Fabricating TiNiCu Ternary Shape Memory Alloy by Directed Energy Deposition via Elemental Metal Powders

Abstract

In this paper, a TiNiCu shape memory alloy single-wall structure was fabricated by the directed energy deposition technique with a mixture of elemental Ti, Ni, and Cu powders following the atomic percentage of Ti50Ni45Cu5 to fully utilize the material flexibility of the additive manufacturing process to develop ternary shape memory alloys. The chemical composition, phase, and material properties at multiple locations along the build direction were studied, using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Vickers hardness testing, tensile testing, and differential scanning calorimetry. The location-dependent compositions of martensitic TiNi and austenitic TiNi phases, mechanical properties, and functional properties were investigated in detail. Variations were found in atomic compositions of Ti, Ni, and Cu elements along the build direction due to the complex interaction between elemental powders and laser processing. Good correlations were present among the chemical composition, phase constituent, hardness, and feature of phase transformation temperatures at various locations. The ultimate tensile strength of the as-deposited TiNiCu alloy is comparable with the previously reported additively manufactured TiNi binary alloys. By adding Cu, a much lower thermal hysteresis was achieved, which shows good feasibility of fabricating ternary TiNiCu shape memory alloys, using elemental powders in the directed energy deposition to adjust the thermal hysteresis.

TiNi-Based Bi-Metallic Shape-Memory Alloy by Laser-Directed Energy Deposition

“…The average atomic composition of the five heights measured by EDS is Ti (52.1 ± 0.5) Ni (43.3 ± 0.9) Cu (4.6 ± 0.4). The fluctuation of Ti, Ni, and Cu compositions among the five heights is much lower than the former work that deposited Ti–45at.%Ni–5at.%Cu alloy on the titanium substrates [ 29 ]. The dilution from the TiNi substrate in this work has less influence on the as-deposited section.…”

“…The elemental powder mixture was used as an alternative form of raw materials other than pre-alloyed powders [ 26 , 27 ]. The SMA with an as-mixed atomic composition of Ti–45at.%Ni–5at.%Cu was fabricated by elemental powders in [ 28 , 29 ] with titanium as the substrate material. In this work, more details will be studied on using elemental powder DED to build Ti–Ni–Cu/TiNi bi-metallic alloys.…”

Synthesizing Ti–Ni Alloy Composite Coating on Ti–6Al–4V Surface from Laser Surface Modification

“…The average hardness values of those tested regions of SL and SM are at the level of 700~750 HV0.2, and SL is slightly higher than SM. Meanwhile, the average hardness value of SH is lower and steady at around 600 HV0.2 since the processing parameters of SH result in a higher composition of ductile TiNi and lower composition of hard Ti 2 Ni [28][29][30]. All substrate zones have a hardness of ~380 HV0.2, which shows the hardness level of Ti-6Al-4V [21].…”