Studies On Ultrasonic Fine Atomization CMP Of TC4 Titanium Alloy

Because of its advantages of high specific strength,non-magnetic properties and excellent high-temperature mechanical properties,titanium alloy has been widely used in military electronic equipment,aerospace,medical instruments,micro-electronic equipment and machine control system（MEMS）and other high precision instruments,and is a very important engineering material.Titanium alloy is difficult to process materials,traditional processing is prone to titanium fire,crack and scratch defects,difficult to meet the surface quality requirements of MEMS parts and other high precision instruments.Chemical mechanical polishing is a popular ultra-precision machining method,which can efficiently achieve ultra-precision flattening of specimen surface.On this basis,ultrasonic fine atomization technology was introduced to improve the polishing liquid supply mode,and the polishing of TC4 titanium alloy was studied.The composition ratio and process parameters of polishing fluid were optimized by single factor test and orthogonal test,and the nano-level smooth titanium alloy surface was finally obtained.The CMP mechanism of titanium alloy was analyzed by combining electrochemical and XPS test.The specific work contents are as follows:（1）Through single factor test,this paper finally determined to use Si O₂ at 50 nm as abrasive,H₂O₂ as oxidant,citric acid as complexing agent,PEG-400 as surfactant,KOH and HNO₃ as p H regulator.According to the experimental results,the applicable range of each component concentration was preliminarily determined and its action mechanism was analyzed.（2）The orthogonal test was designed to optimize the content ratio of each component in the polishing solution,and the influence degree of each component on the atomization polishing effect of titanium alloy was explored.The results show that the concentration of Si O₂abrasive has the greatest influence on the polishing effect.The optimal proportion of each component of the polishing solution is as follows:Si O₂ abrasive mass fraction is 20 wt%,p H is 4,oxidizer mass fraction is 2 wt%,complexing agent mass fraction is 0.1 wt%and surfactant mass fraction is 1.0 wt%.（3）Single factor test and orthogonal test were designed to study and optimize the main process factors affecting the atomization polishing effect of titanium alloy,such as polishing pressure,polishing disc rotation speed and fog flow.According to the test results,the optimal process parameters were determined as follows:spray flow rate 12.5 m L·min^-1,polishing pressure 4.2 psi and polishing speed 70 r·min^-1.Under this condition,the atomization polishing effect was the best,material removal rate was 561.3 nm·min^-1 and surface roughness was 0.63nm.（4）The comparison test between traditional polishing and ultrasonic atomization polishing of TC4 titanium alloy was designed,and the test conditions remained the same except for the difference of polishing fluid flow rate.The experimental results show that atomization polishing can achieve nano-level flattening of TC4 titanium alloy surface under the condition of low consumption of polishing fluid.The material removal rate is similar to that of traditional CMP,and the surface quality is better,which has good economic benefit.（5）Electrochemical and XPS test results support the polishing removal mechanism that titanium alloy is oxidized to form an oxide layer that can be easily removed during the polishing process,and then removed by mechanical action.