Metal Additive Manufacturing Conference - MAMC 2022

NiTi based shape memory alloys (SMA) gained importance in the aerospace industry due to their unique shape recovery properties. Regardless of the great demand, the fabrication of SMAs is rather complex. For instance, forging and machining are limited due to the high strength and reactivity of NiTi alloys. Recently, additive manufacturing (AM) was disrupted as a feasible solution to mitigate these problems related to conventional fabrication methods. Most of the reported AM techniques for NiTi based alloys involve laser in powder-bed fusion. These techniques have achieved considerable success regarding shape complexity and elimination or reduction of secondary post-fabrication operations. However, these technologies have some limitations, such as built shape size and issues regarding interstitial contamination. In this context, wire-based electron beam additive manufacturing (w-EBAM) has shown capable of overcoming or mitigating such drawbacks. W-EBAM uses wire as feedstock and electron beam as an energy source, fabricating medium-to-large near net shape parts in a vacuum chamber. If compared to the current powder-bed fusion, the use of wire allows for more efficient use of feedstock, the electron beam leads to low energy losses, and the vacuum atmosphere hinders built contamination. Therefore, w-EBAM has gained momentum increasingly achieving more acceptance for industrial applications. We have newly demonstrated the w-EBAM feasibility on NiTi SMA. This work aims to evaluate how w-EBAM manufacturing parameters affect the functional properties of a Ni-rich NiTi alloy. Design of experiments and statistical analysis were used to support the understanding of the relationships between process parameters and structural stability, microstructure and transformation temperatures. Finally, post-manufacturing heat treatment was applied. A further enhancement of w-EBAM specimen functional properties was demonstrated through mechanical testing.