Study On Interficial Bonding Mechanism And Corrosion Behavior Of TiB₂/Ni Composites

Nickel has high melting point and high strength.TiB₂ has the property of high melting point,hardness,modulus and perfect thermal stability and is a kind of ideal reinforcement material.TiB₂/Ni composite with high melting point and the strength is higher than that of the matrix can be achieved by fabricating particle reinforced composites using nickel and little content of TiB₂ particles in micron scale.So far,particle reinforced Ni matrix composites have wide application prospects in chemical,shipbuilding industries.In this paper,TiB₂/Ni composites with different TiB₂ content were fabricated by combining the method of SPS and hot rolled.High energy ball milling was used to mix TiB₂ particles with Ni particles uniformly.Spark plasma sintering?SPS?was used to prepare TiB₂/Ni composites and the mechanism of interface reaction was also analysed.TiB₂/Ni composites was also processed by hot rolled method.The microstructure and mechanical properties of hot rolled TiB₂/Ni composites was analysed.By the experiment of electrochemical corrosion test,the corrosion resistance of SPS-ed and hot rolled TiB₂/Ni composites were compared and studied.Besides,the mechanism of corrosion was also investigated.After mixing powder with high energy ball milling process,the higher the content of TiB₂ particles,the smaller the grain size of the nickel matrix in the TiB₂/Ni composite powder.During sintering,the temperature of the interface between TiB₂/Ni is much higher than that of the ceramic particles.In the sintered TiB₂/Ni composites,the interface between nickel matrix and TiB₂particles is well bonded,and the element transition in interface zone is gentle.By using the high resolution transmission electron microscope,it is concluded that the thermal mismatch between the matrix and the enhanced phase leads to a certain of density dislocation around the matrix around the TiB₂particles.From the chemical reaction thermodynamics point of view,the Gibbs free energy of the product of Ni₃Ti and Ni₃B reaction is the least,and the reaction is most likely to occur in the TiB₂/Ni interface reaction system.The hot rolling process is applied to the hot deformation of sintered TiB₂/Ni composites,so as to provide references for the preparation of TiB₂/Ni composite plates.It is found that under the action of rolling force,the microcracks and pores in composite materials are reduced,the particle distribution is more homogeneous and the density of materials is improved.TiB₂particles hinder the growth of matrix grains during thermal deformation,which results in the broadening of the diffraction peaks of nickel.After rolling,the?200?crystal plane is the preferred orientation crystal plane,and the texture coefficient of this crystal plane is the largest in the Ti B₂/Ni composite containing 3vol.%TiB₂ particles.The nanoindentation test shows that the elastic recovery performance of the matrix is higher than that of the interface.In the process of hot rolling,the hardness,modulus of elasticity and dislocation density of the region near the interface between TiB₂ and Ni particle are greater than that far from the interface between TiB₂ and Ni particle,due to the hindering effect of TiB₂ particles on the plastic deformation of the matrix.When TiB₂ particles are added to 3vol.%,the mechanical properties of TiB₂/Ni composites are optimal and the tensile strength is 30%higher than that of pure nickel.The mechanism of strengthening is mainly from Orowan theory,dislocation theory and Load-transfer theory.After rolling,the interfacial bonding of TiB₂/Ni is improved,and there is no interfacial debonding phenomenon.The tensile fracture modes of TiB₂/Ni composites are all ductile fracture.According to the results of electrochemical corrosion test,The corrosion current density of the pure nickel sample is the lowest?2.6?A/cm²?and the polarization potential is the maximum?-0.703V?.When the added TiB2 ceramic particles are increased to 5vol.%,the corrosion current density increases to?4.5?A/cm²?and the corrosion electromotive force is reduced to?-0.752V?.By observing the microstructure of the electrochemical corrosion on the surface of TiB₂/Ni composites,the number of pitting pits on the surface of the TiB₂/Ni composites is increasing with the increase of the content of the TiB₂ particles,and the corrosion resistance of the composites is reduced.