Microstructure and mechanical properties of TC4/NiTi bionic gradient heterogeneous alloy prepared by multi-wire arc additive manufacturing

Abstract

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 + NiTi2 → NiTi2 → NiTi2 + NiTi → NiTi + Ni3Ti. 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 NiTi2 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.