Microstructural and damping behaviour of NiTi-Cu shape memory alloys fabricated using cold metal transfer-based wire arc additive manufacturing

Abstract

Cold Metal Transfer (CMT)-based wire arc additive manufacturing (WAAM) has been proven to be a better method for fabricating shape memory alloys (SMA) for actuators with good dimensional accuracy. Although NiTiCu alloys have been fabricated using the WAAM route using multi-wire approaches, a pre-alloyed NiTiCu alloy has not yet been tested based on the CMT-WAAM-based process, allowing compositional stabilization and lower heat input. In this study, a ten-layer NiTiCu alloy with dimensions of (Formula presented) mm were deposited by the CMT-WAAM process. The microstructural evolution, morphology, mechanical, shape recovery, and damping properties of the top, middle, and bottom layers were investigated and compared. All three regions show a dominant peak of the B2 phase and (Formula presented), minor peaks B19’ phase. The bottom regions show fine equiaxed grain transitions into coarse grain with build height, whereas the top and middle regions show (Formula presented) coarse and fine dendritic structures, respectively. The tensile strength, elongation and microhardness increase from Top to bottom from 408 to 520 HV300 from 568 to 857 MPa and from 3.1% to 7.5%, respectively. The AD-NiTiCu alloy shows a decrease in recovery ratio (η[jls-end-space/]) from bottom to top, from 74% to 65.5% at 2% strain and 45–34% at 3% strain, with a rate of decay of η of 2.34% per loading-unloading cycle at 3% applied strain. Finally, the damping capacity increases from top to bottom, as indicated by tan δ, which varies from 0.004 to 0.007. Therefore, this research work provides insights into how the microstructural evolution influences the properties of the CMT-WAAM-based NiTiCu ternary alloy. © 2026 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license. http://creativecommons.org/licenses/by/4.0/