The Influence Of Thermal Diffusion On The Interface Structure And Corrosion Resistance Of Cu/Ni/Ti

Titanium and its alloys are widely used as functional and structural materials in various fields for their excellent properties of low densities,high specific strength,better thermal stability and biocompatibility.However,the applications of TC4 alloy were limited by the low thermal conductivities and poor wear resistances,especially in the transportation of petrochemical pipelines.At present,Cu/Ni plating was used on the thread of titanium alloy tubing coupling to improve its wear resistance and anti-thread gluing capability.The thermal diffusion treatment of Cu/Ni/Ti structure caused metallurgical bonding between Cu/Ni coatings and the TC4 substrate through the diffusion of atoms,thus eliminating the generation of the internal stress and increasing the adhesion between coating and the substrate.The aim of this paper was to investigate the atomic diffusion behavior of Cu/Ni and Ni/Ti interface and then the effect on the microhardness and surface corrosion resistance of Cu/Ni/Ti structure.Morphology and composition of the Cu/Ni/Ti structure were investigated by scanning electron microscopy?SEM?,X-ray diffraction?XRD?and energy-dispersive spectroscopy?EDS?.Based on the Fick's law and Arrhenius-type equation,the model of interfacial diffusion was established to study the diffusion behavior of Cu/Ni and Ni/Ti interface after different thermal diffusion parameters.The diffusion coefficients and diffusion activation energy of Cu/Ni and Ni/Ti at the interfaces of Cu/Ni/Ti were also calculated.In addition,the influence of the Cu,Ni and Ti elements diffusion behavior on the microhardness and corrosion resistance of samples was studied by using micro-hardness instrument and electrochemical workstation.The results showed that the diffusion coefficients of Cu/Ni and Ni/Ti interface increased with the increase of heat diffusion temperature s and holding times,and formed??Cu,Ni?solid solution,Ni_xTi_y and Cu_x Ti_y intermetallic compounds.The presence of intermetallic compounds in the coating could enhance the micro-hardness values,and the highest micro-hardness value was seen for the specimens at the thermal diffusion of 700°C for3h.While with a further rise in thermal diffusion temperatures and holding times,the micro-hardness of coating decreases,due to the gather and grow of brittle phases caused grain coarsening.Corrosion resistance of Cu/Ni/Ti after corrosion in 3.5 wt.%NaCl solution was studied by electrochemistry tests.The polarization curves and electrochemical impedance spectroscopy?EIS?indicated that with the increase of thermal diffusion temperatures and holding times,the corrosion resistance of Cu/Ni/Ti appeared increased firstly and then decreased.The Cu/Ni/Ti heated at 700°C for 3h after corroded,the dense Cu₂O film,highly stable NiO and TiO oxide layer were formed during immersion in 3.5 wt.%NaCl,which obtained the best corrosion resistance.