructural details.
Selective laser melting proves to be an interesting tool not only to prepare specimens with intricate geometries but to also tailor microstructures and with it the transformation behaviour of Cu-based shape memory alloys.