Fabrication And Characterization Of NiTi/NiTi-Nb Alloys

The excellent mechanical properties of NiTi alloys,such as unique shape memory effect,superelasticity,as well as good biocompatibility,excellent corrosion resistance,low elastic modulus and good ductility,make it an ideal choice for the biomedical,aerospace and intelligent materials field,and other fields with a wide range of practical applications.However,NiTi alloy with itself and dissimilar material connection problems NiTi alloy can only have a simple geometry,thus limiting the NiTi alloy more widely used.For this reason,resistance welding and laser welding are proposed by scholars,but these methods are not widely used due to the fact that welding makes the joint parts easy to produce brittle second phase and large area heat-affected zone,at the same time need a large amount of solder.In 2007,Grummon proposed NiTi-Nb pseudobinary eutectic reaction,the use of Nb as NiTi alloy melting point depressant,so that high temperature conditions in the Nb and NiTi full fusion solidification,the NiTi wire to form a strong metallurgical bonding between the connection.The region has high strength,good ductility and superelasticity,corrosion resistance and biocompatibility.In this paper,NiTi / NiTi-Nb alloy was fabricated by heating niobium and NiTi wires in a high-temperature argon atmosphere furnace at 1185 ℃ for 6min.The microstructures of NiTi wires and Nb foils and element and phase distribution were observed by scanning electron microscopy(EDS),energy dispersive spectroscopy(EDS),and mechanical properties are inverstigated by nanoindentation tests and cyclic tensile tests.The results show that there are 4 diffusion layers,including Nb foil,NiTi-Nb eutectic region,pre-eutectic NiTi region and NiTi matrix at the junction of NiTi wire and Nb foil.In addition,a martensite phase was found inside the NiTi matrix.In the NiTi-Nb eutectic diffusion layer,niobium is inhomogeneous distributed,forming a rod-like Nb-rich phase,facetted Ti-rich phase and stripe-like or equiaxed NiTi-Nb eutectic structure.The strength of NiTi matrix is lower than that of melting zone,and the deformation recovery of NiTi matrix is 53% higher than that of melting zone,35.A large number of dislocations,stripe-like martensite and twin martensite appear in the fusion zone after tension deformation.In addition,also present martensite and austenite phase interwoven structure.The experimental study on the microstructure and mechanical properties of interface interface between NiTi and Nb will help to understand the advantages of using Nb as the NiTi alloy connection material,provide theoretical support for preparation of NiTi lattice materials,and promote NiTi alloy more extensive application.