Interfacial characterization and cracking behavior of NiTi/AlSi12 bimetallic structures fabricated by multi-material laser additive manufacturing

NiTi/AlSi12 bimetallic structures were fabricated by multi-material laser additive manufacturing (MM-LAM). The effects of different process parameters on the interface characteristics and microhardness of NiTi/AlSi12 bimetallic structures were studied. The interfacial layer thickness increases from 198.14 μm to 302.18 μm with the increase of laser energy density . A larger hatch space can alleviate the interfacial cracks . The larger hatch space can generate less continuous intermetallic compounds (IMCs), which leads to fewer cracks in the molten pool. Compared with the microhardness of NiTi and AlSi12 regions, the microhardness of the interface was the highest, with a maximum microhardness range of 650 HV–1000 HV. The interface composition, crack behavior, and crack formation mechanism of NiTi/AlSi12 bimetallic structures were analyzed. The interface mainly included the molten pool boundary region and the multiphase mixing region. In the interface, the molten pool boundary near the NiTi region was enriched with many nano-scale Ti Si grains. The multiphase mixing region in the interface was mainly dominated by many Ti Al, Ni Al IMCs and a small amount of Ti Si intermetallic silicides (IMSs). Cracks were initiated in the multiphase mixing region of the interface, where there were a large number of brittle IMCs and IMSs, with high residual stresses. The transgranular and intergranular propagation occurred along the multiphase mixing region, NiTi grains and grain boundaries in the interface. The crack is arrested in the multiphase mixing region rich in Al 3 Ni 2 . There was lower residual stress in this region. Moreover, it is calculated that Al 3 Ni 2 had a low degree of anisotropy compared to other phases in the NiTi/AlSi12 interface, making it difficult to continue inducing micro-cracks. Therefore, the Al 3 Ni 2 -enriched region acts as a barrier to crack propagation . • Adjusting the hatch space of laser beam can alleviate the interface cracking. • Analyzing the crack initiation and propagation behavior of NiTi/AlSi12 bimetallic structures interface. • Elaboration of crack arrest mechanism in the multiphase mixing region rich in Al 3 Ni 2 .