Investigation And Property Analysis Of Electric Field Assisted Boriding Process On Pure Nickel Substrates

Although nickel has superior high temperature strength and oxidation resistance,the properties of low hardness results the poor high temperature abrasion and erosion wear resistance for nickel materials.The high temperature oxidation resistance and wear resistance for pure nickel materials can be improved greatly by forming a dense boronized layer on the surface of nickel.The boriding layer with low thickness and much of loose or holes on the surface fabricated by traditional process would be difficult to meet the application requirements.In this paper,the traditional formula of boronizing agent is improved by using?-Al₂O₃ powder instead of Si C as the filler in solid boriding agent.The technology,structure and properties of solid powder boronizing and the solid boronizing assisted by AC electric field on pure nickel substrate were studied.And the process of low temperature boronizing assisted by AC electric field on pure nickel substrate was studied.The conclusion is shown as follows:Boronizing on pure nickel substrates with?-Al₂O₃ powder instead of Si C as filler avoids the formation of loose layer which composed of Ni₂Si et al phases.The thickness of boriding layer at the condition of 950?+6h is 23?m.The diffusion activation energy of solid powder boronizing on pure nickel substrate is 205.3kj/mol.The boriding layer is composed of Ni₃B and Ni₄B₃ phases.The holes and looseness exist beneath the surface of boriding layer.A thicker boriding layer can be obtained on pure nickel substrate by AC electric field assisted solid boronizing,and the porosity and looseness in the boriding layer structure can be significantly reduced.Adding a small amount of graphite powder or activated carbon to the boronizing agent can significantly increase the thickness of boriding layer and promote the formation of Ni B and Ni₄B₃ phases in the boriding layer.The phases of boriding layer are Ni₃B,Ni₂B,Ni₄B₃ and Ni B.With the increase of the AC frequency for AC electric field assisted solid boronizing process,the thickness of the infiltration layer first increases and then decreases slightly.The optimal frequency is 200 Hz.Under the boriding process of 200Hz+100V and 800?+4h,the boridzing layer with thickness of 75?m can be obtained.The thickness of the infiltration layer increases rapidly with the increase of the auxiliary AC voltage,and the increase of the thickness slows down when the voltage is over 100V.The external AC power supply produces alternating electric field in the boriding tank,which plays the role of electric field agitation,which can promote the chemical reaction of boronizing agent.The higher the voltage is,the more active B atoms will be produced in the boriding agent reaction,and the higher the frequency is,the stronger the ion oscillation is and the more active B atoms are produced.The increase of voltage and frequency can increase the boron potential in boriding agent tank,promoting the formation of Ni B and Ni₄B₃ phases in boriding layer,and increasing the thickness of boriding layer.After boronizing at 200Hz+130V and 650?+6h,the boriding layer with the thickness of41?m can be obtained on Ni substrate.The holes and looseness in the boriding layer cannot be observed by metallurgical microscope.