Preparation And Properties Of Plasma Sprayed TiB₂-Ni Coating

TiB2 has excellent properties such as high hardness,high elastic modulus and good chemical stability.It is expected to replace WC and Cr3C2 materials as a new wear-resistant and corrosion-resistant material.In this paper,60wt.%TiB2-40Ni composite powder prepared by coating method was used as plasma spray feeding powder,and TiB2-Ni composite coating was deposited on titanium and 45#steel substrate.Phase and microstructure of the powder and coating were characterized by XRD,SEM and EDS etc..The effects of plasma spray parameters on the structure and properties of the as-sprayed coating were investigated,such as microhardness,roughness and porosity.The tribological behavior and electrochemical corrosion performance of the as-sprayed coating were investigated by wear tester and electrochemical workstation.The results show:The powder exhibits a core-shell structure of Ni-coated/semi-coated TiB2 with an average particle size of 28.68?m and a phase composition of TiB₂,Ni and a small amount of C.The TiB2-Ni composite coating has a layered structure.The Ni and TiB2 particles are uniformly distributed and have good bonding with the substrate.The phase composition of the as-sprayed coating are TiB2,Ni and a small amount of Ni20Ti3B6,and Ni4N;the microhardness of the coating is up to 1249.49±341.8 Hv_0.2,surface roughness is 9¹1?m,respectively.The process parameters were optimized based on the wear test of as-sprayed coating.When the Ar/H2 flow rate 40/8 L/min,spraying power 45 kW,spraying distance110 mm,and the powder feeding rate 30 g/min,the as-sprayed coating has good wear resistance and its porosity is lower to about 5.48%.The wear experiments show that the friction conditions have a great influence on the wear resistance of the coating.When the friction pair is steel ball,the friction coefficient changes greatly at 1 N,and the friction coefficient remains unchanged when the load increases from 2 N to 8 N.As the speed increases,the friction coefficient does not change.When the friction pair is ceramic ball,the friction coefficient increases as the load increases,and decreases as the rotation speed increases.TiB2 exhibits a certain degree of ability of friction reducing,but its effect of friction reducing is different,which may be due to the poor fracture toughness of the coating.Comparing the wear tracks morphology and EDS of the two friction pairs,it is found that there are abrasive wear,oxidative wear and adhesive wear mechanism,but the wear track cracks prepared by ceramic ball is very obvious,and there is fatigue wear mechanism.Electrochemical corrosion experiments show that in 0.5mol/L H2SO4 solution,each coating?up to-0.28041 V?has higher self-corrosion potential than the 45#steel substrate?-0.41109 V?,indicating that the coating has better acid corrosion resistance;in 3.5wt.%NaCl solution,the coating with porosity of 5.3%and 5.48%has higher self-corrosion potential than the 45#steel substrate.In the 1mol/L NaOH solution,the coating has a lower self-corrosion potential than the 45#steel substrate,indicating that the coating has poor alkali corrosion resistance.