Additive Manufacturing of Binary Ni–Ti Shape Memory Alloys Using Electron Beam Powder Bed Fusion: Functional Reversibility Through Minor Alloy Modification and Carbide Formation

KROOß, P.; LAUHOFF, C.; GUSTMANN, T.; GEMMING, T.; SOBRERO, C.; EWALD, F.; BRENNE, F.; AROLD, T.; NEMATOLAHI, M.; ELAHINIA, M.; THIELSCH, J.; HUFENBACH, J.; NIENDORF, T.

Shape Memory and Superelasticity

Springer

Año: 2022

2199-384X

Shape memory alloys (SMAs), such as Ni–Ti, are promising candidates for actuation and damping applications. Although processing of Ni–Ti bulk materials is challenging, well-established processing routes (i.e. casting, forging, wire drawing, laser cutting) enabledapplication in several niche applications, e.g. in the medical sector. Additive manufacturing, also referred to as 4D printing in this case, is known to be highly interesting for the fabrication of SMAs in order to produce near-netshaped actuators and dampers. The present study investigated the impact of electron beam powder bed fusion (PBF-EB/M) on the functional properties of C-rich Ni50.9- Ti49.1 alloy. The results revealed a significant loss of Ni during PBF-EB/M processing. Process microstructure property relationships are discussed in view of the applied master alloy and powder processing route, i.e. vacuuminduction-melting inert gas atomization (VIGA). Relatively high amounts of TiC, being already present in the master alloy and powder feedstock, are finely dispersed in thematrix upon PBF-EB/M. This leads to a local change in the chemical composition (depletion of Ti) and a pronounced shift of the transformation temperatures. Despite the high TiC content, superelastic testing revealed a good shape recovery and, thus, a negligible degradation in both, the asbuilt and the heat-treated state.