Study On The Technological Theory And Key Technology In Micro Grinding Nickel-based Single Crystal Superalloy

Nowdays,with the development of the aerospace and defense industry,the micro part or the micro features which keep enough strength in the high-temperature environment is demanded increasingly.The micro parts have a very wide application prospect because of their unique high temperature resistant performance.The nickel-based single crystal superalloy has only one grain,which eliminates the weak link(grain boundary)in high-temperature application.This makes the nickel-based single crystal superalloy owe better mechanical properties in the high-temperature environment and be used extensively.Micro grinding is the end procedure of microscale mechanical processing,the grinding surface quality has influence on the mechanical properities and service life of parts.And due to the inexistence of grain boundary in the single crystal superalloy,which makes the mechanical processing process of single crystal material be different from that of polycrystalline material.The grinding mechanism of the shearing and slipping along the grain boundary based on the theory of elastic-plastic deformation in traditional polycrystalline material is unsuitable for the micro grinding processing of single crystal superalloy.But due to lacking the corresponding theoretical and experimental study on micro grinding nickel-based single crystal superalloy,the actual micro grinding process is difficult to be guided effectively.So,in order to achieve the micro grinding of nickel-based single crystal superalloy and understand the grinding mechanism,this paper adopts the method of combining theory and experiments to explore and study the fracture mechanism of single crystal superalloy,the grinding surface integrity,grinding force,grinding temperature,the wear of micro grinding tool,the recrystallization of part,etc in micro grinding nickel-based single crystal superalloy.The main contents are as following:(1)This paper introduces the crystallography properties of single crystal material,discusses the plastic deformation mechanism of micro grinding nickel-based single crystal superalloy from the atomic structure of single crystal material,and the verification tests are made;In addition,the model of maximum undeformed chip thickness of single abrasive is established from the aspect of grinding geometry in micro grinding;and studies the anisotropic property of the shear modulus and the elastic modulus in the(001)crystal plane,(110)crystal plane and(111)crystal plane of nickel-based single crystal superalloy from the aspect of crystal structure.Besides,based on the theory of shearing and slipping,analyses the formation mechanism and morphology of chips in micro grinding nickel-based single crystal superalloy.(2)This paper establishes the mathematical prediction model,the response surface method prediction model and a multiple quadratic regression prediction model of surface roughness on micro grinding nickel-based single crystal superalloy;and compares the error between the experimental measurements and the predictive value of models.In addition,this paper analyses the influence of micro grinding parameters and anisotropy of single crystal superalloy on the surface roughness of micro grinding nickel-based single crystal superalloy through experiments.Besides,the 3D simulation topography and roughness of grinding surface which is under different grinding parameters is obtained through the simulation of Matlab,and compares the topography and roughness of simulation with those of experimental measurements.(3)Based on the prominent height of abrasives on the micro-grinding tool submitting to Rayleigh distribution,the model of the average undeformed chip thickness of single abrasive is established;based on this model,the mathematical prediction model of micro grinding normal force and micro grinding tangential force is established.In addition,this paper analyses the primary and secondary influence of grinding parameters on grinding force,establishes the regression prediction model of grinding force,and verifies the accuracy of the prediction model;Besides,the influence of the micro grinding parameters and anisotropy on micro grinding force is also analyzed through single-factor experiment.(4)This paper proposes the measurement method of the temperature in grinding zone which is fit for micro grinding nickel-based single crystal superalloy,and analyses the influence of the grinding velocity,the feeding rate and the grinding depth on the grinding temperature.In addition,based on the Hill model in ABAQUS,the simulation model of single abrasive on micro grinding nickel-based single crystal superalloy is established,the temperature distribution in grinding zone is obtained,and analyses the influence of the micro grinding parameters and anisotropy on the grinding temperature field through simulation.(5)This paper analyses the surface morphology and the subsurface plastic deformation of micro grinding nickel-based single crystal superalloy,analyses the influence of micro grinding parameters on the surface morphology and the thickness of subsurface plastic deformation.In addition,this paper analyses the microhardness in the sub surface of micro grinding nickel-based single crystal superalloy,and analyses the hardening of grinding surface from the aspect of dislocation theory through the transmission electron microscope.Besides,through simulating the high-temperature working environment of nickel-based single crystal superalloy parts,this paper studies the recrystallization of micro grinding part,analyses the influence of anisotropy on the subsurface recrystallization layer,and obtains the measures of controlling or restraining the recrystallization of single crystal superalloy parts in the process of application.(6)This paper studies the main wear form and the wear mechanism of micro grinding tool electroplating CBN in micro grinding nickel-based single crystal superalloy,analyses the influence of micro grinding parameters and the removal volume of material on the wear of micro grinding tool.In addition,the influence of the micro grinding tool wear on surface roughness,grinding force,grinding temperature,the thickness of subsurface plastic deformation and the chip morphology is analyzed.Besides,this paper uses the acoustic emission sensor to monitor the micro grinding process and the contact state between the micro grinding tool and workpiece,also studies the influence of micro grinding parameters on the root-mean-square value of the acoustic emission signal,and the acoustic emission signal under different wear condition of micro grinding tool is analyzed from the aspect of time domain and the frequency spectrum.This paper explores and studies the micro grinding nickel-based single crystal superalloy from the aspect of theory and experiment,which is benefit for the mechanism of micro grinding single crystal superalloy and improving the theory system of micro grinding nickel-based single crystal superalloy.This paper has some reference significance to the production of micro parts and micro features of single crystal superalloy.