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Obtaining a reliable NiTi–Ti6Al4V(TC4) heterogeneous alloy component exhibiting excellent strength and elasticity via integrating distinct material benefits can provide design flexibility in multifunctional device fabrication. However, the fabrication of this materials couple is challenging due to the development of excessive Ti 2 Ni intermetallic compound. Inspired by the bioheterogeneous layered structure, Nb interlayer was applied for the wire arc additive manufacturing (WAAM) of NiTi and TC4 to restrict the mixing of alloying elements on both sides. However, the strength of NiTi–Nb-TC4 alloy component was limited by pure Nb characteristics when the NiTi and TC4 was completely separated by the unmolten Nb interlayer. In this work, the tensile strength perpendicular to the interface of NiTi–Nb-TC4 alloy component was enhanced to introduce appropriate amount Ni and Ti in Nb interlayer by adjusting the composite WAAM process at the expense of Ti 2 Ni. Microstructure evolution, composition change and mechanical properties of composite WAAM NiTi–Nb-TC4 alloy component were investigated. It was shown that the compression strength and fracture strain perpendicular to the interface of WAAM NiTi–Nb-TC4 sample was 1549.0 ± 17 MPa and 22.3 ± 8 %, and the compressive strength can reach 63.6 % and 94.5 % of WAAM NiTi alloy and TC4 alloy, respectively. The composite WAAM NiTi–Nb-TC4 sample maintained 65.3 % recovery rate after ten compression cycles, which confirmed that partial superelasticity was maintained in the WAAM NiTi–Nb-TC4 multilayer structure. This fact further proved that WAAM can be successfully applied to deposit shape memory/superelastic alloys. The use of the Nb interlayer enhanced the tensile strength perpendicular to the interface to 460.7 ± 16 MPa. The ultimate tensile strength perpendicular to the interface of composite WAAM NiTi–Nb-TC4 sample can reach 72.0 % and 60.0 % of WAAM NiTi alloy and TC4 alloy, respectively. The formation of NiTi, TiNb and β-Nb phases in Nb interlayer and the network distribution of Ti 2 Ni and TiNb phases explained the improved mechanical performance of the composite WAAM NiTi–Nb-TC4 alloy component. • Integrated additive manufacturing NiTi-TC4 using composite WAAM with Nb interlayer. • Uncover microstructural evolutions and mechanical properties of composite WAAM NiTi–Nb-TC4 heterogeneous alloy component. • The introduction of Ni and Ti in the Nb interlayer improved the strength and toughness of the interlayer. • Provide first-hand observations on NiTi-TC4 WAAM and new insights for dissimilar metal additive manufacturing. [ABSTRACT FROM AUTHOR]

The performance improvement of wire arc additive manufacturing component relies on structural innovation and tailored printing, and the naturally optimized structure can provide inspiration for design and manufacturing. In this work, a layered TC4/Nb multi-material alloy component inspired by the biological structure of the Crysomallon squamiferum shell was designed and fabricated by multi-wire arc additive manufacturing (MWAAM). The interfacial reaction, phase composition, microstructure evolution, crystal growth, mechanical properties and crack propagation of MWAAM-processed bionic heterogeneous TC4/Nb multi-material alloy component were investigated by EDS, SEM, EBSD and mechanical tester. The results indicated that the good metallurgical bond was formed between the different layers of MWAAM TC4/Nb multi-material alloy sample. The Ti/Nb multi-material alloy component was mainly composed of α-Ti, β-Ti and (Nb, Ti) solid solution phases. The morphology of phase underwent a continuous transformation process from TC4 layer to G1 layer with the increase of Nb content: Lamellar α + β →Thin lamellar α + Short rod α + β → Acicular α + β → Thin acicular α + β. In addition, the grain size of TC4/Nb multi material alloy component from TC4 layer to G2 layer gradually from 3.534 μm decreased to 2.904 μm with the increase of Nb content. The microhardness of TC4/Nb multi-material alloy from TC4 layer to G2 layer ranged from 404.04 HV to 245.23 HV. The relatively high compression strength and ultimate tensile strength of TC4/Nb multi-material alloy sample were 2162.64 ± 26 MPa and 663.39 MPa, and corresponding strain were 31.99% and 17.77%, respectively. The excellent mechanical behavior was mainly contributed to the excellent combination of gradient transition of grain size and microstructure evolution between layers. Crack propagation was mainly dominated by crack deflection and multistage cracking during the tensile test process. The strength of TC4 layer was the highest than G1 and G2 layer in the TC4/Nb multi-material alloy component. [ABSTRACT FROM AUTHOR]

TC4/NiTi multi-materials structure components have been successfully fabricated via multi-wire arc additive manufacturing (MWAAM). Here we show the interface characteristics and mechanical properties of TC4/NiTi multi-materials structure component under bionic gradient interlayer build strategy. The results indicated that MWAAM TC4/NiTi gradient heterogeneous alloy with ultimate compression strength (1533.33 ± 26 MPa) was obtained. The excellent compression behaviour was mainly contributed to the excellent transition of gradient region indicated by EBSD analysis showing fine grain sizes and smaller difference Schmidt factor values. The phase composition from TC4 region to NiTi region had evolved with the increasing of NiTi content as follows: α-Ti + β-Ti → α-Ti + NiTi 2 → NiTi 2 → NiTi 2 + NiTi → NiTi + Ni 3 Ti. The microhardness of the gradient heterogeneous alloy ranged from 310 ± 8 HV to 230 ± 11 HV, and the highest hardness value was 669.6 ± 12 HV in region B due to the precipitation of NiTi 2 strengthening phase. The ultimate fracture stress and strain of sample were 1533.33 ± 26 MPa and 28.3 ± 6% respectively. The irrecoverable strain of MWAAM TC4/NiTi gradient heterogeneous alloy gradually approached 2.75% during 10 load/unload cycles of compression test. [ABSTRACT FROM AUTHOR]