Effect Of Tac Addition On The Corrosion Behaviors Of Ni-Based Composite Coating Fabricated By Laser Cladding On Titanium Substrate

Titanium,as a novel structural material,has been widely used in a variety of industrial fields such as the aerophane,navigation,medical apparatus because of the excellent mechanical property(low density,high strength-to-weight ratio,well-down toughness),the corrosion resistance and the biocompatibility.The reason why the titanium alloy exhibits an excellent corrosion resistance is that a Spontaneous compact TiO₂ oxidation film is formed on the surface of titanium alloy.However,the TiO₂oxidation film is easy to be destroyed in the condition of the dynamic wear and the Cl-rich environment,which will seriously reduce the service life and limit the application of titanium alloy.In this study,the Ti₂Ni/TiNi dual-phase matrix coating was fabricated on the Ti6Al4V by laser cladding the mixture of the Ni-based alloy powders,which was used to improve the corrosion resistance of the coatings.In addition,through adding the TaC particles,the electrochemical stability of the passive film formed on the surface of the coating can be promoted.The results of the effect of TaC addition on the corrosion behavior of TiNi/Ti₂Ni dual-phase matrix composite coating indicated that the phase constituents of the coating was TiNi,Ti₂Ni,TiB,Ti B₂,TiC and TaC.By the analyses of the XRD results and SEM morphology,the matrix phases of the coating were TiNi and Ti₂Ni and the reinforcement phases were TiB,TiB₂,TiC and Ta C.Meanwhile,the corrosion potentials of the coatings were increased from-0.639 V to-0.348 V accompanied with the increase in the breakdown potentials(0.003 V to 0.605 V)and the decline in the passive current density(10E-5.4 Acm^-2 to 10E-6.9 Acm^-2)during the increasing in the content of TaC addition.In addition,there was no breakdown of the passive film observed in the coating when the content of TaC addition was beyond 20 wt.%.From the results above,it exhibited that the TaC addition made a positive effect on the corrosion resistance of the coating,especially in the compactness and electrochemical stability of the passive film.The passive film was composed of TiO₂,Al₂O₃,SiO₂,NiO,Ni₂O₃,CrO₃,Cr₂O₃ and Ta₂O₅ in which the last oxide demonstrated the most excellent stability.The results of the corrosion behavior of Ti Ni/Ti₂Ni dual-phase matrix composite coating in the condition of Cl-rich environment demonstrated that the composite coatings showed the higher corrosion potential and the lower passive current density when comparing with the titanium substrate.Meanwhile,the content of Ta₂O₅was increased during the increase in the content of TaC addition.Ta₂O₅ is immune to the attack from the chloride solution because of its glassy chemical properties.Therefore,TaC addition can improve the corrosion resistance of the coating and promote the electrochemical stability and compactness of the passive film.