Improved microstructure and mechanical properties for Sn58Bi solder alloy by addition of Ni-coated carbon nanotubes

Ni-coated Carbon Nanotubes (Ni-CNTs) with weight percentages of 0%, 0.05%, 0.1% and 0.2% were incorporated into Sn58Bi solder alloy. The microstructure and mechanical properties of composite solders were investigated. Experimental results and finite-element simulation show that the tensile strength of solder slabs and joints is improved by the CNT bridging effect and load transfer. The fracture modes of solder joints and slabs change from ductile to brittle fracture. The creep behaviors of solders are improved significantly compared to those of the pristine samples because of the strengthening effect of Ni-CNTs. Hardness transformation is ascribed to the creep, which makes a large contribution to the plastic deformation during indentation process. Finite-element simulation indicates that the Ni3Sn4 and CNTs play the main role in the process of nanoindentation deformation. Besides, the mechanical properties and microstructure are declined when the content of Ni-CNTs exceeds 0.05%.