Investigation Of Chemical Mechanical Polishing For Pure Nickel And Nickel Alloy

Pure nickel and nickel alloy are commonly used metal materials in industry,with the advantages of fatigue resistance,oxidation resistance,high temperature resistance and corrosion resistance,etc.They are widely used in aerospace,petrochemical and electronic fields.With the development of science and technology,the surface roughness of pure nickel and nickel alloy in microelectronic devices,optical precision molds and other products is required to reach sub-nano level,and surface defects such as scratches should be avoided.Currently,the ultra-precision machining technology of pure nickel and nickel alloy includes mechanical polishing,chemical polishing,electropolishing,etc.,but the processing surface quality of these technologies is low,and easy to cause environmental pollution,so this paper adopts chemical mechanical polishing(CMP)technology to solve the above problems.The traditional metal CMP mainly uses nitric acid,hydrofluoric acid and other corrosive and toxic chemical reagents,which is harmful to the environment and operators.Therefore,this paper takes nickel alloy C2000 and pure nickel N4 as research objects,and achieves ultra-smooth and low-damage processing of metal surface by preparing environmentally friendly polishing liquid.Based on the material properties of nickel alloy C2000,a two-step polishing process is proposed.The environmentally friendly polishing slurry contains hydrogen peroxide,silica sol,and the pH value is adjusted by mixing malic acid,sodium hydroxide and deionized water.This slurry effectively avoids the harm to the environment and operators.The process parameters were optimized through the experiment to improve the material removal rate.Finally,the ultra-smooth and low-damage surface of nickel alloy was prepared.Within the evaluation range of 50×70?m~2,the measured optimal surface roughness Ra value was up to0.440 nm,which was lower than the existing results of nickel alloy polishing.In order to study the CMP mechanism of nickel alloy,the chemical action of polishing fluid composition was studied by X-ray photoelectron spectroscopy(XPS),electrochemical and infrared spectroscopy,and the mechanism model of nickel alloy polishing process was proposed.During the CMP process,it has experienced the surface oxidation,oxidation layer decomposition,complex formation and mechanical removal of the surface reaction layer by abrasive particles.Among them,hydrogen peroxide mainly plays an oxidation role,and malic acid dissolves the oxide film to produce nickel ions by ionizing hydrogen ions,and then partial protonated or deprotonated malic acid will coordinate with nickel ions to form complexes,effectively improving the material removal rate and surface quality.On the basis of nickel alloy CMP,the two-step polishing process is also adopted to process pure nickel.The applicability of the nickel alloy polishing solution was compared.The optimized polishing solution contained hydrogen peroxide and nano-aluminum oxide,and the pH value was adjusted by using the same malic acid and other mixed solutions.Finally,the surface roughness of 0.869 nm was obtained,and there were no obvious defects on the surface.Based on the mechanism analysis of nickel alloy CMP,the surface chemical effect of polishing slurry composition on pure nickel was analyzed by XPS,and the machining mechanism of pure nickel CMP was summarized.