Study On Microstructure And Mechanical Properties Of NiTiNbFe Alloy

Most intermetallic compounds have high strength,but their application is limited due to their high brittleness.In recent years,it has been found that Ni Ti-based alloys(as intermetallic compounds)have good plasticity and are expected to be used as a new structural material in the aerospace field.However,a disadvantage of the Ni Ti-based alloy is insufficient strength.It has been reported that the microalloying method can effectively improve the strength of the Ni Ti-based alloy.In this paper,Ni_xTi_yNb_zFe_walloy wire is prepared by adjusting the design of alloying elements,melting under vacuum,forging,wire drawing and annealing at different temperature.The microstructure and chemical composition distribution of the alloy are detected by electron microscopy and three-dimensional atom probe.And in-situ tensile synchrotron radiation high-energy X-rays are used to investigate the stress(strain)induced martensitic transformation and plastic deformation behaviorby.It is found that as the annealing temperature increases,the grain size of Ni_xTi_yNb_zFe_w alloy wire increases,the tensile strength decreases,and the plastic elongation increases.Ni_xTi_yNb_zFe_w alloy wire anneals at 280°C for 10 min consists of columnar nanocrystals with an average size of 200 nm×50 nm×500 nm,and has a texture along the axial direction of the wire.In particular,it is firstly found that there are smaller scale(5-7 nm)chemical composition fluctuations inside the grains by use of three-dimensional atom probe tomography.The study also find that Ni_xTi_yNb_zFe_w alloy wire annealed at 280°C for 10 min has a tensile strength of 2.3 GPa at room temperature and an elongation of 14.7%.The performance is superior to that of high-strength metals reported by Nature and PNAS in recent years.In-situ tensile synchrotron radiation high-energy X-ray results show that during the stretching process,the wire sample undergoes dislocation slip deformation,accompanied by partial stress(strain)induced martensite transformation,and martensite transformation occurs in the macroscopic initial elastic deformation phase of the sample;when the sample is broken,its lattice(B2 crystal structure)strain is as high as 2.5%.We initially believe that the high strength of the sample may be mainly derived from the fine grain strengthening,and strengthening of martensite transformation regions,which are small size and uniform distributed.The high elongation may be related to the stress(strain)induced martensitic transformation plasticization of the martensite transformation.