Investigation Of Diffusion Behavior And Mechanical Properties Of Ni-Zn And Ti-Zn Systems

Hot-dip galvanizing,an economical and effective method of steel corrosion resistance,is widely employed in various fields of modern industrial production and construction.However,the coating of pure Zn has many challenges,such as thick plating,easy peeling,rough surface and insufficient corrosion resistance.Some studies have shown that the addition of appropriate amounts of titanium(Ti)or nickel(Ni)to the zinc bath can effectively optimize the coating structure and enhance the corrosion resistance.The diffusion behavior of the elements and the formation of intermetallic compounds(IMCs)during the dipping process will affect the microstructure,properties and service time of the coating.Therefore,it is important to study the diffusion behavior and properties of IMCs in Ni-Zn and Ti-Zn systems.In this paper,the diffusion behavior and the mechanical properties of Ni-Zn and Ti-Zn systems were investigated using a diffusion couple method,which is given below:Ni-Zn binary diffusion couple and Ni-?(Ni₂Zn₁₁)incremental diffusion couple were prepared and annealed in the temperature range 598-673 K at different time.Three IMCs,?₁(Ni Zn),?(Ni₂Zn₁₁)and?(Ni₃Zn₂₂)were observed by elctron probe microanalysis(EPMA).The square of the thickness of the formed IMCs increases linearly with increasing annealing time,which indicates that the growth process of reaction zone is dominated by volume diffusion.The growth constants,integrated diffusion coefficient,growth activation energy and diffusion activation energies of?and?,which evaluated based on thickness of the phases,reaction temperature and annealing time,indicate that the order of nucleation of three phases in diffusion zone was?<?<?₁.The Young's modulus and hardness of the three phases were evaluated from the displacement-loading curve by nanoindenter testing.The Young's modulus and hardness of the IMCs increased firstly and then decreased with the increasing of Zn concentration,where?has the highest Young's modulus(183.3 GPa)and highest hardness(6.05GPa).The tendency of Young's modulus which calculated by first-principles calculation varying with the composition of Zn is consistent with that of experiments.Ti-Zn diffusion couples were annealed for a series of time at temperature between 573 K and 648 K.Four IMCs,Ti Zn₃,Ti Zn₅,Ti₃Zn₂₂ and Ti Zn₁₆ have been observed in the Ti-Zn diffusion zones.The square of the thickness of the formed IMCs linearly increases with annealing time,indicating a diffusion-control mechanism.The crystal structures of the four IMCs were investigated by electron backscatter diffraction(EBSD),which were consistent with the crystal parameter in the literature.The growth constants,interdiffusion coefficients,the growth activation energies and diffusion activation energies of four IMCs were calculated,which indicated Ti Zn₃ has the shortest nucleation time and the fastedt growth rate.The Young's modulus and hardness of the IMCs were obtained from the load versus displacement graph by nanoindenter testing.The Young's modulus of the four IMCs increased consistently with increasing Zn concentration,and the hardness first increased and then decreased.The highest Young's modulus was found for Ti Zn₁₆(145.36 GPa)and the highest hardness was found for Ti Zn₅(5.86GPa).