Preparation And Performance Of Ni-boride Composite Coatings

Composite plating can play a great role in energy saving,material saving,high quality,high efficiency,environmental protection and sustainable development.This subject regards nickel as metal matrix with Zr B₂ particles and Boron iron nanoparticles as second phase particle,Ni-Zr B₂particle composite coating and Ni-boron iron particle composite coating were deposited onto parts made of No.45 steel.The influence of processing parameters on the microstructure,residual stresses,microhardness,corrosion resistance and wear resistance of the composites were studied.The main content is as follows.(1)In order to improve the hardness and corrosion resistance of the material surface.Ni-Zr B₂ particle composite coating on the surface of 45#steel was prepared by electroplating.We studied the effect of the contents of surfactant and Zr B₂ particles in the plating solution on the volume content of Zr B₂ particle in the coating.And the effect of the volume content of Zr B₂ particle in the coating on the structure,residual stresses,microhardness and corrosion resistance of the composite coating ware investigated.The survey results indicated that the co-deposition of Zr B₂particles in the coating can be promoted by adding a moderate amount of the cationic surfactant cetyltrimethylammonium bromide(CTAB)in the plating solution.However,the volume content of Zr B₂ particles in the composite coating has an upper limit.The addition of the appropriate amount of Zr B₂can change the preferential growth orientation of the nickel matrix grain of the coating and improved the hardness and corrosion resistance of composite coatings,but the residual tensile stress in the composite coating increases.When the content of Zr B₂ particles in the Ni-Zr B₂ composite coating was 9%,the friction coefficient and wear volume of the coating reached the minimum,respectively 0.5398 and 0.07 mg.Compared with the pure nickel coating,the wear volume of the composite coating was reduced by 46%.(2)The boron iron nanoparticles were prepared by simple chemical liquid phase reduction.The effects of the addition of ammonia and the percentage of Fe SO ₄ to Na BH₄on the particles morphologies,size,boron content and phase structures were studied.The results show that the nanoparticles prepared by chemical liquid phase reduction are amorphous and the particles are spherical.The decrease of the addition of ammonia and Fe SO₄/Na BH₄ molar ratio can inhibit the growth of boron iron nanoparticles.The decrease of Fe SO₄/Na BH₄ molar ratio can increase the content of boron element in boron iron nanoparticles.When Fe SO₄/Na BH₄ molar ratio is 1/6,the content of boron element in boron iron nanoparticles is as high as 8.50 wt.%(32.43 at.%).(3)Ni-boron iron particle composite coating on the surface of 45#steel was prepared by electroplating.The choice of bath was studied.In addition,the effects of the addition of boron iron nanoparticles,current density,liquid temperature and heat treatment on the morphology,microhardness,residual stress and corrosion resistance of the composite coatings were studied.The result of research shows that the boric acid in the Watt plating solution causes the boron iron nanoparticles to be deeply reunited in the plating solution.The boron iron nanoparticles are dispersible in the plating solution with trisodium citrate as p H buffer.boron iron nanoparticles content increases in plating solution,current density decreases and solution temperature are conducive to the composite coating surface roughness and the amount of boron iron nanoparticles in composite coating composite.However,the addition of boron iron nanoparticles in the plating solution has limited effect on the increase of boron iron nanoparticles in the composite coating.The addition of Boron iron nanoparticles can improve the microhardness of the composite coating,but the residual stress of the composite coating is increased and the corrosion resistance is declined.The crystal structure of amorphous boron iron nanoparticles change in 483?.There is metal intermetallic Fe₂B precipitation after heat treatment of 1 h at 600?.The cell structure of the composite coated surface of Ni-boron iron after heat treatment gradually decreased The Microhardness of Ni-boron iron composite coating first increase then decrease with the increase of heating temperature.When the heat treatment temperature of 300?,microhardness of the coating in slightly increased.When the heat treatment temperature of600?,the microhardness of the coating in significantly reduced.The heat treatment can not only reduce the residual stress of the composite coating,but also improve the corrosion resistance of the composite coating.