Study On Properties And Mechanism Of Affected Layer On The Surface Of Nickel-Base Superalloy With Coupled Ultrasonic And Electric Pulse Treatment

Nanocrystalline structures can be prepared on the surface of metal materials by surface self-nanocrystallization technology,thus improving the comprehensive properties of metal materials.However,the conventional surface self-nanocrystallization technology has no significant effect on the surface nanocrystallization of high-strength and high-hardness materials such as nickel base superalloy,which limits its application and promotion.In this paper,the coupled ultrasonic and electric pulse treatment(CUEPT)method developed by the research group has been used to process the nickel base superalloy Inconel718 and the nanocrystalline structure has been prepared on its surface.The properties of the grain refinement layer of surface after the treatment have been studied.The following research results have been obtained.The experimental equipment of CUEPT has been developed.The effects of rolling passes and static pressure on the surface roughness have been studied.The effects of ultrasonic amplitude on the surface roughness,the thickness of grain refinement layer,the thickness of plastic deformation layer,the thickness of affected layer and the cutting force during ultraprecision cutting have been studied.The optimal mechanical processing parameters have been obtained,in which the static pressure is 400 N,the ultrasonic rolling passes is 3 and the ultrasonic amplitude is 8μm.Under the optimal mechanical parameters,the CUEPT experiments with peak current of 300 A,600A and 800 A have been carried out.The effects of different peak currents on the surface morphology,surface roughness,cross section hardness,the thickness of affected layer,the thickness of grain refinement layer and the thickness of plastic deformation layer have been studied.It has been found that with the increase of peak current,the surface quality of the material has been improved obviously and the effect of CUEPT has been more significant.The properties of grain refinement layer on the surface of nickel base superalloy Inconel718 after CUEPT have been studied.The effects of grain refinement on the surface hardness,abrasive resistance and corrosion resistance have been obtained.It has been found that the hardness,abrasive resistance and corrosion resistance have been significantly enhanced with the decrease of grain size.The material constitutive model of Inconel718 has been improved based on the conditions of CUEPT,and the finite element software Abaqus has been redeveloped based on Fortran language and improved material constitutive model.The process of CUEPT has been simulated and the mechanism of surface grain refinement has been revealed.The influence of surface grain refinement layer on the cutting force of Inconel718 in ultraprecision machining have been studied.A mathematical model has been established to characterize the relationship between grain size and cutting force.The mathematical model has been verified by the experimental results.The relative errors between the experimental results and the calculated results are less than 13%.The effect of grain refinement on cutting force of Inconel718 has been analyzed.The influence mechanism of grain refinement on cutting force has been revealed.The improvement of stability of grain boundaries and the increase of number of grain boundaries cause the increase of cutting force after grain refinement.