Study On Surface Damage Of Chemical Mechanical Polishing Cemented Carbide

Cemented carbide is a kind of material with excellent mechanical properties,and it is widely used in cutting,drilling and other fields.The surface quality and service life of cemented carbide can be improved effectively by chemical mechanical polishing.But the surface damage in the process of machining has an important influence on the stability and service life of cemented carbide.Therefore,it is necessary to study the formation mechanism of surface damage in the chemical mechanical polishing of cemented carbide,and to explore how to reduce the surface damage of cemented carbide in chemical mechanical polishing.This paper takes YG8 carbide blade as the research object,and studies the surface damage of the cemented carbide by chemical mechanical polishing,and completes the following work:(1)The mechanical effect of abrasive particles in chemical mechanical polishing cemented carbide was studied by discrete element simulation.The simulation results show that the increase of polishing pressure will lead to the increase of indentation depth and local stress,and cause more serious surface damage layer.The surface damage will be serious when the speed of disc throwing increases.However,when the speed of disc throwing reaches a certain value(70rpm),the surface damage will be reduced due to the decrease of contact time between abrasive particles and workpiece.When the polishing pressure is 21 N and the speed is 70 rpm,the better surface quality can be obtained.At this time,the number of cracks is less,the depth of the median crack is small,and the material removal rate can meet the requirements.Then,the correctness of the simulation results is verified by single factor simulation experiment.(2)The chemical effect of chemical mechanical polishing cemented carbide was studied by experiments.Firstly,the corrosion agent of carbide blade CMP is optimized by single factor experiment.The experimental results show that potassium permanganate and hydrogen peroxide are more suitable for the corrosion agent of cemented carbide CMP,which not only has high material removal rate but also good surface quality.Then,the chemical effect of potassium permanganate and hydrogen peroxide on the CMP of cemented carbide is studied through corrosion experiment.The experimental results show that a new corrosion spot was formed on the surface of cemented carbide by potassium permanganate.Due to the corrosion and precipitation of binder Co,hydrogen peroxide will produce small corrosion pits on the surface of cemented carbide.(3)The change of surface damage in the chemical mechanical polishing cemented carbide was studied by experiments.Firstly,CMP surface damage experiments were carried out with potassium permanganate and hydrogen peroxide as corrosion agents respectively.The results show that when potassium permanganate is used as the corrosion agent,the corrosion spots with lower hardness are formed on the surface of cemented carbide blades,and deep scratches and corrosion pits are formed under the action of abrasive particles.When hydrogen peroxide is used as the corrosion agent,the Co precipitate of the bonding phase is caused by the oxidation of hydrogen peroxide,and corrosion pits and shallow scratches are formed on the surface of cemented carbide blade.Then,the formation mechanism of corrosion pits is studied experimentally.It is found that the formation of corrosion pits can be divided into four stages:the formation of original pits and scratches,the increase of area and quantity of corrosion pits formed by chemical and mechanical interaction,the increase of area and quantity of scratch and corrosion pits,and the removal of surface materials.It is also found that when the mechanical action of abrasive particles is reduced,the corrosion pit can be reduced.