Study On The Effect Of Oxidizer On Chemical Mechanical Polishing Performance Of GCr15 Steel

As one of the most typical bearing steels,GCr15 steel has been widely used in the manufacture of some key parts in the machinery industry due to its outstanding performance,such as the production of bearings.Bearings are extensive used in aerospace,high-speed railway,medical facilities and robotics etc.Since the service life and performance of bearings are greatly affected by the final surface finish,it is necessarily required to have a high surface quality and shape accuracy to obtain excellent work performance and a long service life.Although the output of bearings in China is relatively high,but bearings with excellent quality and high requirement still rely on large quantities of imports.Therefore,the research on the manufacture of high-quality bearings,for the development of the construction machinery industry in China,has greatly promoting effect.At present,chemical mechanical polishing technology can achieve sub-nanometer surface roughness,has been gradually used to improve the surface quality and process precision of bearing steel.Oxidant plays a vital important role in chemical mechanical polishing of GCr15 steel.Consequently,in this paper,the effect law and mechanism of oxidants on the GCr15 steel polishing performance is fully studied.Firstly,using the chemical mechanical polishing technology,combined with the static etching experiments,electrochemical experiments,XPS detection techniques and other experimental methods,studied the effects of several commonly used oxidants on the polishing performance of GCr15 steel,and the oxidation ability of oxidants was compared,which provided reference for the subsequent selection of oxidants of GCr15 steel.Secondly,the mechanism of potassium persulfate based polishing slurries in the polishing process of GCr15 steel was revealed.Finally,according to the oxidation process of oxidant on the surface of GCr15 steel,the relevant mathematical model was derived,and the intrinsic relation between model coefficient and polishing performance was preliminarily discussed.The main highlights of this paper are as follows:(1)The effects of several commonly used oxidants on the polishing performance of GCr15 steel was studied systematically.The influence of several common oxidants on the polishing of GCr15 steel was investigated,and the relationship between oxidation and polishing performance was studied.It was found that the material removal rate of GCr15 steel increased firstly and then decreased with the increase of the concentrations of hydrogen peroxide,potassium iodate,potassium periodate and iron nitrate.With the increase of potassium persulfate and ammonium persulfate concentrations,the removal rate was up to 1308 nm/min,and the surface roughness value was about 5.3 nm.Since the iron nitrate always has a low removal rate,and the solubility of potassium periodate is very low and the concentration range is narrow which limits the selectivity of other reagents,they are not suitable for the polishing of bearing steel.Potassium iodate and persulfate can be used as effective oxidants in bearing steel polishing.There are complex oxidation kinetics and chemical reactions between the oxidation ability and the polishing performance,thus experiments show that the standard reduction potential and electrochemical properties of the oxidant is not linearly related with oxidant performance of polishing,but can preliminary judge antioxidant oxidation ability in the polishing process,which is helpful for the selection of bearing steel polishing oxidant based on experimental data and provided some useful guidance.(2)The mechanism of action of potassium persulfate based polishing slurries on the polishing performance of GCr15 bearing steel was investigated.The effects of p H,potassium persulfate concentration and complexing agent on the chemical mechanical polishing performance of GCr15 steel were studied in turn,and the mechanism of action of potassium persulfate-based polishing solution was clarified.The experimental results show that the material removal rate MRR has no connection with p H,but the surface roughness R_a decreases with the increase of p H.At p H 8.0,with the increase of concentration of potassium persulfate,the MRR increases linearly with a slope of 48nm/min/m M,but due to the serious corrosion problems of persulfate,the surface quality of bearing steel gradually deteriorates,accompanied by black residue.This is a result of persulfate oxidation,leading to produce a large number of Fe²⁺and Fe³⁺.Meanwhile,large quantities of Fe²⁺and Fe³⁺react with OH^-to form the rough uneven surface of the Fe₃O₄film.After adding 80 m M ethylenediamine tetraacetic acid(EDTA),iron ions chelate with EDTA,and together with iron oxides form a dense protective composite surface film,which reduces R_a to 1.7 nm.Moreover,the surface of bearing steel is free of black residue,and a high-quality surface can be obtained finally.The research shows that persulfate based polishing slurries can achieve the nanometer surface finish of bearing steel under the condition of weak alkalinity,which has a good application prospect in the field of bearing steel polishing,and provides a new kind of oxidant for the polishing process of bearing steel.(3)The oxidant polishing model of GCr15 steel was established and the effect of correlation coefficient was discussed.The effects of oxidants,complexing agent and mechanical action on the removal rate of GCr15 steel were analyzed by decoupling,and the relevant mathematical model was established.Experimental data of hydrogen peroxide and potassium persulfate,two typical oxidants with different polishing rate trends,were selected for fitting.Fitting results showed that the chemical reaction rate constants k₁ and k₂,which determines the removal rate of GCr15 bearing steel and the reaction mechanism.The mathematical model of oxidant is similar to the actual trend of experimental data,which can more accurately describe the polishing process,and the trend of the fitted curve is corresponding to the mechanism of two kinds of antioxidants.The coefficients k₁ and k₂ are investigated by using the Arrhenius equation.k₁ and k₂ describes the ability of oxidants to interact with iron atoms to form effective molecular collisions in the polishing process,and determines the upper limit of the removal rate from the initial stage,from the point of view of molecular activation energy to obtain the essential reasons affecting the polishing rate.Through the further derivation and analysis of the correlation coefficient,it can be seen that the series of temperature difference experiments can essentially investigate the effect law of oxidizing capacity of oxidants in the process of GCr15 steel polishing.In summary,oxidants are indispensable and crucial in the process of chemical mechanical polishing of GCr15 steel.The research contents of this paper provides the experimental basis and theoretical reference for the selection of oxidants in the polishing of GCr15 steel to avoid the waste of resources.It also proposed to study the relationship between the oxidizing ability of oxidants and the polishing performance from the perspective of molecular dynamics,and provided a new oxidant that can be used for the polishing of GCr15 steel,high-quality bearing steel surfaces can be efficiently obtained.